ISO 15587-2 pdf download – Water quality – Digestion for thedetermination of selected elements inwater — Part 2: Nitric acid digestion

ISO 15587-2 pdf download – Water quality – Digestion for thedetermination of selected elements inwater — Part 2: Nitric acid digestion.
3 Term and definition
For the purposes of this part of ISO 15567. the following term and delinition applieS.
3.1
wet digestion
treatment with reactive liquid chemicals with the aim of brinng anatytes into solution so as to be suitable for subsequent analysis
NOTE The degree to which analyles are brought into solution suitable for subsequent analyses may depend on the principle ci the subsequent analysis Some analytical methods reqisre the element In solution independent of its chemal slate, others reqewe a specific valence or a specifIc ionic species, for instance hydride atomic specttometry, photometry and elecb’ochemical methods. For the letter, special atlention slxxdd be paid to the presence of chemically stable orgarlomelals .
4 Principle
The test portion is digested with nitric acid at a defined temperature. The temperature is at least the boiling point (103C at 101.3 kPa) and at most 175’C. At the boiling point (101,3 kPa), the minimum duration to release the digestible fraction is 120 men. The maximum duration is set at tour times the minimum duration. By convention, both the required minimum and maximum duration are assumed to halve with every 15 C increase in temperature above the boding point (see Figure 1)
After digestion the digest is clarified. if necessary.
5 Reagents
During analysis, use only reagents of recognized analytical grade that meet the purity requirements of the subsequent analysis. Verify their purity by performin9 a blank test
31 Water. complying with grade 1 of ISO 3696. Grade 2 may be used if it meets the purity requirements for the subsequent analyses.
5.2 NItric acid. c(HNO3) = 15.8 moLt. p= 1.4 kg/I.
Nitric acid is available both as p(HNO3) 1.40 kg/I. approximately 65% by mass arid p(HNO3) 1.42 kg)1, approximately 69 % by mass Both are suitable.
5.3 Antlfoaming agent, for instance n-dodecane (C12H26).
5.4 Ammonia solution, approximately 25 $ by mass.
6 Apparatus
6.1 Digestion vessel, temperature- and pressure-resistant and capable of containing the mixture of sample and digest solution.
If a closed vessel Is applied, its inner wall shall be inert and shall not release substances to the digest in excess of the purity requirements of the subsequent analyses.
6.2 Vapour recovery system, capable of recovering the evaporated digest during open digestion (e.g. reftux condenser) and designed to minimize losses.
Materials in contact with the vapour shall be Inert and shall meet the purity requirements of the subsequent analysis.
A.2 Reagents
Use the reagents as specifed n clause 5.
A.3 Apparatus
Usually. borosdicate glass is suitable for parts i’i contact with the digestion solution. If low concentrations of leachable elements are to be analysed, other construction materials may be used, instance quartz (high temperatures) and polyothene or poêypropene (low temperatL%es). Examples of leachable elements are B, Na, K and Al.
&3.1 Digestion vessel, made of borosilicate glass, and having a nominal volume of 100 ml.
A,3.2 Reflux condenser, a straight-through tipe, with conical ground-glass joints and made of bocosiicate glass. Water-cooled condensers with a minimum effective length of at least 200 mm have been found suitable.
A.3.3 Roughened glass beads, having a diameter of 2 mm to 3 mm and acid-washed [for instance with warm nltnc acid (52) diluted to 10 % by volume with grade I water (5.1)).
A,3.4 Temperature-controlled heating apparatus. capable of heating the contents of the digestion vessel to reflux temperature
A.3.5 Volumetric flask, made of borosilicate glass, and having a nominal volume of 100 ml &36 Graduated pipettes or dispensers
A.4 Sampling
Preserve and handle water samples in accordance with ISO 5667-3.
Take a test portion of 40 ml ± 0.2 ml from a well-shaken homogeneous water sample.
If suspended solids make it impossible to deliver a representative test pothon of a known volume, the test portion may be delivered otherwise, for instance by weighing. Calculate the volume from the determination of its mass, possibly corrected for the mass and density of solids. Report the uncertainty of the volume if it is higher than 0.2 ml.