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Q X Li

Publications and source records attributed to Q X Li.

76 records · Page 5Linked to original sources
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Method for determination of xanthene dyes in guava fruits and its application in a field dissipation study.

Xanthene dyes, i.e., phloxine B and uranine or phloxine B alone, are phototoxic to tephritid fruit flies infesting guava fruits. An analytical method was developed for determination of residues of these dyes used in bait solutions for suppression of the tephritid fruit fly population in guava fruits. The procedure involved solvent extraction, anion-exchange cleanup, and determination by liquid chromatography or capillary zone electrophoresis. The dyes were extracted from 50 g guava fruit at 45 degrees degrees with 400 mL methanol-acetonitrile (1 + 1) and 5 g magnesium oxide added as an alkaline and clarifying agent. The guava extract was adjusted to pH 8.5 and subjected to an amino column cleanup. Average recoveries of xanthene dyes added to guava purees ranged from 77 to 99% for phloxine B and from 79 to 102% for uranine at spiking levels of 0.05-1.00 microg/g. The method was applied to the determination of phloxine B residues in guava fruits collected from a dye-sprayed orchard. After phloxine B was applied at a rate of 62.5 g/ha for 14 weekly sprayings, it was found on guava fruits at an average concentration of 111 +/- 18 ng/g 4 h after the llth spraying. The concentration of phloxine B was 426 +/- 94 ng/g in selected fruits with high deposits of the dye 4 h after spraying. Average concentrations of phloxine B 5 days after the 7th and 14th sprayings were 29 +/- 7 and 19 +/- 8 ng/g, respectively.

Coloring Agents↗
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Integration of liquid chromatography with immunoassay: an approach combining the strengths of both methods.

The integration of liquid chromatography (LC) with immunochemical detection combines the superior separation power of LC and the sensitivity and specificity of immunoassays. This approach is shown with 3 LC systems (Perkin-Elmer, C18 RP, 4.6 mm; Varian, C18 RP, 1 mm microbore; Michrom, C18 RP, 1 mm microbore) integrated with an enzyme-linked immunosorbent assay (ELISA) selective for five 4-nitrophenols. The nitrophenols were separated with the 3 LC systems with isocratic runs of 15 to 20 min. Microbore LC separation showed a 10-20 times reduction in solvent amount compared to conventional separation. LC-immunoassay was about 8- to 10-fold more sensitive compared with LC with UV detection. Integrated LC-immuno-assay proved to be a very selective method when 2-methylphenol was injected with an equimolar mixture of 2-amino-4-nitrophenol and 3-methyl-4-nitrophenol; 2-methylphenol does not cross-react with the serum used. Only 2 peaks could be seen in the detection, even when 2-methylphenol was present in very high amounts (3000 pmol). Further, the ELISA-LC detection proved to be selective and sensitive for complex matrixes. 2-Amino-4-nitrophenol was clearly identified in spiked extracts of soil and plant, even when a very small amount (2.4 ng) was injected. Although LC-immunoassay is more labor intensive than LC with UV detection, it offers great advantages in multiresidue analysis and is generally applicable for peak confirmation.

Chromatography, Liquid↗