Dispersive SPE

This section discusses dispersive SPE, matrix solid phase dispersion, solid phase micro-extraction, micro-extraction by packed sorbent, stir-bar sorbent extraction, and the restricted-access materials.  

Primary secondary amine (PSA) is the most common sorbent used in pesticide residue analysis because it can effectively retain organic acids present in food. C18 or a 

PSA/C18 combination is more widely used in the analysis of food of animal origin because of the higher lipid content. In more recent research, it was found that the combination of PSA and C18 provided better clean-up than did PSA or Cl8 alone for 38 anthelmintics in liver and milk. However, PSA/C18 gave a lower recovery for some analytes (due to PSA), compared with Cl8 alone, which gave sufficient clean-up and good recovery for all analytes and was therefore chosen as the preferred sorbent. 

Graphitized carbon black (GCB) has been reported to be a highly effective sorbent for sample clean-up but also removes structurally planar analytes, limiting its applications. Addition of HOAc to the extraction solvent may help to improve recovery of analytes, but it also inhibits the retention of acidic matrix compounds. Several papers have reported the use of Cl8 for dSPE in veterinary residue analysis. The use of PSA, NH2, and silica has also been reported. While dSPE does not provide the same degree of clean-up as SPE, it does provide good recovery and reproducibility, coupled with practical and cost advantages.  

Mastovska and Lightfield have improved a previous analytical method replacing conventional SPE by dSPE for the determination of 11 P-lactams in bovine kidney samples. The method involves solvent extraction/deproteinization with H2O/ACN (20 80, v/v), followed by dSPE clean-up with C18 sorbent and final LC-MS/MS determination. Taking into account the simplicity of this protocol, accuracy was satisfactory with recoveries ranging from 87% to 103% and RSD 16%. Moreover, the use of dSPE increased the number of samples that can be prepared in a day by a factor of 3-4. 

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AcNa centrifugation (b) Dispersive SPE C18 and primary and secondary amine sorbents with MgS04. 

OPA, o-phthalaldehyde NQS, -naphthoquinone-4-sulfonate ex, excitation em, emission ISP, lonspray APCI, atmospheric pressure chemical ionization MSPD, matrix soid-phase dispersion SPE, solid-phase extraction deprtn, deproteinization acidfn, acidification RP, reversed phase NR, not reported. 

QuEChERS (quick, easy, cheap, effective, rugged, and safe) is an acronym used as the name of a sample preparation procedure, generally based on a combination of solvent extraction of analytes from a sample and dispersive SPE applied for cleaning an extractant. 

An evaluation of the scientific literature reveals that over 500 papers on veterinary drug residue analysis were published in the 5-year period of 2005-2009. Liquid extraction (LE) and liquid-solid extraction (LSE) were found to be very popular sample treatment techniques that were used in 30% and 60% of the reported studies, respectively. Here, LE includes all liquid-based approaches such as liquid-liquid extraction (LLE), extrelut liquid-liquid extraction, liquid-liquid micro-extraction, and pressurized liquid extraction (PLE). LSE includes solid phase extraction (SPE) and all other sorbent-based extraction procedures, such as solid phase micro-extraction (SPME), stir bar sorptive extraction (SBSE), restricted-access materials (RAM), turbulent-flow chromatography (TEC), dispersive SPE (dSPE), and matrix solid phase dispersion... 

PSA/MgS04-mixture For dispersive SPE, most samples require a mixture of 25 mg PSA and 150 mg MgS04 anhydrous grit per mL sample extract (e.g., for... 

Note When only lipids are to be removed, freezing out may be replaced by a dispersive SPE (D-SPE)-cleanup, where C18 (ODS) sorbentis used as described in (c). 

Note It is helpful to load the centrifuge tubes with the dispersive SPE sorbents before beginning the extraction procedure needed for one batch of samples. Instead of PS A, other amino-type sorbents may also be employed for... 

QuEChERS, Dispersive SPE, D-SPE, Pesticides, Multiresidue Analysis, LC-MS/MS, PSA, GCB, Ereeze-Out... 

Ci8, Cg, and divinylbenzene polymers) are predominantly used for retention of pesticides from water samples followed by their selective elution by small solvent volumes. In food applications, another SPE approach called chemical filtration , i.e., adsorption of matrix components, such as sugars and fatty acids on aminopropyl (-NH2) or primary secondary amine (PSA) sorbents, while analytes remain in the extract, can be conveniently employed in cartridge or disk formats or as a novel dispersive SPE clean-up (mixing of a small amount of sorbent with the extract). 

EN 15662 Determination of pesticide residues using GC-MS and/or LC-MS(/MS) following acetonitrile extraction/partitioning and cleanup by dispersive SPE—QuECHERS method. In European Committee for Standardization, Technical Committee CEN/TC 275, Food analysis—horizontal methods. Brussels European Committee for Standardization, 2008. 

On the other hand, the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, originally developed for pesticide analysis [23], has been also applied to the determination of multiclass veterinary drugs in different food commodities [24—27], The conventional QuEChERS strategy applies acetonitrile extraction, followed by removal of water and proteins by salting out with sodium chloride and magnesium sulphate. Afterwards, dispersive SPE (d—SPE) is usually applied. The QuEChERS approach has many advantages, as it is simple and quick, reduces the... 

European Standard EN15662. (2008) Foods of Plant Origin - Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extrac-tion/Partitioning and Clean-Up by Dispersive SPE -QuEChERS Method. European Standard. 

The analytical method comprises a triple quadrupole GC-MS/MS system with liquid autosampler. The gas chromatograph is equipped with a temperature programmable PTV injector for splitless injection. The separation is performed using a 5% phenyl phase column of standard dimensions. After a short dispersive SPE clean-up the acetonitrile extract is directly injected after centrifugation. The Thermo Scientific TraceFinder software with compound database of pesticides was used for method setup and data processing (The Pesticides Compound Database, 2014). 

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