Method development and validation for the GC-FID assay of tributyl phosphate in a phospholipid emulsion

This paper describes the development and validation of an isothermal GC-FID method for the assay of tributyl phosphate in a phospholipid emulsion. The emulsion is used as a topical ointment to deliver Triton X-100, a spermicide. The tributyl phosphate is added to the emulsion as a plasticizer or softening agent. The chromatographic conditions of the method employ a J&W DB-Wax capillary column (30 m x 0.53 mm, film thickness 1 microm), isothermal elution with He at a column flow of 2.0 ml/min, injector, detector, and oven temperatures at 210 degrees C, a split ratio of 18.0/2.0, and a 3-microl injection volume. Sample calibration was performed with tributyl phosphate purchased from Aldrich (USP Reference Standard is not available). The linearity of the tributyl phosphate peak area responses was demonstrated from approximately 50 to 150% of the analytical concentration of 100 microg/ml. System precision was determined from five replicate injections of a standard and sample solution. Reproducibility of the tributyl phosphate peak area responses showed R.S.D. of 1.2 and 0.4%, respectively. Method precision was performed by assaying five samples by two different analysts on different days. The mean %LC was 95.5% (R.S.D.=1.0%) for the first analyst, and 95.6% (R.S.D.=1.0%) for the second analyst. The mean %LC value for all ten sample preparations was 95.5% (R.S.D.=0.9%). The limits of detection and quantitation were determined to be 0.2 and 0.7 microg/ml, respectively.