Performance evaluation of a sorbent tube sampling method using short path thermal desorption for volatile organic compounds

Abstract

Air sampling, using sorbents, thermal desorption and gas chromatography, is a versatile method for identifying and quantifying trace levels of volatile organic compounds (VOCs). Thermal desorption can provide high sensitivity, appropropriate choices of sorbents and method parameters can accommodate a wide range of compounds and high humidity, and automated short-path systems can minimize artifacts, losses and carry-over effects. This study evaluates the performance of a short-path thermal desorption method for 77 VOCs using laboratory and field tests and a dual sorbent system (Tenax GR, Carbosieve SIII). Laboratory tests showed that the method requirements for ambient air sampling were easily achieved for most compounds, e.g., using the average and standard deviation across target compounds, blank emissions were < or = 0.3 ng per sorbent tube for all target compounds except benzene, toluene and phenol; the method detection limit was 0.05 +/- 0.08 ppb, reproducibility was 12 +/- 6%, linearity, as the relative standard deviation of relative response factors, was 16 +/- 9%, desorption efficiency was 99 +/- 28%, samples stored for 1-6 weeks had recoveries of 87 +/- 9%, and high humidity samples had recoveries of 102 +/- 12%. Due to sorbent, column and detector characteristics, performance was somewhat poorer for phenol groups, ketones, and nitrogen containing compounds. The laboratory results were confirmed in an analysis of replicate samples collected in two field studies that sampled ambient air along roadways and indoor air in a large office building. Replicates collected under field conditions demonstrated good agreement except for very low concentrations or large (> 41 volume) samples of high humidity air. Overall, the method provides excellent performance and satisfactory throughput for many applications.

Ozone Artifacts and Carbonyl Measurements Using Tenax GR, Tenax TA, Carbopack B, and Carbopack X Adsorbents

“…MDLs were calculated as 3.14 , where 3.14 is the Student's t value appropriate to a 99% confidence level with 6 degrees of freedom, and is the standard deviation of seven replicate analyses that used a loading of 5 ng per compound. This is higher than the typical loading (e.g., 0.2 ng) used for nonpolar VOCs 35 ; thus, only approximate MDLs are obtained for some of the carbonyls (see below). All of the quantitative determinations used normalized abundances, that is, ratios of abundances of the target compound to the internal standard in the same GC/MS run.…”

“…35 Adsorbent-O 3 artifacts were identified on the basis of retention time and ion spectra with confirmation using individual standards. Adsorbent tube samples were analyzed by screwing the downstream side of the tube onto a stainless-steel connector containing a check valve and small VOC trap.…”

Evaluation of the use of Low Flow Passive Sampling Technique in Offset Printing Plants

“…The storage stability of closed tubes is very good. Earlier, Peng and Batterman [7] loaded 20 ng of VOCs in nine passive tubes and analyzed three of them immediately. The remaining tubes were analyzed after one and six weeks of storage.…”

Sorbent Tube Sampling and an Automated Thermal Desorption System for Halocarbon Analysis

“…Air sam pling us ing adsorbents fol lowed by ther mal desorption and Gas chro mato graphic anal y sis with ei ther ECD (Elec tron Cap ture De tec tion) or Mass Spec tro met ric (MS) de tec tion has been es tab lished as a com mon method for de tect ing many vol a tile or ganic com pounds (VOCs) in am bi ent out door and in door en vi ron ments (Tang et al 1995;Ma et al 1997;Pankow et al 1998;Peng and Batterman 2000). An ECD of fers good sen si tiv ity for halogenated compounds while a MS en ables the pos i tive iden ti fi ca tion of peaks in the chromatogram and takes ad van tage of the char ac ter is tic na ture of bro mine and chlo rine con tain ing ion frag ments (Wevill and Car pen ter 2004).…”

“…Risk of ice block age is min i mal in the cold trap and the mod er ate cool ing tem per a tures re quired may be obtained us ing Peltier cool ers rather than liq uid cryogen. Break through in sam pling and arte fact for ma tion dur ing anal y sis can be min i mized by us ing the ap pro pri ate sorbent tubes (Peng and Batterman 2000). This study pro vides a se lec tion of ap pro pri ate sorbents and cold traps for halocarbon trap ping and anal y sis meth ods us ing an au to mated ther mal desorption sys tem fol lowed by GC-ECD with the aim of dem on strat ing the ap pli ca bil ity of the an a lyt i cal sys tem.…”