Simple bacteriological and thin-layer chromatographic methods for determination of individual drug concentrations treated with penicillin-G in combination with one of the aminoglycosides.

For the individual determination of residual drug concentrations in meat when using penicillin-G (PC-G) in combination with one of the aminoglycoside antibiotics, the differentiation of PC-G and the aminoglycoside groups was easily accomplished by incubation of the individual drug with penicillinase (PCase). Each aminoglycoside treated with PCase (50 U/ml) produced a similar clear inhibition zone by the aminoglycoside alone, but PC-G treated with PCase produced no inhibition zone even when a high concentration of 100 microg/ml of PC-G was used on the assay plates seeded with Bacillus subtilis or Micrococcus luteus. Furthermore, these drugs could be distinguished and identified according to their characteristic Rf values and colours by the TLC method using silica-gel 60 F254 plates followed by spraying with various chemical reagents. A solution of n-butanol:acetic acid:water:p-toluenesulphonic acid (3:1:1:0.7) was the best developing solvent for the separation of all the antibiotics.