Matrix solid phase dispersion

Matrix solid phase dispersion (MSPD) is an effective sample preparation technique that combines extraction and purification in one step. Barker et al. defined MSPD procedures as those that use dispersing sorbents with chemical modification of the silica surface (e.g.. Cl8, C8). Samples are blended and dispersed on particles (diameters of 40-100 p.m) using a glass or agate mortar and pestle (Pig. 4.3). The use of ceramic or clay mortars and pestles can result in loss of analytes. A disadvantage of the method is the traditionally high sorbent sample ratios 

More recent reviews on this particular topic suggest that MSPD has attracted many researchers in environmental, clinical, and food analysis. Different bulk materials have been used as matrix dispersing agents the most popular is C18- and C8-bonded silica. 

Zou et al. have described an MSPD procedure for the extraction of eight sulfonamides from honey samples using C18 as solid support. After the MSPD, the sulfonamides were derivatized with 9-lluorenylmethylchloroformate (EMOC-Cl). The derivatives required further purification by silica gel SPE, prior to LC-UV determination. Average recoveries for most sulfonamides were 70%. Other polar sorbents, such as silica gel, CN- or NH2-bonded silica resulted in a strong absorption of the polar sulfonamides, providing very low recoveries. 

As an alternative to the classical C18- or C8 apolar bonded phases, the use of normal phase supports has been proposed to improve the isolation of more polar compounds as well as to perform extraction and clean-up in a single step, prior to reversed phase LC determination. Following this trend, Kishida has developed a simple method for the determination of six sulfonamides in meat samples, using normal phase MSPD with alumina N-S and 70% (v/v) ethanol solution as extraction solvent, followed by the evaporation of the extracts and LC-MS/diode-array detection (DAD) determination. Average recoveries were 90% in all cases, and the LOQs were well below the MRLs established by the EU. 

Perhaps one of the most interesting MSPD-based techniques is MSPD with hot-water extraction. Bogialli et al. have published several papers using this sample preparation technique for the determination of different antibacterials in a great variety of foodsmffs, such as fluoroquinolones in milk.  

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A technique that attempts to combine the extraction and SPE into a single step is matrix solid-phase dispersion (MSPD). In this technique, a nonpolar (such as Cig) SPE sorbent is blended directly into tissue matrix, the mixture is packaged into an SPE cartridge, and the cartridge is eluted like a typical SPE cartridge. The advantage of MSPD is reduced sample size and increased efficiency due to a reduced number of steps. 

Beef kidney samples were analyzed for atrazine by dispersing 0.5-g portions of kidney with 2-g portions of XAD-7 HP resin for matrix solid-phase dispersion. " By using a mortar and pestle, a powder-like mixture was prepared that was subjected to subcritical extraction using ethanol-modified water at 100 °C and 50 atm. The ethanol-water extract was sampled using a CW-DVB SPME fiber for direct analysis using ion-trap GC/MS, and the recoveries were quantitative for atrazine at the 0.2 mg kg fortification level. 

Solid-phase sorbents are also used in a technique known as matrix solid-phase dispersion (MSPD). MSPD is a patented process first reported in 1989 for conducting the simultaneous disruption and extraction of solid and semi-solid samples. The technique is rapid and requires low volumes (ca. 10 mL) of solvents. One problem that has hindered further progress in pesticide residues analysis is the high ratio of sorbent to sample, typically 0.5-2 g of sorbent per 0.5 g of sample. This limits the sample size and creates problems with representative sub-sampling. It permits complete fractionation of the sample matrix components and also the ability to elute selectively a single compound or class of compounds from the same sample. Excellent reviews of the practical and theoretical aspects of MSPD " and applications in food analysis were presented by Barker.Torres et reported the use of MSPD for the... 

Barker, S. A. 2000. Matrix solid-phase dispersion. J. Chromatogr. A. 885 115-127. 

The problems relating to increased contamination levels and/or insufficient sensitivity may be overcome by using matrix-solid phase dispersion, MS detection in selected ion monitoring (SIM) mode, and/or large volume injection. An example of combined analysis that utilizes specific detection is shown in Fig. 2.6. It entails simultaneous analyses of PAHs, PCBs, chlorobenzene, and organochlorine pesticides in soil. 

Ling Y-C, Huang I-P. 1995. Multiresidue matrix solid phase dispersion method for determining 16 organochlorine pesticides and polychlrinated biphenyls in fish. Chromatographia 40(5-6) 259-266. 

Long AR, Crouch MD, Barker SA. 1991b. Multiresidue matrix solid phase dispersion (MSPD) extraction and gas chromatographic screening of nine chlorinated pesticides in catfish (Ictalurus punctatus) muscle tissue. J Assoc Off Anal Chem 74 667-670. 

In the past two decades quite a few new techniques have emerged for the treatment of aqueous samples prior to organic analysis. Perhaps the most important development is that of solid-phase extraction (SPE), which has successfully replaced many off-line steps. This technique can be considered to have introduced a genuine new era in sample handling [1]. The many varieties in which the technique is available and can be applied have made it the key step in handling of aqueous samples. Among the successful varieties are solid-phase microextraction (SPME), matrix solid-phase dispersion, disk extraction and immunosorbent extraction. Several reviews covering these topics have appeared in the literature in the past decade (see e.g. Refs. [2,3] for nonylphenol... 

The chromatographic determination of AEs in the environment has been extensively reviewed [3,4], AEs have been extracted from the aqueous matrix, among others, by solvent sublation [65], LLE [66], SPE with Amberlite XAD-2 [67], cartridges [68-73] (i.e. C1 Ci8, GCB, C8) or Cis disks [74] and matrix solid-phase dispersion for bioconcentration studies in fish samples [75],... 

In matrix solid-phase dispersion (MSPD) the sample is mixed with a suitable powdered solid-phase until a homogeneous dry, free flowing powder is obtained with the sample dispersed over the entire material. A wide variety of solid-phase materials can be used, but for the non-ionic surfactants usually a reversed-phase C18 type of sorbent is applied. The mixture is subsequently (usually dry) packed into a glass column. Next, the analytes of interest are eluted with a suitable solvent or solvent mixture. The competition between reversed-phase hydrophobic chains in the dispersed solid-phase and the solvents results in separation of lipids from analytes. Separation of analytes and interfering substances can also be achieved if polarity differences are present. The MSPD technique has been proven to be successful for a variety of matrices and a wide range of compounds [43], thanks to its sequential extraction matrices analysed include fish tissues [44,45] as well as other diverse materials [46,47]. 

Garcia M, Rodriguez I, Cela R (2007) Optimisation of a matrix solid-phase dispersion method for the determination of organophosphate compounds in dust samples. Anal Chim Acta 590 17-25... 

Campone L, Piccinelli AL, Ostman C, Rastrelli L (2010) Determination of organophosphorous flame retardants in fish tissues by matrix solid-phase dispersion and gas chromatography. Anal Bioanal Chem 397 799-806... 

Examples of Matrix Solid-Phase Dispersion (MSPD) for the Analysis of Drug Residues in Edible Animal... 

In another method for the determination of sulfamethazine in muscle and liver tissues (59), the extraction problem was successfully addressed by applying a matrix solid-phase dispersion procedure for rapid and efficient purification of the tissue extracts. Determination was made by ELISA on the basis of antibodies raised against sulfamethazine-diazo-bovine serum albumin conjugates. 

ABEI, N-(4-aminobutyl)-N-ethyl isoluminol CLIA, chemiluminescence immunoassay SPE, solid-phase extraction MSPD, matrix solid-phase dispersion RP, reversed phase. 

In most published methods, the primary sample extracts are subjected to various types of cleanup procedures including conventional liquid-liquid partitioning, solid-phase extraction, matrix solid-phase dispersion, and online trace enrichment. In many cases, some of these procedures are used in combination in order to help obtaining highly purified extracts. 

Matrix solid-phase dispersion techniques have also been suggested for the determination of aminoglycoside residues in bovine tissues (19, 20). The solid-phase material employed in these methods was a cyanopropylsilyl (CN) sorbent. 

Direct elimination of proteins and other matrix constituents from food samples can also be accomplished with matrix solid-phase dispersion or diphasic dialysis membrane techniques. A matrix solid-phase dispersion technique was used for the determination of chloramphenicol in meat (66) and milk (67) using... 

In contrast to the solid-phase extraction approach, only nonpolar Cis-deriva-tized silica has been used as the sorbent in matrix solid-phase dispersion technique. This technique has been successfully applied in the determination of furazolidone in meat (66), milk (181), and swine tissues (180). 

Cleanup and concentration of quinolones from coextracted matrix constituents can also be accomplished with solid-phase extraction columns that contain either nonpolar reversed-phase (Cis) sorbents (177, 197, 198), or polar sorbents such as alumina (189-191, 194), aminopropyl (182, 187), and propylsulfonic acid (188). Reversed-phase Cis material has also been employed as the sorbent in matrix solid-phase dispersion cleanup for the determination of oxolinic acid in catfish muscle (206). 

A matrix solid-phase dispersion technique has been further applied for the determination of oxytetracycline, tetracycline, and chlortetracycline in milk (290, 311), using octadecylsilyl- (Cjg) derivatized silica as the solid phase. To facilitate extraction of the tetracycline antibiotics from milk, addition of an equal ratio of EDTA to oxalic acid has been found advantageous. 

When liquid samples such as serum, plasma, milk, or honey are not to be extracted using direct liquid-liquid partitions with organic solvents but through use of solid-phase extraction or matrix solid-phase dispersion techniques, dilution with water (323, 324), phosphate buffer saline (325), or phosphoric acid (326, 327) is often the only sample preparation procedure applied. Milk analysis sometimes requires further pretreatment for fat removal (328). Centrifugation at about 7000g at 4-10 C for 20 min is the usually applied procedure for making the fat floating on top of milk readily eliminated. 

The aqueous or organic extract obtained at this step of analysis may be a very dilute solution of the analyte(s) of interest. It may also contain coextractives, which, if allowed in the final extract, will increase the background noise of the detector, making it impossible to determine trace level concentrations of the analyte(s). To reduce interferences and concentrate the analyte(s), the primary sample extracts are subjected to some kind of cleanup including liquid-liquid partitioning, solid-phase extraction, matrix solid-phase dispersion, online trace enrichment, affinity chromatography, immunoaffinity chromatography, and ultrafiltration. In many instances, more than one of these procedures may be used in combination to increase extract purification. 

Matrix solid-phase dispersion has also been applied for the determination of ivermectin residues in bovine liver (373) and milk (372), moxidectin in bovine tissues (374), thiabendazole and mebendazole in meat (66), and five and seven benzimidazoles in bovine liver (375) and milk (322), respectively. 

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