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

Abstract

AB STRACTDe vel op ment and de ploy ment of the an a lyt i cal sys tem, ATD-GC-ECD has been es tab lished to mon i tor a suite of halogenated com pounds found in the at mo sphere at trace con cen tra tions. The in stru ment has been used to mon i tor ur ban back ground emis sion flux lev els in Bris tol, UK as well as Yel low stone Na tional Park, USA and an in door rain forest (Wild Walk@Bris tol, UK). The newly es tab lished sorbent tube sam pling sys tem is small and eas ily por ta ble and has been used for large vol ume sam ple col lec tion from re mote ar eas. Au to mated Ther mal Desorption (ATD) pro vides rou tine at mo spheric mea sure ments with out cryo genic pre-con cen tra tion. The in stru ment pro vides good pre ci sion where the de tec tion limit was £ 3 pptv for the spe cies of in ter est and the reproducibility was within 4% for all of the se lected halocarbons. The re sults from two field ex per i ments have also pro vided insight about natural missing sources of some ozone depleting halocarbons. Ocean. Sci., 20, 345-353, doi: 10.3319/TAO.2008.02.15.01(A) IN TRO DUC TIONAir 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). Trace at mo spheric halocarbon lev els were usu ally de ter mined by the cryo genic pre-con cen tra tion of large vol umes of air be fore anal y sis. The use of liq uid cryogen was lim ited by their cost, availabil ity and prob lems with au to ma tion of such sys tems. The air sam pling, us ing sorbent tubes pre cludes the ne ces sity for liq uid cryo gens al low ing for the de vel op ment of a more robust 'stand alone' sys tem. Sorbent tube sam pling can achieve high re cov ery of po lar and re ac tive com pounds, which can pose prob lems for whole air sam ples col lected in can is ters (Batterman et al. 1998). Sorbent tubes are small in size, fa cil i tat ing col lec tion, trans port and stor age. They can be con di tioned eas ily and con ve niently re used. The as so ciated pre-sam pling sys tems are also small, eas ily por ta ble and can be used in re mote ar eas and are rel a tively in ex pen sive.Au to mated Ther mal Desorption (ATD) is an au to mated and un at tended anal y sis sys tem for up to 50 sam ples. Thermal desorption of sorbents of fers cost sav ings and high sensitivity. The sys tem pro vides cryogen-free op er a tion down to -30°C, re duc ing op er at ing costs. The tube and the sam ple flow path can be purged...

Stable carbon isotope analysis of selected halocarbons at parts per trillion concentration in an urban location

“…The trap on the ATD system was checked by running trap heat cycles, thereby establishing that the sample chromatograms were not affected by artefacts in the system. The multi-bed tubes exhibited no residual traces of any components at the analysis desorption temperature of 380 • C [19] precluding any sample carry-over between the consecutive runs. Previous studies have shown that traps containing Ascarite II do not alter the δ 13 C values obtained for CH 3 Cl.…”

“…In the present study, a preconcentration system suitable for large-volume sample collection was deployed in the Bristol urban area. [19] A new instrumental method is described that enables the application of Automated Thermal Desorber-Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry (ATD-GC-C-IRMS) to the isotope ratio measurement of selected halocarbons at ppt concentrations. Here we present δ 13 C values and mixing ratios of selected halocarbons from an urban background site in the city of Bristol, UK, generated using ATD-GC-C-IRMS and Adsorption Desorption System-Gas Chromatography-Electron Capture Detector (ADS-GC-ECD) systems in tandem.…”