THE IMPORTANCE OF SUBSAMPLE PREPARATION PRACTICES IN THE ANALYSIS OF CRUDE OILS

Abstract

There have been many subsample preparation practices proposed to reduce sources of error in analyses of crude oils. Optimal subsample preparation allows keeping the degree of representativity of the final aliquot going into the laboratory analyzer. The objective of this work was to discuss some experiences in order to understand the importance of sampling practices to obtain representative subsamples of crude oils and petroleum products, and measurements with minimized uncertainty whenever possible. Specific practices, whose effectiveness was tested by experiments, are discussed in this work. The analysis of variance showed that the subsamples should not be used in vapor pressure tests unless in case of interlaboratory crosscheck, and have to be considered as the first test from the bottle subsample. Sometimes long periods of crude oils samples storage are necessary for a complete evaluation, but because of the effect of this storage time it was observed a trend in the reducing of acidity and sulfur content.