A Study on the Qualitative and Quantitative Analysis of Nanogram Samples by Transmission Infrared Spectroscopy with the Use of Silver Island Films

Abstract

Qualitative and quantitative analysis of nanogram amounts of substances by transmission infrared spectroscopy with the use of silver island films was carried out. The effect of silver thickness, the comparison of several plates (Ge, BaF₂, and ZnSe), the dynamic range of intensity enhancement vs. sample amount, and the enhancement stability after sample deposition were investigated extensively to determine the optimum conditions. The limits of detection (LOD) of several substances were also described. LOD values ranging from 5 ng/cm² for polydimethylsiloxane to 10 ng/cm² for diethylphthalate were obtained, and these values show a remarkable improvement in LOD in comparison with results from normal transmission spectroscopy. A quantitative study was also undertaken. A good linear relationship with respect to the amount of triphenyl phosphate, ranging from 25 to 250 ng/cm², was obtained. The data were reproducible with a coefficient of variation of 15%, and this variation was comparable to that obtained with several surface-enhanced Raman scattering methods.