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Determination of mercury by extraction and isotope-dilution mass spectrometry
DETERMINATION OF MERCURY AND ISOTOPE-DILUTION MASS
BY EXTRACTION SPECTROMETRY
Kozu
MATSMOTO, YOUICHE KUNO and TSUGIO TAKEUCHI Department of Synthetic Chemistry, Faculty of Engineering, Furo-cho,
(Rrceiwd 5 Decemhrr
C~ikusa-ku,
Nagoya.
Nagoya
University,
444 Japan
1977. Revised 29 Murch 1978 Accepted 29 May 1978)
use of halides for determination of metals by stable”isoto~ mass spectrometry suggested. and is iliustrated by the use of mercury iodide for mercury determination.
Summary--The
For mass spectra of metals to be obtained by electronimpact mass spectrometry (El-MS), the metals have first to be changed into compounds which have sufficient volatility in the ion-source. For this purpose, many metal cheiate compounds have been used, and applied for determination of metals by stable-isotope dilution mass spectrometry.‘*’ These chelates. however, give many fragment peaks. similarly to organic compounds in general. _ We have reported mass spectra of some metal halides3*4 which have su~~jent volatiiity for El-MS. The Fragmentation paths of the metal halides are very simple, because they are composed of only a few ions. When the iodide is used, the metal can easily be identified from the mass spectrum at a glance. because the isotopic abundance of the metal is shown directly by the peak-ratio of the associated cluster. since iodine is monoisotopic. In this study, mercury extracted as Hgi, by an organic solvent is determined by stable-isotope dilution mass spectrometry.
is
Procedure Extraction. A weighed amount of mercuric oxide (-co.5 mg) was put into a SO-ml separating funnel and mixed with 5 ml of 3N sulphuric acid and excess of potassium iodide. The mixture was shaken vigorously with IO ml of methyl isobutyl ketone (MIBK), then stood for a few minutes to separate the phases. The upper (organic) layer was used for the mass spectrometry. An aiiquot of 1 ~1 of the extract was placed in a glass capillary tube by microsyringe, and this tube was inserted directly into the ionsource. A mixture of accurately weighed enriched HgO (-0.5 mg) and natural-abundance HgO (- 0.5 mg) was treated and analysed in the same way. A suitable region of the spectrum was scanned repeatedly to increase the sensitivity and precision. RESULTS AND DlSCUSSION
In stable-isotope dilution mass spectrometry, the general equation for an element with n isotopes is
EXPERIMENTAL Reagents Mercuric oxide enriched with *“*Hg was purchased from the Japan Isotope Center. Mercuric oxide (natural abtmdance) was used as the reference mercury compound. Other reagents were of guaranteed or pure-chemical grade.
Mass spectromrrry conditions A Hitachi RMS-4 mass spectrometer was used, with sample temperature t70”, electron current 80 PA and ionization voltage 80 eV.
where a quantity Wof the normal element is mixed with a quantity W, of the tracer element, and rij is the ratio of the abundances of isotopes i and j in the normal element, R, is the ratio in the tracer element, Q is the ratio in the mixture, and Ni is the atomic weight of isotope i. A single isotope is selected as j.
460
m/e (01 HqI,
m/e (b) ‘98H&
Fig. 1. Mass spectra of (a) Hgiz, (b) ‘9sHgIz and (c) the mixture. (Molecular
m/e (c 1 Hql,
-I- ‘?=tgI,
peak regions are shown).
702
SHORT
Table
1. Relative
abundances
COMML’NICATIONS
of Hg and enriched spectra in Fig. I.
Relative abundance in natural Mass number
(Mi)
1%(M,) 199 (M,) 200 (Ma) 201 (M4) 202 (M,) 204(/V,)
Hg obtained
from
Relative abundance in enriched
Hg
Hg
1.00 1.74 2.07 1.30 2.80 (=.j) 0.59
I.00 0.092 0.069 0.050 0.087 (= j) 0.02 I
Figure 1 shows the mass spectra of MIBK extracts of HgI, and enriched Hgl,. From these, M,, Rij and r,+ in equation (1) can be determined, and the results are summarized in Table I, An accurately weighed amount of B’, is added as a spike to the unknown amount of sample (W); Q is estimated from the mass spectrum of the mixture. A mass spectrum of a mixture of enriched HgO (23 ng/id) and the sample of HgO (54 ng/pI) is also recorded in Fig. 1, from which Q is calculated from the ratio of peak heights at M/e 198 and 202 (Table 2). From Table 1 and equation (I), the concentration of the HgO sample was calculated to be 56 ng/$, in good agreement with that taken. Stable-isotope dilution mass spectrometry with extraction is very useful for determining metals, even if the extraction is not complete, because the extraction ratio of the normal and labelled elements can be assumed to be the same. We have reported earlier the mass spectra of metal halides extracted with organic solvents. These metals can
the mass
Relative abundance in mixture 1.00
0.70
also be determined by this method. if they are not monoisotopic and isotopically enriched specimens are available. The iodide seems to be the best form for the determination of metals. because iodine is not only monoisotopic but also gives more intense peaks than the corresponding chloride or bromide.
REFEREhCES
N. M. Frew, J. J. Leary and T. L. Isenhour. Atrrri. C’hm, 1972. 44, 665. S. Tuge, J. J. Leary and T. L. Isenhour. ibid.. 1974. 46. 106. K. Matsumoto, N. Kiba and T. Takeuchi. 1975, 22, 321. fdern, ibid.. 1975. 22, 695.
DETERMINATION OF METALLIC IRON IN A MIXTURE OF LIME, CALCIUM SULPHIDE AND PYRRHOTITE” V. S. SASTRI? Metallurgical Chemistry Section, Physical Sciences Laboratory, Mineral Sciences Laboratories, CANMET, Department of Energy. Mines and Resources. 333 Lebreton Street, Ottawa, Canada (Recoiwd
IO March
1978. Accepted
29 Map
1978)
Summary-A method is described
for the determination of metallic iron in a complex matrix consisting of calcium oxide, calcium sulphide, carbon and pyrrhotite. The procedure consists of leaching the sample with So/, ammonium chloride solution (10% sucrose solution in some cases) followed by treatment with mercury(H) chloride solution and titration with dichromate solution.
The pyrometallurgical treatment of metal sulphides involves oxidative roasting followed by a reduction process. The oxidative roasting of sulphides results in atmospheric pollution by the sulphur dioxide liberated. Thus there exists a need for other processes in which the sulphur is removed in a non-polluting form. Studies on the reduction * Crown Copyrights 5 Present address: Canada.
reserved. 1839 Greenacre
Crescent,
Ottawa,
of metallic sulphides such as pyrite and pyrrhotite with carbon in the presence of lime have been carried out in CANMET.’ In order to follow the progress of this reduction process it is necessary to determine the amount of metallic iron formed in the reaction. Metallic iron has been determined by reduction of copper(H)’ or of mercury(l1) chloride3 in aqueous medium followed by a permanganate titration. Determination of metallic iron with copper sulphate is subject to errors due to the formation of soluble copper(l) salts.’ The use of
BY EXTRACTION SPECTROMETRY
Kozu
MATSMOTO, YOUICHE KUNO and TSUGIO TAKEUCHI Department of Synthetic Chemistry, Faculty of Engineering, Furo-cho,
(Rrceiwd 5 Decemhrr
C~ikusa-ku,
Nagoya.
Nagoya
University,
444 Japan
1977. Revised 29 Murch 1978 Accepted 29 May 1978)
use of halides for determination of metals by stable”isoto~ mass spectrometry suggested. and is iliustrated by the use of mercury iodide for mercury determination.
Summary--The
For mass spectra of metals to be obtained by electronimpact mass spectrometry (El-MS), the metals have first to be changed into compounds which have sufficient volatility in the ion-source. For this purpose, many metal cheiate compounds have been used, and applied for determination of metals by stable-isotope dilution mass spectrometry.‘*’ These chelates. however, give many fragment peaks. similarly to organic compounds in general. _ We have reported mass spectra of some metal halides3*4 which have su~~jent volatiiity for El-MS. The Fragmentation paths of the metal halides are very simple, because they are composed of only a few ions. When the iodide is used, the metal can easily be identified from the mass spectrum at a glance. because the isotopic abundance of the metal is shown directly by the peak-ratio of the associated cluster. since iodine is monoisotopic. In this study, mercury extracted as Hgi, by an organic solvent is determined by stable-isotope dilution mass spectrometry.
is
Procedure Extraction. A weighed amount of mercuric oxide (-co.5 mg) was put into a SO-ml separating funnel and mixed with 5 ml of 3N sulphuric acid and excess of potassium iodide. The mixture was shaken vigorously with IO ml of methyl isobutyl ketone (MIBK), then stood for a few minutes to separate the phases. The upper (organic) layer was used for the mass spectrometry. An aiiquot of 1 ~1 of the extract was placed in a glass capillary tube by microsyringe, and this tube was inserted directly into the ionsource. A mixture of accurately weighed enriched HgO (-0.5 mg) and natural-abundance HgO (- 0.5 mg) was treated and analysed in the same way. A suitable region of the spectrum was scanned repeatedly to increase the sensitivity and precision. RESULTS AND DlSCUSSION
In stable-isotope dilution mass spectrometry, the general equation for an element with n isotopes is
EXPERIMENTAL Reagents Mercuric oxide enriched with *“*Hg was purchased from the Japan Isotope Center. Mercuric oxide (natural abtmdance) was used as the reference mercury compound. Other reagents were of guaranteed or pure-chemical grade.
Mass spectromrrry conditions A Hitachi RMS-4 mass spectrometer was used, with sample temperature t70”, electron current 80 PA and ionization voltage 80 eV.
where a quantity Wof the normal element is mixed with a quantity W, of the tracer element, and rij is the ratio of the abundances of isotopes i and j in the normal element, R, is the ratio in the tracer element, Q is the ratio in the mixture, and Ni is the atomic weight of isotope i. A single isotope is selected as j.
460
m/e (01 HqI,
m/e (b) ‘98H&
Fig. 1. Mass spectra of (a) Hgiz, (b) ‘9sHgIz and (c) the mixture. (Molecular
m/e (c 1 Hql,
-I- ‘?=tgI,
peak regions are shown).
702
SHORT
Table
1. Relative
abundances
COMML’NICATIONS
of Hg and enriched spectra in Fig. I.
Relative abundance in natural Mass number
(Mi)
1%(M,) 199 (M,) 200 (Ma) 201 (M4) 202 (M,) 204(/V,)
Hg obtained
from
Relative abundance in enriched
Hg
Hg
1.00 1.74 2.07 1.30 2.80 (=.j) 0.59
I.00 0.092 0.069 0.050 0.087 (= j) 0.02 I
Figure 1 shows the mass spectra of MIBK extracts of HgI, and enriched Hgl,. From these, M,, Rij and r,+ in equation (1) can be determined, and the results are summarized in Table I, An accurately weighed amount of B’, is added as a spike to the unknown amount of sample (W); Q is estimated from the mass spectrum of the mixture. A mass spectrum of a mixture of enriched HgO (23 ng/id) and the sample of HgO (54 ng/pI) is also recorded in Fig. 1, from which Q is calculated from the ratio of peak heights at M/e 198 and 202 (Table 2). From Table 1 and equation (I), the concentration of the HgO sample was calculated to be 56 ng/$, in good agreement with that taken. Stable-isotope dilution mass spectrometry with extraction is very useful for determining metals, even if the extraction is not complete, because the extraction ratio of the normal and labelled elements can be assumed to be the same. We have reported earlier the mass spectra of metal halides extracted with organic solvents. These metals can
the mass
Relative abundance in mixture 1.00
0.70
also be determined by this method. if they are not monoisotopic and isotopically enriched specimens are available. The iodide seems to be the best form for the determination of metals. because iodine is not only monoisotopic but also gives more intense peaks than the corresponding chloride or bromide.
REFEREhCES
N. M. Frew, J. J. Leary and T. L. Isenhour. Atrrri. C’hm, 1972. 44, 665. S. Tuge, J. J. Leary and T. L. Isenhour. ibid.. 1974. 46. 106. K. Matsumoto, N. Kiba and T. Takeuchi. 1975, 22, 321. fdern, ibid.. 1975. 22, 695.
DETERMINATION OF METALLIC IRON IN A MIXTURE OF LIME, CALCIUM SULPHIDE AND PYRRHOTITE” V. S. SASTRI? Metallurgical Chemistry Section, Physical Sciences Laboratory, Mineral Sciences Laboratories, CANMET, Department of Energy. Mines and Resources. 333 Lebreton Street, Ottawa, Canada (Recoiwd
IO March
1978. Accepted
29 Map
1978)
Summary-A method is described
for the determination of metallic iron in a complex matrix consisting of calcium oxide, calcium sulphide, carbon and pyrrhotite. The procedure consists of leaching the sample with So/, ammonium chloride solution (10% sucrose solution in some cases) followed by treatment with mercury(H) chloride solution and titration with dichromate solution.
The pyrometallurgical treatment of metal sulphides involves oxidative roasting followed by a reduction process. The oxidative roasting of sulphides results in atmospheric pollution by the sulphur dioxide liberated. Thus there exists a need for other processes in which the sulphur is removed in a non-polluting form. Studies on the reduction * Crown Copyrights 5 Present address: Canada.
reserved. 1839 Greenacre
Crescent,
Ottawa,
of metallic sulphides such as pyrite and pyrrhotite with carbon in the presence of lime have been carried out in CANMET.’ In order to follow the progress of this reduction process it is necessary to determine the amount of metallic iron formed in the reaction. Metallic iron has been determined by reduction of copper(H)’ or of mercury(l1) chloride3 in aqueous medium followed by a permanganate titration. Determination of metallic iron with copper sulphate is subject to errors due to the formation of soluble copper(l) salts.’ The use of