Towards the use of ICP-OES for the elemental analysis of organic compounds such as glucosamine

Abstract

Inductively coupled plasma optical emission spectrometry with a long demountable torch (whose outer tube is 2.5 cm longer than a standard torch) and a conventional pneumatic nebulisation system was applied to the determination of C, H and O concentrations from an organic compound dissolved in water. The sample solution was simply aspirated directly into the plasma without any sample pre-treatment (such as desolvation or degassing). The long torch was required to significantly decrease the background arising from entrained air. Good linearity was obtained for C, N, H and O upon calibration with standard solutions prepared from ultrapure tris(hydroxymethyl)aminomethane. A weighed blank correction was applied to compensate for the contribution from water, especially in the cases of H and O. Under these conditions, the detection limits for C, N, H and O were, respectively, 0.2, 50, 1000 and 2000 μmol of analyte per g of solution. Accurate concentrations, according to a Student's t test at the 95% confidence level, were measured for C, H and O in a solution of D-glucosamine hydrochloride. No internal standardisation was necessary. However, the N concentration was biased high, irrespectively of the N emission line used (from 149.262 to 593.178 nm), which rules out spectroscopic interference and will be further investigated. Nonetheless, the possibility of accurately determining C, H and O simultaneously with trace elements makes the approach quite promising. It is much simpler than alternate methods that require derivatisation of the compound prior to detection.