INDUSTRIAL HYGIENE -INDUSTRIAL HYGIENE - SAMPLING OF GASES AND SAMPLING OF GASES AND

VAPORS VAPORS

UNIVERSITY OF HOUSTON - CLEAR LAKEUNIVERSITY OF HOUSTON - CLEAR LAKE

PURPOSEPURPOSEIntroduce the techniques available for Introduce the techniques available for Industrial Hygienists to evaluate Industrial Hygienists to evaluate EXPOSURES to gases and vapors arising EXPOSURES to gases and vapors arising in or from the workplace. Also: in or from the workplace. Also:

-- be aware of technology available be aware of technology available for assessment of traditional for assessment of traditional

environmentsenvironments-- indoor and ambient air, and indoor and ambient air, and -- capabilities and limitations of capabilities and limitations of

methods.methods.

SAMPLING GASES AND SAMPLING GASES AND VAPORSVAPORS

When developing a particular sampling When developing a particular sampling strategy, review sampling and analytical strategy, review sampling and analytical methods available for the contaminants of methods available for the contaminants of interest. Select most suitable for the interest. Select most suitable for the specific application.specific application.

e.g. OSHA, NIOSHe.g. OSHA, NIOSHi.e. published and validated methodsi.e. published and validated methods

EPA methods used for lower level indoor air EPA methods used for lower level indoor air pollutants and toxic compounds in ambient pollutants and toxic compounds in ambient air media.air media.

SAMPLING METHODSAMPLING METHOD

Select a method that meets the sampling Select a method that meets the sampling and analytical ACCURACY and and analytical ACCURACY and PRECISION requirements of the standard in PRECISION requirements of the standard in its unique field conditions. Usually stipulate its unique field conditions. Usually stipulate measurement at the PEL within a +/- 25% of measurement at the PEL within a +/- 25% of the “true” value at a 95% confidence level. the “true” value at a 95% confidence level.

EPA – indoor air pollutants and toxic EPA – indoor air pollutants and toxic compounds associated with ambient air. compounds associated with ambient air.

ANALYTICAL LABORATORYANALYTICAL LABORATORYSelect and consult with a qualified analytical Select and consult with a qualified analytical laboratory, e.g. AIHA that participates in Laboratory laboratory, e.g. AIHA that participates in Laboratory Accreditation Programs. Labs can assist in Accreditation Programs. Labs can assist in choosing methods that meet the sensitivity and choosing methods that meet the sensitivity and specificity criteria for the environment being specificity criteria for the environment being evaluated. Choose sampling media and strategy evaluated. Choose sampling media and strategy compatible with method selected and advise on compatible with method selected and advise on special handling. special handling.

Two key factors: knowledge of occupational Two key factors: knowledge of occupational environment AND overall perspective of the environment AND overall perspective of the limitation of the chemistry of sampling/analysis. limitation of the chemistry of sampling/analysis.

SENSITIVITYSENSITIVITYExercise caution when using a traditional Exercise caution when using a traditional workplace sampling method for measuring workplace sampling method for measuring contaminants in indoor or ambient air because the contaminants in indoor or ambient air because the expected concentrations may be below the expected concentrations may be below the working range. To obtain sensitivity, NIOSH working range. To obtain sensitivity, NIOSH recommends exceeding the recommended air recommends exceeding the recommended air volume while observing the recommended volume while observing the recommended maximum flow rate. The conservative value maximum flow rate. The conservative value protects against breakthrough (e.g. primary vs. protects against breakthrough (e.g. primary vs. back-up sections of sampler) under “worst-case” back-up sections of sampler) under “worst-case” conditions of high %RH and/or concentrations.conditions of high %RH and/or concentrations.

GAS/VAPORGAS/VAPORFor IH purposes, a substance is a GAS if For IH purposes, a substance is a GAS if this is normal physical state at room this is normal physical state at room temperature (25 degrees C) and one-temperature (25 degrees C) and one-atmosphere pressure. atmosphere pressure.

ExamplesExamples: CO, Cl, Oxygen, and Nitrogen.: CO, Cl, Oxygen, and Nitrogen.

If substance is normally a liquid at normal If substance is normally a liquid at normal temperature and pressure, then the gaseous temperature and pressure, then the gaseous component in equilibrium with liquid state is component in equilibrium with liquid state is a VAPOR.a VAPOR.

ExamplesExamples: CCl4, HCOH, and Benzene.: CCl4, HCOH, and Benzene.

SAMPLING PLANSAMPLING PLANDesigning a sampling plan involves consideration Designing a sampling plan involves consideration of the following: location of samples, the number of the following: location of samples, the number of workers to be sampled, and the duration of of workers to be sampled, and the duration of sampling. Also consider other factors – noise, sampling. Also consider other factors – noise, equipment, size, flow rate, and security. equipment, size, flow rate, and security.

Two basic types of samples are used to assess Two basic types of samples are used to assess employee exposure to gases and vapors in the employee exposure to gases and vapors in the workplace: workplace:

-- integratedintegrated

-- grab. grab.

INTEGRATED SAMPLINGINTEGRATED SAMPLINGFor gases and vapors, involves passage of For gases and vapors, involves passage of a known volume of air through an absorbing a known volume of air through an absorbing or adsorbing medium to remove the desired or adsorbing medium to remove the desired contaminants from the air during a specified contaminants from the air during a specified period of time. Contaminants of interest are period of time. Contaminants of interest are collected and concentrated over a period of collected and concentrated over a period of time to obtain the average exposure levels time to obtain the average exposure levels during the entire sampling period. during the entire sampling period.

GRAB SAMPLINGGRAB SAMPLINGThis technique involves the direct collection This technique involves the direct collection of an air-contaminant mixture into a device of an air-contaminant mixture into a device (i.e. sampling bag, syringe, or evacuated (i.e. sampling bag, syringe, or evacuated flask) over a short interval of a few seconds flask) over a short interval of a few seconds or minutes. Represents the atmospheric or minutes. Represents the atmospheric concentrations at the sampling site at a concentrations at the sampling site at a given point in time. given point in time.

WHOLE AIR SAMPLINGWHOLE AIR SAMPLINGThis technique involves the collection of air This technique involves the collection of air into a sealable container (e.g. stainless steel into a sealable container (e.g. stainless steel canister or sampling bag) for subsequent canister or sampling bag) for subsequent analysis. Can be collected over a short analysis. Can be collected over a short period of time as grab samples or integrated period of time as grab samples or integrated over a longer period of time to obtain Time-over a longer period of time to obtain Time-Weighted Average (TWA) concentrations. Weighted Average (TWA) concentrations.

INTEGRATED SAMPLINGINTEGRATED SAMPLINGThis type of sampling to cover the entire This type of sampling to cover the entire period of exposure is required because period of exposure is required because airborne contaminant concentrations during airborne contaminant concentrations during a typical work shift vary with time and a typical work shift vary with time and activity. Grab samples do not reflect activity. Grab samples do not reflect average exposures. Most integrated average exposures. Most integrated sampling is done to determine the 8-hour sampling is done to determine the 8-hour TWA and/or STELs to compare with OSHA TWA and/or STELs to compare with OSHA PELs, ACGIH TLVs and NIOSH RELs. PELs, ACGIH TLVs and NIOSH RELs.

INTEGRATED SAMPLINGINTEGRATED SAMPLINGCONSIDERATIONSCONSIDERATIONS

Appropriate sample duration and flow rate Appropriate sample duration and flow rate need to be chosen relative to the purpose of need to be chosen relative to the purpose of sampling, the sensitivity of the analytical sampling, the sensitivity of the analytical method, and the expected concentration of method, and the expected concentration of the contaminant of interest. It is also the contaminant of interest. It is also essential that the flow rate and time be essential that the flow rate and time be accurately measured. The accuracy accurately measured. The accuracy depends on the precise determination of the depends on the precise determination of the mass of contaminant collected as well as mass of contaminant collected as well as the volume of air sampled. the volume of air sampled.

ACTIVE SAMPLINGACTIVE SAMPLINGMeans of collecting an airborne substance Means of collecting an airborne substance that employs a mechanical device such as an that employs a mechanical device such as an air sampling pump to draw the air/contaminant air sampling pump to draw the air/contaminant mixture into or through the sampling device. mixture into or through the sampling device.

ExamplesExamples: sorbent tube, treated filter, or : sorbent tube, treated filter, or impinger containing a liquid media. impinger containing a liquid media.

A key element is calibration that reliably A key element is calibration that reliably measures the pump flow rate, thus allowing measures the pump flow rate, thus allowing for an accurate determination of air volume. for an accurate determination of air volume.

AIR SAMPLING PUMPSAIR SAMPLING PUMPS Integrated methods require a relatively constant Integrated methods require a relatively constant

source of suction that can be calibrated to the source of suction that can be calibrated to the recommended flow rate (within +/- 5% with recommended flow rate (within +/- 5% with collection media in-line).collection media in-line).

Personal sampling within the worker’s breathing Personal sampling within the worker’s breathing zone zone oror can be used as area samplers. can be used as area samplers.

Features – constant flow capabilities/back Features – constant flow capabilities/back pressure; intrinsically safe; electromagnetic pressure; intrinsically safe; electromagnetic susceptibility, etc.susceptibility, etc.

Must be capable of maintaining the desired flow Must be capable of maintaining the desired flow rate over the entire sampling period with the rate over the entire sampling period with the sample collection device in-line. sample collection device in-line.

Pressure drop; constant flow vs. constant pressurePressure drop; constant flow vs. constant pressure

CALIBRATIONCALIBRATIONPump flow must be calibrated with the entire Pump flow must be calibrated with the entire sampling train assembled as it will be used sampling train assembled as it will be used in the field. Good IH practice requires both in the field. Good IH practice requires both pre- and post-pump calibration on the same pre- and post-pump calibration on the same day under pressure and temperature day under pressure and temperature conditions similar to those at site. Should conditions similar to those at site. Should not be done with built-in rotameters (not not be done with built-in rotameters (not precision devices and will not give a precision devices and will not give a quantitative measure of the rate of airflow). quantitative measure of the rate of airflow).

CALIBRATION STANDARDSCALIBRATION STANDARDSTwo terms:Two terms: Primary – direct and measurable linear Primary – direct and measurable linear

dimensions (length and diameter of cylinder)dimensions (length and diameter of cylinder)– Examples: spirometers and bubble metersExamples: spirometers and bubble meters

Secondary – flowmeters that trace Secondary – flowmeters that trace calibration to primary standards and calibration to primary standards and maintain accuracy with reasonable care and maintain accuracy with reasonable care and handling in operation. handling in operation. – Examples: precision rotameters, wet test Examples: precision rotameters, wet test

meters, and dry gas meters.meters, and dry gas meters.

Refer to instructions from manufacturers.Refer to instructions from manufacturers.

SAMPLE COLLECTION MEDIASAMPLE COLLECTION MEDIAConsult published air sampling methods to Consult published air sampling methods to determine the appropriate collection media determine the appropriate collection media for a specific chemical contaminant. for a specific chemical contaminant.

Review methods to determine applicability Review methods to determine applicability relative to field conditions. Such as: vp, bp, relative to field conditions. Such as: vp, bp, reactivity; interferences as well as also reactivity; interferences as well as also humidity/temperature effects, proper humidity/temperature effects, proper measuring range; physical state of the measuring range; physical state of the contaminant being sampled; multiple phases contaminant being sampled; multiple phases (i.e. particulate and vapor phase). (i.e. particulate and vapor phase).

ACTIVE SAMPLING – ACTIVE SAMPLING – ADVANTAGESADVANTAGES

- - Select method to be used by Select method to be used by compliance compliance personnel during OSHA personnel during OSHA inspection.inspection.

- - Offers calibrated, measured airflow for Offers calibrated, measured airflow for assurance in accuracy of sample volume. assurance in accuracy of sample volume.

- - Sorbent tube samples have a secondary Sorbent tube samples have a secondary layer for back-up indicating layer for back-up indicating

breakthrough.breakthrough.

- - Multiple phases can be assessed by a Multiple phases can be assessed by a series of samplers. series of samplers.

ACTIVE SAMPLING – ACTIVE SAMPLING – DISADVANTAGESDISADVANTAGES

- - Cumbersome equipment and may Cumbersome equipment and may interfere interfere with job of workers throughout with job of workers throughout

shift. shift.

- - Pump calibration is time consuming Pump calibration is time consuming and and requires technical training on tasks. requires technical training on tasks.

-- Pump may become somewhat less Pump may become somewhat less reliable at maintaining constant flow reliable at maintaining constant flow

over over the entire sampling period, and more the entire sampling period, and more frequent calibration may be necessary. frequent calibration may be necessary.

PASSIVE SAMPLERSPASSIVE SAMPLERSPassive sampling is the collection of Passive sampling is the collection of airborne gases and vapors at a rate airborne gases and vapors at a rate controlled by a physical process such as controlled by a physical process such as diffusion through a static air layer or diffusion through a static air layer or permeation through a membrane without the permeation through a membrane without the active movement of air through an air active movement of air through an air sampler. Operate on principle of diffusion.sampler. Operate on principle of diffusion.

DIFFUSIVE SAMPLERSDIFFUSIVE SAMPLERSDiffusive samplers rely on the movement of Diffusive samplers rely on the movement of contaminant molecules across a concentration contaminant molecules across a concentration gradient, which for steady-state conditions can be gradient, which for steady-state conditions can be defined by Fick’s first law of diffusion. Consist of defined by Fick’s first law of diffusion. Consist of diffusion gap between external air and a sorbing diffusion gap between external air and a sorbing medium which serves to collect the chemicals of medium which serves to collect the chemicals of interest, but also to maintain the concentration as interest, but also to maintain the concentration as close to zero as possible at the end of the diffusion close to zero as possible at the end of the diffusion path. path. Each gas/vapor sampled has a specified Each gas/vapor sampled has a specified diffusion coefficientdiffusion coefficient (D). Uptake rates can vary (D). Uptake rates can vary under various field conditions. Validation!under various field conditions. Validation!

See Equations and Units on Page 274 (Third See Equations and Units on Page 274 (Third Edition).Edition).

OSHA ISSUESOSHA ISSUESResearch report in 1998 that attempted to Research report in 1998 that attempted to determine sampling rate variation of specific determine sampling rate variation of specific passive sampler designs. Concept of passive passive sampler designs. Concept of passive sampling equated to active sampling with pump sampling equated to active sampling with pump error of +/- 5%. Significant in that use of the error of +/- 5%. Significant in that use of the sampling rate variation for a passive sampler sampling rate variation for a passive sampler along with the analytical error component allowed along with the analytical error component allowed the calculation of the overall sampling and the calculation of the overall sampling and analytical error (SAE). SAE must be used by analytical error (SAE). SAE must be used by OSHA inspectors along with sample results to OSHA inspectors along with sample results to determine if PEL exceeded. Therefore, passive determine if PEL exceeded. Therefore, passive sampling methods can be used by OSHA.sampling methods can be used by OSHA.

PASSIVE SAMPLERSPASSIVE SAMPLERSCommercially available for a variety of airborne Commercially available for a variety of airborne contaminants. Some samplers are designed to contaminants. Some samplers are designed to collect a broad range of compounds, whereas collect a broad range of compounds, whereas others because of their collection media others because of their collection media preferentially collect a single chemical or family of preferentially collect a single chemical or family of chemicals. chemicals. ExamplesExamples: activated charcoal sorbent – organic : activated charcoal sorbent – organic vapors and GC analysis; chemical treated vapors and GC analysis; chemical treated sorbents or filter paper for preferential collection sorbents or filter paper for preferential collection for HPLC analysis.for HPLC analysis.Direct-reading passive samplers based on Direct-reading passive samplers based on colorimetric techniques. May not be as accurate colorimetric techniques. May not be as accurate as lab analytical methods. Discuss examples.as lab analytical methods. Discuss examples.

PASSIVE SAMPLING – PASSIVE SAMPLING – ADVANTAGESADVANTAGES

-- Easy to use, allowing samples to be Easy to use, allowing samples to be collected by personnel with less technical collected by personnel with less technical training. training.

- - Less expensive. Less expensive.

- - Less obtrusive to wearer for monitoring. Less obtrusive to wearer for monitoring.

- For most applications, the mass of - For most applications, the mass of contaminant collected by passive contaminant collected by passive samplers samplers is not significantly affected by is not significantly affected by temperature or temperature or pressure. pressure.

PASSIVE SAMPLING – PASSIVE SAMPLING – DISADVANTAGESDISADVANTAGES

- May not be OSHA/NIOSH methods to reference - May not be OSHA/NIOSH methods to reference in order to insure reliability of data. in order to insure reliability of data.

- Sampling rate, if theoretically calculated, may - Sampling rate, if theoretically calculated, may not prove to be valid under field conditions. not prove to be valid under field conditions.

-- Reverse diffusion may be a factor.Reverse diffusion may be a factor.-- Environmental parameters may influence the Environmental parameters may influence the

collection efficiency of passive samplers. collection efficiency of passive samplers. ExamplesExamples: stagnant air; high face velocities. : stagnant air; high face velocities.

-- Low uptake rates may not provide sensitivity Low uptake rates may not provide sensitivity required for low-level determinations, and required for low-level determinations, and extended sampling times (>24 hours) may extended sampling times (>24 hours) may enhance reverse diffusion effects.enhance reverse diffusion effects.

GRAB SAMPLINGGRAB SAMPLINGThis type of collected sample measures gas and This type of collected sample measures gas and vapor concentrations AT A POINT IN TIME and vapor concentrations AT A POINT IN TIME and are used to evaluate “PEAK” exposures for are used to evaluate “PEAK” exposures for comparison to “Ceiling” limits. comparison to “Ceiling” limits. Can be used to identify unknown contaminants, to Can be used to identify unknown contaminants, to evaluate contaminant sources, or to measure evaluate contaminant sources, or to measure contaminant levels from intermittent processes or contaminant levels from intermittent processes or other sources. Collected using syringes, other sources. Collected using syringes, canisters, or sampling bags.canisters, or sampling bags.Instantaneous (as well as integrated) Instantaneous (as well as integrated) measurements of gases/vapors also may be measurements of gases/vapors also may be performed using detector tubes or direct-reading performed using detector tubes or direct-reading instruments. instruments.

GRAB SAMPLING – GRAB SAMPLING – ADVANTAGESADVANTAGES

-- After collection, can frequently be After collection, can frequently be analyzed immediately by GC or direct-analyzed immediately by GC or direct-reading instruments. reading instruments.

- - Therefore, quick decisions can be Therefore, quick decisions can be made made in field or at the site about source in field or at the site about source of of leaks, Confined Space Entry (CSE), leaks, Confined Space Entry (CSE),

PPE, etc. PPE, etc.

GRAB SAMPLING – GRAB SAMPLING – DISADVANTAGESDISADVANTAGES

- For most applications, contaminants are - For most applications, contaminants are collected but not integrated over time. Only collected but not integrated over time. Only some devices will allow use of a metering some devices will allow use of a metering device to collect sample(s) at or near constant device to collect sample(s) at or near constant

flow over period of time for TWA. flow over period of time for TWA.

- For low contaminant concentrations, analytical - For low contaminant concentrations, analytical instrument may not be sensitive for instrument may not be sensitive for

detection. detection.

-- Using multiple grab samples to assess full-Using multiple grab samples to assess full-shift shift exposures is time-consuming and subject to exposures is time-consuming and subject to

error.error.

OPERATIONAL LIMITS OF OPERATIONAL LIMITS OF SAMPLING AND ANALYSISSAMPLING AND ANALYSIS

Inherent limitations of method:Inherent limitations of method:- Sampler capacitySampler capacity- Limit of Detection (LOD)Limit of Detection (LOD)- Limit of Quantification (LOQ)Limit of Quantification (LOQ)- Upper measurement limits which define the useful Upper measurement limits which define the useful

range of the method. range of the method. These factors determine the minimum, maximum, or These factors determine the minimum, maximum, or

optimum volume of air to be sampled and may optimum volume of air to be sampled and may determine the confidence that can be placed in the determine the confidence that can be placed in the results.results.

Discuss with lab before sampling!Discuss with lab before sampling!

SAMPLER CAPACITYSAMPLER CAPACITYPredetermined conservative estimate of the total Predetermined conservative estimate of the total mass of contaminant that can be collected on the mass of contaminant that can be collected on the sampling medium without loss of overloading.sampling medium without loss of overloading.NIOSH definition of 2/3 of the experimental NIOSH definition of 2/3 of the experimental breakthrough capacity of the solid sorbent, that is breakthrough capacity of the solid sorbent, that is 67% of the mass of contaminant on the sorbent at 67% of the mass of contaminant on the sorbent at the breakthrough volume. the breakthrough volume. Breakthrough volume is defined as that volume of Breakthrough volume is defined as that volume of an atmosphere containing two times the PEL for an atmosphere containing two times the PEL for the contaminant that can be sampled at the the contaminant that can be sampled at the recommended flow rate before the efficiency of the recommended flow rate before the efficiency of the sampler degrades to 95%.sampler degrades to 95%.

LIMIT OF DETECTION (LOD)LIMIT OF DETECTION (LOD)Lowest concentration level that can be Lowest concentration level that can be determined to be statistically different from a determined to be statistically different from a blank sample. blank sample.

Recommended value of the LOD is the Recommended value of the LOD is the amount of analyte that will give rise to a amount of analyte that will give rise to a signal that is three times the standard signal that is three times the standard deviation of the signal derived from the deviation of the signal derived from the media blank. media blank.

LIMIT OF QUANTIFICATION (LOQ)LIMIT OF QUANTIFICATION (LOQ)Concentration level above which Concentration level above which quantitative results may be obtained with a quantitative results may be obtained with a certain confidence. certain confidence.

Recommended value of the LOQ is the Recommended value of the LOQ is the amount of analyte that will give rise to a amount of analyte that will give rise to a signal that is ten times the standard signal that is ten times the standard deviation of the signal from a series of deviation of the signal from a series of media blanks. Corresponds to a relative media blanks. Corresponds to a relative uncertainty in the measurement of +/- 30% uncertainty in the measurement of +/- 30% at 99% confidence level.at 99% confidence level.

DETECTION LIMITDETECTION LIMITDescribed both in terms of detection limit of Described both in terms of detection limit of the analytical procedure, and the detection the analytical procedure, and the detection limit of the overall procedure. limit of the overall procedure.

OSHA reports, in general, that detection OSHA reports, in general, that detection limits are defined as the amount of analyte limits are defined as the amount of analyte that gives a response that is significantly that gives a response that is significantly different (three SD) from the background different (three SD) from the background response. response.

UPPER MEASUREMENT LIMITUPPER MEASUREMENT LIMITUseful limit of the analytical instrument (mg Useful limit of the analytical instrument (mg of analyte per sample). of analyte per sample).

Sample above Upper Measurement Limit, Sample above Upper Measurement Limit, then re-dilute and re-analyze. then re-dilute and re-analyze.

Discuss with analytical lab. Discuss with analytical lab.

TARGET CONCENTRATION TARGET CONCENTRATION Preliminary estimate of the airborne Preliminary estimate of the airborne concentration of the contaminant of interest concentration of the contaminant of interest relative to the purpose of testing. relative to the purpose of testing.

Parameter can be used to determine the Parameter can be used to determine the minimum and maximum air volumes. minimum and maximum air volumes.

Can be estimated by using previous Can be estimated by using previous sampling data, use of direct-reading sampling data, use of direct-reading instruments, or by relying on the instruments, or by relying on the professional judgment of the IH. professional judgment of the IH.

CALCULATIONS CALCULATIONS Sample volumes – minimum and maximum.Sample volumes – minimum and maximum.Working range is range of contaminant Working range is range of contaminant concentration that may be quantitated at a concentration that may be quantitated at a specified air volume. specified air volume. Lower boundary of the working range is Lower boundary of the working range is defined by a sample that has a mass of defined by a sample that has a mass of contaminant equal to the LOQ. The upper contaminant equal to the LOQ. The upper boundary is defined by sampler capacity. boundary is defined by sampler capacity. Refer to Page 278 (Third Edition) for Refer to Page 278 (Third Edition) for formulas.formulas.

SOLID SORBENT MEDIASOLID SORBENT MEDIAAdsorb onto surface; Effectiveness determined by:Adsorb onto surface; Effectiveness determined by: Trap and retain nearly all contaminant from airTrap and retain nearly all contaminant from air Amenable to desorption from sorbent Amenable to desorption from sorbent Sufficient capacity to retain quantity of Sufficient capacity to retain quantity of

contaminant to facilitate analysis without creating contaminant to facilitate analysis without creating large pressure drop across sample medialarge pressure drop across sample media

Not cause chemical change of contaminant except Not cause chemical change of contaminant except by analytical method as neededby analytical method as needed

Absorb contaminant of interest in presence of Absorb contaminant of interest in presence of other contaminants, possibly in higher other contaminants, possibly in higher concentrations than the contaminant of interest.concentrations than the contaminant of interest.

COLLECTION EFFICIENCY OF COLLECTION EFFICIENCY OF SOLID SORBENTSSOLID SORBENTS

Various Factors:Various Factors: TemperatureTemperature Humidity Humidity Sampling RateSampling Rate Other ContaminantsOther Contaminants Sample Breakthrough Sample Breakthrough

-- 25%25%

-- MigrationMigration

DESORPTION DESORPTION -- Solvent extraction - extract Solvent extraction - extract contaminants contaminants of interest from the of interest from the adsorbent materialsadsorbent materials

ExamplesExamples: carbon disulfide; mixtures: carbon disulfide; mixtures

-- Thermal desorption – drive Thermal desorption – drive contaminant contaminant off sorbent by subjection to off sorbent by subjection to high high temperature; entire mass of temperature; entire mass of contaminant contaminant collected introduced directly collected introduced directly into into analytical instrument with no dilution; analytical instrument with no dilution; can can measure low airborne concentrations.measure low airborne concentrations.

DESORPTION EFFICIENCYDESORPTION EFFICIENCYMeasure of how much analyte can be Measure of how much analyte can be recovered from the sorbent tube; recovered from the sorbent tube; determined typically at 0.1, 0.5, 1, and 2 determined typically at 0.1, 0.5, 1, and 2 times the target concentration based on the times the target concentration based on the recommended air volume and expressed as recommended air volume and expressed as a percentage of analyte spike on the sorbent a percentage of analyte spike on the sorbent tube. tube. Should be determined for each lot number Should be determined for each lot number of solid sorbent used for sampling and of solid sorbent used for sampling and should be done in the concentration range should be done in the concentration range of interest. of interest.

TYPES OF SORBENT MATERIALSTYPES OF SORBENT MATERIALS

Inorganic Sorbents – silica gel (polar; %RH); Inorganic Sorbents – silica gel (polar; %RH); less reactive than charcoalless reactive than charcoal

Elemental Carbon – charcoal types; Elemental Carbon – charcoal types; organics; high adsorptive capacity; stable organics; high adsorptive capacity; stable compounds; high humidity parameterscompounds; high humidity parameters

Carbonized or Graphitized Sorbents – low to Carbonized or Graphitized Sorbents – low to moderate surface area; intermediate to high moderate surface area; intermediate to high volatility; stable compounds for thermal volatility; stable compounds for thermal desorptiondesorption

TYPES OF SORBENT MATERIALSTYPES OF SORBENT MATERIALS

Organic Polymers - selectivity to particular Organic Polymers - selectivity to particular applications, and the stability of some applications, and the stability of some polymers at high temps enables thermal polymers at high temps enables thermal desorption (i.e. Tenax – broad range of desorption (i.e. Tenax – broad range of organics can be collected)organics can be collected)

Other Sorbent Materials – Sorbents with Other Sorbent Materials – Sorbents with PUF; sorbent combinations; sorbent/filter PUF; sorbent combinations; sorbent/filter combinations – OVS, etc. combinations – OVS, etc.

OTHER MEDIAOTHER MEDIA Chemically treated filters – derivatize/desorbChemically treated filters – derivatize/desorb Liquid absorbersLiquid absorbers

– Gas washing bottles – e.g. impingersGas washing bottles – e.g. impingers– Fritted glass bubblers Fritted glass bubblers

Sampling bags/partially evacuated rigid containers Sampling bags/partially evacuated rigid containers (canisters) (canisters) – SituationsSituations: use of direct-reading instruments; : use of direct-reading instruments;

leaks/emergencies; peak concentrations; highly volatile leaks/emergencies; peak concentrations; highly volatile compoundscompounds

- Precautions – storage time; reaction; diffusionPrecautions – storage time; reaction; diffusion

Whole Air Sampling [HDS – helium]Whole Air Sampling [HDS – helium] Cold TrapsCold Traps

CALCULATIONSCALCULATIONS

Total Mass of ContaminantTotal Mass of Contaminant Airborne Concentration by sample volume Airborne Concentration by sample volume

(mass over volume)(mass over volume) Air Volume (flow rate x sample time)Air Volume (flow rate x sample time) Unit Conversions – mg/M3 to/from ppmUnit Conversions – mg/M3 to/from ppm Temperature/Pressure CorrectionsTemperature/Pressure Corrections Time-Weighted Averages Time-Weighted Averages Potential Work Shift Adjustments Potential Work Shift Adjustments

Formulas on Page 286-287 (Third Edition).Formulas on Page 286-287 (Third Edition).

REMEMBERREMEMBERCALCULATIONSCALCULATIONS

A range of temperature and pressure changes can A range of temperature and pressure changes can be tolerated before corrections are applied to the be tolerated before corrections are applied to the volumevolume or or air sampledair sampled during an exposure during an exposure assessment. assessment.

All OELs and environmental exposure standards All OELs and environmental exposure standards and limits are expressed at 25 degrees C and 1 and limits are expressed at 25 degrees C and 1 atmosphere (760 mm Hg), defined as normal atmosphere (760 mm Hg), defined as normal temperature and pressure (NTP). temperature and pressure (NTP).

Therefore, corrections needed for meaningful Therefore, corrections needed for meaningful comparisons related to published exposure limits.comparisons related to published exposure limits.