Optimization of an Analytical Method for the Determination of Trace Metals in Urine by ICP-MS

Jan 01, 2012
By Spectroscopy Editors
Volume 27, Issue 1

Urinary metal concentrations may be effective indicators of particulate metal fume exposure and provide a better understanding of specific exposure-response relationships if an analytical method can be developed that is sufficiently sensitive to measure levels at or near background concentrations. Analyzing urine samples by inductively coupled plasma–mass spectrometry (ICP-MS) poses several distinct challenges as the matrix contains components likely to cause false-positives and reduced analytical sensitivity. This study will demonstrate a method that mitigates these problems and produces quantifiable results even at low parts-per-trillion concentrations.

When metals are rapidly liquefied by electric arc forced-gas techniques, such as industrial electric arc induction furnaces and gas metal arc welding, they frequently volatilize into an aerosol of metal particles that can be <1 µm in diameter; such aerosols are sometimes referred to as particulate metal fumes. Previous investigations established that the formation rate and the precise chemical composition of particulate metal fumes are highly dependent on the parameters of specific processes (for example, temperature, gas flow rate, and raw materials) and can contain various metals, including aluminum, cadmium, chromium, copper, iron, lead, magnesium, manganese, molybdenum, nickel, titanium, vanadium, and zinc (1).

For workers that are frequently exposed to the complex metal oxides found in particulate metal fumes (for example, welders, boilermakers, and steel mill workers), the occupational respiratory health hazards and potentially long-term adverse health effects of exposure are of considerable concern. The United States Occupational Safety and Health Administration (Washington, D.C.) recognizes that symptoms such as eye, nose, and throat irritation, fever, chills, headache, nausea, shortness of breath, and muscle pain can result from even brief acute exposure to particulate metal fumes (an illness commonly referred to as metal fume fever). It is suspected that chronic occupational exposure is related to several cardiopulmonary diseases and cancer (2). Although the characteristics of particulate metal fumes and the symptoms of exposure have already been investigated, few studies have identified precise exposure-response relationships between specific metals and adverse health effects. An understanding of these relationships is essential for risk assessment and the development of effective exposure prevention strategies.

Depending on the circumstances, various measures are employed to minimize occupational exposure to particulate metal fumes, such as ventilation and personal respirators, but the effectiveness of these protective measures is typically determined by testing the resulting air for concentrations of metals. However, information regarding actual biological exposure to particulate metal fumes is required to understand exposure–response relationships. Biomarkers are often used in epidemiological and toxicological studies to establish biological exposure to various substances in the environment. In contrast to air measurements, information regarding the concentrations of soluble metals in the urine of workers exposed to particulate metal fumes should provide a better understanding of actual biological exposure, exposure–response relationships, and the effectiveness of protective measures.

As part of a study funded by the National Institute of Environmental Health Sciences (Research Triangle Park, North Carolina) and conducted by the Department of Environmental Health at the Harvard School of Public Health (Boston, Massachusetts), urine samples were collected from nearly 350 individuals known to be occupationally exposed to particulate metal fumes (see Acknowledgments). One phase of this study included analyses of the samples for urinary metal concentrations to investigate the relationship between particulate metal fume exposure and urinary metal concentrations; validate the use of this biomarker as an indicator of exposure; and to contribute further to the investigation of specific exposure-response relationships. Brooks Rand Labs (Seattle, Washington) was contracted to perform analyses of the collected urine samples for the determination of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn. For the results of these analyses to have adequate significance to this study, an analytical method was required that would be sufficiently sensitive to achieve quantifiable results even at low parts-per-trillion concentrations with a high degree of accuracy and precision.

Analysis by inductively coupled plasma–mass spectrometry (ICP-MS) with a quadrupole MS system is widely recognized as one of the most advanced techniques currently available for the determination of trace element concentrations. However, analysis by ICP-MS also has traditionally been challenging in two aspects: the potential formation of polyatomic spectral interferences and an intolerance for elevated concentrations of dissolved solids.

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