Improved Analysis of Sulfur-Containing Anions from
Polysulfide Matrix by Suppressed Ion Chromatography
Rong Lin, Sheetal Bhardwaj, Kannan Srinivasan, and Chris Pohl, Dionex Corporation, Sunnyvale, CA, USA
ABSTRACT
Sulfur-containing inorganic anions are commonly encountered in soil
sediments, hot springs, and lake waters. They are also frequently used in
many industrial applications. Their speciation and quantitation are very
important to the understanding of those processes. However, due to their
redox chemistry, many sulfur-containing species can readily react with
each other, decompose over time, or be oxidized in the presence of air.
They are also very sensitive to the solution pH, which would affect the
distribution of the species over time. All these make the determination
of these sulfur-containing anions a very challenging task. Currently, both
wet chemistry and ion chromatography are used for the sulfur speciation. In this poster, we will focus on the analysis of sulfur-containing
species in polysulfide matrix with suppressed ion chromatography. The
presence of large amount of polysulfide complicates the determination
of sulfur-containing species. Various sample pretreatment techniques
were evaluated, and an optimized pretreatment method will be shown for
improving the analysis of sulfur-containing anions in polysulfide matrix
by suppressed ion chromatography.
INTRODUCTION
Lime sulfur is a mixture of calcium polysuflide formed through the reaction of calcium hydroxide and sulfur, and is an aqueous solution with
reddish-yellow color.
Lime sulfur is used as a spray to control fungi, bacteria, and insects. It
is also used for remediation of hexavalent chromium in chromite ore
processing residue (COPR).
• Typically lime sulfur solutions are strong alkaline
• When acified, it can produce highly toxic hydrogen sulfide
–
Sn2 + H+ → H2S + (n-1)/8 S8
• It can also react with sulfite to form thiosulfate
–
–
–
–
Sn2 + SO32 → (n-1) S2O32 + S2
Table 2 lists the possible inorganic sulfur-containing anions present in
lime sulfur-based aqueous streams or solutions.
Table 2. Possible Inorganic Sulfur Anions
Anion
Formula
–
Sulfide
S2
Sulfite
SO32
Sulfate
SO42
–
–
2–
Polysulfide
Sn
Thiosulfate
S2O32
Thiocyanate
SCN
Dithionate
S2O62
Polythionate
SXO62
–
–
–
–
Table 1. Polysulfide Chemistry Reactions
–
–
2–
–
2–
2–
–
–
S2 + 4 S → S52
S + 5 S → S62
S + 6 S → S7
S2 + 7 S → S82
CURRENT METHODS FOR DETECTION OF
SULFUR CONTAINING ANIONS
• Iodometry (Sulfide)
• Direct current polarography (Sulfide)
• Differential pulse polarography (Sulfide)
• Spectrophotometry after derivatization with Methyl Blue (Sulfide)
• Spectrophotometry after derivatization with Ellman’s reagent (Sulfite)
• Ion chromatography with suppressed conductivity (Sulfite, Sulfate,
Thiosulfate)
• Ion chromatography with Electrochemical Detection (Sulfide)
• Ion-pair chromatography (Polythionate)
1
Figure 1 showed the direct analysis of a diluted polysulfide solution
with an IonPac® AS19 4 mm column. The polysulfide solution was not
stable, as shown by the overlay of chromatograms from run 1 (red) and
run 12 (blue). The amount of thiosulfate and sulfate increased over time
while the amount of sulfite decreased over the same period. The distinct
yellow color has faded away.
Column:
Eluent:
Gradient:
IonPac AS19 4 mm
KOH (EGCII KOH)
Time (min) Conc. (mM)
0
10
10
10
25
45
30
45
Flow Rate: 1.0 mL/min
Temp.:
30 °C
50
Inj. Volume:
Suppressor:
Current:
Sample:
25 µL
ASRS® 300 4 mm
112 mA (Recycle)
0.01% Calcium polysulfide
Peaks:
1. Sulfate
2. Sulfite
3. Thiosulfate
Column:
IonPac AS19 4 mm
Flow Rate: 1.0 mL/min
Suppressor: ASRS 300 4 mm
Current:
161 mA (Recycle)
Temperature: 30 °C
Eluent:
KOH (EGC II KOH)
Time (min) Conc (mM)
55
0
10
10
10
25
45
28
45
28.1
65
30
65
Inj. Volume: 25 µL
Sample:
0.01% Calcium polysulfide
in base.
Peaks:
1. Sulfate 3. Thiosulfate
2. Sulfite 4. Unknown
3
4
• Unstable response (dashed arrows)
µS
3 45.00
2
1
• Unstable response (dashed arrows)
µS
-5
Overlay of run 1 and run 12
0
5
10
15
Minutes
20
25
30
26243
Figure 2. Base effect polysulfide sample was spiked with base.
1
-5
2
REMOVAL OF POLYSULFIDE WITH SILVER
CARTRIDGE
Concentration: 10.00 mM
0
5
10
15
Minutes
20
25
30
26242
Figure 1. Direct injection with AS19 chemistry.
Figure 2 showed the direct analysis of a diluted polysulfide solution
spiked with base. The polysulfide solution was also not stable in the
basic solution, as shown by the overlay of chromatograms from run 1
(red) and run 12 (blue). The amount of thiosulfate, sulfate, and sulfite
increased over time. Again, the distinct yellow color from polysulfide
faded away.
• An OnGuard® II sample pretreatment cartridge was investigated for
matrix removal.
• The OnGuard II line of disposable sample pretreatment cartridges is
designed to remove matrix interferences such as phenols, metals,
cations, anions, or hydrophobic substances that are encountered in
many ion chromatography applications. These cartridges have wide
pH stability and allow low level ion analysis.
• Silver cartridge was chosen for this application due to the high affinity of silver ions for sulfide species.
–
2 Ag+ + S2 → Ag2S
• The diluted sample was pushed through the cartridge.
Figure 3 showed the direct analysis of a thiosulfate solution after the
passage through a silver cartridge. The thiosulfate peak was completely
removed, as shown by the overlay of chromatograms before (red) and
after (blue) the passage.
2
Improved Analysis of Sulfur-Containing Anions from Polysulfide Matrix by Suppressed Ion Chromatography
Inj. Volume: 25 µL
Sample:
10 ppm Sulfate and thiosulfate
Column:
IonPac AS19 4 mm
Flow Rate: 1.0 mL/min
Suppressor: ASRS 300, 4 mm
Current:
112 mA (Recycle)
Temperature: 30 °C
Eluent:
KOH (EGC II KOH)
Time (min) Conc. (mM)
25
0
10
10
10
25
45
30
45
Peaks:
1. Sulfate
2. Thiosulfate
1
45.00
Column:
Eluent:
Flow Rate:
Temperature:
Inj. Volume:
Sample:
The thiosulfate peak was removed after the
passage through the silver cartridge.
µS
–
Figure 5 showed the direct analysis of a diluted polysulfide solution
with electrochemical detection before (red) and after (blue) the passage through an OnGuard H cartridge. The large polysulfide peak was
removed with the OnGuard H cartridge.
–
2 S2O32 + Ag+
[Ag(S2O3)2]3
300
IonPac AS20 2 mm
KOH (EGC II KOH)
0.25 mL/min
30 °C
5.0 µL
0.01% Calcium
polysulfide treated
with OnGuard H
Time
0
25
25.1
35
Waveform
Time Potential (V)
0.00
-0.10
0.20
-0.10 Begin integration
0.90
-0.10 End integration
0.91
-1.00
0.93
-0.30
1.00
-0.30
Gradient
10 mM
10 mM
50 mM
50 mM
2
Sulfide
-5
nC
Concentration: 10.00 mM
0
5
10
15
Minutes
20
25
Unknown
30
Polysulfide
26244
Thiosulfate
Figure 3. Effect of Ag cartridge.
Figure 4 showed the direct analysis of a diluted polysulfide solution after
the passage through a OnGuard H cartridge. The sample was much more
stable, as shown by the overlay of chromatograms from run 1 (blue)
to run 23 (red). Only the amount of sulfite showed noticeable increase,
while the amount of thiosulfate and sulfate were largely unchanged over
time. The yellow color from polysulfide was removed after the passage
through the cartridge.
Peaks:
1. Sulfate
2. Sulfite
3
µS
0
5
10
15
20
Minutes
25
30
35
26246
Figure 5. Electrochemical detection.
NEW SAMPLE PRETREATMENT STEPS PRIOR
TO SUPPRESSED ION CHROMATOGRAPHY
• Dilute the polysulfide containing sample 1000 times.
- Typically present as a 10% aqueous solution
• Push the diluted samples through the OnGuard H and OnGuard Na
cartridges sequentially. These two cartridges have bee prerinsed with
at least 20 mL of DI water each.
• Directly inject the pre-treated samples into the IC system.
Inj. Volume: 25 µL
Sample:
0.01% Calcium polysulfide
treated with OnGuard H
Column:
IonPac AS19 4 mm
Flow Rate: 1.0 mL/min
Suppressor: ASRS 300 4 mm
Current:
161 mA (Recycle)
Temperature: 30 °C
Eluent:
KOH (EGC II KOH)
Time (min) Conc. (mM)
25
0
20
17
20
17.1
45
28
45
28.1
65
35
65
-50
3. Thiosulfate
65.00
Figure 6 showed the direct analysis of a diluted polysulfide solution
after the passage through a OnGuard H and a OnGuard Na cartridge
with an AS17-C column. The AS17-C column provided better resolution
between the sulfite and sulfate peaks, which facilitated their quantitation.
45.00
2
1
Concentration: 20.00 mM
-5
0
5
10
15
20
Minutes
25
30
35
26243
Figure 4. Effect of OnGuard H cartridge.
3
Column:
IonPac AS17-C 4 mm
Flow Rate: 1.0 mL/min
Suppressor: ASRS 300 4 mm
Current:
161 mA (Recycle)
Temperature: 30 °C
Eluent:
KOH (EGC II KOH)
Time (min) Conc. (mM)
25
0
2.0
10
20
15
40
20
40
20.1
65
25
65
CONCLUSIONS
Inj. Volume: 25 µL
Sample:
0.01% Calcium polysulfide
treated with OnGuard H and
OnGuard Na
Peaks:
Current Methods
1. Sulfide 3. Sulfate 5. Unknown
2. Sulfite 4. Thiosulfate
65.00
4
OnGuard SPE Based Treatments
• The OnGuard II H cartridge is capable of removing polysulfide species from the solution. However, the resulting solution is acidic and
many sulfur-containing species are not stable in the presence of acid.
• Combination of OnGuard II H and Na cartridge treatment sequentially
stabilizes the sample and yields more stable response.
• The new pretreatment approach provides a more reliable approach for
analyzing sulfur containing anions in polysulfide matrix.
40.00
µS
20.00
5
Concentration: 2.00 mM
2 3
1
0
0
5
10
Minutes
15
• The diluted polysulfide samples are not stable.
• Quantitation of trace levels of sulfur-containing species is unreliable.
• The use of silver cartridge can remove sulfide, but it also removes
thiosulfate.
20
25
26247
Ion Chromatography
• The AS17-C column provides good separation for sulfur speciation.
Figure 6. Polysulfide analysis.
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Improved Analysis
of Sulfur-Containing Anions from Polysulfide Matrix by Suppressed Ion Chromatography
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