Matrix solvent

The spectrometer provides a mass spectrum of the ions, some of which come from anything dissolved in the solution or matrix (solute ions) and some from the matrix solvent itself. 

The selectivity of a detector is its ability to determine an analyte of interest without interference from other materials present in the analytical system, i.e. the sample matrix, solvents used, etc. 

Whereas the use of conventional fast atom bombardment (FAB) in the analysis of polymer/additive extracts has been reported (see Section 6.2.4), the need for a glycerol (or other polar) matrix might render FAB-MS analysis of a dissolved polymer/additive system rather unattractive (high chemical background, high level of matrix-, solvent- and polymer-related ions, complicated spectra). Yet, in selected cases the method has proved quite successful. Lay and Miller [53] have developed an alternative method to the use of sample extraction, cleanup, followed by GC in the quantitative analysis of PVC/DEHP with plasticiser levels as typically found in consumer products (ca. 30 %). The method relied on addition of the internal standard didecylphthalate (DDP) to a THF solution of the PVC sample with FAB-MS quantitation based on the relative signal levels of the [MH]+ ions of DEHP and DDP obtained from full-scan spectra, and on the use of a calibration curve (intensity ratio m/z 391/447 vs. mg DEHP/mg DDP). No FAB-matrix was added. No ions associated with the bulk of the PVC polymer were observed. It was... 

MALDI-MS studies conducted on whole-cell bacteria prior to 2000 utilized spectra that rarely contained peaks above 20,000 Da. In 2000 a paper describing a methodology was published that extended the mass range for whole-cell bacteria to 100,000 Da.18 The matrix solvent consisted of a mixture of formic acid, acetonitrile, and water in a ratio of 17 33 50. The solvent mixture has been successfully used with most of the common MALDI matrices. The reasons for the success of this solvent are most likely related to the crystal formation of the matrix. When compared to other solvents, smaller and more uniform matrix-analyte crystals were observed with the method using formic acid, acetonitrile, and water as the solution. Figure 14.4 shows an example of E. coli obtained utilizing the described methodology. 

Barber et al. introduced FAB in 1981. In this technique, bombardment of a liquid target surface by a beam of fast atoms such as xenon or argon, causes the continuous desorption of ions that are characteristic of the liquid. In a typical FAB spectrum, the analyte ion is usually formed as protonated or cationized ions in positive FAB, and deprotonated ions in negative FAB mode. A few fragmented ions may also be formed. The spectrum usually contains peaks from the matrix, such as protonated matrix clusters of glycerol if it is used as the matrix solvent. FAB utilizes a liquid matrix such as glycerol. The matrix is used to enhance sensitivity and ion current stability. 

These studies will be followed with experiments that examine the influence of the matrix solvent on the inverse surface-protein binding affinity/MALDI ion signal relationship. 

Extraction In order to extract the toxin from the matrix, solvents or mixtures of solvents (methylene chloride, bicarbonate solution, methanol-water, chloroform-water) are used. Two main types of apparatus are commonly used the mechanical shaker (Ultra-Turrax homogenizer, multi-Wrist, magnetic stirrer) or High-Speed Waring Blenders. Other, rarely used extraction procedures are Soxhlet-type extractors and, more recently, supercritical fluid extraction. The time of extraction ranges from a few minutes (3 - 5) to 1 hour, depending on the procedure employed. 

The general criteria for the solvent selection are high solubility of the analytes and low solubility of the sample matrix. Solvents used in conventional... 

The matrix selection and deposition for MALDI-IMS is another crucial step in the sample preparation protocol. The matrix, solvent, concentration of matrix, and the protocol of coating matrix have to be optimized first and then used for the real samples detection. 

Protein matrix Solvent exposure of heme A dielectric environment destabilizes ferric heme [4, 5, 28]... 

Drug release from swellable matrix tablets is based on the glassy-rubbery transition of the polymer which occurs as a result of water penetration into the matrix. Therefore, the gel layer is physically delimited by the erosion (swollen matrix-solvent boundary) and swelling (glassy-rubbery polymer boundary) fronts. 

The coaxial Cf-FAB interface was originally designed to couple open-tubular LC and MS [42]. It consists of two coaxial fused silica capillaries a 10-pm-ID x 150-pm-OD open-tubular LC column surrounded by a 200-pm-ID x 350-pm-ID makeup or sheath tube. The matrix solvent is added close to the target. Either brass or stainless-steel targets were applied. 

Most recently, Caprioli s group183 have reported a novel method of dry coating tissue sections with MALDI matrix, thus minimizing the problem of the matrix solvent mobilizing the surface analytes. The dry coating procedure proved to be simple and rapid and yielded high-quality images of phospholipids. 

In another similar example nanocomposite was formed in a polyurethane matrix. Solvent soluble polyurethane had pyridine groups attached which formed complexes with metal salts. Films were then formed and subjected to a reducing agent in order to produce particulate metal filler. In this case the distribution of the filler which was formed was not uniform because the filler had tendency to aggregate (even though it was chemically attached to the matrix prior to the reduction). The following were factors controlling size and shape of these metal particles ... 

Wieczorek, P., Tomaszewska, M. (1997). Transport ofamino acids through liquid membranes supported on novel poly(vinylidenefluoride) porous flat-sheet matrix. Solvent Extr. Ion. Exc., 15, 879-94. 

FAB/MS and NMR. FAB/MS spectra were obtained on a VG magnetic sector instrument. The samples were placed on the FAB target probe containing 2-hydroxy-ethyldisulfide as the matrix solvent. The target was bombarded with xenon at 8-9 KV and the data recorded with a UPACS II data system. Matrix ions were subtracted from the samples ions. All NMR experiments were performed at 25° on a Bruker... 

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