C. Yafa, J.G. Farmer / Analytica Chimica Acta 557 (2006) 296–303 299Table 3Results <strong>of</strong> elemental determination in Canadian peat OGS 1878 P-6 prepared for ICP-OES analysis according to the adapted USEPA <strong>methods</strong> 3051 (HNO 3 ), 3051a(HNO 3 /HCl) <strong>and</strong> 3052 (HNO 3 /HF) <strong>and</strong> the st<strong>and</strong>ard aqua regia (HNO 3 /HCl) procedure according to ISO St<strong>and</strong>ard 11466ElementConcentration (mg kg −1 ) a‘Certified’ values bAdapted USEPA method3051 (HNO 3 )Adapted USEPA method3051a (HNO 3 /HCl)ISO St<strong>and</strong>ard procedure11466 (HNO 3 /HCl)Adapted USEPA method3052 (HNO 3 /HF)Al – c 2850 ± 100 3050 ± 60 2600 ± 140 6000 ± 350Co 1.8 ± 0.2 2.0 ± 0.1 2.1 ± 0.1 1.9 ± 0.1 2.7 ± 0.1Cr 8.0 ± 1.0 4.5 ± 0.3 4.3 ± 0.3 2.6 ± 0.4 3.9 ± 0.3Cu 195 ± 16 200 ± 4 201 ± 3 207 ± 8 190 ± 3Fe 8700 ± 600 8050 ± 140 8350 ± 120 8550 ± 250 8450 ± 130Mn 206 ± 30 222 ± 4 230 ± 5 209 ± 7 231 ± 4Pb 78.8 ± 2.9 89.4 ± 3.9 90.8 ± 3.8 92.6 ± 3.4 81.5 ± 3.3Zn 43 ± 3 43 ± 3 46 ± 4 44 ± 2 46 ± 2Confidence intervals are given at 95% level for n = 7–9.a All concentration data are expressed in mg kg −1 on a dry-weight (105 ◦ C) basis, i.e. corrected for moisture content <strong>of</strong> the air-dried peat.b Barbante et al. [27].c Not available.strong anthropogenic ‘pollution’ influence upon the concentrationspresent in OGS 1878 P-6, although it is noticeablethat Fe concentrations determined after HNO 3 extraction wereslightly lower than in the additional presence <strong>of</strong> HCl or HF.The mean elemental concentrations determined by HNO 3 /HF<strong>digestion</strong> were <strong>of</strong> satisfactory precision (R.S.D. < 5%) <strong>and</strong> accuracy,as demonstrated by the agreement with ‘certified’ valuesfor OGS 1878 P-6, where available, with the exception <strong>of</strong> Cr.Such low recoveries for Cr by <strong>acid</strong> <strong>digestion</strong> <strong>methods</strong> have <strong>of</strong>tenbeen attributed in geological analysis to incomplete dissolution<strong>of</strong> chromite [33]. Farmer <strong>and</strong> Gibson [21], employing <strong>total</strong><strong>digestion</strong> by HCl/HNO 3 /HF/H 3 BO 3 , found excellent agreementbetween measured <strong>and</strong> certified values for Cr in three referencematerials (NBS SRM 1645 river sediment, IAEA soil-5 <strong>and</strong>IAEA SL-1 lake sediment) but not in NBS SRM 1648 urbanTable 4Results <strong>of</strong> elemental determination in coal NBS SRM 1635 prepared for ICP-OES analysis according to the adapted USEPA method 3051 (HNO 3 ) <strong>and</strong> theadapted USEPA method 3052 (HNO 3 /HF)ElementCertifiedvalues(mg kg −1 ) aAdapted USEPAmethod 3051(HNO 3 )(mg kg −1 ) aAdapted USEPAmethod 3052(HNO 3 /HF)(mg kg −1 ) aAl 3200 b 2600 ± 350 2900 ± 130Co 0.65 b 1.0 ± 0.2 1.2 ± 0.5Cr 2.5 ± 0.3 2.1 ± 0.1 2.2 ± 0.1Cu 3.6 ± 0.3 6.0 ± 0.2 6.1 ± 0.7Fe 2390 ± 50 2460 ± 100 2400 ± 80Mn 21.4 ± 1.5 21 ± 1 21 ± 1P – c 66 ± 6 59 ± 3Pb 1.9 ± 0.2 2.1 ± 0.7 3.5 ± 2.7S 3300 ± 300 4000 ± 700 3800 ± 300Ti 200 b 172 ± 4 201 ± 6V 5.2 ± 0.5 5.8 ± 0.6 6.7 ± 0.2Zn 4.7 ± 0.5 – c – cConfidence intervals are given at 95% level for n = 3 or 4.a All concentration data are expressed in mg kg −1 on a dry-weight (105 ◦ C)basis.b Information-only values.c Not available.particulate matter, attributing the latter to the presence <strong>of</strong> a substantialfraction <strong>of</strong> the Cr in a carbonaceous matrix resistantto decomposition by the <strong>acid</strong> mixture. However, the HNO 3 /HF<strong>total</strong> <strong>digestion</strong> method employed in the current <strong>study</strong> yieldedthe correct value for Cr in NBS SRM 1635 coal (Table 4) <strong>and</strong>indeed in NIMT/UOE/FM/001 (Table 5). Subsequent work [35],using the HNO 3 /HF method, has also yielded the correct valuefor Cr in Canadian peat OGS 1878 P-6 when using ICP-MS inthe measurement step.In general, however, it was the <strong>acid</strong>-<strong>extractable</strong> <strong>methods</strong> thatdid not <strong>total</strong>ly dissolve the peat <strong>and</strong> it was, therefore, necessaryto filter the solutions to remove undigested particles. In contrast,<strong>digestion</strong>s carried out by the adapted USEPA method 3052(HNO 3 /HF) typically yielded a clear solution. In selecting theTable 5Results <strong>of</strong> <strong>acid</strong>-<strong>extractable</strong> <strong>and</strong> <strong>total</strong> elemental determinations in ombrotrophicpeat bog (low ash) reference material (NIMT/UOE/FM/001) [26] prepared forICP-OES analysis according to the adapted USEPA method 3051 (HNO 3 ) <strong>and</strong>the adapted USEPA method 3052 (HNO 3 /HF)ElementAcid-<strong>extractable</strong> concentration(mg kg −1 ) aTotal concentration(mg kg −1 ) aCertified Measured Certified MeasuredAl 2481 ± 514 2800 ± 60 3692 ± 347 b 3800 ± 150Co 0.71 ± 0.13 1.1 ± 0.1 0.88 ± 0.09 1.3 ± 0.4Cr 3.90 ± 0.90 4.9 ± 0.2 6.36 ± 0.44 6.7 ± 0.3Cu 4.48 ± 0.73 4.3 ± 0.5 c 5.28 ± 1.04 5.0 ± 0.3 cFe 839 ± 54 784 ± 15 921 ± 84 b 867 ± 20Mn 4.74 ± 0.87 4.6 ± 0.2 7.52 ± 0.41 7.0 ± 0.1P 281 ± 7 264 ± 5 265 ± 8 b 265 ± 6Pb 169 ± 8 167 ± 3 174 ± 8 176 ± 3S – d 612 ± 26 – d 626 ± 19Ti 110 ± 11 b 108 ± 3 357 ± 18 b 378 ± 7V 6.37 ± 0.73 6.4 ± 0.3 7.82 ± 1.08 8.0 ± 0.3Zn 28.7 ± 1.6 29 ± 1 28.6 ± 1.9 30 ± 1Confidence intervals are given at 95% level for n = 12.a All concentration data are expressed in mg kg −1 on a dry-weight (105 ◦ C)basis.b Information-only values.c Determined at 324.7 nm.d Not available.
300 C. Yafa, J.G. Farmer / Analytica Chimica Acta 557 (2006) 296–303Fig. 1. Vertical concentration pr<strong>of</strong>iles <strong>of</strong> Al, Co, Cr, Cu, Fe, Mn, P, Pb, S, Ti, V <strong>and</strong> Zn in peat core FM99M prepared for analysis according to: (a) the adaptedUSEPA method 3051 (HNO 3 ) <strong>and</strong> (b) the adapted USEPA method 3052 (HNO 3 /HF).
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