2.5.1.10 - Sea Water Samples
Most procedures described in this handbook are suitable for both freshwater and sea water. However, some special features have to be taken into account. The vast amount of salt in seawater (Na+, Ba2+, etc) limits the application of the distribution methods for sample preparation (e.g. RAD Disk filter methods, extraction chromatography) and acts additionally as carrier. Thus, scavenging with Fe(OH)3 is limited to those nuclides not being carried by inactive dissolved salt ions.
There is no influence for sediment samples, fish, etc because of the vast sample preparation procedures, which demand anyhow for inactive carriers in order to avoid adsorption effects. As corals and mussels consist mainly of CaCO3, adding acids like HCl can easily dissolve them.
A general procedure for the preconcentration of radionuclides followed by specific separation methods is given in figure 24. It combines MnO2, Fe(OH)3, Ca-oxalate and Ca-phosphate precipitation. After Cs is separated by co-precipitating as AMP, the supernatant is further used for Sr analysis.
MnO2, Fe(OH)3, Ca-oxalate and Ca-phosphates udes for preconcentration of radionuclides from water samples or aqueous solutions.
A comprehensive survey of sample preparation procedures for marine samples can be found in l’Annunziata [l’Annunziata 2012].
For direct water measurement, the high salt concentration of seawater does not allow large sample quantities to be homogeniously mixed with a cocktail (see fig. 25). Moreover, the correlation of solubility on temperature has to be taken into consideration (table 6).
Similar information can be found for Revvity's LS cocktail Ultima Gold LLT using sea water samples. A maximum of 5.5 mL sea water uptake per 10 mL of Ultima Gold LLT at 20 °C and 9 mL at 16 °C is reported. Therefore, if saline and ocean water samples have to be measured as aqueous gel, low temperatures are recommended e.g. by storage for cooling in the LS counter.
Materials and Equipment
Gelating cocktail with high salt range amount (Ultima Gold XR, LLT or others)
Procedure
5 mL of sea water sample (or more according to cocktail and temperature) are mixed with 15 mL gelating cocktail.
After storage in a cool place (best in a temperature controlled LS counter), the mixture is measured.
Evaluation
The gross α/β-activity concentration is calculated according to 2.2.1.1. using a chemical quench correction procedure (see chapter 2.1.1.), even though quenching should not be a severe issue as reported by different authors (see [L’Annunciata 2012]). When PSD is applied, interferences of the salt amount for the optimal PLI level have to be considered.
For detection limits see chapter 2.2.1.1.
L’Annunziata M.F. 2012: “Handbook of Radioactivity Analysis”, Chapter 15, 3rd Edition 2012, Elsevier
IAEA 2008: Training Course on Environmental Monitoring; Karlsruhe 2008, International Atomic Energy Agency, Course Material on CD
