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 n@ufl.edu

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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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