ISO 9174 pdf download.Water quality — Determination of chromium — Atomic absorption spectrometric methods
1 Scope
This International Standard specifies two methods for the determination of chromium in water by atomic absorption spectrometry. The two methods are covered in separate clauses as follows: – Clause 3: Determination of chromium by flame atomic absorption spectrometry; – Clause 4: Determination of chromium by electrothermal atomization atomic absorption spectrometry. Clause 3 is applicable to the analysis of water and waste water when the concentration range is between 0,5 mg/l and 20 mg/l of chromium. When the concentration is below 0,5 mg/l, the determination can be carried out after carefully evaporating an acidified sample to small volume, taking care to avoid the formation of a precipitate. NOTE The use of evaporation will increase the effect of interfering substances and therefore for concentrations below 0,1 mg/l the method in clause 4 is given. Clause 4 is applicable to the analysis of water and waste water when the concentration range is between 5 mg/l and 1 00 mg/l of chromium by injecting a sample volume of 20 ml. It is applicable to the determination of higher concentrations by using a smaller sample volume.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 5667-2 : 1 991 , Water quality — Sampling — Part 2: Guidance on sampling techniques . ISO 5667-3 : 1 994, Water quality — Sampling — Part 3: Guidance on the preservation and handling of samples.
3 Determination of chromium by flame atomic absorption spectrometry
3.1 Principle The method is based on the atomic absorption spectrometric measurement of the chromium content of the acidified sample in a nitrous oxide/acetylene flame. Measurement at a wavelength of 357,9 nm. Addition of lanthanum salt to reduce matrix interferences is necessary. 3.2 Reagents All reagents shall be of recognized analytical grade. Use deionized water or water distilled from an all-glass apparatus. The water used for blank tests and for preparing reagents and standard solutions shall have a chromium content that is negligible compared with the smallest concentrations to be determined in the samples.Store this solution in either polyethene or borosilicate glass containers at room temperature. The solution is stable at room temperature for about year if it is stored in the dark and at a pH between 1 and 2. NOTE Chromium stock solutions are commercially available. 3.2.6.2 Chromium, standard solution, with r(Cr) = 50 mg/l. Introduce 50,00 ml ± 0,01 ml of the chromium stock solution (see 3.2.6.1) into a 1 000 ml volumetric flask. Add 1 ml of nitric acid (see 3.2.2), make up to the mark with water and mix. This solution is stable for at least 1 month. 3.3 Apparatus 3.3.1 Atomic absorption spectrometer, equipped with a chromium hollow cathode lamp and a nitrous oxide/acetylene burner, and operated in accordance with the manufacturer’s instructions. It is essential that the manufacturer’s safety recommendations are strictly observed when using the nitrous oxide/acetylene flame. 3.3.2 Glassware. Before use carefully soak all glassware for about 24 h in nitric acid (see 3.2.3), then rinse thoroughly with water. If low concentrations are expected (for example in ground water), the glassware should be kept under nitric acid (see 3.2.3) until use. Do not use glassware which has been cleaned with chromic acid. 3.3.3 Membrane filters, of nominal pore diameter 0,45 mm, washed thoroughly with nitric acid (see 3.2.3) and rinsed with water (see 3.2).