SHIMADZU APPLICATION NEWS
● HIGH PERFORMANCE LIQUID CHROMATOGRAPHY
LAAN-A-LC-E010A
L309A
No.
Analysis of ClO2-, ClO3-, and ClO2 in Tap Water by Ion Chromatography
On 30 May 2003, the Japanese Ministry of Health,
Labor and Welfare released a ministerial ordinance
(No. 101, implemented 1 April 2004) related to new
water-quality
standards.
Subsequently,
27
supplemental water-quality targets were defined
(Ordinance No. 1010004) and their inspection
methods notified on 10th October 2003 (Ordinance
No. 1010001)*.
Of these water-quality targets, chlorous acid, chloric
acid, and chlorine dioxide require particular attention
from the viewpoint of the equipment and chemicals
used for water treatment and from the viewpoint of the
by-products of sterilization. Water-treatment plants that
inject chlorine dioxide into drinking water or use it
during the purification process are required to conform
to these water-quality targets.
Ion chromatography is used as the inspection method
for these components. This Application News
introduces examples of these measurements.
*Partial amemdment on March 30,2006 (Japan’s Ministry of
Health,Labour and Welfare Ordinance No.0330001)
■ Analysis of Standard Solution
Table 1 Analytical Conditions
The target values for chlorous acid, chloric acid, and
chlorine dioxide are each 0.6mg/L. Chlorine dioxide
cannot be measured by ion chromatography, as it
does not exist as ions in water. However, reducing
chlorine dioxide using an aqueous solution of sodium
nitrite permits the quantitation of chlorine dioxide as
chlorite ions.
Fig. 1 shows the chromatogram for a standard mixture
of chlorite and chlorate ions (0.6mg/L each). Fig. 2
shows the chromatogram of nine components, with
seven inorganic anion components in addition to the
chlorite and chlorate ions (0.1mg/L each). Table 1
shows the analytical conditions.
Column
Mobile Phase
Flow Rate
Column Temp.
Detection
Injection Vol.
: Shim-pack IC-SA3(250mmL. × 4.0mmI.D.)
: 3.6mM Na2CO3
: 0.8mL/min
: 45˚C
: CDD-10ASP (Suppressor)
: 50µL
1500
F-
6000
nS/cm
1000
nS/cm
ClO2-
ClO3-
500
Cl-
4000
ClO2-
2000
NO2-
NO3BrClO3-
0
-2000
SO42PO43-
0
-4000
0
2
4
6
8
10
12
min
14
16
18
20
22
Fig.1 Chromatogram of a Standard Mixture of ClO2- and ClO3-
24
0
2
4
6
8
10
12
min
14
16
18
20
22
Fig.2 Chromatogram of a Standard Mixture of 9 Anions
24
No.L309A
A
■ Repeatability
The target values for chlorite and chlorate ions and
chlorine dioxide are each 0.6mg/L. The inspection
method is required to maintain accuracy with 10%
max. CV % at 1/10 concentration (0.06mg/L).
Table 2 shows the repeatability for chlorite and
chlorate ions at 0.06mg/L concentration.
■ Linearity
Fig. 3 shows the linearity between 0.06 and 1.0mg/L
concentration for chlorite and chlorate ions. The
contribution ratio (R2) exceeds 0.9999.
140000
Area value
120000
Table 2 Repeatability of Peak Area
Peak Area
-
-
ClO2
9061
9136
9101
9184
9230
9142.4
0.73
1st
2nd
3rd
4th
5th
AVE
CV%
ClO3
5391
5157
5227
5345
5338
5291.6
1.82
R2 = 0.9999
100000
R2 = 0.9999
80000
60000
ClO3ClO2-
40000
20000
0
0
0.2
0.4
0.6
0.8
1.0
Concentration (mg/L)
1.2
Fig.3 Linearity (0.006 - 1.0mg/L)
■ Sample Preparation
As described above, chlorine dioxide is reduced using
an aqueous solution of sodium nitrite to permit
quantitation as chlorite ions. The concentration of
chlorite ions obtained includes the chlorite ions that
existed in the sample originally. Therefore, the chloriteion concentration derived from the chlorine dioxide is
determined by subtracting the chlorite-ion
concentration measured for a separate, unreduced
sample.
<Procedure>
1) Measurement of chlorite ions (including originally
existing ions)
Into 10mL sample water add 1mL phosphate buffer
(approximately 100mM) and 0.5mL sodium nitrite (1%
w/v), and mix. Measure the chlorite ion concentration
(A) in this sample.
2) Measurement of chlorite ions and chlorate ions
Into 10mL sample water add 1.5mL phosphate buffer
(approximately 100mM). Aerate with nitrogen gas for
15 minutes. Measure the chlorite ion concentration (B)
and the chlorate ion concentration (C) in this sample.
Calculate the chlorine dioxide concentration in the
sample as (A) – (B). (In practice, the dilution due to the
added phosphate buffer and sodium nitrite solution
must be taken into consideration).
This method permits the measurement of low
concentrations of chlorite and chlorate ions in the
presence of high concentrations of phosphate and
nitrite ions. Consequently, the column must provide
good separation and high ion-exchange capacity.
Fig. 4 shows the chromatogram for chlorite ions in tap
water spiked with 0.06mg/L chlorous acid and with
phosphate buffer and sodium nitrite added. Fig. 5
shows the chromatogram for chlorite and chlorate ions
in tap water spiked with 0.06mg/L chlorous acid and
chloric acid and with added phosphate buffer.
These results indicate that analysis is possible in the
presence of high concentrations of phosphate and
nitrite ions.
4000
6000
nS/cm
nS/cm
2000
ClO2-
4000
2000
0
ClO2-
ClO3-
-2000
ClO2-4000
0
0
2
4
6
8
10
12
min
14
16
18
20
22
Fig.4 Chromatogram of Tap Water (ClO2- Spiked 0.06mg/L)
24
0
4
6
8
10
12
min
14
16
18
20
22
24
Fig.5 Chromatogram of Tap Water (ClO2- and ClO3- Spiked 0.06mg/L each)
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