Neutral analytes compounds

The possible mechanism of ionization, fragmentation of studied compound as well as their desoi ption by laser radiation is discussed. It is shown that the formation of analyte ions is a result of a multi stage complex process included surface activation by laser irradiation, the adsoi ption of neutral analyte and proton donor molecules, the chemical reaction on the surface with proton or electron transfer, production of charged complexes bonded with the surface and finally laser desoi ption of such preformed molecules. 

RP-HPLC has been employed for the determination of flavonoids and other phenolic compounds in cranberry juice. The neutral and acidic analytes were preconcentrated octadecyl silica SPE cartridges conditioned with distilled water (neutral analytes) or with 0.01 M HC1 (acidic compounds). Hydrolysis of samples was carried out in aqueous methanol solution acidified with 6 M HC1 at 35°C for 16h. Chromatographic separation was performed in an ODS column (150 X 4.6mm i.d. particle size 5/.an). Solvents A and B were water-acetic acid (97 3, v/v) and methanol, respectively. The gradient started with 0 per cent B (flow rate, 0.9 ml/min), reached 10 per cent B in lQmin (flowrate, 1.0 ml/min) and increased to 70 per cent B in 40min (flowrate, 1.0 ml/min). Analytes were detected at 280 and 360 nm. Some typical chromatograms are presented in Fig. 2.71. The concentrations of flavonoids and phenolic acids are compiled in Table 2.69. It was stated that the SPE-HPLC procedure makes possible the simultaneous determination of phenolic compounds and flavonoids, therefore, it can be employed for the measurement of these classes of analytes in other fruit juices [188],... 

EKC is not restricted to the separation of neutral analytes, as it is widely employed for the simultaneous separations of charged and neutral analytes as well as of ionizable compounds having similar electrophoretic mobility. The separation of ionizable analytes by EKC is governed by differences in the partitioning between the pseudostationary phase and the surrounding electrolyte solution as well as electrophoretic mobility. For these analytes, the retention factor can be described by the following mathematical model ... 

Micellar electrokinetic chromatography has been proven to be a highly efficient separation method for neutral analytes (63,67,68), neutral and charged compounds (69-72), and ionized compounds (67,73) including PTH-amino acids (18). 

A major advantage of using mixed mode phases is that they allow the rapid analysis of ion suppressed acidic and neutral analytes at low pH [26]. With the exception of one recent report by Rozing [76], using a new Zorbax SCX/C18, no success has been reported in analysing basic compounds with SCX mixed mode phases. 

Traditional LC stationary phase, such as Hypersil or Spherisorb ODS1 materials are ideally suited to the analysis of neutral analytes as the phases possess a high content of acidic silanols, hence at pH 7-9 high EOF generation is achieved which facilitates rapid analysis. In marked contrast, many pharmaceutical compounds pos-... 

Once a soil is subsampled, extraction of the organic constituents is typically performed via soxhlet. The sample is chemically dried with anhydrous sodium sulfate, ground to a fine powder and then soxhlet extracted for 16 h with either hexane acetone, dichlor-omethane, or toluene. Soxhlet extraction is used for a wide range of compounds however, the extraction efficiency is the greatest with neutral analytes and drops off with increasing acidity. 

Variation of the mobile-phase pH is a powerful parameter to enhance the chromatographic selectivity and retention for mixtures of basic, acidic, and neutral compounds. Figure 4-22 shows that for neutral analytes (benzamide and llavone) the mobile-phase pH has no effect on the chromatographic retention [57]. However, for the organic acids (hydroxyisophthaUc acid and feno-profen, 4.5) at pH 2, which is at least 2 pH units below the acid analyte pKa values, maximum retention is obtained, while at pH 7 and 12 there is a... 

The potential application of APPI includes analysis of compounds (nonpolar and neutral analytes) that are not effectively ionized by ESI or APCI. APPI appears to be less influenced by matrix suppression as seen in ESI or APCI. It can serve as a complementary ionization source to ESI/APCI. 

A practical summary for the selection of the most appropriate ionization mode is as follows. For ionic compounds the concentration of the volatile electrolytes in the mobile phase should be carefully optimized. For neutral analytes, TSP buffer ionization or a electron-initiated ionization mode may be selected. In TSP buffer... 

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