[Fluorescence analysis of trace glucose using glucose oxidase and horseradish peroxidase].

In acetate buffer solution and in the presence of glucose oxidase (GOD), glucose reduced the dissolved oxygen to form H2O2 that oxidized catalytically the excess KI to from I3- by horseradish peroxidase (HRP). The I3- combines respectively with rhodamine S (RhS), rhodamine 6G(Rh6G), butyl-rhodamine B(b-RhB) and rhodamine B(RhB) to form RhS-I3, Rh6G-I3, b-RhB-I3 and RhB-I3 associated particles that result in fluorescence quenching at 556, 556, 584 and 584 nm, respectively. Under the optimal conditions, the concentration of glucose in the range of 0.083-9.99, 0.17-8.33, 0.33-8.33 and 0.33-9.99 micromol x L(-1) is linear with their fluorescence quenching at 556, 556, 584 and 584 nm, with detection limits of 0.059, 0.17, 0.21 and 0.16 micromol x L(-1) glucose. And the regression equation was deltaF = 40.0c + 3.0, deltaF = 23.9c + 8.1, deltaF = 25.6c + 4.2, and deltaAF = 18.4c + 0.8, respectively. The RhS system was the most sensitive and stable, and was chosen for use. Influence of some foreign substances on the RhS fluorescence quenching determination of 6.67 micromol x L(-1) glucose was examined, with a relative error of +/- 10%. Results showed that 1000-fold Mg2+ and Cu2+, 300-fold Mn2+, 100-fold Zn2+, Al3+ and Co2+, 60-fold L-tyrosine, urea and nicotinic acid, 50-fold Fe3+, HSA and BSA, 10-fold sucrose, vitamin B2, L-lysine, L-glutamic acid and L-cystine did not interfere with the determination. This RhS fluorescence quenching assay was applied to the determination of glucose in the serum samples with satisfactory results.

[Rhodamine 6G association particle based spectrophotometric determination of hydroxy free radical and its application to the selection of antioxidant].

In HCl-NaAc buffer solution, the hydroxy free radical from the Fenton reaction is captured by excess KI and releases I3-. The I3- combines with Rhodamine B (RhB, lamdamax=554 nm), Rhodamine 6G(Rh6G, lamdamax=526 nm), Rhodamine S (RhS, lamdamax=526 nm), and butyl Rhodamine B(b -RhB, A,lamdamax56 nm) to form association particles, so the absorbance at max wavelength decreases. The concentration of hydroxy free radical (calculated by the concentration of hydrogen peroxide) is proportional to the decreased absorbance of the systems of RhB, Rh6G, RhS, b-RhB in the range of 0.136-0.680 microg x L(-1), 0.34-0.680 microg x mL(-1), 0.034-0.680 microg x mL(-1), 0.034-0.680 microg c mL(-1), espectively. Based on this fact, a new method for the determination of scavenging percentage of hydroxy free radical with antioxidant was developed. The resistance to oxidation of four substances and six kinds of tea extract were measured with satisfactory results.