Protein on Cloths: Evaluation of Analytical Techniques

Abstract

Textile detergency studies require methods which can follow the removal and build-up of proteins on cloths. The suitability of X-ray fluorescence spectrometry (XRF), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectrometry (XPS), and nitrogen analysis for these studies was investigated by analyzing blood- and hemoglobin-stained cloths. Protein was measured via nitrogen by XRF, XPS, and the nitrogen analyzer and via an amide band by FT-IR. FT-IR was used with attenuated total reflection (ATR) and with photoacoustic spectrometry (PAS) as sampling techniques. A logarithmic relationship was found between the nitrogen content analyzed on the surface (XPS, XRF, and FT-IR) and in the bulk (N-analyzer). This result can be caused by the fact that the proteins in the cloths with a low quantity of blood or hemoglobin are located more on the outer layer of the cloth. With XRF, FT-IR/PAS, and XPS a significant difference could be detected between the 1% blood- and hemoglobin-stained cloths and a blank cloth, because protein is concentrated on the outer surface of the cloth. With FT-IR/ATR the 1% level can be detected when one is measuring at three different places. The measured surface areas of XRF, FT-IR/PAS, XPS, and FT-IR/ATR are about 37, 10, 5, and 0.2 mm in diameter, respectively. XRF proved to be the most suitable technique, giving a very fast indication of the amount of nitrogen on the outer micrometer layer of the cloths with an acceptable precision [relative standard deviation (RSD) 6%]. However quantitation is difficult due to the logarithmic relationship. XPS is also a valuable technique because protein on washed cloths is located mainly on the outer nanometer layer. The nitrogen analyzer is suitable for quantitative analysis of protein in the bulk sample. However more than 1% of the original blood stain (= 0.018% N) has to be present on the washed cloths.