( Tran T. Nham Varian Australia...)Analysis of urine and seawater samples by ultrasonic nebulization with a high resolution ICP spectrometer

Tran T. Nham Varian Australia Pty Ltd Mulgrave, Victoria, Australia

Introduction

Because of the low detection limit capability of the ultrasonic nebulizer when combined with an ICP spectrometer, it has been widely used to determine trace and ultratrace levels in water samples¹. The purpose of this work was to evaluate the ability of the ultrasonic nebulizer to handle samples with significant amounts of dissolved solids, such as urine and seawater.

Experimental

Instrumentation

All measurements were carried out on Varian Liberty 200 ICP spectrometer. The ultrasonic nebulizer was a Cetac U-5000 AT.

The operating conditions of the instrument system are listed in table 1.

For optimum operation, the use of a higher auxiliary Ar flow of 2.25 L/min lifts the plasma away from the injector tube to minimize the possibility of salt build up at the tip of the injector tube. The use of a 1.8 mm I.D. injector tube can also minimize salt build up at the injector tube, especially while running seawater samples.

Lowering the torch by 1 mm (compared with the normal position) can also minimize salting up at the injector tip. The distance from the injector tip to the top of the intermediate tube is normally set to 3 mm with a demountable torch.

Reagents

All chemicals used were analytical grade. The multielement stock solution was made up from single element standard stock solutions (Spectrosol, BDH Chemicals). The multi-element working standard was prepared by dilution of the multi-element stock solution and contained 0.14 M HNO₃.

Matrix matched standards and blank were employed in this work. As an alternative, the method of internal standardization could also be used, to compensate for differences in transport efficienc
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