INTER-LABORATORY NOTE Direct elemental analysis of lead in micro-samples of human fingernails by rhenium-cup in-torch vaporization-inductively coupled plasma atomic emission spectrometry (ITV-ICP-AES)† Hamid R. Badiei and Vassili Karanassios* Guelph–Waterloo Center for Graduate Work in Chemistry, University of Waterloo, Department of Chemistry, Waterloo, Ontario, Canada N2L 3G1 Received 8th September 1998, Accepted 17th December 1998 Micro-samples of human fingernails were analyzed for lead using Rhenium-cup, in-torch vaporization (ITV) sample introduction and inductively coupled plasma atomic emission spectrometry (ICP-AES).Lead concentrations were found to be in agreement with those reported in the literature. Direct elemental analysis of micro-samples of fingernails, minimum sample pre-treatment and, overall, increased speed of analysis are the main advantages of the approach. ITV, a sample is placed onto or into a probe (e.g., coiled 1 Introduction filament or metal cup), the sample carrying probe is inserted Lead is widely monitored in the environment because of its into a vaporization chamber that clips onto a typical ICP toxicity.For example, chronic lead poisoning is a key concern torch and a seal is formed at the bottom of the chamber.9,12,14 in many parts of the world. In humans, chronic lead poisoning During retraction, the plasma is operated un-interrupted with is manifested by abnormalities such as encephalopathy, ner- the seal open.The sample is vaporized by applying electrical vous irritability, kidney disease and altered heme synthesis power to the sample carrying probe. Due to the use of an and reproductive functions.1–4 Such poisoning is associated with low to intermediate levels of chronic exposure to lead, with primary sources being intake of food, water and air. Suitable indicators are required in order to evaluate the extent of human exposure to Pb. Fingernails are often used as such an indicator.4 From the analytical point of view, fingernail samples do not deteriorate over time and can be obtained easily without traumatizing the donor.The average composition of Pb in fingernail samples from healthy adults cannot be determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) with pneumatic nebulization sample introduction unless a relatively large amount of sample is acid-digested (e.g., multiple fingernail clippings). Further diYculties arise if there is only a small amount of sample available for analysis, as is often the case with fingernails and other micro-samples of biological, clinical or forensic origin.One way of addressing this problem is by using a sample introduction system that permits direct elemental analysis of small amounts of solid samples by ICP-AES, such as, direct sample insertion (DSI),5,6 electrothermal vaporization (ETV)7,8 or in-torch vaporization (ITV).9–14 The object of this work was to bring to ICP-AES the capability of direct elemental analysis of solid micro-samples using Re-cup ITV sample introduction and to use the determination of Pb in fingernails as an example. 2 Instrumentation 2.1 In-torch vaporization A schematic illustration of ITV sample introduction and of the instrumentation used for this work is shown in Fig. 1. In Fig. 1 Schematic illustration of the metal-cup ITV-ICP-AES system †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998. used in this work.J. Anal. At. Spectrom., 1999, 14, 603–605 603external power supply, some in-situ (i.e., inside the vaporization ensure that there was no sample carryover from run to run, the cup was washed with 5 ml of 0.1% (v/v) HCl and this was chamber) sample processing becomes possible. For example, samples can be dried and ashed/charred in-situ by applying followed by another vaporization cycle. Using this approach, memory eVects were not observed. progressively higher power levels to the sample carrying probe.Thus far, coiled-filament ITV-ICP-AES has been tested with In coiled-filament ITV-ICP-AES,14 carrier-gas flow rate, coiled-filament insertion position inside the vaporization micro-samples of liquids and slurries but not for direct elemental analysis of solid micro-samples. For the present work, chamber and vaporization power were found to aVect analytical performance characteristics significantly.These parameters several changes were made to previous ITV designs.9,14 For instance, to facilitate solid micro-samples, the coiled filament were briefly optimized for Re-cup ITV-ICP-AES as well, and examples of optimized analyte emission and blank signals are was replaced by a ~5×5 mm Re cup. Rhenium was chosen due to its high melting point (3186 °C), its low thermal shown in Fig. 2. conductivity, its relatively high electrical resistivity and its resistance to chemical attack.13,14 Also, the ceramic which was 4 Results and discussion used to support coiled filaments14 was replaced by an insulated metallic support with a Teflon collar on its upper part (Fig. 1). Instrument calibration is a key problem in the direct elemental These changes kept the cup centered within the insertion tube analysis of solids, in particular, if there are no standard and the vaporization chamber, thus eliminating the possibility reference materials available, as is the case with fingernails.of cup contamination during insertion/retraction and improv- Calibration curves were constructed using the standard ing the reproducibility of insertion. The support was fastened additions method and the Pb content of the fingernail samples onto a drive mechanism which has been used in our laboratory was found to be 0.7±0.15 mg g-1. This result compares favorfor DSI work6 and it was manually driven in or out of the ably with what has been reported in the literature for healthy vaporization chamber. The vaporization chamber was modi- adults.15 Liquid standards were also used for calibration and fied as well and a new chamber (Fig. 1), with a wider diameter the Pb concentration was found to be 0.7±0.2 mg g-1. The in its lower part (to accommodate the Teflon collar), was tested. relatively large standard deviation is most likely due to uneven distribution of Pb within the fingernail samples. The agreement 2.2 Instrumentation between results obtained using the standard additions method and calibration using liquid standards is most likely due to A JY-48 (Jobin–Yvon Instruments SA, Edison, NJ, USA) use of a micro-amount of a sample with a matrix, such as ICP-AES system which was equipped with a 32-channel ceratin, which vaporizes prior to analyte vaporization (e.g., polychromator was used.The current output of the photomulduring charring/ashing). tiplier tube detector was converted to a voltage using a Stanford Research Systems (Sunnyvale, CA, USA) preamplifier/ low-pass filter (SRA, Model SR570). The analog 5 Conclusions voltage was digitized at 100 Hz using a 12-bit analog-to-digital (ADC) board (NB-MIO-16L-25, National Instruments@, Fingernails are important indicators of human exposure to Pb Austin, TX, USA) and an Apple Macintosh personal com- because they literally ‘freeze’ past exposure in time.2–4 In a puter.The data acquisition software was written in LabViewA broad sense, they can be thought of as metal burden indicators (National Instruments@). in the body or as built-in sensors which, when analyzed, can provide a record of the history of personal exposure.Rhenium-cup ITV-ICP-AES enabled rapid and direct 3 Experimental elemental analysis of Pb in micro-samples of human fingernails, 3.1 Reagents and samples thus opening the door to rapid screening for chronic exposure to lead, to homogeneity studies and to determinations of the Standard solutions were prepared from 1000 ppm standard localized (rather than average) composition of fingernails by stock solution (2–5% (v/v) in HNO3 purchased from SCP ICP-AES.Such applications my be useful in toxicology or ScienceA, Quebec, Canada). The solutions were prepared via in high-risk industries (e.g., battery plants or sheet metal repetitive dilutions using distilled, de-ionized water (18MV). production facilities) for risk assessment and management. Fingernail samples were collected from healthy adults using a Ni-coated steel clipper and were cleaned using stainless steel scissors.Subsequently, the samples were washed in an ultrasonic cleaner with 30 ml of 95% ethyl alcohol for 20 min, rinsed repeatedly with de-ionized water and placed under an infrared lamp for 20 min to dry. Dried micro-samples (from 200 to 400 mg) were weighed using a micro-balance (Cahn Electrobalance, Ventron Instruments Corporation, Cerritos, CA, USA) and were placed into the Re cup of the ITV sample introduction system using stainless steel forceps. 3.2 Plasma and ITV operating conditions Plasma operating conditions were 1200 W of applied forward power, outer-tube gas 13 l min-1 (Ar), intermediate-tube gas 0.6 l min-1 (Ar) and central-tube or carrier gas 0.45 l min-1 (Ar–H2 3% v/v). Hydrogen was added to suppress the formation of volatile Re oxides.14 The observation height was 14.5 mm above the load coil. The cup insertion position inside the vaporization chamber was ~1.5 cm above the carrier gas inlet.Drying and charring were carried out in-situ. For example, drying time was 1 min (at 5 W), ashing/charring time was 1 min (at 15W and, at this power level, analyte loss was Fig. 2 Typical signals obtained following a brief optimization (see text for discussion). not observed) and vaporization power was 75W (~5 s). To 604 J. Anal. At. Spectrom., 1999, 14, 603–6057 V. Karanassios, J. M. Ren and E.D. Salin, J. Anal. At. Spectrom., Acknowledgements 1991, 6, 527. 8 J. M. Carey and J. A. Caruso, Crit. Rev. Anal. Chem., 1992, Part of this work was reported in an undergraduate thesis 23, 397. (Chem 492, April 1998) by HRB. Financial assistance from 9 V. Karanassios, K. P. Bateman and G. A. Spiers, Spectrochim. the University of Waterloo and from NSERC is gratefully Acta, 1994, 49, 847. acknowledged. 10 V. Karanassios, K. P. Bateman and G. A. Spiers, Spectrochim. Acta, 1994, 49, 867. 11 V. Karanassios, K. P. Bateman and G. A. Spiers, Spectrochim. Acta, 1994, 49, 989. References 12 V. Karanassios, P. Drouin and G. G. Reynolds, Spectrochim. 1 A. Taylor, S. Branch, D.J. Halls, L.M.W. Owen and M. White, Acta, 1995, 50, 415. J. Anal. At. Spectrom., 1998, 13, 57R. 13 V. Grishko and V. Karanassios, Proceedings, Second Biennial International Conference on Chemical Measurement and 2 Trace Element Analysis in Biological Specimens, ed. R. F. M. Monitoring of the Environment, ed. R. Clement and B. Burk, 1998, Herber and M. Stoeppler, Elsevier, NY, USA, 1994. vol. 2, p. 507. 3 Biological Monitoring of Exposure to Chemicals: Metals, ed. H. K. 14 V. Karanassios, V. Grishko and G. G. Reynolds, J. Anal. At. Dillon and M. H. Ho,Wiley, NY, USA, 1991. Spectrom., 1999, 14, 565. 4 Quantitative Trace Analysis of Biological Materials, ed. H. A. 15 http://www.arup-lab.com/ug/u8–1251.htm (#P30235, Test No. McKenzie and L. E. Smythe, Elsevier, NY, USA, 1988. 0099044). 5 V. Karanassios and G. Horlick, Spectrochim. Acta Rev., 1990, 13, 89. 6 V. Karanassios and T. J. Wood, Appl. Spectrosc., 1999, 53, 197. Paper 8/07033D J. Anal. At. Spectrom., 1999, 14, 603–605 605