Chemically Modified Capillaries for Sample Introduction into ICP-MS

Raquel Garcia-Sanchez

October 2001

Department of Environmental Sciences, University of Plymouth, Plymouth, U.K.

The development and use of silica capillaries with modified inner surfaces for sample introduction into an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) by a Direct Injection Nebuliser (DIN) is described and demonstrated. A novel approach to attach organic molecules to the silanol groups of activated fused silica capillaries is presented. These capillaries were extensively tested in terms of their matrix interference removal, separation of species and chromatographic behaviour. The effects of sample pH, carrier solution, eluent strength, sample size and flow rate characteristics were studied in addition to the optimisation of DIN-ICP-MS conditions.

The elimination of 40Ar23Na+ interference on 63Cu determination has been demonstrated by the modification of the capillaries with 2-(2-ethylamino)pyridine as complex forming reagent that interact with copper ions and retard them on the capillary. This nucleophilic phase was attached to a cyanuric chloride functional group by using trimethoxysilane as mediating molecule. To examine the progress of the coating reactions, the inner surface of the capillaries were scanned via electron microscopy at every stage of the coating procedure. With this method the copper content of two certified reference materials (SLEW-2 and NASS-4) was determined and the results obtained were in good agreement with the certified values.

Capillaries coated with strong cation exchangers have been used for lead speciation. The strong cation exchanger covering has been tested for its stability over a wide pH range. The interaction of Et3Pb+ with the strong cation exchanger was negligible while the inorganic lead can be selectively retained at pH>7. Upon flushing with 10-2 mol L-1 hydrochloric acid, the capillary can be easily regenerated. The detection limits for triethyllead and for inorganic lead were 90 and 200 ng L-1 respectively, i.e., absolute detection limits of 0.3 and 0.7 pg respectively. In order to demonstrate the capability of the technique for the analysis of an environmental matrix, a sample of urban rainwater was analysed.

Capillaries modified by an internal coating of an anion exchanger (amminopropyltrimethoxysilane) proved to be an effective means of separating vanadium species with different oxidation states, i.e., V(V) and V(IV).

The newly developed sample introduction method has proved to be a valid technique for the analysis of environmental samples, with shorter analysis times, minimum sample pretreatment and improved sensitivity compared to other analytical techniques.

© 2001 by Raquel Garcia-Sanchez. All Rights Reserved

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