BS ISO 5647:2019 pdf download – Paper and board – Determination of titanium dioxide content
8.1 Carry out the determination in duplicate. Weigh, to the nearest 0,01 g, two test portions of about 10 g of paper or board and place each test portion in a clean dish (6.1). Determine the moisture content of a separate test sample as prescribed in ISO 287. NOTE Select the amount of sample to be ashed, taking into account the anticipated titanium dioxide content. If a 10 g portion is ashed, the optimum range of the titanium dioxide content is from 1,5 g/kg to 8 g/kg (spectrophotometric procedure) or from 0,8 g/kg to 3,2 g/kg (flame atomic absorption spectrophotometric procedure).
8.2 Ash the test portion as described in ISO 2144. Allow the dish to cool in a desiccator. If the ash content of the sample is of interest, weigh the dish with its contents and calculate the amount of ash obtained.
8.3 Transfer the ash to a 250 ml glass beaker. Add 4 g of ammonium sulphate (5.3) and 10 ml of the sulphuric acid (5.2). Mix well and cover the beaker with a watch glass. Heat in a fume hood until fumes of sulphur trioxide are evolved and continue heating for 30 min. Allow the solution to cool to room temperature and then carefully add it, drop by drop, to about 50 ml of water contained in another beaker. Allow the solution to cool and decant it into a 100 ml volumetric flask. Rinse both beakers with water and add the rinsings to the flask. Finally, make up to the mark with water and mix well.
10.1 Preparation of the calibration graph
Into one of a series of six 50 ml volumetric flasks, place 25,0 ml of the reagent blank solution (Clause 9). Into the remaining five 50 ml volumetric flasks, transfer the quantities of the standard titanium dioxide solution (5.5), shown in Table 1. To each flask, add 7,5 ml of the hydrogen peroxide solution (5.6), and make up to the mark with the diluted sulphuric acid (5.4), and mix well.
For each solution, measure within 1 h of the preparation, the absorbance at 410 nm using 10 mm cells. Use the diluted sulphuric acid (5.4) in the reference cell. Construct a calibration graph by plotting the absorbance readings against the corresponding titanium dioxide concentrations. NOTE If an instrument is used equipped with a system for automatic calculation of data, the instructions in the paragraph above may be disregarded.
10.2 Preparation of the test solutions
If the ash solution (8.3) contains undissolved matter, filter it through a hardened ashless filter. Do not wash the filter. With a pipette, transfer 25,0 ml of the filtrate to a 50 ml volumetric flask. Add 15 ml of diluted sulphuric acid (5.4) and 7,5 ml of the hydrogen peroxide solution (5.6). Make up to the mark with the diluted sulphuric acid (5.4) and mix well.
10.3 Spectrophotometric determination
If the test solution (10.2) is turbid or coloured, prepare a reference solution by transferring 25 ml of the filtrate to a 50 ml volumetric flask and making it up to the mark with diluted sulphuric acid (5.4). If the test solution is clear and colourless, use the diluted sulphuric acid (5.4) in the reference cell. Within 1 h, measure the absorbance at 410 nm in 10 mm cells. Subtract the value obtained for the reagent blank (Clause 9) and read the titanium dioxide concentration from the calibration graph. Proceed to Clause 12.