Quantitative 19F NMR method validation and application to the quantitative analysis of a fluoro-polyphosphates mixture

Quantitative 19F NMR (QNMR) was developed and employed to determine the amounts of four kinds of fluoropolyphosphates (FPPs) in a mixture containing sodium monofluoro-phosphate (MFP), sodium monofluoro-dipolyphosphate (MFDPP), sodium monofluoro-tripolyphosphate (MFTPP) and sodium difluoro-tripolyphosphate (DFTPP). The amounts of these ingredients cannot be measured by high-performance liquid chromatography (HPLC) because no high-purity standard samples are available. The main parameter “delay time (d1) between two scans” of affecting the response of NMR signal was determined by measuring longitudinal relaxation time (T1) to be 25 s. By using NaF as an internal reference to measure the amount of MFP solution with known concentration and then to compare the deviation between experiment value and real value, a simple and effective approach for checking out the validity of 19F QNMR method was carried out. Six experiments with different mole ratios of NaF/MFP over 200 times were repeated and the relative standard deviation (R.S.D.) of results is less than 2.0%, the limit of detection of 19F QNMR can reach to 1.0 mmol/L. NaF was used as an internal reference for the quantitative analysis of FPPs mixture. The amount of each FPP in FPPs mixture obtained by 19F QNMR was calculated and the R.S.D.s of results were less than 4.81%.