Application Note · multi X® 2500

Linearity Test According to DIN EN ISO 9562
(Column Method)

Challenge
To pass the linearity test
according to DIN EN ISO 9562

Solution ast and cost-effective procedureF
applying adsorption of theAOX samples on an automatic
preparation unit followed byanalysis with an AOX analyzer

Introduction
AOX (AOX - adsorbable organically bound halogens) is an analytical convention
which represents the sum of all organically bound halogens (except fluorine),
mainly used in water and waste water analysis. Solid samples like sludge orsediments can also contain AOX. The solid AOX however has to be determined by
the batch method which is not part of this application. The compounds containing
halogens are adsorbed onto the surface of activated carbon (charcoal) in dissolved
or suspended form. The activated carbon is washed afterwards with aqueous
nitrate washing solution to remove inorganic halides. During the combustion of
the loaded charcoal in pure oxygen at high temperatures hydrogen halides areformed. After absorption of the halides the final detection takes place inside acoulometric cell by means of argentometric titration.

Instrumentation
A multi X® 2500 AOX analyzer equipped with an autoX36 auto sampler was usedin combination with an automatic sample preparation unit of the APU series.
Thanks to the perfect combination of sample preparation and analysis idle time
is minimized and sample throughputvis increased. The multiWin software allows
fast sample analysis and data evaluation simultaneously. In combination with theSelf Check System the multi X® 2500 ensures trouble-free and fully automatedoperation.

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Linearity Test According to DIN EN ISO 9562 (Column Method)

Samples and ReagentsThe following reagents were used for sample and standard preparation■■ Deionized water/ ultra-pure grade■■ Nitric acid >65% p.a.
■■ p-chlorophenol aqueous stock solution; 1 mg/l Cl; (Bernd Kraft GmbH)Standard preparation
The p-chlorophenol stock solution was diluted with ultra-pure water according the ISO 9562 to obtain different concentration
as follows: 10, 50, 100, 200 and 250 µg/l.
100 ml of these solutions was adjusted to pH 2 with concentrated nitric acid. The low pH value inhibits bacterial growing andenables the storage of the samples at 0 - 4 °C.
Determination
The determination was carried out using a multi X® 2500 AOX analyzer. The adsorption of the AOX samples was performedon an automatic preparation unit of the APU series.
p-chlorophenol was used as organic standard solution to evaluate the system and method in terms of sample recovery. For
this a linearity test was performed. According to the column method, two quartz glass containers filled with activated carbon
were used. Both are positioned vertically, one behind the other. The different standard solutions were adsorbed with a flowrate of 3 ml/min. After rinsing with 25 ml washing solution at the same flow rate the columns with the loaded charcoal werecombusted at 950 °C in pure oxygen stream.
Results and Discussion
According to DIN EN ISO 9562 the results are acceptable if the correlation coefficient is ≤ 0.999. The slope of the linearity
should be within 0.95 and 1.05. The results of the determinations are shown in table 1.
Table 1: Results of the linearity test of the AOX determination of p-chlorophenol in waterStandard concentration

Abs. value 1st column

Abs. value 2nd column

Blank value

RecoveryAverage[µg/l][µg Cl][µg Cl][µg Cl][µg/l][µg/l]

10

1.08

0.06

0.265

8.75

9.65

10

1.08

0.24

0.265

10.55

50

4.86

0.09

0.265

46.85

50

5.01

0.11

0.265

48.55

100

9.63

0.17

0.265

95.35

100

9.79

0.14

0.265

96.65

200

19.38

0.27

0.265

193.85

200

19.35

0.35

0.265

194.35

250

24.02

0.33

0.265

240.85

250

24.43

0.28

0.265

244.45

47.7

96.0

194.1

242.65

Two replicate measurements have been performed for each standard concentration level. According to the column method
two pre-filled charcoal containers were used for each sample. Each container was filled with 50 mg of activated carbon.
The absolute value shows the chlorine value of each single container. The result of standard concentration is already blankcorrected. The average of the two replicates is given in bold numbers. For each standard recovery (shown in table 2) theobtained and the theoretical chlorine value should not differ more than 10 %; e.g. 90 % up to 110 %.

Linearity Test According to DIN EN ISO 9562 (Column Method)

Table 2: Standard recovery of p-chlorophenole
Min. value

Theoretical AOX value

Max. value

Obtained AOX value[µg/l][µg/l][µg/l][µg/l]

910119.745505547.7

9010011096.0180200220

194.1225250275242.7

The recovery rates, correlation coefficient, and slope of the linearity test fulfill the specifications of the DIN EN ISO 9562. Thisconfirms a correct adsorption behavior of the APU system and the excellent analytical performance of the analyzer.

Figure 1: Regression Linearity Test

The parameters of the linear regression are as follows: y = 0.9728x – 0.6565 with R2 = 1.
Conclusion
This linearity test shows that the multi X® 2500 AOX analyzer and the APU sample preparation unit provide accurate
standard recovery. This enables fast and reliable analysis for water quality monitoring. Due to the high automation level, theAPU sample preparation unit allows fast sample preparation without any manual handling. An overnight sample treatment
followed by analysis with multi X® 2500 during day time is extremely timesaving. The AOX analysis by column method is
cost-effective compared to the time intensive batch method.

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