Aminoglycoside antibiotics are always a mixture of structurally related amino sugars, which do not have a chromophore or fluorophore. The aim of the study was to find one method for evaluation of the components and impurities of the antibiotics. Derivatization with o-phthaldialdehyde and thioglycolic acid is found to be appropriate for all antibiotics. The components of gentamicin (GM), sisomicin, netilmicin, kanamycin, amikacin, and tobramycin were tried to separate by means of micellar electrokinetic chromatography. The background electrolyte was composed of sodium tetraborate (100 mM, pH 10.0), sodium deoxycholate (20 mM), and beta-cyclodextrin (15 mM). This method is valid for evaluation of GM, kanamycin, and tobramycin. It has to be improved for amikacin and netilmicin. In addition, 46 bulk samples of GM of different manufacturer or pharmaceutical companies were investigated. Many samples were found to contain many minor products and different amounts. Beside different patterns of the main compounds GM C1, GM C1a, GM C2a, and GM C2, many lots were found consisting of a substantial number of minor products. The appearance of a high number of minor products is always associated with the existence of sisomicin, which is not found in "pure" samples. However, almost all samples met the requirements of the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP).

The antibiotic agent gentamicin sulfate is a mixture of several structurally very similar aminoglycosides. The major components of gentamicin are gentamicin C1, C1a, C2 and C2a. These major components were separated by means of column chromatography. The 1 H and 13 C NMR spectra of the free bases and the corresponding sulfates were assigned using HMQC, HMBC and selective TOCSY experiments. Additionally, the 1 H and 13 C NMR spectra of the sulfates and hydrochlorides, respectively, of the minor components were assigned. The full assignment of all components of gentamicin is necessary for the quantitative analysis of batches of gentamicin. By means of coupled liquid chromatography-NMR, several different batches were studied, revealing different compositions of batches from various sources.

SummaryA capillary electrophoretic method has been developed for determination of the components of the paromomycin mixture salt. Paromomycin was detected at 330 nm after pre-capillary derivatization with o-phthaldialdehyde and thioglycohc acid. The electrophoretic separation was performed in a fused-silica capillary at 25 ~ and 18 kV with a background electrolyte comprising 40 mM sodium tetraborate, 3 mM fl-cyclodextrin, and 12.5% (v/v) methanol.Although the analysis time was reduced to 10 min, five peaks could be separated to baseline. The relative standard deviation of the ratios (peak area/internal standard peak area) was <5% for all peaks.

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The components of the aminoglycosides, e.g., gentamicin, sisomicin, netilmicin, kanamycin, amikacin, and tobramycin, and related impurities of these antibiotics can be separated by means of micellar electrokinetic chromatography (MEKC). Derivatization with o-phthaldialdehyde and thioglycolic acid is found to be appropriate for these antibiotics. The background electrolyte was composed of sodium tetraborate (100 mM), sodium deoxycholate (20 mM), and β-cyclodextrin (15 mM) having a pH value of 10.0. This method is valid for evaluation of gentamicin, kanamycin, and tobramycin. It has to be adopted for amikacin, paromomycin, neomycin, and netilmicin.