Solid phase extraction recovery

GC, utilizing flame ionization detection (FID), has been used to measure diisopropyl methylphosphonate in meat, grain, or milk (Caton et al. 1994). Sample preparation steps include homogenization, filtration, dialysis, and extraction on a solid sorbent. Two common solid phase extractants, Tenax GC and octadecylsilane bonded silica gel (C18 Silica), were compared by Caton et al. (1994). They reported 70% recovery when using Tenax GC and 85% recovery when using C18 Silica. Sensitivity was not reported. Equilibrium experiments indicate that 8-10 mg of Tenax GC are required to achieve maximum recovery of each g of diisopropyl methylphosphonate (Caton et al. 1994). By extrapolating these... 

The study concluded that Once wash steps are optimized, samples prepared by solid phase extraction are cleaner than those prepared by protein precipitation. Samples prepared by extraction with a Multi-SPE plate resulted in lower LOQs than samples prepared by solvent precipitation. Drug recoveries were acceptable (>80%) for both the SPE and the solvent precipitation methods. Well-to-well reproducibility of samples was slightly better with extraction with a Multi-SPE plate. Evaporation and reconstitution, while more time-consuming, yield better chromatographic performance, allow analysis of lower concentration samples, and require optimization for good analyte recovery. 

We usually conduct solid phase extractions on small scale and have not focused on the recovery of the tin reagents. However, in principle this should be possible for many types of reactions. 

Lopez-Avila et al. [59] used microwave assisted extraction to assist the extraction of polyaromatic hydrocarbons from soils. Another extraction method was described by Hartmann [60] for the recovery of polyaromatic hydrocarbons in forest soils. The method included saponification of samples in an ultrasonic bath, partitioning of polyaromatic hydrocarbons into hexane, extract cleanup by using solid-phase extraction, and gas chromatography-mass spectrometric analysis using deuterated internal standards. Polyaromatic hydrocarbons were thermally desorbed from soils and sediments without pretreatment in another investigation [61]. 

Gustavson et al. (2000) developed a convenient and novel solid phase extraction (SPE) method for the removal of methyl oleate from SPMD dialysates containing PAHs. A small SPE column (1 g or 0.5 g) containing a dual-zone silica (normal phase)-based restricted-access sorbent (Diazem, Midland, MI, USA) is used for the separation. The capacity of this sorbent to remove methyl oleate is about 1.8% (lipid/sorbent wt wt ). The PAHs are eluted with 19 mL of hexane and methylene chloride (97 3 VV ) and recoveries of all PAHs are typically >72%. 

A pivotal step in the analytical process is sample preparation. Frequently liquid-liquid extractions (LLEs) are used. Solvents, pH, and multiple back extractions are all manipulated to increase selectivity and decrease unwanted contaminants before injection on the GC system. Solid phase extraction (SPE) is more convenient than it used to be because of an increase in commercially available SPE columns. SPE columns are packed with an inert material that binds the drug of interest, allowing impurities to pass through. As with LEE, solvent choices and pH affect retention and recovery. There are three commercially available types of SPE columns, diatomaceous earth (which uses the same principles as LLE), polystyrene-divinylbenzene copolymer, and mixed mode bonded silica (Franke and de Zeeuw, 1998). 

Animal fat was studied using sweep codistillation (Brown et al. 1987). Good recovery (90%) was measured at 0.4 mg/kg no LOD information was given. Diazinon in liver and rumen content was determined by GC/FPD after methanol/dichloromethane (1 9) extraction and clean-up using either gel permeation chromatography (GPC) or silica gel solid phase extraction (SPE). The LODs were reported to range from 10 to 50 pg/g using a 5 g sample with measured recoveries of diazinon from rumen content of 95% at 0.1 pg/g and from liver of 88% at 0.05 pg/g. 

Extraction efficiency. Recovery of the analyte from biological matrix after sample pretreatment (i.e., liquid-liquid extraction, solid-phase extraction, protein precipitation, etc.) to remove endogenous substances. 

Unlike clenbuterol, salbutamol is a difficult compound to analyze due to its particular chemical attributes. It is a basic compound subjected to protein binding poor recoveries are obtained especially when protein precipitation techniques are used to prepare the extracts (145). In addition, salbutamol is charged at all pH values and does not readily lend itself to simple, specific back-extracting procedures. This severely restricts the options of sample cleanup. However, a Subtilisin protease digestion step followed by acid clarification and solid-phase extraction has been suggested (146) as an adequate extraction and cleanup procedure prior to the end-point determination of salbutamol by an enzyme immunoassay (139) based on the cross-reactivity of anticlenbuterol antibodies. 

Cleanup of nitro furans from coextracted substances and concentration of the extracts can also be accomplished with solid-phase extraction columns. Nonpolar sorbents such as reversed-phase (Cis) (37, 159-161, 170, 173, 177) or XAD-2 (178) materials are usually employed, since they provide high recovery of the analytes. However, in many cases, cleanup on these nonpolar sorbents is not effective in removing interfering substances from the extracts. Therefore, polar sorbents such as silica (29, 162), alumina (160, 179, 180), or aminopropyl (175, 176) materials are also frequendy employed as a more powerful alternative for extract cleanup. 

Solid-phase extraction was also evaluated for its potential to achieve the desired cleanup. Either Cig or Cg cartridges were loaded with defatted and deproteinized milk extracts, washed with water or water-methanol, and elution of the analytes was performed with methanol (553). The recoveries in this case were also poor. These results of poor recovery for solid-phase extraction and both acidic and basic extractions are consistent with those reported in the literature (553, 557). 

---