Accurate measurement of female genital tract fluid dilution in cervicovaginal lavage samples

•Uncertainty in collected vaginal fluid volume is key drawback of lavage technique.•Validated IC method for accurate and precise measurement lithium, marker of dilution.•Chromatograms of samples collected in vivo underscore method utility.

An ion chromatographic method with conductivity detection for the precise and accurate analysis of lithium ions in phosphate-buffered saline, used as a cervicovaginal lavage (CVL) fluid, was developed and validated. The lithium ion dilution factor during the CVL is used to calculate the volume of cervicovaginal fluid (CVF) collected. Initial CVL Li+ concentrations of 1 mM and 10 mM were evaluated. The method is robust, practical, and afforded an accurate measurement (5% of the measurement, or better) at 24 μL of vaginal fluid simulant collected per mL of CVL fluid, as low as 5 μL mL−1 using 10 mM Li+ with a measurement accuracy of 6.7%. Ion chromatograms of real-world CVL samples collected in vivo from common animal models (sheep and pig-tailed macaque) and a human volunteer demonstrate that the analysis is interference-free. The method is readily transferrable and should enable the accurate measurement of CVF volume collected during CVLs benefitting a broad range of research disciplines, including pharmacokinetic, pharmacodynamic, metabolomic, and microbiome studies.