The Application and Potential Artifacts of Zeeman Cold Vapor Atomic

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Environmental Measurements Methods

The Utility and Potential Artifacts by Zeeman Cold Vapor Atomic Absorption Analysis of Mercury Stable Isotopes Xia Lu, Jiangtao Zhao, Xujun Liang, Lijie Zhang, Yu-Rong Liu, Xiangping Yin, Xiangkai Li, and Baohua Gu Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.9b00067 • Publication Date (Web): 07 Feb 2019 Downloaded from http://pubs.acs.org on February 12, 2019

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Environmental Science & Technology Letters

1

The Utility and Potential Artifacts by Zeeman Cold Vapor Atomic Absorption Analysis

2

of Mercury Stable Isotopes

3 4

Xia Lu,1,2,#,* Jiangtao Zhao,3# Xujun Liang,2,# Lijie Zhang,2 Yurong Liu,2 Xiangping Yin,2 Xiangkai Li,1

5

Baohua Gu2,4,*

6 7 8 9

1Key

Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University,

Lanzhou 730000, China 2Environmental

10

3School

11

4Department

12

Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, TN

37996, USA

13 14

# These

authors contributed equally.

15 16 17 18 19

1 ACS Paragon Plus Environment


20

ABSTRACT

21

Zeeman cold vapor atomic absorption spectrometry (CVAAS) has been widely used for

22

environmental mercury (Hg) detection and quantification for decades, but little is known about its utility

23

and potential artifacts in analyzing Hg with varying isotope compositions. We show that each Hg isotope

24

responds differently by CVAAS analysis, with 200Hg and 202Hg isotopes exhibiting ~10 times greater

25

signal intensities than 198Hg and 201Hg isotopes. However, all Hg isotopes show a linear correlation

26

between Hg concentrations and the signal intensity, validated by both measurements and theoretical

27

simulations. Zeeman CVAAS could thus offer a convenient, inexpensive tool for determining Hg

28

isotopes, particularly in using single- or dual-labeled Hg isotopes for tracing Hg biogeochemical

29

transformations, such as partitioning, ion exchange, sorption-desorption, and methylation-demethylation

30

in environmental matrixes. We also caution that care must be taken when CVAAS is used for quantifying

31

Hg in samples with changing isotope compositions to avoid measurement errors.

32


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34 35


INTRODUCTION Cold vapor atomic absorption spectrometry (CVAAS) is widely used for mercury (Hg) detection

36

and quantification in environmental samples because of its high sensitivity, capable of detecting sub-

37

picogram (pg) quantities of Hg.1-5 It is also a preferred choice for field and air monitoring applications

38

because of its affordability and portability.1,2,6 However, a common issue with CVAAS is potential

39

interferences resulting from molecular absorption of gaseous impurities, such as benzene. To resolve this

40

issue, Zeeman background correction is used to improve the sensitivity, selectivity, and measurement

41

accuracy.7,8 This is done by splitting the Hg resonance line (λ=254 nm) into three polarized Zeeman

42

components (π, σ-, σ+), although the photodetector detects only the radiation of two σ components (see

43

Supporting Information (SI) “Zeeman CVAAS and theory” for details). The σ components are separated

44

by the polarization modulator, and the spectral shift of the σ components is less than 0.1 nm or equivalent

45

to a frequency of ~22 GHz (due to the hyperfine structure of Hg), which is much smaller than the widths

46

of molecular absorption bands and/or scattering spectra of most interfering molecules. When the light

47

passes through the sample chamber, the signal intensity is defined by the difference between the

48

intensities of the two  components of the sample.7 Consequently, the background absorption from any

49

interferences in σ- and σ+ is always the same and thus canceled. However, the absorption line profiles of

50

most Hg isotopes fall within the σ- component, except 199Hg, which falls mostly in the σ+ component (SI,

51

Zeeman CVAAS and theory, Figure S1). The difference between σ- and σ+ intensities thus changes with

52

changing Hg isotope compositions and their vapor concentrations, thereby providing a tool for

53

quantifying Hg or Hg isotope concentrations.

54

Mercury has six stable isotopes with high natural abundances ranging from 6.9% to 29.9%.

55

Enriched Hg isotopes are often used as tracers for investigating Hg fate and transformations in

56

environmental systems, such as transport, sorption-desorption, methylation-demethylation, precipitation-

57

dissolution, biological uptake, and ion exchange reactions.9-13 However, to date few studies have taken the

58

advantage of Zeeman CVAAS for quantifying Hg isotopes,8 a technique that has been largely overlooked



59

in both laboratory and field investigations. Equally important is to realize that, if the Hg isotope effect is

60

not considered, CVAAS analysis could potentially lead to large measurement errors if Hg isotope

61

compositions in the reactant and the product change over the course of reactions. Although cold vapor

62

atomic fluorescence spectrometry (CVAFS) is also widely used because of its low cost, it does not

63

discriminate Hg isotopes as CVAFS measures the broad atomic fluorescence of Hg.14,15

64

The primary objective of this study was to demonstrate potential artifacts and the practical utility

65

of Zeeman CVAAS for determining Hg isotopes in tracing Hg biogeochemical transformations, such as

66

partitioning and concurrent Hg sorption-desorption reactions, in environmental matrixes. We provide

67

theoretical basis for quantifying individual Hg isotopes or their mixtures and compare the advantages and

68

disadvantages of using CVAAS for Hg isotope analyses. We suggest that CVAAS could offer a

69

convenient, inexpensive tool for quantifying Hg isotopes without using specialized equipment, such as

70

inductive coupled plasma–mass spectrometer (ICP-MS).9,12,13

71

MATERIALS AND METHODS

72

Standard solution of the natural Hg (1 µg mL-1 in 2% HNO3) was purchased from Brooks Rand

73

Laboratories (Seattle, WA). Enriched Hg stable isotopes (198Hg, 200Hg, 201Hg, and 202Hg) were supplied by

74

Oak Ridge National Laboratory, Oak Ridge, Tennessee, and the purity of these isotopes is certified as

75

follows: 198Hg (92.78%), 200Hg (96.41%), 201Hg (96.17%), and 202Hg (95.86%).11 All impurity isotopes are

76

listed in Supporting Information (SI Table S1). These isotopes were received as HgO or HgCl2 solids, and

77

their stock solutions were prepared by dissolving HgO or HgCl2 in 1–3% HCl and diluting to 1 mg/L in

78

1% HCl. The concentration of each Hg isotope was validated by ICP-MS analysis (Elan DRC-e,

79

PerkinElmer Inc.). The isotope and natural Hg working solutions at 10 µg/L were preserved in 0.5%

80

BrCl, and an aliquot (in the mass range of 200–1200 pg) was used and analyzed by CVAAS (Lumex RA-

81

915+, Ohio Lumex Co.), as described previously.3-5,16,17 The peak intensity as a function of the Hg mass

82

or concentration was plotted by linear fitting using the OriginPro software (OriginLab).5


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Standard additions of Hg isotopes were performed to evaluate the utility and artifacts by CVAAS

84

analyses in an environmental water sample obtained from the contaminated East Fork Poplar Creek

85

(EFPC) in Oak Ridge, Tennessee, as described previously.18, 19 The filtered water contained ~3 mg/L

86

dissolved organic matter and 25 ng/L Hg at pH 7.8. Following the addition of a Hg isotope (~85 ng/L),

87

the total Hg (THg) concentration was determined after samples were oxidized in BrCl (5% v/v)

88

overnight.3,4,20,21 Additionally, sequential extraction was used to compare the partitioning and

89

immobilization of the freshly added 200Hg (as a tracer) with previously deposited old Hg in a

90

contaminated EFPC soil.22,23 The extractable pools of Hg included (1) deionized water, (2) 0.01M

91

HCl/0.1M acetic acid, (3) 1M KOH, (4) 12M nitric acid, and (5) aqua regia, and were used as a proxy of

92

Hg bioavailability in soil (see SI “Hg sequential extraction”).22,23 Furthermore, concurrent Hg adsorption

93

and desorption on mineral hematite were conducted using dual-labeled Hg isotopes (e.g., 200Hg and

94

198Hg),

95

a small aliquot (40 µL) of 198Hg (15 µg/L, final concentration). Hematite particles were then removed by

96

filtration (0.2 m), and Hg concentrations in supernatant solutions before and after 198Hg addition were

97

determined. The amounts of 198Hg and 200Hg adsorbed (or 200Hg desorbed) were calculated by the

98

difference between the amounts added and that found in the supernatant solution. The average

99

concentrations of duplicate samples were reported, and error bars represent the deviation between the two

100 101

in which 200Hg (17 µg/L) was equilibrated with hematite first for 24 h, followed by the addition of

replicates (X1 and X2), defined as the absolute value of (X1–X2)/2. The CVAAS method detection limit (MDL) was determined for four available Hg isotopes

102

(198Hg, 200Hg, 201Hg, and 202Hg) in both deionized water and the simulated water consisting of 1 mM

103

NaHCO3, 2 mM CaCl2, 2 mM MgCl2, and 1 mM ZnCl2 as interfering ions.24 No significant differences

104

were observed between samples prepared in deionized water or the simulated water (SI Figure S2) since

105

all Hg was converted to gaseous elemental Hg(0) by Sn(II) reduction and ultimately detected by CVAAS.

106

Therefore, MDLs were computed as an average (from deionized water and the simulated water). They

107

were 8.08±1.78, 3.90±0.73, 13.54±1.96, and 3.13±0.12 pg for 198Hg, 200Hg, 201Hg, and 202Hg, respectively.



108

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RESULTS AND DISCUSSION 250

Total Hg (ng/L)

200

CVAAS (no correction) ICP-MS

(a)

150

100

50

0

109

EFPC water

+ 198Hg

+ 200Hg

+ 201Hg

+ 202Hg

20

CVAAS (no correction) ICP-MS

Hg (g/g)

15

(b) 10

5

0 110 111 112 113 114 115 116

er s Wat

le /HCl 1 M) olub a c id c i OH ( t e K c A

(1 HNO 3

2 M)

a re Aqu

gia

Figure 1. Comparisons between Zeeman CVAAS and ICP-MS for determining Hg concentrations in environmental matrixes. (a) EFPC creek water spiked with or without Hg stable isotopes of 198Hg, 200Hg, 201Hg, and 202Hg (85 ng/L each), and (b) sequential extraction of Hg in a contaminated EFPC soil with freshly added 200Hg as a tracer (see SI, Hg sequential extraction for details).22, 23 Without correction of the Hg isotope effect, CVAAS analysis results in large measurement errors. 6 ACS Paragon Plus Environment

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“Artifacts” by Zeeman CVAAS analysis Potential artifacts associated with Zeeman CVAAS analyses of Hg isotopes in environmental

119

matrixes were first realized during measurements of Hg concentrations in the contaminated EFPC water

120

by standard addition of Hg isotopes of 198Hg, 200Hg, 201Hg, or 202Hg (85 ng/L each). Using standard

121

calibration of the ambient natural Hg, we found that the measured THg concentrations after additions of

122

201Hg, 198Hg, 202Hg,

123

the anticipated THg should be ~110 ng/L (analyzed by ICP-MS) (as the creek water contained ~25 ng/L

124

Hg). The results thus indicate that, for samples spiked with 198Hg and 201Hg, CVAAS substantially

125

underestimated the Hg concentration by 64.4% and 53.8%, respectively, but overestimated the Hg

126

concentration by 85.5% and 107.5% in samples spiked with 202Hg, and 200Hg, respectively.

127

and 200Hg were 39.2, 50.8, 204.1, and 228.2 ng/L, respectively (Figure 1a), whereas

Similarly, in a comparative study of sequential extraction of the previously deposited Hg and the

128

freshly added 200Hg (as a tracer) in a contaminated EFPC soil (SI, Hg sequential extraction),22 we found

129

that CVAAS substantially overestimated the four extractable fractions of Hg when compared to the

130

amounts analyzed by ICP-MS (Figure 1b). The measured THg concentrations by CVAAS in fractions of

131

water, acetic acid/HCl, KOH, HNO3, and aqua regia were 0.01, 1.28, 6.17, 6.42 and 14.35 g/g,

132

respectively, compared to the ICP-MS measured concentrations of 0.01, 0.29, 3.41, 3.46, and 10.75 g/g,

133

respectively (Figure 1b). In total, CVAAS overestimated the extractable Hg by about 56%. The result

134

again signifies serious measurement artifacts by CVAAS when the Hg isotope is used as a tracer and the

135

isotope effect is not accounted for (described below).

136

Theory and utility of Zeeman CVAAS in Hg isotope analysis

137

To provide theoretical basis for the observed CVAAS measurement errors (Figure 1), we

138

analyzed four Hg isotopes in hand, including 198Hg, 200Hg, 201Hg, and 202Hg, and performed simulations of

139

CVAAS responses to all six Hg isotopes (SI, Zeeman CVAAS and Theory). Results indicate that each Hg

140

isotope gave vastly different signal responses by CVAAS (Figure 2a). With the same amount of Hg added

141

to solution (200–1200 pg), the measured peak intensities of 200Hg and 202Hg were ~10 times higher than


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those of 201Hg and 198Hg, although they all showed a linear correlation with the added Hg mass. The

143

measured slopes of the signal intensity against the added Hg mass were 83.41±0.36, 73.65±0.40,

144

9.46±0.07, and 7.21±0.10 counts/pg for 200Hg, 202Hg, 198Hg, and 201Hg, respectively. Obviously, these

145

large differences in CVAAS responses to Hg isotopes explained large discrepancies observed when Hg

146

isotope tracers were used in the standard addition and sequential extraction experiments (Figure 1), in

147

which Hg isotope effects were not accounted for. However, when corrected using the calibration curve (or

148

the slope) of each Hg isotope shown in Figure 2a, the measured Hg concentrations by CVAAS matched

149

well with those determined by ICP-MS (SI Figure S3). 12 Experiment 198 Hg 200 Hg 201 Hg 202 Hg

Peak intensity (104 counts)

10 8 6

Simulation 198 Hg 200 Hg 201 Hg 202 Hg 199 Hg 204 Hg

200

Hg

202

Hg

(a)

199

Hg

4 204

Hg

2

198

Hg

201

Hg

0 0

200

400

600

800

1000

1200

Total Hg (pg) 12 Experiment Natural Hg 200 Hg:198Hg=3:7 200 Hg:198Hg=7:3

10


1.


Simulation Natrual Hg

8 200

Hg:198Hg=7:3

(b)

6

Natural Hg

4 200

Hg:198Hg=3:7

2 0 0

150

200

400

600

800

Total Hg (pg)


1000

1200

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151 152 153


Figure 2. Zeeman CVAAS determination of (a) 198Hg, 200Hg, 201Hg, and 202Hg isotopes (symbols) and the simulation results (solid lines), and (b) mixed isotopes of 200Hg and 198Hg, and the natural Hg.

154

Why Hg isotopes respond differently by CVAAS is attributed to the absorption profiles of the

155

hyperfine structures of Hg which overlap with Zeeman - and + components of the light source profile

156

(SI, Zeeman CVAAS and Theory; Figure S1). As described earlier, the absorption line profiles of most

157

Hg isotopes fall within the σ- component, except 199Hg and part of 201Hg, which fall within the σ+

158

component. The difference between signal intensities of σ- and σ+ components changes with changing Hg

159

isotope compositions and concentrations and is defined by Eq. 1 (SI, Zeeman CVAAS and Theory).

160

Using Eq. 1, we can simulate the signal response to each individual Hg isotope, and the simulation results

161

for 198Hg, 199Hg, 200Hg, 201Hg, 202Hg, and 204Hg were plotted in Figure 2a as solid lines. The calculated

162

slopes are also listed in SI Table S2, in which Columns 4 and 5 are the adjusted slopes, corrected for

163

impurities present in the four measured Hg isotopes. The simulation results showed an excellent

164

agreement with the measured values (symbols) of four Hg isotopes (198Hg, 200Hg, 201Hg, 202Hg). Data for

165

199Hg

166

isotopes, simulation results gave a linear relationship between the signal intensity and the Hg

167

concentration (Figure 2a), although the slope varied with different Hg isotopes due to their differences in

168

hyperfine structures.

169

and 204Hg were not available because of their limited source availability. However, for all Hg

Both experiments and simulations (Figure 2a) clearly show the usefulness of CVAAS for

170

quantitative analyses of Hg isotopes because each Hg isotope gives a linear correlation and a distinct

171

slope, which is a constant for a given instrument with preset conditions. Importantly, when the two Hg

172

isotopes were mixed in solution, we found that the measured slope was additive, equal to the sum of the

173

products of the slope and the mass fraction of each isotope in the mixture. For example, at the 200Hg to

174

198Hg

175

(=0.3×83.41 + 0.7×9.46), which is in excellent agreement with the measured slope of 31.92 (Figure 2b,

176

dashed line and symbol). Similarly, at the 200Hg to 198Hg ratio of 7:3, the measured slope of the mixture

atomic ratio of 3:7, the slope of the total Hg (THg = 200Hg + 198Hg) was calculated to be 31.65



177

was 61.23, consistent with the calculated slope of 61.23 (Figure 2b). We also measured the instrument

178

response to the natural Hg and observed a slope of 36.24±0.17 (Figure 2b). However, this slope was

179

lower than the expected additive value of the four measured Hg isotopes (SI Table S2) and their

180

respective natural abundances (i.e., 198Hg, 9.97%; 200Hg, 23.10%; 201Hg, 13.18%; 202Hg, 29.86%). The

181

expected slope of the natural Hg should be at least 41.45 (by accounting the four measured isotopes), if all

182

Hg isotopes would obey the additive rule described above. The main cause of this deviation is attributed

183

to the 199Hg hyperfine structure overlapping mostly with the + component, and its signal intensity is

184

therefore subtractive when mixed with other Hg isotopes (SI, Eq. 1). This result thus explained why the

185

measured slope of the natural Hg was lower than the value expected from the summation of the four

186

measured isotopes (198Hg, 200Hg, 201Hg, 202Hg). Therefore, except for 199Hg, the signal intensity of any of

187

the mixed isotopes of 198Hg, 200Hg, 201Hg, 202Hg, and 204Hg equals to the summation of each individual Hg

188

isotope, confirmed by the measured values of any binary mixtures of 198Hg and 200Hg at varying atomic

189

ratios (Figure 2b; SI Figure S4a) or a mixed sample containing 198Hg, 200Hg, 201Hg, and 202Hg (SI Figure

190

S4b). These results thus indicate the robustness of using CVAAS as a tool for Hg isotope analysis.

191

Environmental applications of CVAAS for Hg isotope tracer studies: Pros and Cons

192

Enriched Hg isotopes are often used in tracing Hg biogeochemical transformations in both

193

laboratory and field investigations,9-13 such as standard addition, sorption and desorption, methylation and

194

demethylation, and ion exchange reactions in environmental systems. As illustrated in Figure 1b,

195

sequential extraction was used to assess Hg species distributions between the freshly added 200Hg tracer

196

(after 24 h) and the old Hg in a contaminated EFPC soil.22, 23 The freshly added 200Hg was determined

197

after subtracting the old Hg in the untreated soil (without 200Hg). Based on the measured 200Hg calibration

198

curve (Figure 2a, Table S2), we found that the distribution of 200Hg in extractable pools resembled the old

199

Hg (Figure 3a), in which negligible amounts of 200Hg were found in water- and acetic acid/HCl-

200

extractable pools (presumably more bioavailable than other Hg pools). Most of the added 200Hg seems

201

immobilized in the pools associated with soil organic matter (1M KOH) and minerals (12M HNO3 and

202

aqua regia) (Figure 3a). These results confirm previous observations that freshly added Hg is often rapidly 10 ACS Paragon Plus Environment

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immobilized and becomes unavailable for biological uptake,10, 25 although detailed discussion of the

204

mechanisms of Hg immobilization in soil is beyond the scope of this work. 100 Water soluble Acetic acid/HCl KOH (1 M) HNO3 (12 M) Aqua regia

Hg distribution (%)

80 60

(a) 40 20 0

205

(b)

Hg in solution

12 198

10 8 6 4

200

Hg

(200Hg+198Hg)

Hg added

After sorption

200

Peak intensity (105 counts/mL)

14

New 200Hg

"Old" Hg in soil

Hg added

200

Hg

2 0

120

No hematite

(c)

Hematite

Hg adsorbed

Hg adsorbed (mg/g)

100 80 200

60

198

Hg Hg

40 20 0

206 207 208 209 210 211 212 213

No hematite

Hematite

Figure 3. (a) Comparisons between the new, freshly added 200Hg (as a tracer) and old Hg species distributions in a contaminated EFPC soil by sequential extraction.22, 23 (b, c) Determination of 200Hg sorption and then desorption by 198Hg on hematite (0.1 g/L) at pH 6.5. The initially added 200Hg was 17 µg/L. After equilibration with hematite, approximately an equal molar concentration of 198Hg (~15 µg/L) was added. Plot (b) is the measured CVAAS peak intensities of 200Hg and (200Hg +198Hg) in solution before and after their adsorption on hematite, and (c) is the amount of Hg adsorbed on hematite. 11 ACS Paragon Plus Environment


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Perhaps the most important application of CVAAS is the use of dual-labeled Hg isotopes (e.g.,

215

200Hg

216

Hg adsorption and desorption reactions, as illustrated in Figure 3b,c. Because of a large difference (~10×)

217

in CVAAS responses to 200Hg and 198Hg (Figure 2a, Table S2), any desorption or displacement of one Hg

218

isotope by the other could be readily detected. Results show that, after pre-equilibration of 200Hg with

219

hematite for 24 h, the CVAAS intensity in the supernatant decreased from 12.51×105 (Initial) to 5.67×105

220

counts/mL (Figure 3b, 2nd column). However, a substantially increased intensity (10.3×105 counts/mL)

221

was observed (Figure 3b, 3rd column) following the addition of 198Hg. This intensity was much higher

222

than that expected (7.6×105 counts/mL, Figure 3b, 4th column) by the summation of 200Hg (assuming no

223

desorption) and the total added 198Hg in solution (assuming no adsorption of 198Hg). Evidently, a large

224

fraction of the pre-adsorbed 200Hg was desorbed by 198Hg, resulting in a substantially increased intensity

225

because CVAAS response of 200Hg is ~10 times higher than that of 198Hg (SI Table S2). Since the

226

supernatant solution now contained both 200Hg and 198Hg, the measured total intensity cannot be directly

227

converted to the Hg concentration unless the THg concentration or the ratio of 200Hg to 198Hg in solution

228

is known. In this case, THg is quantified using techniques such as CVAFS, as described earlier, so that

229

200Hg

230

and 198Hg adsorbed on hematite determined (Figure 3c). Interestingly, we found that the addition of 198Hg

231

to the hematite suspension that had been pre-equilibrated with 200Hg resulted in desorption or exchange of

232

200Hg

233

and 198Hg) to trace simultaneous Hg transformations in environmental systems, such as concurrent

and 198Hg in solution can be calculated using the slopes given in Table S2, and the amounts of 200Hg

by 198Hg and led to approximately an equal distribution of 200Hg and 198Hg on hematite. Together, these two case studies (Figure 3) demonstrate the practical utility of Zeeman CVAAS

234

for accurate determination of single or dual-labeled Hg isotopes in studies such as tracing Hg fate and

235

transport, sorption-desorption, and transformation reactions in environmental systems, as reported

236

previously.9-13 Another major advantage of using Zeeman CVAAS is its low detection limit, field

237

portability, and wide availability in many Hg labs because of its low cost (~10× less expensive than a

238

typical ICP-MS). It could also be used in real-time analysis and monitoring. A disadvantage is that

239

CVAAS measures the total signal intensity and cannot resolve individual Hg isotopes when mixed. 12 ACS Paragon Plus Environment

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Fortunately, most tracer studies use only one or two Hg isotopes (Figure 3). In the latter case, only a

241

secondary measurement is necessary to determine the THg by techniques such as CVAFS and ICP-MS.

242

However, regardless of its application, realizing the utility and potential artifacts of CVAAS in Hg

243

isotope analysis is critically important, as it is among the most widely used technique for Hg

244

quantification and monitoring in both laboratory and field investigations.

245 246

ASSOCIATED CONTENT

247

Supporting Information

248

All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supporting

249

Information, which is available free of charge via the Internet at http://pubs.acs.org.

250 251

AUTHOR INFORMATION

252

Corresponding author:

253

Email: [email protected]; [email protected]

254

Notes:

255

The authors declare no competing financial interest.

256 257

ACKNOWLEDGMENTS

258

This research was sponsored by the Office of Biological and Environmental Research within the Office of

259

Science of the U.S. Department of Energy (DOE), as part of the Mercury Science Focus Area project at

260

the Oak Ridge National Laboratory (ORNL) and by the National Natural Science Foundation of China

261

(41807477). The Department of Energy will provide public access to these results of federally sponsored

262

research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-

263

access-plan). ORNL is managed by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with

264

DOE.

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12 Experiment Natural Hg 198 Hg 200 Hg 201 Hg 202 Hg

8

4


10

Simulation Natural Hg 198 Hg 200 Hg 201 Hg 202 Hg 199 Hg 204 Hg

200

Hg

202

Hg

6 199

Hg

4

Natural

204

Hg

2

198

Hg

201

0

0

200

400

600

800

1000

Added Hg (pg)

ACS Paragon Plus Environment

Hg

1200

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The Application and Potential Artifacts of Zeeman Cold Vapor Atomic

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