ISO 09698:2010 pdf free download – Water quality一Determination of tritium activity concentration – -Liquid scintillation counting method.
B.2.2.3 Distillation equipment, consisting of the following.
B.2.2.3.1 Distillation flask, with a capacity of 500 ml.
B.2.2.3.2 Splash head.
B.2.2.3.3 Distillation column, length 40 cm.
B.2.2.3.4 Condenser.
B.2.2.3.5 Adapter, bent type.
The equipment shall be dried before use.
B.2.2.3.6 Borosilicate glass or polyethylene bottles, of capacity about 100 ml.
B.3 Distillation
Place the test sample in the distillation equipment. Add a quantity of oxidant agent to convert iodine into iodide and enough alkaline agent to make the sample alkaline. Add porous porcelain or carborundum or glass beads in order to facilitate a homogeneous and smooth boiling.
Assemble the distillation equipment and start the distillation process.
Distil, discard the first part of distillate, and collect about half of the middle fraction in a clean and dry bottle.
Discard the residue in the flask.
B.3.1 Sample preparation
Place an aliquot of the water sample (100 ml to 250 ml) in the distillation flask. If a suspended matter is observed, it can be eliminated by filtering.
All the employed material has to be well dried.
The initial sample should not be acidified and should be kept in an hermetic glass container.
B.3.1.1 Oxidation in alkaline medium
Add the necessary reagents to obtain an adequate medium for the oxidation. The following can be used:
a) 0,1 g of potassium permanganate and 0,5 g of sodium hydroxide; or
b) 0,25 g of sodium thiosulfate and 0,50 g of sodium carbonate.
NOTE If the above reagents are not added, the possible presence of organic matter and/or volatile isotopes in the sample can affect the results.
B.3.1 .2 HomogenizatIon
Add porous porcelain or carborundum or glass beads in order to facilitate a homogeneous and smooth boiling.
B.3.2 Discard
The first millilitre of distilled water (10 % to 30 % of the initial aliquot) can be kept for isotopic control if needed.
C.1 Principle
A tritium standard solution can be added in sample. This method is recommended for samples with high
chemical and/or colour quenching value to assess the counting efficiency.
C.2 Sample preparation
For each water sample, fill, preferably in dimmed light, two counting vials, with a volume “1 in millilitres (see note) of scintillation solution followed by a volume V= 20 — 171, in millilitres, of sample. Identify separately the two counting vials, for example N and S. Add, using a pipette (for example, 100 p1), a known quantity of a tritium standard solution to one of these counting vials, labelled S. The added activity is called A. Fill, in the same way, the appropriate number, as required by the counting procedure, of background counting vials with a volume in millilitres, of scintillation solution followed by a volume V= 20 — in millilitres, of blank water. The total inaccuracy of each addition should be less than or equal to I %. Mark the lids of these counting vials, for example with the designations Ni, S1, N2, 2’ N3, S3, etc. Shake the counting vials thoroughly and uniformly, for example using a shaking machine.
The above-mentioned operations should take place in dimmed light (preferably light from an incandescent source or red light). Avoid direct sunlight or fluorescent light in view of the possible interference by luminescence in some batches of counting vials.
For routine control determinations of similar samples, a small difference in the counting efficiency between samples may be experienced. If this occurs, it would be acceptable to determine a mean counting efficiency from an internal standard in addition to the two to three samples of the group or to use the efficiency indicated by a calibrated external standard technique.
The use of an internal standard is recommended when polyethylene counting vials are used. When using an external standard in polyethylene counting vials, interference may arise because the counting rate of the external standard changes as a function of time, on account of the loss of components of the scintillation solution by diffusion into the wall of the counting vial. The effects are considerably smaller at lower temperatures (4 °C to 10 °C) than at higher temperatures (e.g. 20 °C to 25 °C).