title: Column-switching technique for the sensitive determination of ertapenem in human cerebrospinal fluid using liquid chromatography and ultraviolet absorbance detection.
abstract: A sensitive reversed-phase high-performance liquid chromatographic (RP-HPLC) assay with on-line extraction was developed for quantifying ertapenem in human cerebrospinal fluid (CSF). This assay is at least five times more sensitive than previously published ertapenem methods with a lower limit of quantitation at 0.025 microg/ml. In this assay, a CSF sample is extracted on-line using a RP extraction column and an aqueous acidic mobile phase (0.1% formic acid) to wash away polar endogenous materials, while ertapenem is retained on the column. Ertapenem is then back-flushed off the extraction column and directed to a RP analytical column using an acidic mobile phase with an organic modifier (acetonitrile/0.1% formic acid, 15:85 (v/v)) and detected using UV absorbance. The acidic mobile phase provided a sharper chromatographic peak and on-line extraction allowed large injection volumes (> or = 150 microl) of buffered CSF to be injected without compromising column integrity. These assay conditions were necessary to quantify ertapenem at levels expected to be found in human CSF (< 0.05 microg/ml). The method was successfully validated and implemented for a clinical study: intraday precision and accuracy of the CSF assay for calibration standards (0.025-10 microg/ml) and quality control samples (0.1, 0.5, and 2.5 microg/ml) were < 6.2% coefficient of variation and 96.8-104.0% of nominal concentration, respectively.
authors.affiliation: Merck Research Laboratories, WP75A-303, West Point, PA, USA. chet_kitchen@merck.com
authors.forename: Chester J
authors.initials: CJ
authors.lastname: Kitchen
authors.forename: Donald G
authors.initials: DG
authors.lastname: Musson
authors.forename: Alison L
authors.initials: AL
authors.lastname: Fisher
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation / Q000379:methods*; D000077727:Ertapenem; D006801:Humans; D007769:Lactams / Q000134:cerebrospinal fluid*; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D047090:beta-Lactams
chemical_list: D007769:Lactams; D047090:beta-Lactams; D000077727:Ertapenem