AS NZS 1301.421:2020 pdf free.Method of test for pulp and paper Method 421: Paper, board and pulps一 Determination of pH of aqueous extracts一Cold extraction.
8.1 Weighing
Weigh 2,0 g ± 0,1 g of air-dry sample (6.2) in a 250 ml flask (5.1).
NOTE Since the amount of sample is not critical, there is no need to determine the dry matter content to adjust for minor differences in moisture content.
8.2 Extraction
Add 100 ml of water (5.1) to the flask (6.1) containing the sample pieces. Check that all pieces are soaked. Seal the flask with its ground-glass stopper and leave it to stand for 1 h at a temperature between 20 °C and 25 °C. Shake the flask at least once during this time.
Filter the extract through a coarse, fritted glass filter into a small beaker (6.1). Immediately add 2 ml of potassium chloride solution (5.3) and continue with the measurement.
8.3 Determination of pH
Operate the pH-meter in accordance with the manufacturer’s instruction. Wash the electrodes with water (5.1); allow the water to drain from the electrodes, but do not wipe them. Calibrate the pH-meter (5.2), at a temperature between 20 °C and 25 °C, with two different buffer solutions (5.2) having pH- values such that the pH of the extract is between the pH-values of the buffer solutions. The first buffer solution shall be chosen so that the pH-value of the buffer solution is in the same region as the electric zero point of the pH-meter (usually = 7). The reading for the second buffer solution should agree with its correct value to within 0,1 pH-unit.
If the pH-meter fails to show the correct pH-value for the second buffer solution, consult the manufacturer’s manual. A deviation of, or exceeding, 0,2 pH-units, rounded to the nearest 0,1 pH unit, indicates a faulty electrode. In addition, a slow but continuous increase or decrease in the reading indicates a faulty electrode.
After calibration, rinse the electrodes several times with water (5.1) and once in a small quantity of the extract. Check that the temperature of the extract is between 20 °C and 25 °C. Immerse the electrodes in the extract. Record the pH when there is no measurable drift, within 30 s.
Before measuring the next sample, rinse the electrodes carefully with water (5.1) to remove any traces of sample or buffer solution.
At the end of a series of measurements, check the electrodes with the same buffer solutions. The results for both solutions should agree with their correct value to within 0,1 pH unit. Otherwise repeat the procedure in 8.3.
9 Calculation
Calculate the mean of the duplicate determinations.
Report the pH-value to the nearest 0,1 pH-unit. The individual results should not differ by more than 0,2 pH-unit; if they do, repeat the determination with two additional extracts, and report the mean and the range of all measurements.AS NZS 1301.421 pdf download.