Abstract
A new method has been developed for the discrimination of white cotton fiber by the detection and comparison of residual surfactants from detergents using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS).
Twenty three brands of powder-type laundry detergents were collected from 10 manufacturers and used for the study. Standard samples of the surfactants contained in the powdered laundry detergents were offered by the manufacturers of raw materials for detergents. A sample of a washed textile was prepared after washing a T-shirt (cotton 100%) with one of the detergents and drying it. The surfactants in a cotton thread (5 mm in length) taken from the washed T-shirt were extracted into 30 μl of methanol and analyzed by LC/ESI-MS. Analyses of surfactants by LC/ESI-MS was also performed on a detergent itself after the extraction of surfactants into methanol by mixing 400 mg of detergent and 8 ml of methanol followed by centrifuge and subsequent dilution of supernatant 50 times by volume.
The powder detergents could be classified into 14 groups on the basis of the difference in the combination of 5 surfactants, polyoxyethylene alkyl ether (POE), linear alkylbenzene sulfonate (LAS), α-sulfonato fatty acid methyl ester (α-SF), alkylsulfuric ester (AS), and fatty acid (FAT). Residual surfactants in the washed T-shirt could be detected using 5 mm of thread. The patterns of residual surfactants were found to be similar to those of the detergents except the absence of peaks for some surfactants with relatively short alkyl chains. Mass chromatograms of POE's fragment ion measured at m/z 133 and cone voltage of 50 V in the positive mode allowed the simultaneous detection of POEs with a different length of alkyl chain at a higher sensitivity than those obtained by measuring the molecular ion of each POE at cone voltage of 20 V. Comparison of residual surfactants patterns obtained by the present method was significantly useful for the discrimination of white cotton fiber, which were difficult to differentiate by the morphological characteristics, when the fibers had originated from textiles washed by different detergents.
