An interlaboratory comparison of sample presentation methods for the analysis of aqueous solutions using fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) spectroscopy is becoming much more widely used as an analytical technique. It appears to be particularly useful for quantitative analysis, especially of aqueous solutions. However, there is a considerable variation in the cost and quality of instrumentation as well as a large number of accessories for sample presentation employing attenuated total reflectance (ATR). The objectives of the work reported in this paper were to investigate the effect of the choice of instrumentation on the quality of quantitative analyses as well as the effect of variable acquisition parameters. A series of experiments was designed in which samples were distributed to a number of workers using a range of FTIR instruments from different manufacturers and of differing quality. The workers were allowed to use the accessory of their own choice and to carry out a quantitative analysis of glucose solutions using their normal operating parameters. In following experiments the effects of instrumental and purge were considered and quantitative analysis was performed using a set of prescribed acquisition conditions. The results showed that there were significant differences in the quality of the spectra produced on the different combinations. However, although each worker produced quite different linear calibrations (in terms of slope and intercept), they all predicted the concentration of an unknown with a similar accuracy. However, later experiments showed that the low-cost bench-top instruments were not always so successful when the peaks used in the analysis were affected by residual water vapour interferences. Instrumental drift was noticeably worse for the low-cost instruments but this was an effect that could easily be eliminated by suitable baseline correction.