Low-flow interface for liquid chromatography–inductively coupled plasma mass spectrometry speciation using an oscillating capillary nebulizer

Abstract

The application of a novel nebulizer, the oscillating capillary nebulizer (OCN), is described for use in speciation studies. The nebulizer has certain features which make it very suitable for this application, without modification, at both micro-flows (1 µl min^–1) and macro-flows (1 ml min^–1). Short- and long-term precision at typical operating flows are comparable to a normal (1 ml min^–1) concentric glass nebulizer. Column-to-nebulizer dead volume is approximately 1 µl. The narrow drop size distribution for the nebulizer at low flows leads to excellent sensitivity when coupled to a micro-LC column. Post-column peak broadening introduced by the interface is minor at flows 5 µl min^–1, but widens the peaks noticeably at flows between 1 and 5 µl min^–1. The very high efficiency of the nebulizer at flows <50 µl min^–1 is exemplified by the fact that no drain is necessary at these flows in the open spray chamber, as no visible liquid condenses on the chamber walls. The ICP-MS response for the OCN (counts per ng of Se injected) does not change when water is replaced by methanol as solvent, whereas with a conventional nebulizer, a solvent change of this type inevitably results in a significant change in response. The OCN was used for the reversed-phase LC separation of a mixture of five organic Se compounds of pharmacological significance, at flows of 12, 50 and 400 µl min^–1. With use of a 0.5 mm id column, a flow rate of 12 µl min^–1 and a 60 nl injection, good peak separation was found, with an average efficiency of ≈ 10000 plates and a detection limit of around 30 pg.