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.