Supplementary Material
Methodology for Assessing Thioarsenic Formation Potential in Sulfidic Landfill Environments
Jianye Zhang1, Hwidong Kim1,2, Timothy Townsend1*
1 Department of Environmental Engineering Sciences, University of Florida,PO Box 116450 Gainesville, FL 32611 – 6450, USA
2 Department of Environmental Science and Engineering, Gannon University,109 University Square, Erie, PA 16541-0001, USA
Chemosphere
List of supporting figures and tables
Figure S1. Schematics of simulated C&D debris landfills
Figure S2. Sodium monothioarsenate crystal and its ion chromatogram
Figure S3. ESI-TOF MS spectrum of synthesized sodium monothioarsenate
Figure S4. ESI-TOF MS spectrum of IC Fraction 4
Figure S5. Calibration curves of thioarsenates and arsenate
Figure S6. Linearity curves of thioarsenates
Table S1. Ion chromatograph conditions
Table S2. Typical mass spectrometer conditions
Table S3. Concentrations and corresponding IC peak areas of thioarsenates
Table S4. Determination of repeatability by replicate injections of the same sample
Table S5. Determination of limit of detection and limit of quantitation
* Corresponding author. Phone: +1-352-392-0846, Fax: +1-352-392-3076; email: tto w [email protected]
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Calculation of mass error in mass spectrometric data
An error (mass accuracy) is calculated based on observed and theoretical masses. When
a known compound is used to calibrate the instrument, the mass accuracy indicates the
deviation of the instrument response from the known calculated monoisotopic mass. Usually
the mass accuracy is expressed in parts per million (ppm) as shown in the equation below:
error (massaccuracy )=observedmass−calculated theoreticalmasscalculated theoreticalmass
×106 ppm
Mass error (mass accuracy) is also calculated for compound identification purposes, a mass
accuracy of less than 10 ppm can usually be considered as a good confirmation of the
formula.
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0.6 m HDPE
LeachateCollectionPort
5m
REMOVABLE CAPS
Sand Layer, 0.45 m
Waste Layer, 3.0 m
Water Addition Port
0.18 m HDPE
LeachateCollectionPort
1.2 m
REMOVABLE CAPS
Drainage Layer Pea Gravel0.15 m
Glass Chips Layer, 0.15 m
Waste Layer, 0.9 m
Water Addition Port
Drainage Layer Pea Gravel/Rock0.20 m
S-CD1 S-CD2Figure S1. Schematics of simulated C&D debris landfills.
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Figure S2. Monothioarsenate crystal and its ion chromatogram
Figure S3. ESI-TOF MS spectrum of synthesized sodium monothioarsenate
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Isocratic Elution35 mM NaOH
Na3AsO3S Crystal
Figure S4. ESI-TOF MS spectrum of IC Fraction 4
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Quantification of Thioarsenates
The gradient elution method was chosen for quantification purposes. The
concentrations of the various forms of arsenic in the original injected thioarsenate synthesis
mixture were calculated and listed in Table S3. Calibration curves were obtained based on
arsenic concentrations and their corresponding peak areas (Figure S5).
The detailed calculation of arsenic concentrations in each fraction was calculated as
follows. A certain volume (Vi or Vo) of the synthesis mixture with unknown concentrations of
thioarsenates (Co) was injected into and separated by IC. Fractions corresponding to each
thioarsenate were collected, diluted to a certain volume (Vd), and analyzed for arsenic
concentration (Cd) by an off-line inductively coupled plasma mass spectrometer (ICP-MS) in
another service lab. Then the arsenic concentration (Co) in the original synthesis mixture was
calculated according to the arsenic concentration in the diluted fraction (Cd), the volume of
the diluted fraction (Vd), and the initial injection volume (Vi or Vo) using the mass relationship
CoVo = CdVd. Calibration curves for each thioarsenate were plotted based on the obtained
arsenic concentration (Co) and its corresponding peak area in the IC chromatogram.
For identification purposes, specificity may be demonstrated by separating an analyte
from other components in the sample. In the current gradient method, all thioarsenate anions
are eluted after 9 minutes, which is longer than most common inorganic anions. Phosphate
has a retention time of approximately 11.5 minutes, which is longer than the retention time for
monothioarsenate but shorter than the retention time for other thioarsenate anions. For C&D
landfill leachate specifically, baseline separations from major anions such as sulfate (eluted at
4.2 minute) and sulfide (eluted at 6.0 minute) can be achieved for these thioarsenates,
especially for dithioarsenate-, trithioarsenate, and tetrathioarsenate anions. However, this
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method is not suitable for the analysis of common inorganic anions, such as bromide,
chloride, fluoride, nitrate, sulfate, or sulfide, since these anions are all eluted between 2 and 6
minutes and peak overlap may occur.
y = 113194x
0E+0
2E+5
4E+5
6E+5
8E+5
0 1 2 3 4 5 6 7
Area
As (mg/L)
Dithioarsenate
y = 282539x
0E+0
4E+5
8E+5
1E+6
0 0.5 1 1.5 2 2.5 3 3.5
Area
As (mg/L)
Tritioarsenate
y = 43609x
0E+0
5E+4
1E+5
2E+5
0 0.5 1 1.5 2 2.5
Area
As (mg/L)
Monothioarsenate
y = 147172x
0E+0
1E+5
2E+5
3E+5
4E+5
0 0.5 1 1.5 2 2.5
Area
As (mg/L)
Tetrathioarsenate
y = 21157x
0E+0
1E+5
2E+5
3E+5
4E+5
0 5 10 15 20
Area
As (mg/L)
Arsenate
Trithioarsenate Tetrathioarsenate
Figure S5. Calibration curves of thioarsenates and arsenate
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R² = 0.9924
0
5
10
15
20
0 5 10 15 20 25
Arse
nic (m
g/L)
Relative Concentration
R² = 0.9993
0
0.4
0.8
1.2
1.6
2
0 5 10 15 20 25
Arse
nic (m
g/L)
Relative Concentration
R² = 0.9955
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0 5 10 15 20 25
Arse
nic (m
g/L)
Relative Concentration
a
b
c
Figure S6. Linearity curves of thioarsenates: (a) monothioarsenate; (b) dithioarsenate; (c) trithioarsenate. For monothioarsenate, the point at the highest concentration was not included for R2 calculation.
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Table S1. Ion chromatograph conditions
Item Details
Columns IonPac AS16/AG16, 4 mm ´ 250 mm (Dionex)
Detector CD20 DS3-1 (Dionex)
Pump GP40 gradient pump (Dionex)
Autosampler AS40 (Dionex)
Eluent 35 mM NaOH, 70 mM NaOH
Gradient 0 - 11.5 min: 35 mM
11.5 - 15.5min: 35 mM® 70 mM
15.5 -35 min: 70 mM
35 – 38 min: 70 mM ® 35 mM
38 – 40 min: 35 mM
Anion suppression ASRS Ultra II 4 mm (Dionex)
Regeneration mode External water addition, 10 mL/min
Suppression current 300 mA
Sample volume 5 mL
Injection volume 70 mL
Typical retention times of thioarsenates AsSO33-: 9.38 min
AsS2O23-: 15.08 min
AsS3O3-: 17.68 min
AsS43-: 20.65 min
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Table S2. Typical mass spectrometry conditions
Item Details
Instrument Aglient 6210 TOF MS
Ionization mode Electrospray, Negative mode
Fragmentor voltage 175 V
Capillary voltage 4000 V
Skimmer voltage 65 V
Drying gas temperature 350 oC
Drywall gas flow 10 L/min
Injection volume 2 mL
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Table S3. Concentrations and corresponding IC peak areas of thioarsenates
ReplicateMonothioarsenate Dithioarsenate Trithioarsenate Tetrathioarsenate
Concentration(mg As/L) Area Concentration
(mg As/L) Area Concentration(mg As/L) Area Concentration
(mg As/L) Area
1 2.0914 92312.8 6.1379 610859.9 3.4019 846781.8 2.1039 251143.42 2.3507 97317.6 6.1179 696594.4 3.3729 963436.4 1.7203 287186.33 2.1135 96249.5 5.8008 736451.4 3.2137 1011921 1.9029 304522.4
Average 2.1852 95293.3 6.0189 681301.9 3.3295 940713.2 1.9090 280950.7Standard deviation 0.1438 0.1892 0.1013 0.1919
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Table S4. Determination of repeatability by replicate injections of the same sample
InjectionSample 1 (high concentration)
Peak AreaaSample 2 (low concentration)
Peak Areaa
Monothioarsenate Dithioarsenate Trithioarsenate Monothioarsenate Dithioarsenate Trithioarsenate1 107864.4 78209.6 54326.6 23992.0 23470.0 24511.02 112795.8 81852.9 57259.2 24630.4 21653.6 28022.03 109036.8 82874.7 58688.6 22204.8 23456.8 25663.04 120308.8 84564.9 61348.1 22483.6 20685.1 25716.05 118563.9 84943.1 59278.0 23392.8 22055.3 26532.86 110404.5 88276.1 60935.0 22956.1 23117.0 25986.5
Mean 113162.4 83453.6 58639.3 23276.6 22406.3 26071.9StandardDeviation 5159.0 3379.6 2589.3 920.7 1130.7 1162.1
RSD 0.046 0.040 0.044 0.040 0.050 0.045a The peak areas of only three thioarsenates were listed, since no tetrathioarsenate was observed in these 2 samples.
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Table S5. Determination of limit of detection and limit of quantitationReplicate monothioarsenate dithioarsenate trithioarsenate
1 0.31 0.29 0.102 0.31 0.28 0.113 0.29 0.29 0.094 0.29 0.27 0.105 0.29 0.30 0.096 0.30 0.28 0.087 0.31 0.29 0.098 0.30 0.27 0.099 0.28 0.27 0.08
Average 0.297 0.283 0.093Standard deviation 0.012 0.011 0.009
t 80.01 2.90 2.90 2.90
Limit of detectiona 0.035 0.032 0.026Limit of quantitationb 0.12 0.11 0.09a The limit of detection was calculated by multiplying the standard deviation and the Student’s t-value (9 replicates, 8 degrees of freedom, 99% confidence level, =0.01, single side).bThe limit of quantitation is defined as equal to 10 times the standard deviation.
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