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Analyses of paper, pulp and lyes

 
   
 
DRYING
Pulp and chip samples consist to a large extent of water. Variations in water content cause variations in element concentrations. These are eliminated if the content is expressed as dry sample content, e.g. mg/kg DW (dry matter, dry matter). Samples are dried at 105°C and the dry matter content is determined from the weight loss.

Samples intended for determination of mercury are dried at 50°C before analysis, or analysed without prior drying, due to the volatility of mercury. If contents are to be expressed in dry weight, the dry matter content is determined separately (at 105°C) and the concentrations recalculated to dry weight.

OXIDATION
Like other organic material, pulp and chip samples are characterised by mainly consisting of compounds that are dominated by carbon, hydrogen and oxygen. Prior to determination of e.g. metals, this main component is usually eliminated by oxidation to carbon dioxide and water. This is achieved by heating the dry sample in the presence of oxygen (dry ashing) in analytical packages MF-3. MF-4 and MF-5. Metals and other elements remaining in the sample after oxidation constitute the inorganic residue (ash) which is then analysed in digested form.

DIGESTION
Acid digestion is carried out in sealed teflon containers in a microwave system using nitric acid in the MF-6 package, and a mixture of nitric acid and hydrogen peroxide in packages MF-1, MF-2 and MF-5. Use of sealed vessels prevents the loss of volatile components. In MF-3, a special method is used (see the description of this package)

Acid digestion is used as a complement in packages MF-5 and MF-6 because certain elements are lost when exposed to the fusion process (see below).

 
FUSION
In analytical packages MF-4 - MF-7, a fusion method is used, either for all or for part of the elements. In packages MF-6 - MF-7, samples are dried before fusion. In packages MF-4 and MF-5, samples are ashed prior to fusion. The sample is ignited in a carbon crucible together with a flux (lithium metaborate) at 1000°C. The "bead" which forms on cooling is then dissolved in dilute nitric acid.

LYES
Residual lyes are by-products from the manufacture of chemical pulp. It contains a mixture of lignin and chemicals which remains after removal of the cellulose fibres in the wood. Like most other sample types, lyes are analyzed in the form of dilute aqueous solutions. So-called black lyes are often relatively hard to dissolve, but good results have been obtained by means of the special microwave digestion technique that is applied by Analytica to these samples.

LOSS ON IGNITION
LOI (Loss On Ignition) is determined by ignition at 1000°C of part of the sample. The resulting weight reduction, LOI, usually reflects the content of organic material in the sample. However, some inorganic components may be driven off during ignition (such as carbon dioxide from carbonates) and contribute to the LOI.
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