cámara argentina de laboratorios independientes ... · pdf fileiii. la estabilidad de...

Cámara Argentina de Laboratorios Independientes Bromatológicos, Ambientales y Afines

Av. de Mayo 981 2° Piso Of. 220. I C1084AAE I Buenos Aires, Argentina I Tel: 5274‐0444 I Fax: 5274‐0450 I E‐mail: [email protected]

ENSAYO DE APTITUD INTERLABORATORIO DE AGUAS SUPERFICIALES POTENCIALMENTE CONTAMINADAS

1. OBJETIVOS: a) Evaluar el desempeño de los laboratorios cuando efectúan ensayos o mediciones

ambientales y efectuar el seguimiento del desempeño de dichos laboratorios, proveyendo confianza adicional a sus clientes.

b) Aportar a la comunidad información confiable sobre el estado de la contaminación costera de la Ciudad Autónoma de Buenos Aires, en un punto de la Costanera Norte.

c) Realizar un Taller al finalizar el EAI, en que se discutan los resultados obtenidos, se obtengan conclusiones sobre éstos y se brinden herramientas para la mejora del desempeño de cada laboratorio en particular y del EAI en general.

2. DESARROLLO: El desarrollo del EAI contempla mediciones in situ y en los laboratorios de los participantes, a saber: Analitos a medir in situ Oxígeno disuelto pH Temperatura Cloro residual libre Analitos a investigar en el laboratorio en la muestra extraída tal cual Sólidos sedimentables a 10 minutos en ml/l Sólidos sedimentables a 2 horas en ml/l Sulfuros en mg/l Sólidos solubles en éter etílico en mg/l DQO en mg/l DBO5 en mg/l Coliformes totales en NMP/ 100 ml Coliformes fecales en NMP /l00 ml Detergentes (SAAM) en mg/l Sustancias fenólicas en mg/l Arsénico en mg/l Cromo total en mg/l Cadmio en mg/l Plomo en mg/l Mercurio en mg/l Conductividad en μS/cm Hidrocarburos totales en mg/l Cianuros totales en mg/l



Analitos a investigar en el laboratorio en la muestra adicionada con metales pesados

Arsénico en mg/l Cromo total en mg/l Cadmio en mg/l Plomo en mg/l Mercurio en mg/l Analitos a investigar en el laboratorio en la muestra adicionada con metales pesados en rango de potabilidad Arsénico en mg/l Cromo total en mg/l Cadmio en mg/l Plomo en mg/l Mercurio en mg/l

3. METODOLOGÍA: La metodología de trabajo se describe a continuación: a) Se solicitará a los laboratorios interesados enviar a su respectivo personal y equipos toma

muestras (incluyendo las botellas con los conservadores que indican las normas respectivas para cada analito) para encontrarse en la desembocadura del arroyo Medrano al Río de la Plata, cruces de Av. Leopoldo Lugones y Av. Comodoro Rivadavia, detrás del Museo de la Memoria.

b) Allí se procederá a tomar la muestra de agua a ser utilizada en el ensayo interlaboratorios, colocándola en un recipiente de volumen suficiente, filtrándola por un tamiz para eliminar los sólidos gruesos y homogeneizándola. Inmediatamente después, se procederá a investigar in situ los siguientes analitos: oxígeno disuelto, pH, temperatura y cloro.

c) i. La muestra de agua extraída del arroyo, contenida en un tanque con agitación constante,

con el fin de mantenerla homogénea, se va distribuyendo a cada uno de los laboratorios presentes, quienes van tomando alícuotas para cada grupo de analitos, con idénticas condiciones de envasado y conservación. ii. La homogeneidad de las muestras se verifica tomando 20 alícuotas durante el proceso de distribución de las mismas a los distintos laboratorios, y posteriormente la medición de la DQO en dos laboratorios certificados y habilitados OPDS. Los resultados son enviados al evaluador estadístico según el procedimiento descripto más abajo. iii. La estabilidad de los distintos analitos de las muestras está descripto en la tabla 1060:1 del Standard Methods of Water and Wastewater Examination edición 22 (Ver anexo I). iv. Aquellos laboratorios que no puedan asistir, deberán informar a CALIBA dentro de las 48 horas hábiles anteriores al día de la toma muestra. En estos casos, el personal de CALIBA fraccionará la muestra en las botellas acordes a lo requerido por los procedimientos normalizados, con los conservantes indicados para cada analito, siguiendo la misma secuencia que para los laboratorios presentes y procederá a embalar el material para ser enviado al domicilio de estos laboratorios, ese mismo día a través de transporte previamente evaluado.

d) Se adicionará una parte de la muestra con Pb, Cd, Hg, As y Cr, la concentración teórica de los mismos será del orden de 0,5 mg/l para As, Cd, Cr y Pb y de 0,005 mg/l para el Hg. Esta



muestra se preparará en el lugar conservándola con HNO3 p.a., de acuerdo a los

procedimientos del Standard Methods for the evaluation of water and wastewater Edición 22th (SM). Cabe señalar que el laboratorio en la planilla de inscripción al EAI deberá informar su interés de participar en estas determinaciones.

e) Se adicionará a una parte de la muestra con Pb, Cd, Hg, As y Cr, en el rango de los límites

de potabilidad de agua, la concentración teórica de los mismos será del orden de lo establecido por el art 982 del CAA. Esta muestra se preparará en el lugar conservándola con HNO3

p.a., de acuerdo a los procedimientos del Standard Methods for the evaluation of water and wastewater Edición 22th (SM). Cabe señalar que el laboratorio en la planilla de inscripción al EAI deberá informar su interés de participar en estas determinaciones.

f) Los analitos mencionados en los ítems precedentes serán investigados mediante las siguientes normas: Environmental Protection Agency- EPA, Standard Methods for the evaluation of water and wastewater - SM o lineamientos Aguas y Saneamiento Ambiental S.A. Será requisito indispensable la especificación del método utilizado a la hora de volcar los datos en la Planilla de Informes de resultados.

g) Los resultados serán remitidos a CALIBA por parte de los participantes, en el formato preestablecido1, donde se consignará la técnica analítica utilizada para cada ensayo, tanto en formato digital, como en copia escrita con la firma del o los responsable/es del área técnica del laboratorio. En esta planilla, CALIBA asignará a cada laboratorio un número identificatorio inequívoco, que permitirá establecer la confidencialidad de los resultados emitidos. Con esta identificación se entregará la totalidad de los resultados, y a un mismo tiempo, a los profesionales estadísticos responsabilizados de la misma (Docentes del Departamento de Estadística de la Universidad Nacional de Luján). Para evitar futuros inconvenientes, aquellos participantes que tuvieran problemas con la carga de datos, deberán comunicarlo a la brevedad posible al personal de CALIBA a los fines de brindarles una solución antes del vencimiento de la entrega. Dentro del plazo mencionado, CALIBA remitirá al laboratorio un acuse recibo por correo electrónico de los resultados dentro de las 48 hs. de recibido el informe. En caso de no recibir en 72 horas esta confirmación, el laboratorio deberá reclamar el mismo por las vías de comunicación establecidas.

h) Una vez finalizada la evaluación estadística, el evaluador remitirá a CALIBA los informes preliminares tanto individuales concernientes a cada laboratorio, como un informe global del EAI. CALIBA, a través de su Área de Calidad, revisará estos informes tanto desde el punto de vista de la transcripción de los resultados como de la pertinencia de las conclusiones, y, posteriormente, propondrá a la Comisión Directiva la emisión de los Diplomas de participación y/o aprobación de cada laboratorio.

i) Se confeccionarán los certificados correspondientes y se imprimirán los informes individuales, los cuales se entregarán en una carpeta a cada laboratorio. En vistas de preservar el medio ambiente por la impresión innecesaria de todo el documento, en esta carpeta también se incluirá un CD con el informe global.

1 No se tomarán en cuenta las planillas que no se correspondan con el formato preestablecido por Caliba, sin excepción.



j) Taller y entrega de resultados: CALIBA organizará un taller de discusión de los resultados obtenidos, a cargo de los responsables del Área de Calidad y con el acompañamiento del estadístico. En dicho taller, que también deberá contar la presencia de al menos el cincuenta por ciento de los participantes, se sugerirá a los laboratorios la implementación de las mejoras que surgieran de la discusión realizada. Asimismo, este interlaboratorio se retroalimentaría a partir de las propuestas de mejoras resultantes de la discusión (Aplicación del objetivo de mejora continua). Por último, se deja asentado que en el desarrollo del mismo, se hará entrega de los diplomas correspondientes junto con los informes individuales y el informe estadístico global. Para aquellos participantes del interior o exterior que no puedan concurrir, los diplomas serán remitidos por el transporte previamente señalado en el formulario de inscripción.

k) Si el laboratorio participante desea hacer llegar críticas, sugerencias, opiniones, las mismas deben ser enviadas por correo electrónico, separado de los resultados, a la Sra. Marta Sancho.

Para más consultas:

Tel.: +54 11 5274-0444 Fax: +54 11 5274-0450 E-mail: [email protected]



Figura 1 Mapa de localización

ATENCIÓN, CAMBIO DE INGRESO AL PUENTE: En la actualidad existe una colectora que separa la Avenida de los clubes y el río. Se puede acceder a la colectora por el Puente Labruna (hay un rond point y luego se entra en la colectora). La otra alternativa es pasar el puente del arroyo y doblar a la derecha antes de encarar el puente hacia la Av. Gral. Paz; esa salida a la derecha dice Parque de los Niños. Luego de salir se vuelve para atrás por la colectora hasta llegar al puente del arroyo Medrano. Allí hay un estacionamiento sobre la calle. Figura 2 Fotos de la toma de muestras y la realización de los ensayos in situ

figures, puts the limit on the number of places that justifiablymay be carried in the sum or difference. Thus the sum

0.007212.024.007825.9

48864927.9350

must be rounded off to ñ4928,ò no decimals, because one ofthe addends, 4886, has no decimal places. Notice that anotheraddend, 25.9, has only three significant figures and yet it doesnot set a limit to the number of significant figures in theanswer.The preceding discussion is necessarily oversimplified. The

reader is referred to mathematical texts for more detailed dis-cussion.

1060 COLLECTION AND PRESERVATION OF SAMPLES*

1060 A. Introduction

It is an old axiom that the result of any testing method can beno better than the sample on which it is performed. It is beyondthe scope of this publication to specify detailed procedures forthe collection of all samples because of varied purposes andanalytical procedures. Detailed information is presented in spe-cific methods. This section presents general considerations, ap-plicable primarily to chemical analyses. See appropriate sectionsfor samples to be used in toxicity testing and microbiological,biological, and radiological examinations.The objective of sampling is to collect a portion of material

small enough in volume to be transported conveniently and yetlarge enough for analytical purposes while still accurately rep-resenting the material being sampled. This objective implies thatthe relative proportions or concentrations of all pertinent com-ponents will be the same in the samples as in the material beingsampled, and that the sample will be handled in such a way thatno significant changes in composition occur before the tests aremade.Frequently the objective of sampling and testing is to demon-

trate whether continuing compliance with specific regulatoryrequirements has been achieved. Samples are presented to thelaboratory for specific determinations with the sampler beingresponsible for collecting a valid and representative sample.Because of the increasing importance placed on verifying theaccuracy and representativeness of data, greater emphasis isplaced on proper sample collection, tracking, and preservationtechniques. Often, laboratory personnel help in planning a sam-pling program, in consultation with the user of the test results.Such consultation is essential to ensure selecting samples andanalytical methods that provide a sound and valid basis foranswering the questions that prompted the sampling and that willmeet regulatory and/or project-specific requirements.This section addresses the collection and preservation of water

and wastewater samples; the general principles also apply to thesampling of solid or semisolid matrices.

1. General Requirements

Obtain a sample that meets the requirements of the samplingprogram and handle it so that it does not deteriorate or becomecontaminated or compromised before it is analyzed.Ensure that all sampling equipment is clean and quality-

assured before use. Use sample containers that are clean and freeof contaminants. Bake at 450ÁC all bottles to be used for organic-analysis sampling.Fill sample containers without prerinsing with sample; prerinsing

results in loss of any pre-added preservative and sometimes can biasresults high when certain components adhere to the sides of thecontainer. Depending on determinations to be performed, fill thecontainer full (most organic compound determinations) or leavespace for aeration, mixing, etc. (microbiological and inorganic anal-yses). If a bottle already contains preservative, take care not tooverfill the bottle, as preservative may be lost or diluted. Exceptwhen sampling for analysis of volatile organic compounds, leave anair space equivalent to approximately 1% of the container volume toallow for thermal expansion during shipment.Special precautions (discussed below) are necessary for sam-

ples containing organic compounds and trace metals. Becausemany constituents may be present at low concentrations (micro-grams or nanograms per liter), they may be totally or partiallylost or easily contaminated when proper sampling and preserva-tion procedures are not followed.Composite samples can be obtained by collecting over a period of

time, depth, or at many different sampling points. The details ofcollection vary with local conditions, so specific recommendationsare not universally applicable. Sometimes it is more informative toanalyze numerous separate samples instead of one composite so thatvariability, maxima, and minima can be determined.Because of the inherent instability of certain properties and

compounds, composite sampling for some analytes is not rec-ommended where quantitative values are desired (examples in-clude oil and grease, acidity, alkalinity, carbon dioxide, chlorineresidual, iodine, hexavalent chromium, nitrate, volatile organiccompounds, radon-222, dissolved oxygen, ozone, temperature,and pH). In certain cases, such as for BOD, composite samples* Joint Task Group: 20th EditionðLawrence H. Keith (chair), Clifford G. Annis,

Gary L. DeKock, Carleton P. Edmunds, Scott J. Mickelson, Mark Wyzalek.

COLLECTION AND PRESERVATION OF SAMPLES (1060)/Introduction 1-27

CALIBA PC2

Texto escrito a máquina

ANEXO I

are routinely required by regulatory agencies. Refrigerate com-posite samples for BOD and nitrite.Sample carefully to ensure that analytical results represent the

actual sample composition. Important factors affecting resultsare the presence of suspended matter or turbidity, the methodchosen for removing a sample from its container, and the phys-ical and chemical changes brought about by storage or aeration.Detailed procedures are essential when processing (blending,sieving, filtering) samples to be analyzed for trace constituents,especially metals and organic compounds. Some determinationscan be invalidated by contamination during processing. Treateach sample individually with regard to the substances to bedetermined, the amount and nature of turbidity present, and otherconditions that may influence the results.Carefully consider the technique for collecting a representative

sample and define it in the sampling plan. For metals it often isappropriate to collect both a filtered and an unfiltered sample todifferentiate between total and dissolved metals present in thematrix. Be aware that some metals may partially sorb to filters.Beforehand, determine the acid requirements to bring the pH to �2on a separate sample. Add the same relative amount of acid to allsamples; use ultrapure acid preservative to prevent contamination.Be sure that the dilution caused by acidifying is negligible orsufficiently reproducible for a dilution correction factor. Whenfiltered samples are to be collected, filter them, if possible, in thefield, or at the point of collection before preservation with acid.Filter samples in a laboratory-controlled environment if field con-ditions could cause error or contamination; in this case filter as soonas possible. Often slight turbidity can be tolerated if experienceshows that it will cause no interference in gravimetric or volumetrictests and that its influence can be corrected in colorimetric tests,where it has potentially the greatest interfering effect. Sample col-lector must state whether or not the sample has been filtered.Make a record of every sample collected and identify every

bottle with a unique sample number, preferably by attachingan appropriately inscribed tag or label. Document sufficientinformation to provide positive sample identification at a laterdate, including the unique sample identification number, thename of the sample collector, the date, hour, exact location,and, if possible, sample type (e.g., grab or composite), andany other data that may be needed for correlation, such aswater temperature, weather conditions, water level, streamflow, post-collection conditions, etc. If space for all pertinentinformation for label or attached tag is insufficient, recordinformation in a bound sample log book at the sampling siteat the time of sample collection. Use waterproof ink to recordall information (preferably with black, non-solvent-basedink). Fix sampling points by detailed description in the sam-pling plan, by maps, or with the aid of stakes, buoys, orlandmarks in a manner that will permit their identification byother persons without reliance on memory or personal guid-ance. Global positioning systems (GPS) also are used andsupply accurate sampling position data. Particularly whensample results are expected to be involved in litigation, useformal ñchain-of-custodyò procedures (see Æ B.2 below),which trace sample history from collection to final reporting.Before collecting samples from distribution systems, flush

lines with three to five pipe volumes (or until water is beingdrawn from the main source) to ensure that the sample is repre-sentative of the supply, taking into account the volume of pipe to

be flushed and the flow velocity. If the distribution systemvolume is unavailable, flush with tap fully open for at least 2 to3 min before sampling. An exception to these guidelines, i.e.,collecting a first draw sample, is when information on areas ofreduced or restricted flow is desired or when samples for lead indrinking water are being collected.Although well pumping protocols depend on the objectives of

an investigation and other factors such as well characteristics andavailable equipment, a general rule is to collect samples fromwells only after the well has been purged sufficiently (usuallywith three to ten well volumes) to ensure that the sample repre-sents the groundwater. Purging stagnant water is critical. Some-times it will be necessary to pump at a specified rate to achievea characteristic drawdown, if this determines the zones fromwhich the well is supplied; record purging rate and drawdown, ifnecessary. By using methods with minimal drawdown, purgingvolumes can be reduced significantly.When samples are collected from a river or stream, observed

results may vary with depth, stream flow, and distance from eachshore. Selection of the number and distribution of sites at whichsamples should be collected depends on study objectives, streamcharacteristics, available equipment, and other factors. If equip-ment is available, take an integrated sample from top to bottomin the middle of the main channel of the stream or from side toside at mid-depth. If only grab or catch samples can be collected,preferably take them at various points of equal distance acrossthe stream; if only one sample can be collected, take it in themiddle of the main channel of the stream and at mid-depth.Integrated samples are described further in Æ B.1c below.Rivers, streams, lakes, and reservoirs are subject to consider-

able variations from normal causes such as seasonal stratifica-tion, diurnal variations, rainfall, runoff, and wind. Choose loca-tion, depth, and frequency of sampling depending on local con-ditions and the purpose of the investigation.Use the following examples for general guidance. Avoid areas of

excessive turbulence because of potential loss of volatile constitu-ents and of potential presence of denser-than-air toxic vapors. Avoidsampling at weirs if possible because such locations tend to favorretrieval of lighter-than-water, immiscible compounds. Generally,collect samples beneath the surface in quiescent areas and opensampling container below surface with the mouth directed towardthe current to avoid collecting surface scum unless oil and grease isa constituent of interest; then collect water at the surface. If com-posite samples are required, ensure that sample constituents are notlost during compositing because of improper handling of portionsbeing composited. If samples will be analyzed for organic constit-uents, refrigerate composited portions. Do not composite samplesfor VOC analysis because some of the components will be lostthrough volatilization.

2. Safety Considerations

Because sample constituents may be toxic, take adequateprecautions during sampling and sample handling. Toxic sub-stances can enter through the skin and eyes and, in the case ofvapors, also through the lungs. Ingestion can occur via directcontact of toxic materials with foods or by adsorption of vaporsonto foods. Precautions may be limited to wearing gloves or mayinclude coveralls, aprons, or other protective apparel. Often, thedegree of protection provided by chemical protective clothing

1-28 INTRODUCTION (1000)

(CPC) is specific for different manufacturers and their productmodels1; ensure that the clothing chosen will offer adequateprotection. Always wear eye protection (e.g., safety glasses withside shields or goggles). When toxic vapors may be present,sample only in well-ventilated areas, or use an appropriate res-pirator or self-contained breathing apparatus. In a laboratory,open sample containers in a fume hood. Never have food in thelaboratory, near samples, or near sampling locations; alwayswash hands thoroughly before handling food.2Always prohibit eating, drinking, or smoking near samples,

sampling locations, and in the laboratory. Keep sparks, flames,and excessive heat sources away from samples and samplinglocations. If flammable compounds are suspected or known to bepresent and samples are to be refrigerated, use only speciallydesigned explosion-proof refrigerators.2Collect samples safely, avoiding situations that may lead to

accidents. When in doubt as to the level of safety precautions

needed, consult a knowledgeable industrial hygienist or safetyprofessional. Samples with radioactive contaminants may re-quire other safety considerations; consult a health physicist.Label adequately any sample known or suspected to be haz-

ardous because of flammability, corrosivity, toxicity, oxidizingchemicals, or radioactivity, so that appropriate precautions canbe taken during sample handling, storage, and disposal.

3. References

1. FORSBERG, K. & L.H. KEITH. 1998. Instant Gloves and CPC Database.Instant Reference Sources, Inc. Austin, Tex.

2. WATER POLLUTION CONTROL FEDERATION. 1986. Removal of Haz-ardous Wastes in Wastewater FacilitiesðHalogenated Organics.Manual of Practice FD-11, Water Pollution Control Fed., Alex-andria, Va.

1060 B. Collection of Samples

1. Types of Samples

a. Grab samples: Grab samples are single samples collectedat a specific spot at a site over a short period of time (typicallyseconds or minutes). Thus, they represent a ñsnapshotò in bothspace and time of a sampling area. Discrete grab samples aretaken at a selected location, depth, and time. Depth-integratedgrab samples are collected over a predetermined part or theentire depth of a water column, at a selected location and time ina given body of water.A sample can represent only the composition of its source at

the time and place of collection. However, when a source isknown to be relatively constant in composition over an extendedtime or over substantial distances in all directions, then thesample may represent a longer time period and/or a largervolume than the specific time and place at which it was collected.In such circumstances, a source may be represented adequatelyby single grab samples. Examples are protected groundwatersupplies, water supplies receiving conventional treatment, somewell-mixed surface waters, but rarely, wastewater streams, riv-ers, large lakes, shorelines, estuaries, and groundwater plumes.When a source is known to vary with time, grab samples col-

lected at suitable intervals and analyzed separately can documentthe extent, frequency, and duration of these variations. Choosesampling intervals on the basis of the expected frequency ofchanges, which may vary from as little as 5 min to as long as 1 h ormore. Seasonal variations in natural systems may necessitate sam-pling over months. When the source composition varies in space(i.e., from location to location) rather than time, collect samplesfrom appropriate locations that will meet the objectives of the study(for example, upstream and downstream from a point source, etc.).The same principles apply to sampling wastewater sludges,

sludge banks, and muds, although these matrices are not specificallyaddressed in this section. Take every possible precaution to obtaina representative sample or one conforming to a sampling program.

b. Composite samples: Composite samples should provide amore representative sampling of heterogeneous matrices in

which the concentration of the analytes of interest may vary overshort periods of time and/or space. Composite samples can beobtained by combining portions of multiple grab samples or byusing specially designed automatic sampling devices. Sequential(time) composite samples are collected by using continuous,constant sample pumping or by mixing equal water volumescollected at regular time intervals. Flow-proportional compositesare collected by continuous pumping at a rate proportional to theflow, by mixing equal volumes of water collected at time inter-vals that are inversely proportional to the volume of flow, or bymixing volumes of water proportional to the flow collectedduring or at regular time intervals.Advantages of composite samples include reduced costs of ana-

lyzing a large number of samples, more representative samples ofheterogeneous matrices, and larger sample sizes when amounts oftest samples are limited. Disadvantages of composite samples in-clude loss of analyte relationships in individual samples, potentialdilution of analytes below detection levels, increased potential an-alytical interferences, and increased possibility of analyte interac-tions. In addition, use of composite samples may reduce the numberof samples analyzed below the required statistical need for specifieddata quality objectives or project-specific objectives.Do not use composite samples with components or character-

istics subject to significant and unavoidable changes duringstorage. Analyze individual samples as soon as possible aftercollection and preferably at the sampling point. Examples aredissolved gases, residual chlorine, soluble sulfide, temperature,and pH. Changes in components such as dissolved oxygen orcarbon dioxide, pH, or temperature may produce secondarychanges in certain inorganic constituents such as iron, manga-nese, alkalinity, or hardness. Some organic analytes also may bechanged by changes in the foregoing components. Use time-composite samples only for determining components that can bedemonstrated to remain unchanged under the conditions of sam-ple collection, preservation, and storage.Collect individual portions in a wide-mouth bottle every hour

(in some cases every half hour or even every 5 min) and mix at

COLLECTION AND PRESERVATION OF SAMPLES (1060)/Collection of Samples 1-29

the end of the sampling period or combine in a single bottle ascollected. If preservatives are used, add them to the sample bottleinitially so that all portions of the composite are preserved assoon as collected.Automatic sampling devices are available; however, do not

use them unless the sample is preserved as described below.Composite samplers running for extended periods (weeks tomonths) should undergo routine cleaning of containers and sam-ple lines to minimize sample growth and deposits.

c. Integrated (discharge-weighted) samples: For certain pur-poses, the information needed is best provided by analyzingmixtures of grab samples collected from different points simul-taneously, or as nearly so as possible, using discharge-weightedmethods such as equal-width increment (EWI) or equal dis-charge-increment (EDI) procedures and equipment. An exampleof the need for integrated sampling occurs in a river or streamthat varies in composition across its width and depth. To evaluateaverage composition or total loading, use a mixture of samplesrepresenting various points in the cross-section, in proportion totheir relative flows. The need for integrated samples also mayexist if combined treatment is proposed for several separatewastewater streams, the interaction of which may have a signif-icant effect on treatability or even on composition. Mathematicalprediction of the interactions among chemical components maybe inaccurate or impossible and testing a suitable integratedsample may provide more useful information.Both lakes and reservoirs show spatial variations of composi-

tion (depth and horizontal location). However, there are condi-tions under which neither total nor average results are especiallyuseful, but local variations are more important. In such cases,examine samples separately (i.e., do not integrate them).Preparation of integrated samples usually requires equipment

designed to collect a sample water uniformly across the depthprofile. Knowledge of the volume, movement, and composition ofthe various parts of the water being sampled usually is required.Collecting integrated samples is a complicated and specializedprocess that must be described adequately in a sampling plan.

2. Chain-of-Custody Procedures

Properly designed and executed chain-of-custody forms will en-sure sample integrity from collection to data reporting. This in-cludes the ability to trace possession and handling of the samplefrom the time of collection through analysis and final disposition.This process is referred to as ñchain-of-custodyò and is required todemonstrate sample control when the data are to be used forregulation or litigation. Where litigation is not involved, chain-of-custody procedures are useful for routine control of samples.A sample is considered to be under a personôs custody if it is

in the individualôs physical possession, in the individualôs sight,secured and tamper-proofed by that individual, or secured in anarea restricted to authorized personnel. The following proceduressummarize the major aspects of chain of custody. More detaileddiscussions are available.1,2

a. Sample labels (including bar-code labels): Use labels to pre-vent sample misidentification. Gummed paper labels or tags gener-ally are adequate. Include at least the following information: aunique sample number, sample type, name of collector, date andtime of collection, place of collection, and sample preservative.Also include date and time of preservation for comparison to date

and time of collection. Affix tags or self-adhesive labels to samplecontainers before, or at the time of, sample collection.

b. Sample seals: Use sample seals to detect unauthorizedtampering with samples up to the time of analysis. Use

self-adhesive paper seals that include at least the following informa-tion: sample number (identical with number on sample label),collector’s name, and date and time of sampling. Plastic shrinkseals also may be used.

Attach seal in such a way that it is necessary to break it to openthe sample container or the sample shipping container (e.g., acooler). Affix seal to container before sample leaves custody ofsampling personnel.

c. Field log book: Record all information pertinent to a fieldsurvey or sampling in a bound log book. As a minimum, include thefollowing in the log book: purpose of sampling; location of sam-pling point; name and address of field contact; producer of materialbeing sampled and address, if different from location; type ofsample; and method, date, and time of preservation. If the sample iswastewater, identify process producing waste stream. Also providesuspected sample composition, including concentrations; numberand volume of sample(s) taken; description of sampling point andsampling method; date and time of collection; collector’s sampleidentification number(s); sample distribution and how transported;references such as maps or photographs of the sampling site; fieldobservations and measurements; and signatures of personnel re-sponsible for observations. Because sampling situations varywidely, it is essential to record sufficient information so that onecould reconstruct the sampling event without reliance on the col-lector’s memory. Protect log book and keep it in a safe place.

d. Chain-of-custody record: Fill out a chain-of-custodyrecord to accompany each sample or group of samples. Therecord includes the following information: sample number; sig-nature of collector; date, time, and address of collection; sampletype; sample preservation requirements; signatures of personsinvolved in the chain of possession; and inclusive dates andtimes of possession.

e. Sample analysis request sheet: The sample analysis requestsheet accompanies samples to the laboratory. The collector com-pletes the field portion of such a form that includes most of thepertinent information noted in the log book. The laboratoryportion of such a form is to be completed by laboratory person-nel and includes: name of person receiving the sample, labora-tory sample number, date of sample receipt, condition of eachsample (i.e., if it is cold or warm, whether the container is full ornot, color, if more than one phase is present, etc.), and determi-nations to be performed.

f. Sample delivery to the laboratory: Deliver sample(s) tolaboratory as soon as practicable after collection, typically within2 d. Where shorter sample holding times are required, makespecial arrangements to insure timely delivery to the laboratory.Where samples are shipped by a commercial carrier, include thewaybill number in the sample custody documentation. Insurethat samples are accompanied by a completed chain-of-custodyrecord and a sample analysis request sheet. Deliver sample tosample custodian.

g. Receipt and logging of sample: In the laboratory, the sam-ple custodian inspects the condition and seal of the sample andreconciles label information and seal against the chain-of-cus-tody record before the sample is accepted for analysis. Afteracceptance, the custodian assigns a laboratory number, logs


sample in the laboratory log book and/or computerized labora-tory information management system, and stores it in a securedstorage room or cabinet or refrigerator at the specified temper-ature until it is assigned to an analyst.

h. Assignment of sample for analysis: The laboratory super-visor usually assigns the sample for analysis. Once the sample isin the laboratory, the supervisor or analyst is responsible for itscare and custody.

i. Disposal: Hold samples for the prescribed amount of timefor the project or until the data have been reviewed and accepted.Document the disposition of samples. Ensure that disposal is inaccordance with local, state, and U.S. EPA approved methods.

3. Sampling Methods

a. Manual sampling: Manual sampling involves minimalequipment but may be unduly costly and time-consuming forroutine or large-scale sampling programs. It requires trained fieldtechnicians and is often necessary for regulatory and researchinvestigations for which critical appraisal of field conditions andcomplex sample collection techniques are essential. Manuallycollect certain samples, such as waters containing oil and grease.

b. Automatic sampling: Automatic samplers can eliminatehuman errors in manual sampling, can reduce labor costs, mayprovide the means for more frequent sampling,3 and are usedincreasingly. Be sure that the automatic sampler does not con-taminate the sample. For example, plastic components may beincompatible with certain organic compounds that are soluble inthe plastic parts or that can be contaminated (e.g., from phthalateesters) by contact with them. If sample constituents are generallyknown, contact the manufacturer of an automatic sampler re-garding potential incompatibility of plastic components.

Program an automatic sampler in accordance with samplingneeds. Carefully match pump speeds and tubing sizes to the typeof sample to be taken.

c. Sorbent sampling: Use of solid sorbents, particularly mem-brane-type disks, is becoming more frequent. These methodsoffer advantages of rapid, inexpensive sampling if the analytes ofinterest can be adsorbed and desorbed efficiently and the watermatrix is free of particulates that plug the sorbent.

4. Sample Containers

The type of sample container used is of utmost importance.Test sample containers and document that they are free ofanalytes of interest, especially when sampling and analyzing forvery low analyte levels. Containers typically are made of plasticor glass, but one material may be preferred over the other. Forexample, silica, sodium, and boron may be leached from softglass but not plastic, and trace levels of some pesticides andmetals may sorb onto the walls of glass containers.4 Thus, hardglass containers* are preferred. For samples containing organiccompounds, do not use plastic containers except those made offluorinated polymers such as polytetrafluoroethylene (PTFE).3

Some sample analytes may dissolve (be absorbed) into thewalls of plastic containers; similarly, contaminants from plasticcontainers may leach into samples. Avoid plastics whereverpossible because of potential contamination from phthalate es-

ters. Container failure due to breakdown of the plastic is possi-ble. Therefore, use glass containers for all organics analyses suchas volatile organics, semivolatile organics, pesticides, PCBs, andoil and grease. Some analytes (e.g., bromine-containing com-pounds and some pesticides, polynuclear aromatic compounds,etc.) are light-sensitive; collect them in amber-colored glasscontainers to minimize photodegradation. Container caps, typi-cally plastic, also can be a problem. Do not use caps with paperliners. Use foil or PTFE liners but be aware that metal liners cancontaminate samples collected for metals analysis and they mayalso react with the sample if it is acidic or alkaline. Serum vialswith PTFE-lined rubber or plastic septa are useful.

In rare situations it may be necessary to use sample containers notspecifically prepared for use, or otherwise unsuitable for the partic-ular situation; thoroughly document these deviations. Documenta-tion should include type and source of container, and the preparationtechnique, e.g., acid washed with reagent water rinse. For QApurposes the inclusion of a bottle blank may be necessary.

5. Number of Samples

Because of variability from analytical and sampling procedures(i.e., population variability), a single sample is insufficient to reachany reasonable desired level of confidence. If an overall standarddeviation (i.e., the standard deviation of combined sampling andanalysis) is known, the required number of samples for a mobilematrix such as water may be estimated as follows:4

N �� ts

U�2

where:N � number of samples,t � Student-t statistic for a given confidence level,s � overall standard deviation, and

U � acceptable level of uncertainty.

To assist in calculations, use curves such as those in Figure1060:1. As an example, if s is 0.5 mg/L, U is � 0.2 mg/L, anda 95% confidence level is desired, approximately 25 to 30samples must be taken.

The above equation assumes that total error (population vari-ability) is known. Total variability consists of all sources ofvariability, including: the distribution of the analytes of interestwithin the sampling site, collection, preservation, preparation,and analysis of samples, and data handling and reporting. Insimpler terms, error (variability) can be divided into samplingand analysis components. Sampling error due to populationvariability (including heterogeneous distribution of analytes inthe environmental matrix) usually is much larger than analyticalerror components. Unfortunately, sampling error usually is notavailable and the analyst is left with only the published error ofthe measurement system (typically obtained by using a reagentwater matrix under the best analytical conditions).

More accurate equations are available.5 These are based on theZ distribution for determining the number of samples needed toestimate a mean concentration when variability is estimated inabsolute terms using the standard deviation. The coefficient ofvariation (relative standard deviation) is used when variability isestimated in relative terms.

The number of random samples to be collected at a site can beinfluenced partly by the method that will be used. The values for* Pyrex or equivalent.


standard deviation (SD) or relative standard deviation (RSD)may be obtained from each of the methods or in the literature.6However, calculations of estimated numbers of samples neededbased only on this information will result in underestimatednumbers of samples because only the analytical variances areconsidered, and the typically larger variances from the samplingoperations are not included. Preferably, determine and use SDsor RSDs from overall sampling and analysis operations.

For estimates of numbers of samples needed for systematicsampling (e.g., drilling wells for sampling groundwater or forsystematically sampling large water bodies such as lakes), equa-tions are available7 that relate number of samples to shape ofgrid, area covered, and space between nodes of grid. The gridspacing is a complex calculation that depends on the size andshape of any contaminated spot (such as a groundwater plume)to be identified, in addition to the geometric shape of the sam-pling grid.

See individual methods for types and numbers of qualityassurance (QA) and quality control (QC) samples, e.g., fornormal-level (procedural) or low-level (contamination) bias orfor precision, involving sampling or laboratory analysis (eitheroverall or individually). Estimates of numbers of QC samplesneeded to achieve specified confidence levels also can be calcu-lated. Rates of false positives (Type I error) and false negatives(Type II error) are useful parameters for estimating requirednumbers of QC samples. A false positive is the incorrect con-

clusion that an analyte is present when it is absent. A falsenegative is the incorrect conclusion that an analyte is absentwhen it is present. If the frequency of false positives or falsenegatives desired to be detected is less than 10%, then

n �ln �

ln (1 � Y)

where:� � (1 � desired confidence level), andY � frequency to detect (�10%).

If the frequency that is desirable to detect is more than 10%,iterative solution of a binomial equation is necessary.5,8

Equations are available as a computer program† for comput-ing sample number by the Z distribution, for estimating samplesneeded in systematic sampling, and for estimating required num-ber of QC samples.

6. Sample Volumes

Collect a 1-L sample for most physical and chemical analyses.For certain determinations, larger samples may be necessary.Table 1060:I lists volumes ordinarily required for analyses, butit is strongly recommended that the laboratory that will conductthe analyses also be consulted to verify the analytical needs ofsampling procedures as they pertain to the goals and data qualityobjective of an investigation.

Do not use samples from the same container for multipletesting requirements (e.g., organic, inorganic, radiological, bac-teriological, and microscopic examinations) because methods ofcollecting and handling are different for each type of test. Al-ways collect enough sample volume in the appropriate containerin order to comply with sample handling, storage, and preserva-tion requirements.

7. References

1. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1986. Test Methods forEvaluating Solid Waste: Physical/Chemical Methods, 3rd ed. Publ.No. SW-846, Off. Solid Waste and Emergency Response, Wash-ington, D.C.

2. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1982. NEIC Policies andProcedures. EPA-330/9/78/001/-R (rev. 1982).

3. WATER POLLUTION CONTROL FEDERATION. 1986. Removal of Hazard-ous Wastes in Wastewater Facilities—Halogenated Organics. Man-ual of Practice FD-11, Water Pollution Control Fed., Alexandria,Va.

4. Methods for the Examination of Waters and Associated Materials:General Principles of Sampling and Accuracy of Results. 1980. HerMajesty’s Stationery Off., London, England.

5. KEITH, L.H., G.L. PATTON, D.L. LEWIS & P.G. EDWARDS. 1996.Determining numbers and kinds of analytical samples. Chapter 1 inPrinciples of Environmental Sampling, 2nd ed. ACS ProfessionalReference Book, American Chemical Soc., Washington, D.C.

† DQO-PRO, available (free) by downloading from American Chemical SocietyDivision of Environmental Chemistry home page at http://acs.environmental.duq.edu/acsenv/envchem.htm, and also as part of the tutorial, Reliable Environ-mental Sampling and Analysis, Instant Reference Sources, Inc., http://instantref.com/inst.ref.htm.

Figure 1060:1. Approximate number of samples required in estimatinga mean concentration. Source: Methods for the Examina-tion of Waters and Associated Materials: General Principlesof Sampling and Accuracy of Results. 1980. Her Majesty’sStationery Off., London, England.


TABLE 1060:I. SUMMARY OF SPECIAL SAMPLING AND HANDLING REQUIREMENTS*

Determination Container†

MinimumSample

SizemL

SampleType‡ Preservation§

Maximum Storage

Recommended Regulatory�

Acidity P, G(B) 100 g Refrigerate 24 h 14 dAlkalinity P, G 200 g Refrigerate 24 h 14 dBOD P, G 1000 g, c Refrigerate 6 h 48 hBoron P (PTFE) or quartz 1000 g, c HNO3 to pH �2 28 d 6 monthsBromide P, G 100 g, c None required 28 d 28 dCarbon, organic,

totalG (B) 100 g, c Analyze immediately; or refrigerate and

add HCl, H3PO4, or H2SO4 to pH �27 d 28 d

Carbon dioxide P, G 100 g Analyze immediately 0.25 h N.S.COD P, G 100 g, c Analyze as soon as possible, or add

H2SO4 to pH �2; refrigerate7 d 28 d

Chloride P, G 50 g, c None required N.S. 28 dChlorine, total,

residualP, G 500 g Analyze immediately 0.25 h 0.25 h

Chlorine dioxide P, G 500 g Analyze immediately 0.25 h N.S.Chlorophyll P, G 500 g Unfiltered, dark, 4°C 24–48 h

Filtered, dark, �20°C 28 d(Do not store in frost-free freezer)

Color P, G 500 g, c Refrigerate 48 h 48 hSpecific conductance P, G 500 g, c Refrigerate 28 d 28 dCyanide

Total P, G 1000 g, c Add NaOH to pH �12, refrigerate indark#

24 h 14 d; 24 h ifsulfide present

Amenable tochlorination

P, G 1000 g, c Add 0.6 g ascorbic acid if chlorine ispresent and refrigerate

stat 14 d; 24 h ifsulfide present

Fluoride P 100 g, c None required 28 d 28 dHardness P, G 100 g, c Add HNO3 or H2SO4 to pH �2 6 months 6 monthsIodine P, G 500 g Analyze immediately 0.25 h N.S.Metals, general P(A), G(A) 1000 g, c For dissolved metals filter immediately,

add HNO3 to pH �26 months 6 months

Chromium VI P(A), G(A) 1000 g Refrigerate 24 h 24 hCopper by

colorimetry*g, c

Mercury P(A), G(A) 1000 g, c Add HNO3 to pH �2, 4°C, refrigerate 28 d 28 dNitrogen

Ammonia P, G 500 g, c Analyze as soon as possible or addH2SO4 to pH �2, refrigerate

7 d 28 d

Nitrate P, G 100 g, c Analyze as soon as possible; refrigerate 48 h 48 h (28 d forchlorinatedsamples)

Nitrate nitrite P, G 200 g, c Add H2SO4 to pH �2, refrigerate 1–2 d 28 dNitrite P, G 100 g, c Analyze as soon as possible; refrigerate none 48 h

Organic, Kjeldahl* P, G 500 g, c Refrigerate, add H2SO4 to pH �2 7 d 28 dOdor G 500 g Analyze as soon as possible; refrigerate 6 h N.S.Oil and grease G, wide-mouth

calibrated1000 g Add HCl or H2SO4 to pH �2, refrigerate 28 d 28 d

Organic compoundsMBAs P, G 250 g, c Refrigerate 48 h N.S.Pesticides* G(S), PTFE-lined

cap1000 g, c Refrigerate, add 1000 mg ascorbic acid/L

if residual chlorine present7 d 7 d until

extraction;40 d afterextraction

Phenols P, G, PTFE-linedcap

500 g, c Refrigerate, add H2SO4 to pH �2 � 28 d untilextraction

Purgeables* bypurge and trap

G, PTFE-lined cap 2 � 40 g Refrigerate; add HCl to pH �2; add 1000mg ascorbic acid/L if residual chlorinepresent

7 d 14 d


6. KEITH, L.H. 1996. Compilation of EPA’s Sampling and AnalysisMethods, 2nd ed. Lewis Publ./CRC Press, Boca Raton, Fla.

7. GILBERT, R.O. 1987. Statistical Methods for Environmental Pollu-tion Monitoring. Van Nostrand Reinhold, New York, N.Y.

8. GRANT, E.L. & R.S. LEAVENWORTH. 1988. Statistical Quality Con-trol, 6th ed. McGraw-Hill, Inc., New York, N.Y.

9. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1996. 40 CFR Part 136,Table II.

10. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1992. Rules and Regula-tions. 40 CFR Parts 100-149.

1060 C. Sample Storage and Preservation

Complete and unequivocal preservation of samples, whetherdomestic wastewater, industrial wastes, or natural waters, is apractical impossibility because complete stability for every con-stituent never can be achieved. At best, preservation techniquesonly retard chemical and biological changes that inevitably con-tinue after sample collection.

1. Sample Storage before Analysis

a. Nature of sample changes: Some determinations are more af-fected by sample storage than others. Certain cations are subject to loss

by adsorption on, or ion exchange with, the walls of glass containers.These include aluminum, cadmium, chromium, copper, iron, lead,manganese, silver, and zinc, which are best collected in a separate cleanbottle and acidified with nitric acid to a pH below 2.0 to minimizeprecipitation and adsorption on container walls. Also, some organicsmay be subject to loss by adsorption to the walls of glass containers.

Temperature changes quickly; pH may change significantly in amatter of minutes; dissolved gases (oxygen, carbon dioxide) may belost. Because changes in such basic water quality properties mayoccur so quickly, determine temperature, reduction-oxidation po-tential, and dissolved gases in situ and pH, specific conductance,

TABLE 1060:I. CONT.

Determination Container†

MinimumSample

SizemL

SampleType‡ Preservation§

Maximum Storage

Recommended Regulatory�

Base/neutrals &acids

G(S) amber 1000 g, c Refrigerate 7 d 7 d untilextraction;40 d afterextraction

Oxygen, dissolved G, BOD bottle 300 gElectrode Analyze immediately 0.25 h 0.25 hWinkler Titration may be delayed after

acidification8 h 8 h

Ozone G 1000 g Analyze immediately 0.25 h N.S.pH P, G 50 g Analyze immediately 0.25 h 0.25 hPhosphate G(A) 100 g For dissolved phosphate filter

immediately; refrigerate48 h N.S.

Phosphorus, total P, G 100 g, c Add H2SO4 to pH �2 and refrigerate 28 dSalinity G, wax seal 240 g Analyze immediately or use wax seal 6 months N.S.Silica P (PTFE) or quartz 200 g, c Refrigerate, do not freeze 28 d 28 dSludge digester gas G, gas bottle — g — N.S.Solids9 P, G 200 g, c Refrigerate 7 d 2–7 d; see cited

referenceSulfate P, G 100 g, c Refrigerate 28 d 28 dSulfide P, G 100 g, c Refrigerate; add 4 drops 2N zinc

acetate/100 mL; add NaOH to pH �928 d 7 d

Temperature P, G — g Analyze immediately 0.25 h 0.25 hTurbidity P, G 100 g, c Analyze same day; store in dark up to

24 h, refrigerate24 h 48 h

* For determinations not listed, use glass or plastic containers; preferably refrigerate during storage and analyze as soon as possible.† P � plastic (polyethylene or equivalent); G � glass; G(A) or P(A) � rinsed with 1 1 HNO3; G(B) � glass, borosilicate; G(S) � glass, rinsed with organic solvents or baked.‡ g � grab; c � composite.§ Refrigerate � storage at 4°C � 2°C; in the dark; analyze immediately � analyze usually within 15 min of sample collection.� See citation10 for possible differences regarding container and preservation requirements. N.S. � not stated in cited reference; stat � no storage allowed; analyzeimmediately.# If sample is chlorinated, see text for pretreatment.


turbidity, and alkalinity immediately after sample collection. Manyorganic compounds are sensitive to changes in pH and/or temper-ature resulting in reduced concentrations during storage.

Changes in the pH-alkalinity-carbon dioxide balance maycause calcium carbonate to precipitate, decreasing the values forcalcium and total hardness.

Iron and manganese are readily soluble in their lower oxida-tion states but relatively insoluble in their higher oxidationstates; therefore, these cations may precipitate or they maydissolve from a sediment, depending on the redox potential ofthe sample. Microbiological activity may affect the nitrate-ni-trite-ammonia content, phenol or BOD concentration, or thereduction of sulfate to sulfide. Residual chlorine is reduced tochloride. Sulfide, sulfite, ferrous iron, iodide, and cyanide maybe lost through oxidation. Color, odor, and turbidity may in-crease, decrease, or change in quality. Sodium, silica, and boronmay be leached from the glass container. Hexavalent chromiummay be reduced to trivalent chromium.

Biological activity taking place in a sample may change theoxidation state of some constituents. Soluble constituents may beconverted to organically bound materials in cell structures, orcell lysis may result in release of cellular material into solution.The well-known nitrogen and phosphorus cycles are examples ofbiological influences on sample composition.

Zero head-space is important in preservation of samples withvolatile organic compounds and radon. Avoid loss of volatilematerials by collecting sample in a completely filled container.Achieve this by carefully filling the bottle so that top of meniscusis above the top of the bottle rim. It is important to avoid spillageor air entrapment if preservatives such as HCl or ascorbic acidhave already been added to the bottle. After capping or sealingbottle, check for air bubbles by inverting and gently tapping it;if one or more air bubbles are observed then, if practical, discardthe sample and repeat refilling bottle with new sample until noair bubbles are observed (this cannot be done if bottle containedpreservatives before it was filled).

Serum vials with septum caps are particularly useful in that asample portion for analysis can be taken through the cap byusing a syringe,1 although the effect of pressure reduction in thehead-space must be considered. Pulling a sample into a syringeunder vacuum can result in low bias data for volatile compoundsand the resulting headspace precludes taking further subsamples.

b. Time interval between collection and analysis: In general,the shorter the time that elapses between collection of a sampleand its analysis, the more reliable will be the analytical results.For certain constituents and physical values, immediate analysisin the field is required. For composited samples it is commonpractice to use the time at the end of composite collection as thesample collection time.

Check with the analyzing laboratory to determine how muchelapsed time may be allowed between sample collection andanalysis; this depends on the character of the sample and thestability of the target analytes under the conditions of storage.Many regulatory methods limit the elapsed time between samplecollection and analysis (see Table 1060:I). Changes caused bygrowth of microorganisms are greatly retarded by keeping thesample at a low temperature (�4°C but above freezing). Whenthe interval between sample collection and analysis is longenough to produce changes in either the concentration or the

physical state of the constituent to be measured, follow thepreservation practices given in Table 1060:I. Record timeelapsed between sampling and analysis, and which preservative,if any, was added.

2. Preservation Techniques

To minimize the potential for volatilization or biodegradationbetween sampling and analysis, keep samples as cool as possiblewithout freezing. Preferably pack samples in crushed or cubedice or commercial ice substitutes before shipment. Avoid usingdry ice because it will freeze samples and may cause glasscontainers to break. Dry ice also may effect a pH change insamples. Keep composite samples cool with ice or a refrigerationsystem set at 4°C during compositing. Analyze samples asquickly as possible on arrival at the laboratory. If immediateanalysis is not possible, preferably store at 4°C.1

No single method of preservation is entirely satisfactory;choose the preservative with due regard to the determinations tobe made. Use chemical preservatives only when they do notinterfere with the analysis being made. When they are used, addthem to the sample bottle initially so that all sample portions arepreserved as soon as collected. Because a preservation methodfor one determination may interfere with another one, samplesfor multiple determinations may need to be split and preservedseparately. All methods of preservation may be inadequate whenapplied to suspended matter. Do not use formaldehyde as apreservative for samples collected for chemical analysis becauseit affects many of the target analytes.

Methods of preservation are relatively limited and are in-tended generally to retard biological action, retard hydrolysis ofchemical compounds and complexes, and reduce volatility ofconstituents.

Preservation methods are limited to pH control, chemicaladdition, the use of amber and opaque bottles, refrigeration,filtration, and freezing. Table 1060:I lists preservation methodsby constituent. See Section 7010B for sample collection andpreservation requirements for radionuclides.

The foregoing discussion is by no means exhaustive andcomprehensive. Clearly it is impossible to prescribe absoluterules for preventing all possible changes. Additional advice willbe found in the discussions under individual determinations, butto a large degree the dependability of an analytical determinationrests on the experience and good judgment of the person col-lecting the sample. Numbers of samples required for confidencelevels in data quality objectives, however, rely on statisticalequations such as those discussed earlier.

3. Reference

1. WATER POLLUTION CONTROL FEDERATION. 1986. Removal of Hazard-ous Wastes in Wastewater Facilities—Halogenated Organics. Man-ual of Practice FD-11, Water Pollution Control Fed., Alexandria, Va.

4. Bibliography

KEITH, L.H., ed. 1996. Principles of Environmental Sampling, 2nd ed.ACS Professional Reference Book, American Chemical Soc.,Washington, D.C.

COLLECTION AND PRESERVATION OF SAMPLES (1060)/Sample Storage and Preservation 1-35

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