Solid phase extraction 3601 Subject

Crop material is homogenized with acetonitrile-water (9 1, v/v). The crop extract is centrifuged and an aliquot is rotary evaporated to a small volume. The sample is subjected to a Cig solid-phase extraction (SPE) cleanup procedure. The concentrated eluate is subjected to liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis. 

In a related approach from the same laboratory, the perfluorooctylsulfonyl tag was employed in a traceless strategy for the deoxygenation of phenols (Scheme 7.82) [94], These reactions were carried out in a toluene/acetone/water (4 4 1) solvent mixture, utilizing 5 equivalents of formic acid and potassium carbonate/[l,T-bis(diphe-nylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl2] as the catalytic system. After 20 min of irradiation, the reaction mixture was subjected to fluorous solid-phase extraction (F-S PE) to afford the desired products in high yields. This new traceless fluorous tag has also been employed in the synthesis of pyrimidines and hydantoins. 

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. 

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. 

Using mentioned extraction/deproteinization procedures, the obtained aqueous or organic extracts often represent very dilute solutions of the analyte(s). These extracts may also contain coextractives that, if not efficiently separated prior to analysis of the final extract, will increase the background noise of the detector making it impossible to determine the analyte(s) at the trace residue levels likely to occur in the analyzed samples. Hence, to reduce potential interferences and concentrate the analyte(s), the primary sample extracts are often subjected to some kind of additional sample cleanup such as liquid-liquid partitioning, solid-phase extraction, or online trace enrichment and liquid chromatography. In many instances, more than one of these cleanup procedures may be applied in combination to allow higher purification of the analyte(s). 

The primary sample extract is subsequently subjected to cleanup using several different approaches including conventional liquid-liquid partitioning, solid-phase extraction, liquid chromatography, immunoaffinity chromatography, and supercritical fluid extraction cleanup. In some instances, more than one of these purification procedures can be applied in combination for better results. 

Following extraction, the primary sample extract is subsequently subjected to some type of cleanup including conventional liquid-liquid partitioning and/ or solid-phase extraction. The liquid-liquid partitioning cleanup applied differs with the initial extraction system. Thus, for isolating fat from analytes, the primary dichloromethane sample exttact was partitioned with IN hydrochloric acid in the analysis of leucogentian violet in chicken fat (491-494). The acidic layer was then neutralized with trisodium citrate to facilitate back extraction of the analytes into dichloromethane. 

Retention times of the peaks are subject to the particular type of column. The acidic fraction from solid-phase extraction consists of phenolic acids such as cis-coutaric, trans-coutaric, and trans-caftaric acids. Isocratic elution is suitable because of the limited number of compounds found in the acidic fraction. Analysis of the acidic fraction is completed within 30 min. See Figure 11.3.1 for an HPLC chromatogram of the acidic polyphenolics isolated from Niagara grapes. 

In a method proposed by Booth et al. (141) for the determination of phylloquinone in various food types, extracted samples are subjected to silica solid-phase extraction followed, in the case of meat or milk samples, by further purification using reversed-phase solid-phase extraction or liquid-phase reduction extraction, respectively. The final test solution is analyzed by NARP-HPLC, and the fluorescent hydroquinone reduction products of phylloquinone and the internal standard are produced online using a postcolumn chemical reactor packed with zinc metal. 2, 3 -Dihydrophylloquinone, a synthetic analog of phylloquinone, is a suitable internal standard for the analysis of vegetable juice, whole milk, and spinach. Another synthetic analog, Ku23), is used for the analysis of bread and beef, because a contaminant in the test solution coelutes with dihydro-phylloquinone. 

Adjustment of pH Adjustment of pH (to 3 and 11) provides additional information on the nature of the toxicants, and provides blanks for subsequent pH adjustment tests performed in combination with other treatments (/.< ., filtration, aeration). Samples are adjusted to pH 3 and 11, and then subjected to filtration, aeration, or solid phase extraction with a Cl8 column. The treated samples (including the pH adjusted samples without additional treatment) are re-adjusted to the initial pH of the effluent (pH 7) prior to testing. 

Before any sample can be subjected to chromatography, some type of sample preparation is required, which can be as simple as filtration or an involved solid-phase extraction protocol. Sample preparation is that activity or those activities necessary to prepare a sample for analysis. The ultimate goal of sample preparation is to provide the component of interest in solution, free from interferences and at a concentration appropriate for detection. This entry will briefly discuss seven topic areas included in sample preparation standard methods, solid-phase extraction (SPE), matrix solid-phase dispersion (MSPD), solid-phase microextraction (SPME), microdialysis, ultraliltration (UF), and automated systems. 

In principle, care must be taken in the analysis of waste water samples so that the ion exchanger being used does not be contaminated by organic material such as fats, oils, surfactants, etc. They can be removed from the sample via solid phase extraction on suitable materials (e.g. OnGuard cartridges). Further details regarding the subject of sample preparation may be found in Section 8.9... 

---