Colorimetric detection and spectrophotometric determination of the aminothiazolyl-alkoxyimino beta-lactams

The 2-aminothiazolyl-4-yl-2-alkoxyiminoacetamido substituent-containing beta-lactam antibiotics (cephalosporins and monobactams) develop a stable, concentration-dependent purple or cherry-red color after reaction with sodium nitrite in acidic condition. The color-formation is highly specific; it requires certain defined structural features such as the simultaneous presence of the intact aminothiazole-ring and an alkoxyimino substituent in the syn configuration. Other substituents on the beta-lactam nucleus have effect only on the intensity of the color. This simple and fast colorimetric procedure was found to be useful not only for the detection of this class of beta-lactam antibiotics but also for their quantitative spectrophotometric determination (lambda max 500 nm). A linear relationship exists between the intensity of the color plotted on a logarithmic scale and the concentration (12.5-200 micrograms/ml) of the compounds on an arithmetic scale. The beta-lactams studied in this class with definitely positive purple-red color reaction are; cefotaxime, ceftizoxime, ceftazidime, ceftriaxone, cefmenoxime, cefodizime, ceftiolene, cefpirome, aztreonam, HR 109, FK 027 (cefixime), FR 19346, SK&F 88070, FR 13300, carumonam, YM 13115, BMY 28142, DN 9550, deacetylcefotaxime, deacetoxycefotaxime and deacetylcefotaxime lactone.