In the Laboratory
Measurement of Trace Metals in Tobacco and Cigarette Ash W by Inductively Coupled Plasma–Atomic Emission Spectroscopy W. Wang and B. J. Finlayson-Pitts* Department of Chemistry, University of California, Irvine, CA 92697-2025; *
[email protected] Inductively coupled plasmas (ICP) in combination with atomic emission spectrometry (AES) or mass spectrometry (MS) are increasingly supplanting other methods of trace metal analysis (1–3). ICP–AES is ideal for measuring trace metals in a variety of samples because many elements can be measured simultaneously; this is in contrast to atomic absorption, where only one or two elements are typically measured at once and changing the element studied requires changeover of the lamps. ICP has a higher linear dynamic range, lower detection limits for some metals, and shorter analysis time. In addition, some nonmetallic elements such as bromine can be measured by ICP–AES (1–3). The application of ICP in undergraduate experiments to measure trace metals present in core sediments has been described previously by Mabury and coworkers (4). They compared ICP measurements to those using graphite furnace atomic absorption spectroscopy. Page et al. (5) described a physical chemistry experiment to determine the plasma temperature in an ICP.
Here we report an experiment in which ICP–AES is used to quantify Zn, Fe, and Cr present in cigarette tobacco, the cigarette filter, and in the ash from burning the cigarette. Tobacco smoke is known to contain a number of toxic metals (6–8) as well as nicotine and polycyclic aromatic hydrocarbons that are harmful to human health (9). Hence, measurement of such metals in tobacco and the associated ash pose a relevant problem for an undergraduate instrumental analysis laboratory. This experiment complements a number of other undergraduate laboratories previously published in this Journal that focus on tobacco and cigarette smoke (10–19). Methods
Standards A stock solution containing As, Se, Sb, Zn, Co, Fe, Cu, and Cr was obtained by diluting 10 mL of an ICP standard (Spex CertiPrep, Inc.) by a factor of 10 with a 0.5% HNO3兾5% HCl mixture (both concentrated TraceMetal
Table 1. Concentrations of Metals in Tobacco, Cigarette Ash, and in the Filter before and after Smoking Sample
Camel tobacco
Camel cigarette ash Marlboro tobacco
Extraction Temperature / ⬚C
Concentration /(g/g) (± 2sa) Zn
Fe
Cr
25
48 ± 7
91 ± 7
ndb
100
50 ± 4
107 ± 9
nd
25
196 ± 7
1147 ± 67
3.0 ± 3.3
100
177 ± 10
1293 ± 76
3.5 ± 2.0
25
43 ± 4
83 ± 7
nd
100
40 ± 4
102 ± 8
nd
25
194 ± 6
1435 ± 80
4.6 ± 1.9
100
174 ± 5
1722 ± 121
5.8 ± 2.6
Marlboro filter before smoking
25
26 ± 2
6±4c
nd
Marlboro filter after smoking
25
29 ± 3
27 ± 3 c
nd
Marlboro cigarette ash
a Two standard deviations for a sample of observations, defined as s = {∑(xi − xav)2/ (N − 1)}1/2, where xi and xav are the individual and average concentrations, respectively, and N is the total number of measurements. b Below the detection limit of 2.5mg/g in these experiments. c Only room temperature extraction carried out; based on results from tobacco and ash, the iron should be adjusted upward by 15%.
JChemEd.chem.wisc.edu • Vol. 80 No. 1 January 2003 • Journal of Chemical Education
83
In the Laboratory
Grade, Fisher). Three additional calibration solutions were generated from this stock solution by diluting it with the 0.5% HNO3兾5% HCl solution in ratios of 1:2, 1:4, and 1:8, respectively (the last number is the total volume of the solution). The fifth standard is a blank solution of the acid mixture.
Sample Preparation Two different cigarette brands were used in these experiments: an unfiltered Camel cigarette and a Marlboro cigarette with a filter. The tobacco sample was prepared by grinding the tobacco with its paper wrap, weighing 0.1 g of the mixture, and dissolving it in 2 mL of concentrated HNO3 (Fisher, TraceMetal Grade, 69%) for 30 min at room temperature. To test the extraction efficiency, some samples were digested with the concentrated HNO3 at ~100 ⬚C for about 2 min in high pressure vials (Kontes Microflex, 5 mL) until the tobacco completely dissolved; the sample was then cooled to room temperature. The mixture was diluted with Nanopure water (Barnsted, 18 M⍀ cm) to 25 mL using a volumetric flask and then filtered through a 45 m Acrodisc filter (Gelman Science). To “smoke” the cigarette, a rubber pipette bulb was used to draw air slowly through the cigarette. Cigarette ash was collected in a beaker and prepared as described above for the tobacco sample preparation. Filter samples were prepared as
for the tobacco sample; one filter was from an unused cigarette and the other had smoke drawn through it. To test for recovery of the metals using this method, two of the tobacco samples were spiked with Zn and Fe. Solutions of ZnCl2 (Fisher Certified ACS) and FeCl3 (Fisher Purified grade) in Nanopure water at a concentration of 1 mg metal per mL were prepared; 4.0 L of the zinc solution and 9.0 L of the iron solution were added to 0.1 g of tobacco. The extraction and analysis was then carried out as for the unspiked samples. The 0.5% HNO3兾5% HCl mixture used for dilution of the standards was drawn through the Acrodisc filter and analyzed as a blank. Results and Discussion Of the metals in our calibration mixture, Zn and Fe were the only metals detected in both the cigarette tobacco and ash; chromium was detected only in the ash. The results are summarized in Table 1. There is no significant difference in the results for Zn from the tobacco samples that were extracted at room temperature compared to those that were digested at 100 ⬚C; the differences in the results for the ash samples extracted using these two temperatures were ≤ 10%. The concentrations of Fe in the tobacco and ash
Table 2. Comparison of Metals in Tobacco and Cigarette Ash Measured in this Study to Literature Values Element
Range in Tobacco / (g/g)
Range in Ash / (g/g)
Concentration Factora
Reference
Zn
40–50
174–196
3.5–4.4
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17–31 d
35
21 304
9
4–64e
6
14–56f
Fe
22
77-–180g
234-–1189
3–7
7
102–107
1300–1700
12–17
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1580
9
20
325–520 175d
21
257–1031e
6
420–680f
Cr
20
22
2864–7859g
5657–24,349
2–3
7
b
4–6
> 2c
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5.8
9
20
0.1–3.5 0.66d
21
0.2–8e
6
