Metrological characteristic of the pipette method (GOST 12536-2014) for determining soil granulometric composition

Abstract

The aim of the study. To calculate precision indicators (repeatability and reproducibility) and uncertainty in determining the granulometric (grain) composition of soils using the pipette method.   

Methods. Using the pipette method  the content of the following granulometric fractions was determined in soil samples: 0,1–0,05 mm, 0,05–0,01 mm, 0,01–0,005 mm, 0,005–0,002 mm, 0,002–0,001 mm, less than 0,01 mm, less than 0,001 mm. The determination of pH of the salt extract was carried out by potentiometric technique, and organic matter was measured photometrically. For each aliquot of the sample 16 single measurements were obtained for each soil fraction. Based on these data, precision indicators were assessed under conditions of intra-laboratory repeatability and reproducibility, uncertainty indicators were assessed as well.  

Main results. The following intralaboratory quality indicators were obtained for the method of determining the granulometric (grain) composition of soils using the pipette method:

1) The value of the intralaboratory repeatability indicator of analysis results (σ_r) ranged 0,4–1,8%.

2) The relative indicator of intralaboratory precision (σ_R) was within the 0,7–2,9% range.

3) Expanded uncertainty (U) for different soil fractions ranged from 0,9 to 3,9%.

Conclusions. The calculated metrological characteristics of determining the granulometric (grain) composition of soils using the pipette method facilitates the internal control of the measurements quality, promoting the quality and confidence in the laboratory work.