The first simultaneous method for quantification of neomycin and polymyxin B in the presence of dexamethasone using HPLC with an Evaporative Light Scattering Detector (ELSD). Analysis was performed using a phenyl Waters X Bridge column, an evaporation temperature of 50οC, a nitrogen pressure 320 kPa. Mobile phase consists of a combination of methanol and trichloroacetate acid (40 mM, pH 1.70-1.80) in gradient mode, flow rate at 1.0 mL/min, detector gain of 6, analysis time of 35 minutes. The linearity was achieved with a concentration of 100-500 µg/mL (r=0.99955) for neomycin and concentration of 30-100 µg/mL (r=0.99703) for polymyxin B. Recovery results were obtained between 99.150% - 104.773% for neomycin and 96.538% - 105.139% for polymyxin B. Analysis sample from the market were found 102.27% for neomycin and 100.79% for polymyxin B. The result was compared to standard microbiological method. Based on the T-test results of two samples with a 95% confidence level (α = 0.05), it was concluded that there was no significant difference between HPLC-ELSD and microbiological methods for determining neomycin and polymyxin B. The HPLC-ELSD method has a potential for routine analysis because advantages in terms of increasing precision, accuracy and shorter testing time.
Key words: Antibiotics, ELSD, neomycin, polymyxin B
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