Atomic Absorption Spectrometry (AAS) for Measuring Caesium in Tap Water and Soil

There has been considerable research on technologies that can efficiently remove radioactive isotopes of caesium (chiefly Cs-137) from water and soil. The study and evaluation of these removal technologies can be conducted using Cs-133, an easy-to-handle, stable substance, yet chemically similar to Cs-137.

It is possible to analyze caesium using atomic absorption spectrometry and ICP emission spectroscopy, which are therefore effective for researching and evaluating the various removal technologies. Examples of analysis of caesium in tap water and soil using the AA-7000 atomic absorption spectrophotometer are introduced in this article.

Sample Preparation

The tap water was used without doing any pretreatment. As for the soil, 1g of sample was accurately weighed into a beaker and after adding aqua regia and heating on a hot plate to decompose, the mixture was filtered through 5B filter paper, and 50mL of the filtrate was used as the process solution.

Analytical Method and Conditions

Water

The furnace technique (electric furnace ETAAS) was used to conduct measurement by the calibration curve method. The measurement samples included tap water and tap water spiked with 1µg/L caesium. Furthermore, a solution containing a mixture of Na, Ca, and Mg was added as an interference suppression agent.

Soil

The flame and furnace techniques were used to measure the soil by the calibration curve method. With the flame technique, the process solution and standard solution were measured after sodium was added as an interference suppression agent to both at a final concentration of approximately 0.1%.

Measurement was done after diluting the process solution by a factor of 10 with the furnace technique. A solution containing a mixture of Na, Ca, and Mg was added as an interference suppression agent. Table 1 shows the main spectrometer parameters and the main atomization conditions using the furnace and flame techniques are shown in Table 2 and 3, respectively.

Table 1. Optics Parameters

Analysis wavelength 852.1nm
Slit width 0.7nm
Current value 16mA
Lighting mode NON-BGC


Table 2. Atomization Parameters by ETAAS

Temperature program Temperature °C Time sec Mode Sensitivity Gas Flowrate L/min
1
2
3
4
5
6
120
250
600
600
600
2000
20
10
10
10
3
3
Ramp
Ramp
Ramp
Step
Step
Step
Reguler
Reguler
Reguler
Reguler
High
High
0.1
0.1
0.2
0.2
0.0
0.0
7 2500 2 Step Regular 0.5
Atomization stage: 6
Tube type Pyrolytic graphite tube
Interference suppressant Mixture of Na, Ca, Mg
Sample injection volume

20µL (tap water), 10µL (soil)



Table 3. Atomization Parameters by Flame AAS

Flame type Air-C2H2
Burner height 7mm
Interference suppressant Na 0.1%


Measurement Results

Tap Water

Figures 1 and 2 show the calibration curve and peak profiles. The measurement results for the unspiked and spiked samples are shown in Table 4. Caesium was not detected in the unspiked tap water, and excellent recovery was obtained for the caesium-spiked tap water.

Calibration Curve by ETAAS (Tap Water)

Figure 1. Calibration Curve by ETAAS (Tap Water)

Peak Profiles of Standard Solution and Tap Water Samples by ETAAS

Figure 2. Peak Profiles of Standard Solution and Tap Water Samples by ETAAS

Table 4. Measurement Results for Tap Water by ETAAS

Tap Water (Unspiked) Tap Water (Spiked)
Spike Recovery < 0.2µg/L
0.97µg/L 97%


Soil

Figure 3 shows the calibration curve obtained by the flame technique. Figures 4 and 5 show the calibration curve obtained by the furnace technique, and the peak profiles, respectively. The measurement results for the soil sample are shown in Table 5. The lower limit of quantitation was 3µg/g (ppm) by the flame technique and 0.2µg/g (ppm) by the furnace technique, converted to the concentration in solid soil.

The flame technique offers rapid analysis, while high sensitivity measurement is possible with the furnace technique, thus permitting selection of the type of analysis depending on the purpose.

The AA-7000 permits automatic switching between the flame and furnace measurement techniques, and because troublesome adjustment of the optical axis is eliminated, switching between atomization methods is quickly accomplished. Moreover, space-saving is achieved by the back-to-front placement of the two atomizers.

Calibration Curve by Flame AAS (Soil)

Figure 3. Calibration Curve by Flame AAS (Soil)

Table 5. Measurement Results for Soil by Flame AAS and ETAAS

Flame Technique Furnace Technique
3µg/g
3.1µg/g

Calibration Curve by ETAAS (Soil)

Figure 4. Calibration Curve by ETAAS (Soil)

Peak Profiles of Standard Solution and Soil Sample by ETAAS

Figure 5. Peak Profiles of Standard Solution and Soil Sample by ETAAS

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.

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