Post separation adjustment of pH to enable the analysis of aminoglycoside antibiotics by microchip electrophoresis with amperometric detection.

Five aminoglycoside antibiotics (AGs), namely spectinomycin, streptomycin, amikacin, paromomycin, and neomycin, were analyzed by microchip electrophoresis with amperometric detection. Although the electrophoretic separation of AGs was carried out under acidic conditions, the amperometric detection was performed under alkaline conditions with an electrode fabricated by electrodeposition of an alloy of Cu-Sn-Cr. To achieve this, an alkaline solution was introduced into the end of the separation channel through two auxiliary channels, allowing the use of different conditions for each analytical operation. Along with the proposed pH adjustment, the use of electrodes modified with Cu-Sn-Cr enabled extending the lifetime of the electrodes. The alloy was co-electrodeposited on a 25-μm diameter platinum wire, which was then integrated in the microchip and used as working electrode. Furthermore, the effects of the pH and composition of buffer, separation potential, injection time, and detention potential were investigated in an effort to optimize both the separation and detection of AGs. Under the optimum conditions, linear relationships between the signal and the concentration were obtained in the 4.9-316.8 μM range, with regression coefficients of at least 0.99 and LODs ranging from 2.1 μM for amikacin to 4.6 μM for spectinomycin. Applicability of the method was demonstrated by analyzing five aminoglycoside antibiotics in spiked milk samples. The results showed that this alternative method is rapid, sensitive, and portable and enables the analysis of aminoglycoside antibiotics in milk sample.