Tandem sample treatment

Fernandez Moreno, J. L., Arrebola Liebanas, F. J., Garrido Frenich, A., and Martinez Vidal, J. L. 2006. Evaluation of different sample treatments for determining pesticide residues in fat vegetable matrices like avocado by low-pressure gas chromatography-tandem mass spectrometry. J. Chromatogr. A 1111 97-105. 

For the identification of surfactants in influent and effluent samples from German and Greek wastewater treatment plants, Schroder and co-workers [4,5] employed an analytical approach comprising SPE, selective elution and screening analysis by flow-injection analysis (FIA)-MS(MS) in combination with liquid chromatography-(tandem)... 

Figure 6 Detection ofthe 8-oxoGua/formylamine tandem lesions in isolated DNA exposed to gamma radiation in aerated aqueous solution. DNA was digested by a mild enzymatic treatment in order to release the lesions without cleavage of the phosphodiester bond. The sample was then injected onto a reverse phase HPLC column. The detection was provided by a mass spectrometer monitoring the main fragmentation ofthe two tandem base lesions.

Installation of the butenolide appendage was carried out by addition of the lithium anion of 4-methoxy-3-methyl-2(5//)furanone (241) to aldehyde 238 to provide a 2 1 mixture of diastereoisomeric alcohols 239, which was converted to a 2 1 mixture of diastereoisomeric ketones after Dess-Martin oxidation. Treatment of the respective ketones with trifiuoroacetic acid, followed by adjustment of the pH to 10, triggered a tandem triple cychzation to give stemofoline hydrate 240 in 67% yield. Dehydration of 240 proved surprisingly difficult due to the propensity for 240 to undergo retro-aldolization to provide pentacyclic lactone 242. Treatment of 240 with triflic anhydride provided a 12% yield of a single dehydration product (along with 24% of pentacyclic ketone 242) which proved to be identical by TLC and H-NMR spectroscopy with an authentic sample of natural isostemofoline. The synthetic sample was compared and shown to be identical to isostemofoline (224). 

Four of the entries shown in the comment column of Table 3 for macromolecules also indicate that problems exist. The subjects of the first, tenth and thirteenth entries in Table 3, namely sample pre-treatment procedures, choice of detector and collection of separated fractions, are all connected in that they arise from the complexity of the analyte mixtures, a subject discussed previously. The subject of the first entry constitutes the major, at present unsolved, problem in the separation of macromolecules. As a result it may be confidently predicted that much of the instmment manufacturers research and development efforts at the present time lies in this area of automated sample pretreatment devices suitable for mixtures of macromolecules because this area must be automated if the whole HPLC process is to be automated. The problem indicated in the tenth entry of Table 3, concerning the choice of detector for macromolecules was also discussed in the previous part. Therefore it is sufficient to note here that because of the lack of a universal, sensitive detector for macromolecules two or more of the available detector molecules, arranged in tandem, may need to be employed. Alternatively if a single detector module of the type already discussed in the previous section is used, then discrete fractions of the eluate must be collected for subsequent off-line analysis by say, gel electrophoresis, immuno- or bio-assay procedures. This alternative practice accounts for the optional entry number 13 in Table 3 regarding the provision of a fraction collector. 

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