Sample application aqueous samples

Presently, the on-line coupling of NPLC and GC via heart-cutting is an established procedure which has been used successfully for several bioanalytical applications. Obviously, dfrect analysis of aqueous samples is not possible by NPLC, and therefore, a solvent switch by a sample pretreatment step (e.g. liquid-liquid extraction or SPE) is always requfred when biological samples are analysed by NPLC-GC. 

Another example is the determination of bentazone in aqueous samples. Bentazone is a common medium-polar pesticide, and is an acidic compound which co-elutes with humic and/or fulvic acids. In this application, two additional boundary conditions are important. Eirst, the pH of the M-1 mobile phase should be as low as possible for processing large sample volumes, with a pH of 2.3 being about the best that one can achieve when working with alkyl-modified silicas. Secondly, modifier gradients should be avoided in order to prevent interferences caused by the continuous release of humic and/or fulvic acids from the column during the gradient (46). 

FIGURE 5.2 Aqueous samples can cause breaking up and breaking off of the layer (left side) during application. 

FIGURE 5.5 Application pattern for a large aqueous sample applied as 160 X 10 mm area (left) in contrast to the standard pattern of 160 X 1 mm (right). 

Supercritical fluid extraction (SFE) is generally used for the extraction of selected analytes from solid sample matrices, but applications have been reported for aqueous samples. In one study, recoveries of 87-100% were obtained for simazine, propazine, and trietazine at the 0.05 ug mL concentration level using methanol-modified CO2 (10%, v/v) to extract the analytes, previously preconcentrated on a C-18 Empore extraction disk. The analysis was performed using LC/UV detection. Freeze-dried water samples were subjected to SFE for atrazine and simazine, and the optimum recoveries were obtained using the mildest conditions studied (50 °C, 20 MPa, and 30 mL of CO2). In some cases when using LEE and LC analysis, co-extracted humic substances created interference for the more polar metabolites when compared with SFE for the preparation of the same water sample. ... 

Diazinon SOW was applied by air blast sprayers in accordance with typical application practices for orchards. Application began in March and continued until early-to mid-July. Dormant sprays typically contained diazinon in an oil mixture. Aqueous emulsions were applied as foliar sprays thereafter. Eqmpment was calibrated to provide an application rate of 3.4 kg active ingredient (a.i.)ha At least five applications were made at approximately 2-week intervals. During these applications, 233 samples were taken from spray tanks across the four treatment fields to estimate the application rate in PA, and 244 samples were collected in WA. 

Applications On-line SPE-GC and SPE-GC-MS couplings find wide application for sample cleanup of biological, environmental and industrial analysis of aqueous samples [67]. SPE-GC-AED/MS is ideally suited for the (nontarget) screening of hetero-atom-containing compounds in aqueous samples, and allows confirmation plus identification in one run [68]. Specific applications of hyphenated SPE-GC systems for polymer/additive analysis were not identified. 

Until recently, it was accepted that the fundamental limit of detection of these sensors was at micromolar levels of the target ion in an aqueous sample, and the main application has been the determination of ions like sodium, potassium and calcium in blood samples, where the... 

The biological applications of NMR include the study of the structure of macromolecules such as proteins and nucleic acids and the study of membranes, and enzymic reactions. Newer methods and instruments have overcome, to a large extent, the technical difficulties encountered with aqueous samples and the analysis of body fluids is possible, permitting the determination of both the content and concentration of many metabolites in urine and plasma. NMR is not a very sensitive technique and it is often necessary to concentrate the sample either by freeze drying and dissolving in a smaller volume cm- by solid phase extraction methods. 

Similar to the previous section, we discuss only selected works to highlight the development of SPMDs. Also, we include some discussion of several unpublished pilot smdies (Huckins, 1989) that influenced our early development of SPMDs. These pilot studies were directed solely toward sampling the aqueous phase. The flrst application of SPMDs for sampling organic vapors did not occur until several years later (Petty et al., 1993). To our knowledge, only SPMDs, PESs and SPMEs are being applied in both air and water, because the use of many passive samplers is limited to a specific medium and exposure scenario. 

PIS Example 2 The detennination of caustic concentration in an aqueous sample containing NaOH (caustic) and a salt using NIR spectroscopy is examined in this example. This application and the experimental details are discussed thoroughly in Section 5.2.2,2. These data are also analyzed by MtR in Section 5.3.1.2. 

Commoner, B., A. J. Vithayathil, and P. Dolara, Mutagenic Analysis of Complex Samples of Aqueous Effluents, Air Particulates, and Foods, in Application of Short-Term Bioassays in the Fractionation and Analysis of Complex Environmental Mixtures (M. D. Waters, S. Nesnow, J. L. Huisingh, S. Sandhu, and L. Claxton, Eds.), pp. 529-570, Plenum, New York, 1979. 

The foremost conclusion is that synthetic polymers are applicable to a wide range of organic compounds present in many different kinds of aqueous samples, and the polymers are being used extensively. The extensive current and expected future use of polymers will force the availability of pure polymers from the commercial suppliers. The users will have to pay the price for this convenience in the same way they are now willing to pay a premium for the convenience of high-purity solvents. 

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