Thin-layer sample preparation method

In our experience, an ultra-thin layer sample preparation method (Cadene Chait, 2000) using ammonium acetate as an additive gave best results for MALDI-TOF MS of sulfotyrosine peptides (Seibert et al., 2002, 2008). 

The second method is sandwich method which was developed from the two-layer method and used first for the analysis of the single mammalian cell lysates [67], The first thin layer is formed by the matrix-only solution. It is followed by deposition of the analyte solution and then deposition of second layer of matrix on the top of analyte layer. The sample is basically sandwiched between the two matrix layers and preparation results in a matrix-sample-matrix sandwich. This method is specifically used for detecting protein and peptides [67-69], The three-layer matrix-sample preparation method was also used as matrix-matrix-sample mode [70],... 

This entry describes the classical and modem sample preparation methods that have been used prior to qualitative and quantitative analysis by thin-layer chromatography (TLC) and high-performance (HP) TLC. Extraction and cleanup methods that are covered include classical methods such as liquid-liquid extraction (LLE) and Soxhlet extraction, as well as modern methods such as solid-phase extraction (SPE), pressurized liquid extraction (PLE), and supercritical fluid extraction (SEE). Modern methods have not been as widely apphed in TLC as for other modes of chromatography, e.g., column high-performance liquid chromatography (HPLC). 

Most early efforts focused on the development of thin layer matrix precoated membranes, including those made of nylon and other synthetic polymers, nitrocellulose, anion- and cation-modified cellulose and regenerated cellulose. Several manufacturers currently offer 96-well plates with proprietary coatings for LC-MALDI-MS applications. This approach was described in more detail above. As mentioned previously, all of these sample preparation methods were originally developed for pre-purified samples or fractions, not for analytes eluting from an HPLC or capillary electrophoresis column. 

Sample preparation of the porous eleetrode for TEM investigation is eritieal in order to obtain elear images of all phases in the eatalyst layer. Ultra-mierotome, solvent dispersion and FIB (fast ion beam bombardment) sample preparation methods have been investigated. The ultra-mierotome teehnique, introdueed first by Blom et al. in Oak Ridge National Laboratory [32], is often used to make thin slides of a eatalyst layer sample impregnated with epoxy for TEM investigation. 

Int Microbiol 7 173-180. http //www.im.microbios.oig/0703/0703173.pdf Fay LB, Ah S, Gross GA (1997) Determination of heterocyclic aromatic amines in food products automation of the sample preparation method prior to HPLC and HPLC-MS quantification. Mutat Res 376 29-35. http //www.doi.org/10.1016/S0027-5107(97)00022-5 Fekete A, Malik AK, Kumar A, Schmitt-KoppUn P (2010) Amines in the environment. Crit Rev Anal Chem 40 102-121. doi 10.1080/10408340903517495 Franc J, Koudelkova V (1979) Thin-layer chromatography of aromatic amines rmd their derivatives after reactions with l-fluoro-2,4-dinitrobenzene. J Chromatogr A 170 89-97. doi 10.1016/ 80021-9673(00)84241-7... 

All previous discussion has focused on sample preparation, i.e., removal of the targeted analyte(s) from the sample matrix, isolation of the analyte(s) from other co-extracted, undesirable sample components, and transfer of the analytes into a solvent suitable for final analysis. Over the years, numerous types of analytical instruments have been employed for this final analysis step as noted in the preceding text and Tables 3 and 4. Overall, GC and LC are the most often used analytical techniques, and modern GC and LC instrumentation coupled with mass spectrometry (MS) and tandem mass spectrometry (MS/MS) detection systems are currently the analytical techniques of choice. Methods relying on spectrophotometric detection and thin-layer chromatography (TLC) are now rarely employed, except perhaps for qualitative purposes. 

Thin-layer chromatography (TLC), sometimes also called planar chromatography, employ a stationary phase immobilized on a glass or plastic plate and an organic mobile phase. It is a rather old technique whose application in residue analysis has been limited in the past by poor chromatographic resolution, inadequate selectivity, and insufficient sensitivity (49). This was due to inherent problems in the quality of the available stationary phase materials and in the uniformity of the layers prepared. Today, the availability of affordable, precoated plates with acceptable performance and consistency has led to the general acceptance of TLC as an efficient procedure for residue analysis (50). The method is used preferentially when analysts must process large numbers of samples in a short period of time (51). 

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