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TheReporterVOL 18.7

www.sigma-aldrich.com/TheReporter

a member of the Sigma-Aldrich familyGCissue

G001386

CONTENTS

:

l The Importance ofPure Air for MaximumFID Performance

Page 2:

l New ProductsGas Generation, Purification, and DeliverySample Preparation and IntroductionFittings and AccessoriesColumns

Page 3:

l New Applicationsl Seminarsl New Literaturel GC Performance Tip

Mass #100 Isn’t the Column

Page 4:

l The Importance of PureAir...(contd.)

l Case Study 3A Drifting Baseline

T200007

The Importance of Pure Air for Maximum FID PerformanceHave you ever asked yourself why your baseline driftswhen using a flame ionization detector (FID)? Do

you have difficulty integrating peaks because your baselineisn’t flat? While you may have chosen the best grade of car-rier gas and have installed purifiers to guarantee purity, thereare special considerations for air that feeds the FID.Determining air purity may not be straightforward. Gaspurity is usually expressed in terms of “nines”. For example,a cylinder may be referred to as 99.999%, or “5 nines” pure.These values are stated in terms of contaminants measuredsubtracted from 100. Unfortunately, not all contaminantsare measured. Methane, for example, is commonly ignoredin cylinder air. If you look closely, the manufacturer’s puritycertificate will often state that methane is not assayed.

The ProblemConventional gas purifiers do not remove methane from air.A catalytic purifier employed in a zero air generator is neededto remove methane. Within the gas industry, the “zero” term(“zero air” for example) means that all hydrocarbons, includ-ing methane, are reduced. Residual methane can cause drift-ing baselines (sinusoidal effect), limit GC sensitivity, and causepeak integration problems. Because of this, zero air is criticalfor optimum performance of your FID.Gas cylinders, house systems and laboratory compressors areall acceptable sources of air but each needs special consid-eration to supply air that is both methane and hydrocarbonfree. But what is the best approach to removing hydrocar-bons, including methane, from air?

The ApproachCylinders - The use of cylinders is ideal because the purity ofthe air is largely known. With cylinder air, in-line moistureand hydrocarbon purifiers such as the Supelco molecularsieve water trap and Supelcarb hydrocarbon trap must beinstalled to insure that the maximum cylinder impuritiesare below 100ppm for moisture and hydrocarbons, respec-tively. Next, add a zero air generator (Figure 1). Be sure tomatch the capacities of your purifiers with your expectedflow requirements. Exceeding the flow capacity of a purifierwill allow contaminants to break through.A further advantage of zero air generators is in its costsavings. What many GC users do not realize is that a zeroair generator used in conjunction with conventional pu-

rifiers yields the highest attainable purityair even from low-grade cylinder air! Be-cause expensive ultra high-purity cylinderair is not required, significant cost savingsare achieved.

(continued on page 4)

House Air - With proper precautions, house air is a goodalternative to cylinder air. Most house air systems utilizeoil-sealed compressors. While new house air systems pro-vide low hydrocarbon and moisture emissions, older sys-tems are more likely to pass oil vapors. Often, the qual-ity, flow capacity, or available pressure of house air isunknown. Even if the house air system has moisture andhydrocarbon traps installed, this does not guarantee thatall of the contaminants have been eliminated. Often,contaminants will accumulate in the lines over time. Thesolution is to install a high flow Pure Air Generator onyour house system. These automatic cleaning and switch-ing generators (purifiers) remove contaminants that ap-pear seasonally with ambient temperature changes andsafeguard your zero air generators. They have flow ca-pacities ranging from 85L/min up to 366L/min.Compressors - In some situations, the best solution is toinstall a non oil-sealed air compressor such as the Jun-Air oilless air compressor in the lab. Lab compressorseliminate your dependence on the scheduled plant main-tenance of house systems and provide a dedicated sys-tem with full control of all aspects of the gas purity. Typi-cal payback for a compressor is less than one year. Thesehigh flow compressors (42 – 100 L/min) come with mois-ture and hydrocarbon-trapping systems that meet theinput specifications for zero air purity. Smaller units maynot contain built in purifiers and may lack other featuressuch as sound cabinets. All compressors should have ameans to dampen compressor pressure surges.

Figure 1. Three Approaches to Pure Air

*optional purifiers used withsmall compressor with no

onboard purification

2.House

AirPure AirGenera-

tor

Zero Air

GC

1. Cylinders

3. Compressors

Moisture trap

Hydrocarbon trap

Moisture trap

Hydrocarbon trap

P000752a

E000837

E000774

P000699

P000258

E000775

NEW PRODUCTS

Gas Generation, Purification and Delivery

domnick hunter Pure Air GeneratorNitrox UHP pure air generators remove water, dirt, and oilfrom air using reliable pressure swing adsorption technol-ogy. Two beds of high performance desiccant alternate be-tween moisture removal mode and regeneration mode, forcontinuous delivery of air at specified purity levels. Highefficiency pre-desiccant and post desiccant filtration ensurestotal air quality.Note: These units do not remove methane. Methane freeair requires a zero air generator.Model 070 ................................................................ 27751-UModel 140 ................................................................ 27752-UModel 300 ................................................................ 27753-U

For more information, request T499200.

domnick hunter Zero Air GeneratorNitrox zero air generators employ a catalytic oxidationsystem to produce a continuous supply of air that is virtu-ally free of hydrocarbons, including methane. Incomingcompressed air is filtered to remove oil, water and par-ticles and then passed through a heated catalyst that re-duces hydrocarbon concentrations to below 0.1 ppm whenthe incoming air contains less than 10ppm hydrocarbons(as methane).Model 10 .................................................................. 27758-UModel 35 .................................................................. 27759-U


Packard Model 9000 Hydrogen GeneratorHydrogen generators are a safe and economic alternative tohigh-pressure gas cylinders. Supelco has added the PackardModel 9000, the newest member of the Packard generatorfamily to our product line. This new model utilizes the samereliable Solid Polymer Electrolyte (SPE) technology as thehigher capacity models of Packard hydrogen generators toproduce 80 cc/min of 99.9999+% hydrogen. This afford-able new model is an ideal source of hydrogen as fuel forone or two FID’s.Model 9000 hydrogen generator ............................... 27773-U


Sample Preparation and Introduction

Inlet Seals for Agilent GC’sLow cost, replacement inlet seals for Agilent GC’s fromSupelco reduce the need for cleaning and reuse. Supelcometal selection yields a better inlet seal. Seals are availablein stainless steel and gold plated versions. Precise, comput-erized machining reduces dimensional variation that canoccur with other seals.Stainless Steel HP Inlet Seals, Pk. of 2 ......................... 23316-UStainless Steel HP Inlet Seals, Pk. of 10 ....................... 23317-UGold Plated HP Inlet Seals, Pk. of 2 ............................. 23318-UGold Plated HP Inlet Seals, Pk. of 10 ........................... 23319-U


domnick hunter Zero Air Generator

Packard Model 9000 HydrogenGenerator

Inlet Seals for Agilent/HP GC’s

domnick hunter Pure Air Generator

Fittings and Accessories

ms-NoVentA new time saving acces-sory for GC/MS systems,the ms-NoVent allowscapillary users to begin us-ing the mass spec withinminutes after changingcolumns. The ms-NoVentsupplies the mass specwith carrier gas during column change, eliminating systempump down. It consists of a pressure switching valve, fusedsilica restrictor, and an external control module. Installa-tion in Agilent, Varian, Shimadzu, and other systems is typi-cally less than 30 minutes.ms-NoVent System .................................................... 26191-URestrictors for ms-NoVent SystemRestrictor for HP5970, Qty. 2 ..................................... 26192-URestrictor for HP 5971/5972, Qty. 2 ........................... 26193-URestrictor for HP 5973, Qty. 2 .................................... 26194-URestrictor for Varian Saturn, Qty. 2 ............................. 26195-URestrictor for Shimadzu 5000/5050, Qty. 2 ................ 26196-U


Septum Insertion ToolChange a septum quickly without cooling theinjector thanks to Supelco’s new patented sep-tum insertion tool. This tool installs a septuminto any GC injection port that uses 9.5 - 11mmdiameter septa. The tool compresses the septaand makes inserion into the injector easier. Itreduces the potential for burned fingers andcontamination from finger oils or other sources.Septum Inserter ...................................... 21385-U


Columns

Capillary Columns for Agilent 6850Supelco makes it easy to purchase off-the-shelf capillary GCcolumns for the Agilent 6850! By referencing order codePRO100060, you can purchase any stock or custom Su-pelco capillary column wound on an authentic AgilentTechnologies 6850 cage. To order, simply provide order codePRO100060 plus the stock capillary item number or cus-tom column information. Supelco will coil the column ontoa 6850 cage and ship the column within 24 hours.


All literature mentioned in this issue can be obtained fromthe website, www.sigma-aldrich.com/TheReporter, bycompleting the Literature Request section on the reply card,or by calling our Technical Service Department.

Len Sidisky - R&D Manager,Gas Separations Business Unit

Mass #100 Isn’t the ColumnMany GC/MS chromatographers are used to seeing mass#207 or #73 background from methyl silicone columns.Sometimes you see mass #100. Where does this come from?Graphite/Vespel ferrules used to connect the column tothe MSD interface are rich sources of mass #100 and maycause background if the ferrule is incorrectly installed or ifthe wrong ferrule is used. If you see background, check thecolumn installation and the ferrule used at the interface.

GC PERFORMANCE TIP

NEW LITERATURE

Gas Purification Guide UpdatedSelecting the proper purifiers for a GC system begins withdetermining the contaminants to be removed, the levels towhich they must be reduced, and the flow and pressure needsof the system. The best purifier system includes multiplepurifiers that help protect each other while protecting col-umns and detectors. This updated bulletin includes infor-mation needed to select suitable purifiers for carrier gas,and for air and hydrogen used as fuel gases.


SPME Application Guide UpdateThe SPME Applications Guide is a bibliographic resourceof more than 600 published technical articles about solidphase microextraction. With the continued growth ofSPME, and its expansion into environmental, food, foren-sic, and other fields, we recognize the need for an organizedbibliography. This updated guide should serve a useful pur-pose in your SPME research and analyses.


Updated Gas Management Systems for GCThe information in this bulletin will help you to use yourgas management resources wisely and obtain efficient per-formance from one, several, or many gas chromatographs.This updated bulletin includes installation information anddiagrams specific for 1, 2-4, or 5-20 gas chromatograph sys-tems. Common installations are illustrated. The bulletindiscusses how to choose, clean, and connect tubing, thecomparative merits of gas cylinders and generators, and howto attain suitable levels of gas purity. We recommend youread this updated bulletin along with your instrumentmanual before installing a GC(s).


Supelco Petroleum Guide UpdatedThis 48-page guide contains information about Supelco prod-ucts and technology for separating hydrocarbons by chro-matographic methods. The updated guide illustrates nearlyone hundred different hydrocarbon separations includingPONA, PIANO, and SIMDIS applications. Multiple capil-lary and HPLC products are included to help with your ana-lytical hydrocarbon needs. The guide is recently updated toreflect current products and applications available at Supelco.


NEW APPLICATIONS

GC/MS Analysis of Impurities in Denatured EthanolSDA is the most common form of denatured ethyl alcohol.It is also a solvent commonly used in industrial applica-tions. Organic impurities can affect the product in whichSDA is used. This application illustrates analysis of 19 im-purities commonly found in SDA-3A, which is ethanoldenatured with 5% methanol. GC/MS was used for thepositive identification of contaminants. The application isunusual in that special precautions were taken to protectthe MSD during the analysis.


Analysis of Fusel Oils in Alcoholic BeveragesAlcoholic beverage and coffee producers regularly analyzefor fusel oils resulting from the fermentation and/or agingprocess. This separation has traditionally been run usingpacked column GC. In this application, an SPB-20 columnis used to resolve twelve different contaminants from a rumstream at PPM levels. The application illustrates separa-tion of the critical iso-amyl and active-amyl alcohol peaks.Total analysis time is less than 25 minutes.


SEMINARS

Analysis of Flavors and Off-Flavors in Foods andBeverages Using SPMESPME is a convenient, solventless extraction technique thatcan be used to extract analytes from both liquid and solidmatrices. The use of SPME for the analysis of flavors andoff-flavors in food and beverages is important. In this pre-sentation, sample types such as non-alcoholic and alcoholicbeverages, candy, and fruits are analyzed for flavor composi-tion. The detection of off-flavors from rancid oils and fatsand methods for quantifying pyrazines in peanut butter andcaffeine in coffee are presented. This poster was recentlypresented at the International Capillary Symposium in Rivadel Garda, Italy.


Optimization of Extraction Conditions and Selectionof SPME Fibers for VOA and Semi-VOA AnalytesThe selection of an appropriate SPME fiber for an appli-cation can be a difficult process. Two experiments wereperformed. In the first experiment, volatile analytes of simi-lar size from a variety of analyte classes were extracted fromwater. The second study is a repeat of this work using semi-volatile analytes. Results are discussed from evaluation ofnine different SPME fibers on the extraction of fifteensemi-volatile analytes. The data illustrate the relationshipof fiber coating thickness and polarity to analyte size andpolarity. The differences between adsorbent and absorbenttype fibers are explored. This poster was recently presentedat the International Capillary Symposium in Riva delGarda, Italy.


TheSIGMA-ALDRICHFamily

Biochemicals andReagents for LifeScience Research

Organics andInorganics for

Chemical Synthesis

Specialty Chemicalsand Analytical

Reagents for Research

ChromatographyProducts for Analysis

and Purification

Laboratory Chemicalsand Reagents for

Research and Analysis

© 2000 Sigma-Aldrich Co. Printed in USA. Supelco brand products are sold through Sigma-Aldrich, Inc. Sigma-Aldrich, Inc. warrants that its products conform to the informationcontained in this and other Sigma-Aldrich publications. Purchaser must determine the suitability of the product(s) for their particular use. Additional terms and conditions may apply.Please see reverse side of the invoice or packing slip.

SUPELCO l Supelco Park, Bellefonte, PA 16823-0048 l 800-247-6628 l www.sigma-aldrich.com

3

041

G001399

G0014000 20 40

Time (min)

0 20 40Time (min)

A Drifting Baseline

Supelco chemists were generating fatty acid methyl ester(FAME) chromatograms recently and were having difficultywith baseline drift during the analyses. Randomly, thebaseline drifted during otherwise acceptable chromatogra-phy. The chemists could not explain the drift. Figure 2 il-lustrates the chromatography observed by the chemists.The Investigation – Reviewing chromatograms, the chem-ists observed that the FID baseline drifted as high as 20pA.A normal FID baseline is smooth and at a level of about5pA. This pointed to a contaminated detector. However,after cleaning the high, drifting baseline remained. Chem-ists investigated the house gas used to supply the GCs tolearn that deliveries or other changes to the bulk gas sys-tem had not occurred.They then rechecked the basics, inspecting every facet ofthe gas purification system. Gases plumbed to the GC sys-tem were scrubbed using the appropriate high capacity andindicating purifiers. Traps had been changed only a fewweeks earlier during routine system maintenance, and ac-ceptable chromatography was generated less than one dayearlier. The drifting baseline suggested that contamina-tion was randomly being introduced to the detector dur-ing analysis. Someone then recalled that a similar prob-lem occurred during an unusually hot June several yearsearlier before the zero air generator was installed. Pursu-ing this concept, chemists decided to examine the zero airgenerator more closely.The Solution – After examining the system, the chemistsdiscovered that the zero air generator was installed on a

CASESTUDY

The Importance of Pure Air...(continued from page 1)

When thinking about a compressor, consider site location,total flow, and pressure requirements. Since compressors vi-brate, they should be located on the floor away from hydro-carbon sources. Compressors require a water vent since theycan condense gallons of water per day from the air. Althoughmost compressors are quiet (<60 decibels), locate them awayfrom desks to avoid distractions. Moisture and hydrocarbontraps are required with compressors that don’t have them.Remember that a zero air generator is required to eliminateppm levels of methane normally present in air.When sizing a compressor, be sure to include all your lab flowdemands and allow a little extra. If supplying air for perme-ation type nitrogen generators, for example, you may need asmuch as 66L/min of air per 1L/min of nitrogen generated.

ConclusionPurified air, whether the source is from cylinder, house, orcompressor, is less expensive when obtained using purifiers

Trademarks and RegisteredTrademarks:

Agilent - Agilent Technologies, Inc.domnick hunter, Nitrox - domnickhunter LimitedJun-Air - Jun Air A/SPackard - Hewlett PackardCompanyShimadzu - Shimadzu CorporationSupelcarb - Sigma AldrichVarian - Varian Associates

Patents:SPME - Technology licensedexclusively to Supelco. US patent#5,691,206; European patent#523092.

different electrical circuit than the rest of the system. In-termittent electrical maintenance was being performed onthe circuit supplying power to the unit, and occasionalpower loss was interrupting normal generator operation.The problem was corrected and after a short warm up, theFID baseline stabilized. Figure 3 illustrates the results oncepower was fully restored to the device.


and generators. The long term cost savings of using low-grade cylinder air are significant and should be consideredwhen designing your air system. Any of the three air sourcesdiscussed, when passed through purifiers and a zero air gen-erator, will provide air containing less than 1ppm of all hy-drocarbons, including methane, and will result in increasedsensitivity and smoother baselines from your FID.If you need help selecting the correct equipment for your spe-cific application, give our Technical Service department a call.Also, consider the following literature available from Supelco.

Recommended Reading:Bulletin T196898 for information on installing cylinders,tubing, regulators, compressors, and gas generatorsBulletin T197918 for information on purifier capacity andthe cost effectiveness of purifiers versus high quality gasesBulletin T198921 for the cost effectiveness of usinggenerators and purifiers in place of high purity cylinder gases

Figure 2. Poor Baseline – Zero Air Generator not Working

Figure 3. Stable Baseline – Zero Air Generator Working Correctly

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