Investigations of a W-Rh permanent modifier for the determination of Pb in blood by electrothermal atomic absorption spectrometry

doi:10.1016/S0584-8547(02)00085-X

Spectrochimica Acta Part B: Atomic Spectroscopy

Volume 57, Issue 8, August 2002, Pages 1291-1300

https://doi.org/10.1016/S0584-8547(02)00085-X Get rights and content

Abstract

A tungsten-rhodium coating (250 μg W+200 μg Rh) on the integrated platform of a transversely heated graphite atomizer (THGA) was used as a permanent chemical modifier for the direct determination of lead in whole blood by electrothermal atomic absorption spectrometry (ETAAS). Blood samples were diluted 1+9 with a diluent consisting of 0.2% v/v HNO₃ and 0.5% v/v TritonX-100, and 12 μl of the diluted sample was deposited on the platform. With use of the W-Rh modifier, tube lifetime was improved by a factor of 2–3 when compared with a conventional NH₄H₂PO₄ modifier. With a standard THGA tube, use of the W-Rh permanent modifier allows simple calibration with aqueous standard solutions for blood Pb measurement. However, matrix-matched calibration is still necessary when an end-capped THGA tube is used. The method detection limit (3σ) based on integrated absorbance measurements is 1.5 μg dl⁻¹ (0.092 μmol 1⁻¹) for the standard THGA and 1.0 μg dl⁻¹ (0.048 μmol l⁻¹) for the end-capped tube. Various blood-based certified reference materials and proficiency testing samples, certified for Pb, were analyzed for validation purposes. All results were well within the range considered acceptable. Analysis of human blood samples for blood Pb measurement provided additional validation data against an established blood Pb ETAAS method that uses phosphate modifier.

Introduction

Lead is a non-essential, toxic element that has been shown to be particularly harmful to young children [1]. In many countries, children are routinely screened for lead poisoning as part of routine pediatric health care or public health care programs. The recommended clinical test for assessing lead exposure is the determination of lead in whole blood [2]. Electrothermal atomic absorption spectrometry (ETAAS) employing a graphite furnace atomizer is one of the most successful and widely used techniques for direct determination of lead in blood and urine. The main reason for its success is that the blood specimens can be analyzed with good accuracy and precision after fast pretreatment within the atomizer during the pyrolysis step, thus avoiding unnecessary use of digestion or deproteination procedures, and thereby, minimizing sample manipulation and contamination [3], [4], [5]. Currently, there is a consensus ETAAS method recommended for blood lead [2] that is based on simple dilution of whole blood with a phosphate modifier, followed by platform atomization and integrated absorbance measurement [5].

Use of a modifier is a recommended component of the stabilized temperature platform furnace (STPF) concept [6]. Modifiers improve analyte thermal stability, allowing a higher pyrolysis temperature for better separation of matrix components. In 1998, Lima et al. [7] proposed a W-Rh coating as permanent modifier for the determination of Cd, Pb and Se in aqueous solutions by furnace ETAAS. They reported that the W-Rh permanent modifier stabilized Pb in aqueous samples up to 1000 °C in a THGA, equivalent to the efficiency of the universal Pd/Mg(NO₃)₂ modifier. These authors reported that a single W-Rh coating remains stable on the platform for 300–350 firings and can be recoated to recover its effectiveness. Tube lifetime is thus improved 100% when compared to the universal Pd/Mg(NO₃)₂ modifier. They concluded that use of the W-Rh permanent modifier is an attractive alternative to conventional modifiers because of extended tube lifetime and improvement in detection limits over the Pd/Mg(NO₃)₂ modifier. The W-Rh permanent modifier has also been successfully used for the determination of As in sediment and soil slurries [8], Cd and Pb in digested biological and sediment samples [9], [10], Bi in urine and whole blood [11], and Se in whole blood [12]. Improved tube lifetimes and a reduced need for frequent re-calibration were reported in these studies.

The principal aim of this work is to show the feasibility of using a W-Rh permanent modifier for direct blood Pb measurement by ETAAS.

Section snippets

Apparatus

The analytical work reported here was the result of a collaboration between two facilities: (i) Wadsworth Center, New York State Department of Health in Albany, New York, USA; and (ii) Centro de Energia Nuclear na Agricultura, Universidade de São Paulo at Piracicaba-SP, Brazil. Preliminary experiments were carried out by the Brazilian group. However, most of the data reported here were obtained by the US group.

Both groups used a Perkin-Elmer (Perkin-Elmer, Inc., Shelton, CT, USA) model 4100ZL

Stabilization of lead in blood using tungsten-rhodium permanent modifier

Pyrolysis and atomization curves were used to find the optimum heating program for lead atomized from a W-Rh treated platform (Fig. 1). Both standard and end-capped THGA tubes were evaluated using an aqueous Pb standard (40 μg l⁻¹) and a blood Pb RM (Lot 049, Target value 42.2 μg dl⁻¹) that, when diluted 1+9 with diluent, gave a lead concentration of 42.2 μg l⁻¹. In a previous study [7], Pb thermal stability was reported up to 1000 °C in aqueous solutions with the use of W-Rh coated platform in

Conclusions

We explored the use of a W-Rh permanent modifier with standard and end-capped THGA tubes for blood lead measurement by ETAAS. In both THGA tubes, the W-Rh coating remained stable on the platform for at least 350 firings. Recoating with W-Rh improved the tube lifetime, by a factor of 2–3, to over 1000 firings. The method detection limit (3 S.D.) is 1.5 μg dl⁻¹ for standard THGA tubes and 1.0 μg dl⁻¹ for end-capped THGA tubes, comparable with that obtained with phosphate modifier. When a standard

Acknowledgements

The authors are grateful to Dr E.A.G. Zagatto and O.M. Matsumoto for critical comments, and to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) processos: 99/04081-6 and 99/07645-8, Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (CNPq), and Financiadora de Estudos e Projetos (PRONEX) for financial support and fellowships. We thank the staff in the Blood Lead Laboratory at Wadsworth Center for their support, especially Mr Ciaran Geraghty for his technical assistance.

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Investigations of a W-Rh permanent modifier for the determination of Pb in blood by electrothermal atomic absorption spectrometry

Abstract

Introduction

Section snippets

Apparatus

Stabilization of lead in blood using tungsten-rhodium permanent modifier

Conclusions

Acknowledgements

Anal. Chim. Acta

Spectrochim. Acta Part B

Spectrochim. Acta Part B

Anal. Chim. Acta

Spectrochim. Acta Part B

Environ. Res.

Spectrochim. Acta Part B

Spectrochim. Acta Part B

Preventing lead poisoning in young children [Report]