AOCS Tb 1a-64-2009

INDUSTRIAL OILS AND DERIVATIVES

APPARATUS

1. Electric hot plate—the surface should have a high polish, otherwise cover with a heat-resistant pad to prevent wear on the

moisture dish.

2. Glass beakers—100–150 mL, or other similar and convenient dish.

3. Desiccator—containing an efficient desiccant. Calcium chloride is not satisfactory. See AOCS Specification H 9-87. PREPARATION OF TEST SAMPLE

1. Since water tends to settle in test samples that have been softened or melted, care must be taken to mix the test samples

thoroughly so as to distribute the water uniformly.

PROCEDURE

1. Weigh accurately 5–20 g of well-mixed test sample into a tared beaker which has been previously dried and cooled in a

desiccator.

2. Heat the test sample on a hot plate, rotating the beaker gently by hand to avoid splattering which will result from a rapid

moisture loss.

3. The approach of the end point may be judged by the absence of foam. Another good method of judging the end point is to

place a clean, dry watch glass on top of the beaker. The evaluation of steam is indicated by condensation on the watch glass.

The temperature of the test sample is at no time allowed to exceed 130°C, except at the end of the test.

4. When the apparent end point has been reached, heat momentarily to the point of incipient smoking, but use caution not to

overheat.

5. Cool to room temperature in a desiccator and weigh.

CALCULATIONS

1. Moisture and volatile matter, % =

loss in mass

mass of test portion,g

×100

PRECISION

1. Repeatability—The absolute difference between two independent single test results, obtained with the same method on

identical test material in the same laboratory by the same operator using the same equipment within short intervals of time, should not be greater than the repeatability limit (r) as calculated from the formulas in Table 1.

2. Reproducibility—The absolute difference between two single test results, obtained with the same method on identical test

material in different laboratories with different operators using different equipment, should not be greater than the repro-ducibility limit (R) as calculated from the formulas in Table 1.

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INDUSTRIAL OILS AND DERIVATIVES

Tb 1a-64 ? Moisture and Volatile Matter Fatty Acids Hot Plate Method

Table 1

The interlaboratory study carried out by Lincoln D. Metcalfe

in 1975, in which eight laboratories participated, each

obtaining four test results for each test portion analyzed by

AOCS Official Method Tb 1a-64, gave the statistical results

(evaluated in accordance with ISO 5725-1986) summarized

in the table.

Test Sample a

A B

Number of

labs after

removal of

outliers 8 8

n 31 30

Outliers 1 2

Mean, %b0.03 0.14

Repeatability, S r0.02 0.02

RSD r51.70 16.25

r (2.8 × S r) 0.056 0.056

Reproducibility, S R0.03 0.04

RSD R80.81 24.80

R (2.8 × S R) 0.084 0.112

a Key to test samples: A, industrial tallow; B, corn oil.

b Mean value for moisture, %.

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