This recommendation describes a gravimetric method for the determination of non-volatile oil and grease in all types of water. With the method, loss of varying amounts of substances with a boiling point below approx. 1 50 °C. With the method, either the total content of non-volatile oil and fat or these substance groups are determined separately. The minimum content that can be determined by the method is 2 mg/l, (see 7.1). The solubility of oil and fat in water varies from well below 1 mg/l up to several mg/l. Samples containing dispersed oil (the oil is finely divided using a surfactant) may contain more than 100 mg/l. In order for this recommendation to be used with good accuracy and precision, it is required that the organic substances sought are evenly distributed in the sample. Provided that the entire amount of sample taken is used for the analysis, an acceptable result can be obtained, even if the oil or fat is not evenly distributed in the sample. To determine the average concentration over a longer period, random samples are often taken and mixed together to form a mixed sample. This method is unsuitable for oil and fat determination because oil and fat easily adhere to the sampling apparatus. Oil and fat can only be determined by random samples. The present method is not specific for oil and fat, but these substance groups are defined according to the method. Oil and fat can be divided physico-chemically into two groups: non-polar and polar substances. The non-polar group includes i.a. the majority of the substances included in mineral oil, certain organic solvents, the mineral oil part in lubricating grease, petroleum-based waxes, etc. The polar group includes, among other things, animal and vegetable fats and fatty oils (rapeseed oil etc.), the saponified part of lubricating fat, milk fat, glycols and many organic solvents (alcohols, ketones etc.), humic substances, certain components of mineral oil (high molecular aromatic compounds) and surfactants. It should be noted that in order to be able to say something qualitative about the substances which are determined according to the method (eg whether it is fat or not) the result of the analysis must be put in relation to the origin of the sample.
DS/R 208:1980 history
1980DS/R 208:1980 Determination of oil and gresse in water. Gravimetric