Trapping column direct injection into

Solid waste matrices Purge (inert gas) trap (Tenax or Chromosorb W) or thermally desorb or headspace sampling or direct injection into capillary GC column GC/PID 0.005 pg/L Enviromnental Protection Agency (1996a) [Method 8021B]... 

GC-MS analysis For GC-MS analysis, withdrawals were lyophilized, the residue dissolved in methanol, and directly injected into a GC-MS instrument. Analyses were carried out on Saturn 2000 apparatus (Varian) equipped with an ion trap detector. A DB5-MS-fused silica column (30 m x 0.25 bmm ID, 0.25 pm film thickness) was used. Helium was the carrier gas with a 1 mL min- flow rate. The MS detector was operated in the El mode, scanning in the range of40-640 amu. When required, the residue was treated with 1,1,1,3,3,3-hexamethyldisilazane (200 pL), anhydrous pyridine (200 pL), and chlorotrimethylsilane (50 pL). The resulting mixture was shaken vigorously for 1 min and centrifugated to separate the precipitate formed prior to injection into the chromatograph. 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

HPLC with column switching and mass spectrometry was applied to the online determination and resolution of the enantiomers of donepezil HC1 in plasma [38]. This system employs two avidin columns and fast atom bombardment-mass spectrometry (FAB-MS). A plasma sample was injected directly into an avidin trapping column (10 mm x 4.0 mm i.d.). The plasma protein was washed out from the trapping column immediately while donepezil HC1 was retained. After the column-switching procedure, donepezil HC1 was separated enantioselectivity in an avidin analytical column. The separated donepezil HC1 enantiomers were specifically detected by FAB-MS without interference from metabolites of donepezil HC1 and plasma constituents. The limit of quantification for each enantiomer of donepezil HC1 in plasma was 1.0 ng/ml and the intra-and inter-assay RSDs for the method were less than 5.2%. The assay was validated for enantioselective pharmacokinetic studies in the dog. 

These semi-preparative methods are useful where identification is required but for quantitative and comparative analytical purposes much more rapid sampling techniques, such as automated headspace and solid phase microextraction (SPME), may be preferred. Both of these techniques give similar results for most volatiles. In the former, the vapour above a heated sample is removed by a syringe or gas flushing and injected onto a GC column, either directly or after trapping on a suitable absorbent and thermal desorption. In SPME, the vapour is absorbed on to a suitable bonded medium on a special needle and then injected into the gas chromatogram. 

When the extracted analytes are to be retained directly on the chromatographic column or at the retention interface, their insertion can be accomplished in various ways, namely (a) by injection into the column, whether directly (SFC, GC) or with the aid of a cooling system (GC, HPLC) (b) by split-splitless injection (SFC, GC) (c) by using a programmed temperature vaporizer (GC) or (d) by injection into a cold trap and subsequent thermal desorption (GC) or elution (HPLC). 

Static headspace isolation normally involves taking a sample of the equilibrium headspace (a few ml) immediately above the food. This can be directly injected onto the GC column or more usually first concentrated on an adsorbent trap. The GC analysis of this small sample can give useful information such as the detection of rancidity in a food by measuring hexanal concentration (20). Static headspace can also be useful for the analysis of very volatile compounds such as acetaldehyde and dimethyl sulfide. However, in order to get enough material into the headspace, the sample frequently has to be heated to 60-100° C which, in some cases, could give an unrealistic picture of the volatiles of the food or plant material. Static headspace is a very rapid method, but it does not give a comprehensive analysis of the volatiles, and in the case of foods, may miss the most important. 

This automated method involves the direct injection of a measured aliquot of plasma by an autosampler into a liquid chromatograph. A precoliunn is used to trap the urapadil and its metaboUtes and wash the majority of the interfering plasma components to waste. A valve then switches the precoliunn inline with the analytical column and the analytes are washed off the precolumn and separated by the analytical column. During the analysis, the precolumn is reconditioned to accept the next sample. 

Modern chromatographic systems are equipped with autosamplers. Samples can be injected directly into the separation column, or they can be passed through enrichment (trapping) columns. The concentrated analytes can subsequently be directed to the separation columns. This step extends analysis time however, it may be indispensable in the case of analysis of low abundance components of matrix-rich samples. 

Because most organics are present at ppb-ppt concentrations in air, sample preconcentration is required. This is typically accomplished by direct cryotrapping of air, trapping on a solid sorbent, or sampling into an evacuated canister followed by cryotrapping the canister contents prior to injection onto the GC column. Combinations of these, such as cryotrapping followed by transfer to a solid sorbent, have also been used (e.g., Shepson et al., 1987). 

In direct headspace analysis, the sample e g. serum or urine, is equilibrated with the headspace in a suitable container. A protion of headspace gas is then injected for analysis. More elaborate headspace trapping devices combine separation of the volatiles from the sample matrix with subsequent enrichment of the constituents. Such a system, suitable for small volumes of body fluids, is known as the transevaporator sampling technique. It contains a microcolumn packed with Porasil E (pore silica gel), into which the sample is injected. In one mode of use, helium is passed through the column to remove the volatiles which are then collected in a trap (Tenax-GC, a porous polymer, 2,6-diphenyl-p-phenylene oxide). 

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