Solid-phase microextraction contamination with

A database also allows instant access to the spectrum of a molecule by searching its name or CAS (Chemical Abstract Service) number. Suppose we must verify immediately that water has not been contaminated by toluene. We plan to use a GC-MS coupling device equipped with a quadrupole. The best way to proceed is by injecting toluene to determine its retention time (under the correct chromatographic conditions) and the main ions of its mass spectrum. One must then analyze the water (after liquid-liquid extraction with an organic solvent or directly by solid phase microextraction coupled with GC-MS) in SIM on the two or three main ions of toluene to reach a limit of detection that is as low as possible. If toluene cannot be injected in the laboratory, quick access to its El spectrum is available in databases. Ions for SIM acquisition will then be chosen from the reference spectrum. 

Pretreatment of hair samples also includes an extraction, usually with an alkaline sodium hydroxide solution, followed by cleaning up with LLE with n-hexane/ethyl acetate. Instead of LLE, the employment of SPE is also possible. Furthermore, the solid phase microextraction (SPME) in combination with head-space analysis is usable [104-106]. In the case of using hair samples, possible external contamination (e.g., by passive smoking of Cannabis) has to be considered as false positive result. False positive results can be avoided by washing of the hair samples previous to extraction [107]. Storage of collected samples is another important fact that can cause false results in their content of A9-THC and metabolites [108-110]. 

During the last few years, miniaturization has become a dominant trend in the analysis of low-level contaminants in food and environmental samples. This has resulted in a significant reduction in the volume of hazardous and expensive solvents. Typical examples of miniaturization in sample preparation techniques are micro liquid/liquid extractions (in-vial) and solvent-free techniques such as solid-phase microextraction (SPME). Combined with state-of-the-art analytical instrumentation, this trend has resulted in faster analyses, higher sample throughputs and lower solvent consumption, whilst maintaining or even increasing assay sensitivity. 

The sample introduction system must be capable of introducing a known and variable volume of sample solution reproducibly into the pressurized mobile phase as a sharp plug without adversely affecting the efficiency of the column. The superiority of valve injection has been adequately demonstrated for this purpose and is now universally used in virtually all modern instruments for both manual and automated sample introduction systems [1,2,7,31,32]. Earlier approaches using septum-equipped injectors have passed into disuse for a several reasons, such as limited pressure capability, poor resealability, contamination of the mobile phase, disruption of the column packing, etc., but mainly because they were awkward and inconvenient to use compared with valves. For dilute sample solutions volume overload restricts the maximum sample volume that can be introduced onto the column without a dramatic loss of performance. On-column or precolumn sample focusing mechanisms can be exploited as a trace enrichment technique to enhance sample detectability. Solid-phase extraction and in-column solid-phase microextraction provide a convenient mechanism for isolation, concentration and matrix simplification that are easily interfaced to a liquid chromatograph for fully or semi-automated analysis of complex samples (section 5.3.2). 

Thermal desorption from a solid phase microextraction (SPME) fiber has shown considerable potential for selectively introducing semivolatile chemicals into an IMS. ° The SPME approach is a simple design patterned after the early platinum wire introduction thermal desorption system described. With SPME, semivolatile compounds are extracted by either absorption or adsorption onto a nonvolatile polymeric coating or solid sorbent phase that has been coated onto a small fiber. Normally, the adsorption liber is housed in the needle of a syringe to permit puncture of a sample bottle septum and to protect the fiber from contamination during transfer of the fiber from the sample to the IMS instrument. After the analytes are adsorbed onto the SPME fiber, the fiber is retracted into the needle and then injected in a normal syringe technique such that the fiber is extended into the heated region of the IMS and the analytes are desorbed from the fiber into the clean carrier gas of the IMS. 

GC-MS is used to detect both common and emerging explosive compounds. A review of GC-MS methods used to detect organic explosive compounds is available [129]. T vo common GC-MS sample introduction techniques are solid-phase microextraction (SPME) and headspace vapor collection [130-133], TTiese sample introduction methods are employed in the analysis of water and soil samples with suspected explosive residue contamination [134-137]. The U.S. EPA Method 8095, Explosives by Gas Chromatography, is recommended as a resource for sample preparation of soil and water samples analyzed for the common nitroaromatic, nitra-mine, and nitrate ester explosive compounds [138]. 

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