Sample application interferences during

A lot of emphasis is laid on three possible basic interferences during the application process (1) single constituents of the sample solution crystallize out, (2) the property of the solvent used for dissolution, and (3) the concentration of the solution generating an imacceptably broad application zone. Such interferences could be avoided with proper planning before application. 

These results show that in a MISPE procedure one may encounter substances with different patterns of behavior. In the ideal case the template (or the template and a group of its analogs which need to be carried on for further analysis) are retained 100% during the sample application and the wash step. All other substances (or at least those which interfere with further analysis) should be fully removed. In the non-ideal case some interferents will not be removed by a particular protocol. In this case it is useful to observe the behavior of these interferents on the NIP. If they are retained by the NIP, too, then their retention is likely due to nonspecific binding. In this case a better choice of the solvents in the protocol may help to eliminate the interferent. The danger here is that the new protocol may also reduce the retention of the template and reduce its recovery. It is therefore interesting to note that even in this good paper it has not been shown that the addition of 1 % methanol to the dichloromethane sample was really necessary with the real sample matrices. 

The development of the MW technique has been towards higher pressures and temperatures, which is important in applications where the complete destruction of all organic material is needed. Residues of organic material can interfere with the determination of the analytes of interest through altered viscosity of the sample solution or chemical interferences during the determination. Exhaustive information on MW digestion can be found in, for example, the book by Kingston and Jassie [5]. 

Anaerobic sediments frequently contain large amounts of elementary sulfur (S8) which may cause serious interference during GC analysis. The traditional method that is applicable to chemically stable analytes is treatment with activated copper, but an elegant and milder procedure in which elementary sulfur is converted into water-soluble thiosulfate by reaction with tetrabutyl ammonium sulfite has been developed 0ensen et al. 1977). This method cannot, however, be applied to samples containing sensitive compounds such as phenols in such cases, the sulfur may be removed from the phenol acetates by silica gel chromatography and elution with cyclohexane (Allard et al. 1991). 

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). 

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