Solid phase microextraction sample pretreatment

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]. 

Microwave-assisted desorption coupled to in situ headspace solid-phase microextraction (HS-SPME) was first proposed as a possible alternative pretreatment of samples collected from workplace monitoring. Therefore, pretreatment that takes a short time and uses little or no organic solvents has led to the recent development of a new extraction technique. Solid-phase micro-extraction (SPME) coupled with GC analysis has been used successfully to analyze pollutants in environmental matrices. MHS has been developed to achieve one-step, in situ headspace sampling of semivolatile organic compounds in aqueous samples, vegetables, and soil [7, 55-58]. 

Generally, samples are injected in the chromatographic system without any dilution or pretreatment step, using the split mode (i.e., with sample division), which is suitable for the analysis of the major compounds in beverages.When the objective of analysis is the determination of compounds present in small quantities (p.g/L), some extraction and/or concentration step is necessary, followed by the sample injection in the spMess mode (without sample division). This last sample introduction mode is usually combined with extraction techniques such as liquid-liquid extraction (LLE), solid-phase extraction (SPE), " and solid-phase microextraction (SPME). ... 

Lambropoulou, D. A., Konstantinou, I. K., and Albanis, T. A. 2006. Sample pretreatment method for the determination of polychlorinated biphenyls in bird livers using ultrasonic extraction followed by headspace solid-phase microextraction and gas chromatography-mass spectrometry. 7. Chromatogr. A 1124 97-105. 

A major disadvantage of the small column internal diameters used in open capillary GC is the limited injection volume. This limitation can partly be reduced by the use of preconcentrating sample pretreatment, such liquid-liquid extraction (LLE), solid-phase extraction (SPE), and solid-phase microextraction (SPME). These sample pretreatment techniques are widely applied throughout the daily practice of GC-MS, as exemplified by the sample pretreatment procedures de scribed in the various chapters of this book. 

A set of local anesthetics was measured by GC-MS in SIM mode using solid-phase microextraction (SPME) [26] for sample pretreatment. Decadeuter-ated lidocaine was synthesized and used as the internal standard. This technique... 

Different sample pretreatment operations include dilution, membrane-extraction (gas diffusion, dialysis), liquid-phase extraction techniques (liquid/liquid extraction, liquid-phase microextraction, single-drop microextraction) and solid reactors and packed columns aiming to facilitate online chemical derivatization, chromatographic separation of target species, removal of interfering matrix compounds, enzymatic assays, or determination of trace levels of analyte via sorptive preconcentration procedures (Marshall et al., 2003 Economou, 2005 Miro and Hansen, 2006 Theodoridis et al., 2007 McKelvie, 2008 Ruzicka, 2014). In this context, BIA and the LOV configurations are particularly useful. Acid-base titrations can also be automated using simple SIA manifolds and potentiometric (van Staden et al., 2002) or photometric (Kozak et al., 2011) detection. Typically, a zone of the sample to be titrated is sandwiched between two zones of titrant by aspiration. In the case of photometric detection, an additional zone of a suitable pH-sensitive colored indicator is aspirated. The stacked zones are delivered to the detector and the width of the peaks is monitored and related to the pH of the solution. 

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