Modified direct injection high efficiency nebulizer with minimized dead volume for the analysis of biological samples by micro- and nano-LC-ICP-MS

Abstract

A direct injection high efficiency nebulizer (DIHEN) was modified for µLC-ICP-MS by inserting an additional internal capillary with od 90 µm and id 20 µm to minimize the interface dead volume. The modified DIHEN was compared with a conventional microflow nebulizer with a spray chamber interface with respect to sensitivity, signal stability and organic modifier dependency at flow rates ranging from 0.5 to 5 µl min−1. Although the modified DIHEN was slightly less sensitive, its signal stability was superior, its modifier dependency was less pronounced and its chromatographic resolution was much better due to its extremely small dead volume. These characteristics were demonstrated by the analysis of a mixture of synthetic phosphopeptides (31P detection) and synthetic thyroxine (127I detection). The influence of an organic modifier in the analyte solvent on the detection sensitivity was tested using the bioelements sulfur, phosphorus and iodine as examples. Phosphorus and iodine show an increased signal proportional to the amount of organic modifier with an intensity maximum of between 40% and 60% of modifier, which corresponds to a metal-like characteristic. For the detection of sulfur this characteristic is counteracted by a signal suppression effect proportional to the amount of organic modifier, which is caused by the formation of polyatomic species such as sulfur oxide.