Cryogenic trapping

The collection medium for gases can be liquid or solid sorbents, an evacuated flask, or a cryogenic trap. Liquid collection systems take the form of bubblers which are designed to maximize the gas-liquid interface. Each design is an attempt to optimize gas flow rate and collection efficiency. Higher flow rates permit shorter sampling times. However, excessive flow rates cause the collection efficiency to drop below 100%. 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Figure 13.3 Schematic diagram of the parallel cryogenic trap MDGC-IR-MS system A, splitless injection port B, RC-5 non-polar first-stage separation column C, HP 5970B MSD D, HP 5965B IRD E, four-poit two-way valve (300 °C maximum temperature) F, external auxiliary earner gas G, six-poit selection valve (300 °C maximum temperature) H, stainless-steel cryogenic caps I, tliree-poit two- way valve (300 °C maximum temperature) ...

Multiple cryogenic traps between the pre-column and the analytical column were developed in 1993 by Ragunathan et al. (23). These authors found that a multiple trap configuration provided the necessary resolution and automated sampling for simultaneous GC/IR and GC/MS determination of very complex mixtures. A... 

Collected in stainless steel canister preconcentrated by cryogenic trapping thermally desorbed... 

Other quantitative SFE-cryogenic trapping SFC-FID analyses have been reported for additives in LDPE [82]. 

Dynamic headspace GC-MS involves heating a small amount of the solid polymer sample contained in a fused silica tube in a stream of inert gas. The volatile components evolved on heating the sample are swept away from the sample bulk and condensed, or focused on a cryogenic trap before being introduced onto the chromatographic column via rapid heating of the trap. The technique can be used qualitatively or quantitatively DHS-GC-MS is considered to be well suited towards routine quantitative analysis. 

Air (particulate and organolead) Collection of particulate matter collected onto nucleopore filters filtered gases cryogenically trapped and thermally desorbed XRF (particulate) GC/GFAAS (gaseous) 0.3 pg/m3 0.2 ng/m3 46->90 90-100 De Jonghe et al. 19 ... 

Water (TAL) Purging of sample with gas followed by cryogenically trapping volatile species onto solid sorbent GC column GC/AAS 0.5 ng/g No data Chau et al. 1980... 

Interaction is violent and may be explosive, even with ice, oxygen being evolved [1]. Part of the water dropped into a flask of the gas was expelled by the violent reaction ensuing [2], An analytical procedure, involving absorption of chlorine trifluoride into 10% sodium hydroxide solution from the open capillary neck of a quartz ampoule to avoid explosion, was described [3], Inadvertent collection of chlorine trifluoride and ice in a cryogenic trap led to a small but violent explosion when the trap began to warm up overnight [4],... 

Dimethyl sulfide (DM) and dimethyl disulfide have been measured in seawater and in the atmosphere by gas chromatography [309] and by GC-MS [310]. Some variety of cryogenic trapping is often used. 

Determination of the various elements collected in the cryogenic trap can be done by fractional volatilization followed by AAS24. 

An ultasensitive simultaneous multi-element method of determination for As, Se, Sb and Sn in aqueous solution, consists of hydride generation, collection in a cryogenic trap and end analysis by GC-PID (photoionization detector) LOD ca 1 ng Sn/L for a 28 mL sample. No drying or CO2 scrubbing is necessary before the cold trap35. 

Blood Headspace cryogenic trapping thermal desorption cap. GC/MSD 15 ng/L Not reported Brugnone et al. 1991... 

In this procedure methylstannanes were generated directly in buffered sample, purged and cryogenically trapped on the head of a chromatographic column. Gas flow was diverted from the hydride generator while the purge tube was filled with up to lOmL of fluid, usually consisting of 5mL of sample and 5mL of buffer (saturated... 

The main comparisons between extraction methods have been made between the Soxhlet, ultrasonication, and supercritical fluid extraction [377, 398,456,461,462]. This has primarily been prompted by the need to evaluate critically the relative merits of SFE as an alternative to the more established methods. Richards and Campbell [456] made a comparison between SFE, Soxhlet, and sonication methods for the determination of some priority pollutants in soil. The SFE apparatus was the same, relatively standard system as described by Campbell et al. [457] with the addition of a C02 cryogenic trap to... 

Second, no work has yet been done on the application of the transpiration method to the preparation of samples for chemical analysis. In this area the same strictures on odour sampling apply, even where sub-ambient-temperature trapping techniques are used. Especially where cryogenic trapping is proposed, preparation of the odour sample in the laboratory is a considerable advantage. 

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