Application Note · multi X® 2500

Determination of Adsorbable Organic Halogens
in Highly Saline Water Samples after Solid Phase
Extraction (SPE-AOX)

Challenge
Measuring the AOX content
properly in the presence of morethan > 1g/L inorganic bound Cl.

Solution
Using the smart solid phaseextraction autosampler APU 28
SPE offers a fast, effortless, andfully automated SPE-AOX sample
preparation.

Introduction
An easy and fully automated method for the correct determination of AOX
contents in the presence of extremely high (c > 1 g/L) quantities of inorganic
halides is often needed when analyzing marine water samples, industrial
wastewater and brine applications (SPE-AOX according to ISO 9562:2004). The
presence of high amounts of inorganic halogen compounds negativetely affects
the determination of AOX. When such samples are analyzed directly by meansof common AOX methods (adsorption on charcoal and combustion), results will
be falsified and too high. To avoid this, the interfering compounds have to beremoved before the adsorption. Solid phase extraction (SPE) has proven to be themost efficient and easy method to do this.
For the measurement, the samples were enriched on SPE cartridges. To achieve aneasy and effective segregation between organic and inorganic matter, a polymer
resin was used for separation. The resin captures only the organic halogen
compounds, while letting the inorganic material pass through. The AOX was theneluted with methanol and diluted in ultrapure water. This mixture was adsorbed
on prefilled charcoal columns, followed by a final washing process to ensure acomplete separation of inorganic and organic halogen compounds.

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Determination of Adsorbable Organic Halogens in Highly Saline Water Samples after SPE

Since this is a time-consuming process, laboratories facing increasing time and work pressure strive to facilitate the workflow.
The sample preparation unit APU 28 SPE enables fast and unattended, fully automated preparation of SPE-AOX samples,
thus highly shortening processing time. Combined with the multi X® 2500 AOX analyzer, the APU 28 SPE ensures fast, precise and reliable results, which are mandatory for laboratories.
Materials and Methods
Samples and Reagents■■ Water samples with high load of inorganic chlorides (> 1 g/L)■■ Standard solution: 100 µg/L p-chlorophenol■■ NaNo3 washing solution■■ 0.01 M HCl
As micro coulometric Cl determination is an absolute method, no calibration was needed.
Instrumentation
The samples were prepared automatically using an APU 28 SPE system. For the combustion of samples, a multi X® 2500
analyzer in vertical operation mode with AOX combustion tube and the standard sensitive cell was used. Sample introduction
was carried out fully automated by means of the autoX 36 autosampler.
Method parameters
The parameter and method settings for the combustion process are summarized in the following table.
Table 1: Settings for sample preparation (ISO 9562:2004)
Parameter APU 28 SPE
Sample Preparation

Specification

Sample volume (SPE cartridge)

100 mL

Sample volume (AOX column)

100 mL

Washing volume (SPE and AOX step)

25 mL

Methanol volume (conditioning)

10 mL

Methanol volume (elution)

5 mL

Adsorption speed

3 mL/minTable 2: Settings for AOX determination (acc. ISO 9562:2004)
Parameter multi X® 2500
AOX determination

Specification

Furnace temperature> 950 °C

Titration delay

approx. 240 s

Max. titration time

1200 sCell temperature

18–35 °C

Quality oxidation/carrier gas

Oxygen 4.5

Working range coloumetric cell (AOX)

1 µg–100 µg Cl abs.

Working range chlorine module

10 ng–1000 µg Cl abs.

Automation

autoX 36 or autoX 112

Determination of Adsorbable Organic Halogens in Highly Saline Water Samples after SPE

Method Parameters
Standard method settings from the method library were applied. The parameter settings for the combustion process and thesample transfer are summarized in table 1. The evaluation parameters for the detection of chlorine are given in table 2.
Results and Discussion
The column method was used according to ISO 9562:2004. Before being enriched on activated carbon, the sample
underwent an SPE process to separate inorganic from organic bound halides (Figure 1). Figure 2 shows the APU 28 SPE
during the automatic elution of the SPE cartridges with methanol. The SPE procedure, which works without any manualintervention, and the adsorption step itself were performed automatically by the APU 28 SPE sample preparation unit.

Figure 1: SPE process, which takes place in SPE cartridges

Figure 2: APU 28 SPE sample rack

The treated water samples ran through two adsorption columns (prefilled charcoal containers) with a flow rate of 3 mL/min.
The charcoal-filled containers were then rinsed with 25 mL of nitrate washing solution to remove the inorganic salt load at
the same flow rate.
The prepared charcoal containers were placed into the autoX 36’s sample plate. This sampling system automaticallyintroduces the loaded columns into the vertically arranged open AOX combustion tube. The furnace temperature of 950
degrees Celsius was chosen in compliance with DIN EN ISO 9562:2004. The organic halogen compounds were convertedin the presence of a surplus of oxygen to HCl gas. After sufficient drying with concentrated sulphuric acid, the HCl gas wastransferred into the sensitive cell. The cell has a wide working range from 1 µg to 100 µg chlorine absolute. The chlorine
detection was carried out by means of microcoulometric titration. Proper operation of the analysis system was confirmed byanalysis of a commercial standard solution (4-chloro-phenole in water).

Table 2: Settings for AOX determination (acc. ISO 9562:2004)
Sample ID

Adsorption
Volume [mL]

Dilution ratio

abs. Cl valueColumn 1 [µg]abs. Cl value
Column 2 [µg]Blank value[µg abs.]

Result[µg/L]

Standard

100

1:1

10.5

0.23

0.3

104.3

1100

50:100

1.51

0.18

0.3

27.8

2

100

20:100

2.67

0.62

0.3

149.5

3

50

50:100

0.64

0.51

0.3

34.0

Standard

100

1:1

9.67

0.52

0.3

9.89

3

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Table 4: Signal profile of a para-chloro-phenole standard solution and of sample 2Sample ID

Specification

Standard 100 µg/L
p-chloro-phenoleSample 2Conclusion
The APU 28 SPE system is fully suited for the automatic preparation of AOX and SPE-AOX samples. Due to its workflow
automation, including all adsorption and rinsing steps, the APU 28 SPE is an ideal partner for high sample throughput. Incombination with its continuous flow principle, a fast, efficient and accurate analysis is achieved. The multi X® 2500 is an
excellent instrument for AOX (EOX, POX, and TX/TOX) determination in all kinds of water, sludge, and soil samples, as well asother organic liquids and solids (e.g., used oil). Due to its enormous flexibility, changing between different parameters is fastand easy. This makes the multi X® 2500 very efficient, saving valuable time and costs.

This document is true and correct at the time of publication; the information within is subject to change. Other documents may supersede this document, including technical modifications andcorrections.

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