Determination of monovalent and divalent cations and chloride in the carbacephalosporin loracarbef by ion chromatography

Abstract

Sensitive determination of monovalent and divalent cations and chloride in the carbacephalosporin antibiotic loracarbef can be achieved by separation on a high-capacity cation-exchange column followed by chemically suppressed conductivity detection. The methods developed in our laboratory for these determinations are characterized by the absence of matrix interference, rapid separation, ease of sample preparation and good sensitivity. Of these benefits, it is the minimization of matrix interference supplied by micromembrane chemical suppression that has made this technique so powerful for this application. Advantage is taken of the acid-base chemistry of loracarbef, resulting in a drastic reduction in its concentration in the eluent prior to detection of the analytes of interest. Linearities in the presence of the matrix (coefficient of determination ⪢ 0.995) and recoveries from the matrix are excellent (100 ± 2%). However, when the suppression components exhibit decreased efficiency, systems employing eluents composed of both hydrochloric and diaminopropionic acids are susceptible to problems such as poor peak shape, high background conductivity, and noise thus making accurate determinations difficult. Both the suppression system and the eluent are assessed in relation to the sources of high background conductivity and noise.