High Carrier Gas Flow Rates Research Articles

Comparison of a jet separator and an open splitter as an interface between a multi-capillary gas chromatographic column and a time-of-flight mass spectrometer

A gas chromatographic/time-of-flight mass spectrometric (GC/TOFMS) interface is being developed for fast on-line analysis utilizing multi-capillary column technology. A variable gap-distance jet separator has been constructed and its performance compared with that of a commercially supplied post-column open splitter recommended for use between the multi-capillary column and a mass spectrometer. Both interfaces were found to be compatible with the GC/TOFMS system at high carrier gas flow-rates, facilitating high-speed and high-resolution separations. The systems were investigated and tested with a mixture of volatile organic compounds (VOCs) with molecular masses from 85 to 166: dichloromethane, toluene, m-dichlorobenzene, o-dichlorobenzene and tetrachloroethylene. The optimum tip-to-tip gap distance corresponding to the highest efficiency of the jet separator was found to be 0.030 mm for each compound at carrier gas flow-rates of 20, 40 and 60 ml min−1 giving, in the ion source housing, ion gauge pressure readings of 1.6 × 10−6, 5.0 × 10−6 and 5.8 × 10−6 mbar, respectively. The efficiency of the jet separator (10–30% yields) was significantly higher than that of the open splitter (6–9% yields). The observation that the open splitter did not provide a constant flow-rate to the ion source was not in agreement with the manufacturer's specifications. A method for measuring the gas flow-rates in all parts of the equipment is described. The correlation between yield in the jet separator and molecular mass for the heterogeneous set of compounds studied was found to be less linear than usually reported for homologous series of compounds in jet separator studies. The result suggests that the pressure conditions in the jet may be sufficient for the separation process to be partly controlled by diffusion rather than predominately by effusion. Copyright © 2000 John Wiley & Sons, Ltd.

CONTROL OF SIZE AND MORPHOLOGY OF NANO PARTICLES USING CO 2 LASER DURING FLAME SYNTHESIS

An attempt has been made to control size and morphology of nanoparticles generating and growing in a co-flow oxy-hydrogen flame combining CO 2 laser irradiation. The coalescence characteristic time could be controlled nearly independent of the collision characteristic time of particles by raising particle temperature rapidly with laser beam irradiation during flame synthesis. Silica aggregates generated by hydrolysis of SiCl 4 in a flame are irradiated by a high-power CO 2 laser beam, and rapidly heated up to temperatures that are high enough to enhance sintering, but lower than evaporation temperature. Sintering of aggregates is rapidly enhanced to change aggregates into more spherical particles. Since spherical particles have much smaller collision cross sections than volume-equivalent aggregates, much slower growth of particles is observed when the flame is irradiated by CO 2 laser beam and as a result, the diameter of resulting spherical particles decreases to about 60% of the size observed without CO 2 laser beam as the laser power increases. A higher precursor flow rate even resulted in the change of non-spherical particles into smaller spherical particles as CO 2 laser power increased. Light-scattering measurement with an Ar-ion laser and TEM observation through a localized thermophoretic sampling were used to confirm the above effects of CO 2 laser irradiation in a flame. Depending on the irradiation height of CO 2 laser beam in a flame, significantly different mechanisms were found. The radial distributions of scattering intensity and morphological change were also studied. The proposed method controlling the sintering characteristic time of particles using CO 2 laser irradiation in a flame seems to be promising to produce smaller and, at the same time, spherical nanoparticles even for high carrier gas flow rate.

Comparison of a jet separator and an open splitter as an interface between a multi-capillary gas chromatographic column and a time-of-flight mass spectrometer

A gas chromatographic/time-of-flight mass spectrometric (GC/TOFMS) interface is being developed for fast on-line analysis utilizing multi-capillary column technology. A variable gap-distance jet separator has been constructed and its performance compared with that of a commercially supplied post-column open splitter recommended for use between the multi-capillary column and a mass spectrometer. Both interfaces were found to be compatible with the GC/TOFMS system at high carrier gas flow-rates, facilitating high-speed and high-resolution separations. The systems were investigated and tested with a mixture of volatile organic compounds (VOCs) with molecular masses from 85 to 166: dichloromethane, toluene, m-dichlorobenzene, o-dichlorobenzene and tetrachloroethylene. The optimum tip-to-tip gap distance corresponding to the highest efficiency of the jet separator was found to be 0.030 mm for each compound at carrier gas flow-rates of 20, 40 and 60 ml min(-1) giving, in the ion source housing, ion gauge pressure readings of 1.6 x 10(-6), 5.0 x 10(-6) and 5.8 x 10(-6) mbar, respectively. The efficiency of the jet separator (10-30% yields) was significantly higher than that of the open splitter (6-9% yields). The observation that the open splitter did not provide a constant flow-rate to the ion source was not in agreement with the manufacturer's specifications. A method for measuring the gas flow-rates in all parts of the equipment is described. The correlation between yield in the jet separator and molecular mass for the heterogeneous set of compounds studied was found to be less linear than usually reported for homologous series of compounds in jet separator studies. The result suggests that the pressure conditions in the jet may be sufficient for the separation process to be partly controlled by diffusion rather than predominately by effusion. Copyright 2000 John Wiley & Sons, Ltd.

Process‐Property Relationships of SiC Chemical Vapor Deposition in the Si/H/C/O System

A comprehensive thermodynamic analysis has been performed for the Si/H/C/O system from which a priori process‐property relationships of the chemical vapor deposition (CVD) of silicon carbide (SiC) are obtained. The parameter space for pure silicon carbide growth is reported for five orders of magnitude of the system water vapor level (1 ppb‐100 ppm), four orders of magnitude of system pressure (0.1‐760 Torr), and two orders of magnitude of C/Si feed ratio (0.25‐20) and feed ratio (50‐10,000). Lower growth temperatures for pure SiC are predicted in clean systems with low system water vapor levels, at stoichiometric to near carbon excess conditions (C/Si ≅ 1 to C/Si > 1), at high carrier gas flow rates (large feed ratios), and at low operating pressures. Because relative C/Si and feed ratios have been considered, the predictions in this study are applicable to both multiple and single precursor systems. Further, these results are valid for the CVD of α‐SiC as well as β‐SiC. Experimental data reported on the growth of α‐SiC and β‐SiC are found to be in satisfactory agreement with our theoretical predictions, for numerous systems that include multiple and single source, silicon and carbon, species. © 1999 The Electrochemical Society. All rights reserved.

Non-isobaric adsorption analysis of SO 2 on molecular sieve 13X and activated carbon by dynamic technique

Sulfur dioxide is one of the major pollutants resulting from fuel combustion. In this study non-isobaric pulse chromatography was used for the investigation of the adsorption properties of sulfur dioxide on molecular sieve 13X and activated carbon. The experimental procedure consists of introducing a pulse of sulfur dioxide on the inlet of a column packed with molecular sieve 13X and activated carbon adsorbents and measuring the concentration versus time response peak leaving the other end of the column. Adsorption equilibrium constants were calculated using the moment analysis of the chromatographic peaks. Non-isobaric pulse chromatographic technique necessitates the use of high carrier gas flow rates which avoids the tailing of the response peaks and reduces considerably the uncertainty in the measurement of the moments. The adsorption of sulfur dioxide was investigated in a temperature range of 353–453 K with the activated carbon, which is a typical temperature range of desulfurization of flue gas, and in a temperature range of 523–673 K with molecular sieve 13X. Adsorption equilibrium constants of sulfur dioxide were found to decrease considerably with increasing temperature. At 453 K, the adsorption equilibrium constant was found to be 18.78, whereas it has a value of 330.2 at 353 K with the activated carbon. At 673 K, the adsorption equilibrium constant was found to be 11.52, whereas it has a value of 167.82 at 523 K with molecular sieve 13X. Heat of adsorption of sulfur dioxide on molecular sieve 13X and the activated carbon was determined as −12.4 and −8.99 kcal mol −1, respectively.

Injection by Programmed Temperature Vaporization Injection (PTV) of Gaseous Samples for Gas Chromatography – Atomic Emission Spectrometry (GC-AED)

Programmed temperature vaporization injection (PTV) coupled to gas chromatography and atomic emission detector (AED) has been studied for large volume injection of gaseous samples. As examples of the effectiveness of the technique, the results of the analysis of a series of headspace samples of foods such as garlic and onion, and of landfill gases are presented. The volumes of gaseous samples reconcentrated varied from a few milliliters up to liters depending on analyte dilution, through focusing onto a sorbent trap, then rapid liberation into the GC-AED system by programmed thermal desorption. Despite the high carrier gas flow rates associated with direct PTV-GC, AED performance and sensitivity were unaffected. The detailed elemental information obtained from the PTV-GC-AED analyses was confirmed using a PTV coupled to a gas chromatograph with ion trap detector mass spectrometer as detector (PTV-GC-ITD/MS).

Laser Desorption Fast Gas Chromatography–Mass Spectrometry in Supersonic Molecular Beams

A novel method for fast analysis is presented. It is based on laser desorption injection followed by fast gas chromatography-mass spectrometry (GC-MS) in supersonic molecular beams. The sample was placed in an open air or purged laser desorption compartment, held at atmospheric pressure and near room temperature conditions. Desorption was performed with a XeCl Excimer pulsed laser with pulse energy of typically 3 mJ on the surface. About 20 pulses at 50 Hz were applied for sample injection, resulting in about 0.4 s injection time and one or a few micrograms sample vapor or small particles. The laser desorbed sample was further thermally vaporized at a heated frit glass filter located at the fast GC inlet. Ultrafast GC separation and quantification was achieved with a 50-cm-long megabore column operated with a high carrier gas flow rate of up to 240 mL/min. The high carrier gas flow rate provided effective and efficient entrainment of the laser desorbed species in the sweeping gas. Following the fast GC separation, the sample was analyzed by mass spectrometry in supersonic molecular beams. Both electron ionization and hyperthermal surface ionization were employed for enhanced selectivity and sensitivity. Typical laser desorption analysis time was under 10 s. The laser desorption fast GC-MS was studied and demonstrated with the following sample/matrices combinations, all without sample preparation or extraction: (a) traces of dioctylphthalate plasticizer oil on stainless steel surface and the efficiency of its cleaning; (b) the detection of methylparathion and aldicarb pesticides on orange leaves; (c) water surface analysis for the presence of methylparathion pesticide; (d) caffeine analysis in regular and decaffeinated coffee powder; (e) paracetamol and codeine drug analysis in pain relieving drug tablets; (f) caffeine trace analysis in raw urine; (g) blood analysis for the presence of 1 ppm lidocaine drug. The features and advantages of the laser desorption fast GC-MS are demonstrated and discussed.

DYNAMIC ADSORPTION OF S02 ON ZEOLITE MOLECULAR SIEVES†

Sulfur dioxide is one of the major pollutants resulting from fuel combustion. Numerous dry, semi-dry and wet processes have been developed for pollution control of sulfur dioxide. Solid carbonates, natural and synthetic zeolites, ion exchange resins and carbon based sorbents are the most commonly used dry sorbents for sulfur dioxide removal In this study, measurements of the adsorption properties of sulfur dioxide on zeolites were investigated. The adsorbents used in this work are 5A, 4A and AW300 type molecular sieve zeolites. Adsorption equilibrium parameters were determined from the pulse chromatographic response to injections of low concentrations of sulfur dioxide. The method of moments were used to evaluate the adsorption equilibrium parameters from pulse chromatographic experiments. Data, such as adsorption equilibrium constants or reaction rate parameters are essential in the design of adsorption systems or reactors in which sulfur dioxide is removed The experiments were conducted in a temperature range of 523-718 K. The relatively strong adsorption properties of sulfur dioxide on zeolites necessitated the use of high carrier gas flow rates and subsequently non-isobaric operation. Non-isobaric pulse chromatography theory was found to describe accurately the adsorption trends." printpubdate="Adsorption equilibrium constants of S02 were found to decrease considerably with increasing temperature. It was also found out that adsorption of SO2 on the adsorbents investigated were found to decrease in the order of AW300 ⩽ 4A ⩽ 5A. The adsorption equilibrium parameter of S02 on 5A was found as 11.78 at 673 K, whereas it has a value of 157.11 at 523 K. The adsorption equilibrium parameter of S02 on 4A zeolite was determined to be 8.63 at 718 K and 213.78 at 523 K.

Comparison of the effect of acetic acid with axially and radially viewed inductively coupled plasma atomic emission spectrometry: influence of the operating conditions

Acetic acid was selected as a highly perturbing matrix for the comparison of matrix effects between axial and radial viewing modes in ICP-AES. The effect of acetic acid (5 and 10% v/v) on the intensities of various ionic lines in ICP-AES was studied under extreme operating conditions,i.e., robust and non-robust conditions. A cross-flow nebulizer associated with a double-pass spray chamber was chosen as a sample introduction system. The influence of the operating conditions on the Mg II 280 nm/Mg I 285 nm line intensity ratio was also studied. This work confirmed that, under so-called robust conditions, i.e., high rf power and low carrier gas flow rate, the acetic acid caused an enhancement of the signal intensity, regardless of the energy line and the viewing mode, which could be assigned to a change in the aerosol formation and transport. An increase in the solvent transport rate and a significant modification of the primary, and especially the tertiary, aerosol drop size distributions were observed in the presence of acetic acid. Hence, finer aerosols were obtained when acetic acid was present.

Fast GC—MS in Supersonic Molecular Beams

AbstractThe features of supersonic molecular beams (SMB) are used to improve gas chromatography—mass spectrometry (GC–MS) performance and establish a new method of fast GC–MS. In SMB, the sample compounds are vibrationally cooled such that their electron impact mass spectra are characterized by enhanced M+ peaks, together with library‐searchable fragments. A new ionization method, hyperthermal surface ionization (HSI), provides ultrasensitive ionization coupled with a tunable degree of selectivity for nitrogen‐containing drugs. SMB enables the use of very high carrier gas flow rates which, when a short megabore column is used, results in ultra‐fast GC–MS having conventional chromatographic peak widths. Thus, fast GC–MS in SMB can be performed with conventional quadrupole analyzers. The slightly reduced GC resolution can, in many cases, be compensated for by the selectivity of hyperthermal surface ionization or by the increased EI selectivity through enhanced M+. “Fast”, “very‐fast”, and “ultra‐fast” GC–MS are defined and demonstrated with drugs, and the ability to analyze underivatized steroids is shown. Practical examples are shown including ultra‐fast GC–MS of lidocaine in human plasma extract achieved in a few seconds and screening of other drugs, without any sample preparation or extraction, achieved in less than three minutes. We conclude that GC–SMB–MS exhibits a combination of faster analysis with improved sensitivity and selectivity, a wider range of molecules amenable to GC–MS, improved MS information, and higher a degree of flexibility.

Effect of power and carrier gas flow rate on the tolerance to water loading in inductively coupled plasma atomic emission spectrometry

The effects of the carrier gas flow rate and the power on the amount of water that can be tolerated by the plasma have been studied by ICP-AES. Pneumatic nebulization, ultrasonic nebulization associated with desolvation and laser ablation have been used to obtain wet, partially desolvated and dry aerosols. It has been found that water is beneficial in improving the plasma electron number density and the excitation temperature when so-called robust conditions are used, i.e. high power and low carrier gas flow rate. This can be explained by the release of hydrogen. Under these conditions, desolvation had almost no effect on the plasma characteristics. When non-robust conditions were used, the plasma was highly sensitive to water loading. Desolvation led to an improvement in the plasma conditions. In this instance, the addition of hydrogen was most useful to restore the properties of the plasma and to act as a load buffer to minimize the matrix effects. The plasma characteristics have been evaluated based on simple diagnostics such as the Mg II/Mg I line intensity ratio, the Fe excitation temperature, the Ar line and the Ar continuum.

Adsorption parameters for strongly adsorbed hydrocarbon vapours on some commercial adsorbents

High-temperature measurements of the adsorption properties of strongly adsorbed hydrocarbon vapours on a wide range of commercially available adsorbents are presented. These adsorbents include various cationic forms of the type A, X and Y zeolites, activated alumina and carbon, and some clays. The studies are based upon pulse chromatography experiments using low concentrations of hydrocarbon vapours (toluene and methylcyclohexane) in nitrogen carrier gas. The temperature range of investigation was chosen as 400–700 K, which is typical for the catalytic dehydrogenation of methylcyclohexane to toluene. Even at these temperatures, the relatively strong adsorption properties of the hydrocarbons necessitated the use of high carrier gas flow rates. As a consequence, significant deviation from isobaric operation existed. In this work, non-isobaric pulse chromatography theory was applied to the first moment data, and found to describe accurately the adsorption trends. Furthermore, the temperature dependence of the adsorption equilibria parameters could be determined. The data provide a useful reference in the design and assessment of processes in which the simultaneous operations of high-temperature chemical reaction and adsorptive separation take place, as in chromatographic and pressure swing based reactors.

Fast, high temperature and thermolabile GC—MS in supersonic molecular beams

This work describes and evaluates the coupling of a fast gas chromatograph (GC) based on a short column and high carrier gas flow rate to a supersonic molecular beam mass spectrometer (MS). A 50 cm long megabore column serves for fast GC separation and connects the injector to the supersonic nozzle source. Sampling is achieved with a conventional syringe based splitless sample injection. The injector contains no septum and is open to the atmosphere. The linear velocity of the carrier gas is controlled by a by-pass (make-up) gas flow introduced after the column and prior to the supersonic nozzle. The supersonic expansion serves as a jet separator and the skimmed supersonic molecular beam (SMB) is highly enriched with the heavier organic molecules. The supersonic molecular beam constituents are ionized either by electron impact (EI) or hyperthermal surface ionization (HSI) and mass analyzed. A 1 s fast GC—MS of four aromatic molecules in methanol is demonstrated and some fundamental aspects of fast GC—MS with time limit constraints are outlined. The flow control (programming) of the speed of analysis is shown and the analysis of thermolabile and relatively non-volatile molecules is demonstrated and discussed. The tail-free, fast GC—MS of several mixtures is shown and peak tailing of caffeine is compared with that of conventional GC—MS. The improvement of the peak shapes with the SMB—MS is analyzed with the respect to the elimination of thermal vacuum chamber background. The extrapolated minimum detected amount was about 400 ag of anthracence- d 10, with an elution time which was shorter than 2s. Repetitive injections could be performed within less than 10 s. The fast GC—MS in SMB seems to be ideal for fast target compound analysis even in real world, complex mixtures. The few seconds GC—MS separation and quantification of lead (as tetraethyllead) in gasoline, caffeine in coffee, and codeine in a drug is demonstrated. Controlled HSI selectivity is demonstrated in the range of 10 1 to 10 4 anthracene/decane which helped to simplify the selective analysis of aromatic molecules in gasoline. The contribution of SMB to the operation of the fast GC—MS is summarized and the compatibility with conventional GC having a megabore column is shown. Splitless injections of 100 μL sample solutions for trace level concentration detection is also presented (with a conventional GC).

Reduction of polyatomic interferences in inductively coupled plasma mass spectrometry by selection of instrumental parameters and using an argon–nitrogen plasma: effect on multi-element analyses

The effect of instrumental parameters and argon-nitrogen plasmas on polyatomic ion formation has been studied in order to reduce their magnitude in routine multi-element analysis without losing detection capability. Special emphasis was placed on the chlorine based polyatomic interferences on V, Cr, Zn, As and Se. A significant reduction in signals from polyatomic ions was attained by using a high aerosol carrier gas flow rate (0.955 l min–1) instead of the default flow rate (0.755 l min–1), or by adding nitrogen (8%) to the aerosol carrier flow. The ArCl+ interference produced by 0.05% Cl (the maximum concentration expected in digested food stuff samples) was effectively removed by both methods and ClO+ and ClO2+ by addition of nitrogen. Detection limits for elements along the mass range (from Li to U) were, on average, 2–3 times higher with the mixed gas plasma. This slight degradation of detection limits was not judged to be deterimental to multielement determinations in five reference materials when the results from using an argon-only plasma (with low and high aerosol carrier flow rates) were compared with the results from the argon–nitrogen plasma.

Determination of topanol antioxidants in methacrylates using capillary gas-liquid chromatography

This paper presents a method to identify and determine topanol A and topanol O antioxidants in methylmethacrylate and 11-bromoudecylmethacrylate. The method is both simple and rapid. Analysis is performed on a 10 m × 0.53 mm I.D. HP-1 capillary gas chromatography column with a temperature gradient and a high carrier gas flow-rate (16.5 ml/min). Quantitation is by internal standardisation. Validation of the method is described for both topanols at concentrations of approximately 50 ppm in methylmethacrylate and 250 ppm in 11-bromoundecylmethacrylate.

Carrier gas flow-rate and injection system in capillary gas chromatography of unconjugated and glycine-conjugated bile acids

The first description of successful capillary gas chromatography of intact glycine-conjugated bile acid derivatives used an automatic solid injection system and required very high carrier gas flow-rates (approximately 20 ml/min) to obtain satisfactory peak shape. Peak heights of unconjugated bile acid derivatives using this injection system and the low flow-rates (1–2 ml/min) usually used for such gas chromatographic analyses were very susceptible to small changes in flow-rate. This system has been re-examined in an attempt to explain this anomalous behaviour. An alternative injection system, the all-glass dropping needle, was also investigated. No explanation for the very high carrier gas flow-rates required when using the automatic solid injection system was found. The dropping needle injection system, however, produced excellent separation of bile acids and their glycine conjugates as dimethylethylsilyl ethers—methyl esters on non-polar wall-coated capillary columns using normal carrier gas flow-rates of 1–2 ml/min. It is clear that the automatic solid injection system originally used has some problem associated with it which can only be overcome, in the case of bile acids and their glycine conjugates, by increasing the carrier gas flow-rate to very high levels.

Melting metal powder particles in an inductively coupled r.f. plasma torch

A numerical model is developed for the prediction of melting metal powder particles in an inductively coupled r.f. plasma torch. The model is developed for dilute spray conditions where the gas phase flow is not affected by the loading condition. The governing equation for the gas phase flow contains the source terms from the electromagnetic field. The theoretical calculations have shown that particle thermal history and its velocity are greatly affected by the plasma operating conditions (i.e., carrier gas flow rate, injector location, and power level,etc.). Without the proper control of particle trajectories, particles may bounce around the fireball and exit the torch as unmelted or resolidified solid particles. With the insertion of an injector or injecting particles with a high carrier gas flow rate, the predictions show that even relatively small size particles can be directed into the fireball and maintained in the molten state before they impact on the substrate. Consequently, more uniform and dense deposits can be achieved.

Capillary gas-liquid chromatography of glycine-conjugated bile acids without prior hydrolysis.

A method is described for the gas-liquid chromatographic (GLC) analysis of intact glycine conjugates of the major bile acids present in human plasma. It is, therefore, now possible to analyze glycine-conjugated and unconjugated bile acids together on a single GLC column without the necessity for a hydrolytic step. A large number of derivatives of bile acid glycine conjugates were examined, but only acetate- and silyl ether-derivatives of carboxylic acid methyl esters were found initially to be suitable. It was not possible to make acetates consistently, and trimethylsilyl ethers did not allow resolution of the glycine conjugates of cholic and chenodeoxycholic acids. Dimethylethylsilyl ether methyl ester derivatives were subsequently found to give the best results. Chromatographic conditions for successful analysis of these derivatives were examined and it was found to be necessary to use wall-coated capillary columns of thin film thickness (0.12 micron) and very high carrier gas flow rates (ca. 20 ml/min hydrogen). Using acetonitrile and Bond Elut extraction, fractionation on Sep-Pak SIL cartridges, and derivatization as dimethylethylsilyl ether methyl esters, the capillary gas-liquid chromatography of intact glycine-conjugated bile acids from human plasma was demonstrated for the first time.

Concurrent solvent evaporation for on‐line coupled HPLC‐HRGC

AbstractA technique is proposed which allows introduction of very large volumes of liquid (10 ml were tested) into capillary columns equipped with short (1–2 m long) retention gaps. It is based on concurrent solvent evaporation, i.e. evaporation of the solvent during introduction of the sample. The technique presupposes high carrier gas flow rates (at least during sample introduction) and column temperatures near the solvent boiling point. The major limitation of the method is the occurrence of peak broadening for solutes eluted up to 30°, in some cases up to 100°, above the injection temperature. This is due to the absence of solvent trapping and a reduced efficiency of phase soaking. Therefore, use of volatile solvents is often advantageous. Application of the concurrent solvent evaporation technique allows introduction of liquids which do not wet the retention gap surface. However, the method is still not very attractive for analysis of aqueous or water‐containing solutions (reversed phase HPLC).

Effects of flow rate and temperature on the thermal desorbability of polycyclic aromatic hydrocarbons and pesticides from Tenax-GC

One factor limiting adsorption/thermal desorption (ATD) preconcentration techniques is the thermal desorbability of the analyte compounds. The behavior of a set of compounds including polynuclear aromatic hydrocarbons (PAH) and several pesticides on 0.110 g of the sorbent Tenax-GC was investigated as a function of desorption temperature and carrier gas flow rate. The recoveries obtained with helium at 11.2 mL/min are as follows: naphthalene, 99 +/- 1; fluorene, 70 +/- 1; ..cap alpha..-BHC, 97 +/- 8; heptachlor, 26 +/- 5; fluoranthene, 99 +/- 1; pyrene, 93 +/- 1; dieldrin, 120 +/- 3; DDD, 60 +/- 2;DDT 20 +/- 1; benzo(k)fluoranthene, 93 +/- 3; perylene, 89 +/- 2; and benzo(ghi)perylene, 88 +/- 5. The desorbing compounds were trapped on a fused silica capillary column at -30/sup 0/C. Excellent resolution and separation number performance was maintained despite the use of high desorption carrier gas flow rates. Estimates were made of the retention volume and desorbing peak width characteristics of several of the compounds on Tenax-GC at the desorption temperatures studied. 5 figures, 3 tables.