The entire spectrum of analytical methods used for the chemical testing of paper ranges from gravimetric methods to spectroscopy, electrochemical and enzymatic methods, as well as sensoric tests on taste and odour and microbiological tests.
Most of the testing methods to determine the composition are destructive. The components to be determined must be extracted with water or organic solvents. For example, the resin content of paper is determined gravimetrically in the extrac¬tion residue by using an organic solvent as an extracting agent.
The inorganic fillers contained in paper are determined as residue on ignition (ash content). In accordance with ISO 2144 (1997), the sample is ignited at 900 °C until no change in weight is observed. The ignition residue is then determined gravimetrically and expressed as a percentage of the original weight of the sample.
Other ignition temperatures are used for chemical pulp (575 °C) and filter papers (800 °C) (DIN 54 370 (1999). Determination of CaCO3 is calculated from the differ¬ence in weight loss between 575 °C and 900 °C (CO2). X-ray microanalysis is em¬ployed for the quantitative determination of the types and amounts of fillers.
Elements such as calcium, magnesium, and metals in trace amounts can be analyzed by atomic absorption spectroscopy. For the determination of organic substances in paper extracts, IR spectrophotometric and chromatographic methods are applied,
e. g., gas chromatography for volatile components and high performance liquid chromatography for thermally sensitive constituents.
Other chromatographic methods are used for the determination of chlorides, nitrates, and sulfates, or for the differentiation and characterization of dyes and optical brighteners.
Apart from the analytical methods mentioned above, the sum parameters are of special importance. These include the ash content, pH (ISO 6588, 2003), electrical conductivity of aqueous extracts (ISO 6587, 1992), and the resin content of paper.
Apart from the ISO standards mentioned above, other standards for chemical testing of paper are, e. g., the ZELLCHEMING, SCAN, and TAPPI test methods.