ISO 15587-2:2002 pdf download
ISO 15587-2:2002 pdf download.Water quality -Digestion for the
determination of selected elements inwater — Part 2: Nitric acid digestion.
6.3 Volatile species trap, in an open digestion system capable of trapping one or more volatile measurement species which may pass through the vapour recovery system (6.2).
This trap may comprise condensation equipment or equipment to absorb these species in nitric acid or aqua regia. Materials in contact with the vapour shall be inert and shall meet the purity requirements of the subsequent analysis.
6.6 Anti-bumping granules or roughened glass beads, having a diameter of 2 mm to 3 mm and acid-washed [for instance with warm nitric acid (5.2) diluted to 10 % by volume with water (5.1)].
6.7 Volumetric flask, usually of nominal capacity 50 ml or 100 ml.
6.8 Graduated pipettes or dispensers.
7 Sampling
Handle and preserve the water sample in accordance with ISO 5667-3.
The digestion procedure (see clause 8) is based on a test portion of 25,0 ml ± 0,1 ml taken from a well-shaken homogeneous water sample. Any test portion larger than 20 ml is allowed, provided that the volume of nitric acid is modified proportionally.
If suspended solids make it impossible to deliver a representative test portion of a known volume, deliver the test portion 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 0,1 ml for a volume of 25 ml.
8 Procedure
8.1 Preparation
Carefully acid-wash digestion equipment in contact with the digestion solution and volumetric ware [for instance with warm nitric acid (5.2) diluted to 10% by volume with water (5.1)] and rinse with water (5.1).
Add a test portion of 25,0 ml ± 0,1 ml to the digestion vessel (6.1).
Add 6,25 ml ± 0,1 ml of nitric acid (5.2). The boiling point of this mixture is equal to 103 °C.
If excessive foaming occurs, add one or more drops of antifoaming agent (5.3).
Swirl and allow the mixture to stand until any visible reaction has stopped.
If the digestion vessel is of the open type, proceed with 8.2. If not, proceed with 8.3.
Examples of digestion in an open system are given in annexes A and B.
8.2 Digestion in an open system
Connect the digestion vessel (6.1) to the vapour recovery system (6.2).
Connect the volatile species trap (6.3), so as to prevent volatile measurement species from passing through the vapour recovery system.
Place the digestion vessel in the heating device (6.4).
Increase the temperature to the boiling point.
Maintain boiling for at least 120 mm. As the boiling point decreases with altitude add 20 mm to the minimum duration for every 1 000 m above sea level. The maximum allowed duration equals four times the minimum duration.
Once the digestion period is completed, allow the digestion vessel to cool. If silver is an analyte, add 30 ml of ammonia solution (5.4) to the digestion vessel immediately after cooling.
If the volatile species trap (6.3) is used, add the contents to the digestion vessel.
Rinse the trap and/or the condenser with water (5.1), for instance 10 ml, and decant. Collect the water in the digestion vessel.
Dismount the digestion vessel from the digestion system.
Examples of digestion in an open system are given in annexes A and B.
8.3 Digestion in a closed system
Cap the digestion vessel (6.1) and weigh it.
Connect the digestion vessel to or place it in the heating device (6.4).
Increase the temperature of the digestion mixture slowly to temperature Td between the boiling point (103 °C at 101,3 kPa)and 175 °C.
Maintain digestion for a period & of at least 10 mm and at most 480 mm (101,3 kPa).
Given the digestion period &, expressed in minutes, the digestion temperature Td, expressed in degrees Celsius,
shall meet the following condition:
NOTE I Boundary conditions in equation (I) reflect the assumption of clause 4 on release kinetics and duration time.
The permitted domain of digestion temperature and duration is shown in Figure 1.
Once the digestion period is completed, allow the digestion vessel to cool. Weigh the digestion vessel and accept the digest if the mass loss is consistent with the mass loss of a well documented reference material known to lead to acceptable results.
Uncap and vent the digestion vessel in a fume hood.
If silver is an analyte, add 30 ml of ammonia solution (5.4) to the digestion vessel immediately after cooling.
Examples of digestion in a closed system are given in annexes C and D.
NOTE 2 Several microwave units control power rather than temperature. A procedure to establish the relationship between microwave power and temperature is given in C.6.