A fluorescence method to determine picomole amounts of Zn(II) in biological systems

The formation of complexes between n-(6-methoxy-8-quinolyl)-p-toluensulfonamide (TSQ) and Zn(II) in methanol has been used as an analytical procedure for Zn(II) determination in biological systems. Using 1 ml cuvettes, the limit of detection of the method was approximately 20 pmoles of Zn(II). Linearity between fluorescence and zinc concentration was obtained up to approximately 1 microM Zn(II). Common multivalent cations present in biological systems like Al3+, Cu2+, Fe3+, Ca2+, and Mg2+, interfered with the measurement of Zn(II) only when present in excess of 20, 33, 60, 500 and 30,000 times the Zn (II) concentration, respectively. In human serum and semen, deproteinization of the samples permitted a good correlation between the TSQ method and the total Zn content determined by atomic absorption measurements. In rat spermatids, deproteinization and Zn (II) determination using the TSQ method gives approximately a 20% underestimation of the total Zn (II) content of the cells as compared to atomic absorption spectrophotometry. The method gives low resolution of Zn (II) peaks when tested as an analytical procedure to measure Zn (II) binding to protein fractions eluted during column chromatography.