Lactic acid is an active ingredient in feminine wash for maintaining the pH level in the female genital area. A high concentration of lactic acid may cause irritation in the said part of the body. With this in mind, the need for an efficient method to monitor the amount of lactic acid in different brands of feminine wash is found to be significant.
Lactic acid was extracted using the classical way of precipitation reaction from different brands of commercial feminine wash. The sample obtained was quantified using two instrumentation methods: High Performance Liquid Chromatography (HPLC) and Gas Chromatography-Mass Spectrometry (GC-MS). The sampling technique of Solid Phase Microextraction (SPME) in headspace was also incorporated in the use of GC-MS to maximize the semi-volatile property of the analyte.
The conditions for the headspace sampling of lactic acid using SPME were optimized. Two fiber types were tested in this study: polydimethylsiloxane/divinylbenzene (PDMS/DVB) and carboxen/polydimethyl-siloxane(CAR/PDMS). This study showed that PDMS/DVB is most suitable for sampling lactic acid. The optimum sampling temperature was at room temperature.
The equilibration time was determined to be 50 minutes. The headspace SPME method was likewise tested for sampling underivatized and methylated lactic acid. This study illustrated that polydimethylsiloxane(PDMS) and polydimethylsiloxane/divinyl benzene is not suitable for extracting lactic acid when it was derivatized. This study also showed that PDMS/DVB is more sensitive to adsorbing underivatized lactic acid.
It was found out that SPME could be more effectively utilized if the standard addition method, rather than a calibration curve, is employed. In HPLC, on the other hand, the calibration curve method is evaluated to be more efficient than standard addition. Furthermore, better results were obtained by using the normal phase column and not subjecting the sample to hydrolysis reaction than by using a reverse phase column and hydrolyzing the samples.
Quantitative evaluation of three brands of feminine washes A, B and C revealed that their lactic acid concentrations have an average ranging from 9,000-11,000 ppm which is close to the concentration claimed by the manufacturers.