BS 6603:1985 download.British Standard Method for Determination of castor oil glycerides content of raw, natural rubber by thin layer chromatography [ISO title: Rubber, raw, natural — Determination of castor oil content — Part 1 : Determination of castor oil glycerides content — Thin layer chromatographic method].
0 Introduction
Certain grades of natural rubber are treated with castor oil to fadlitate crumbing of the rubber during production. BS 6603 is intended to facilitate estimation of the amount of castor oil remaining in the rubber.
The principal constituent of castor oil, making up about 80 to 85 % (‘n/In), Is the tiiglycetide of ricinoleic acid. This glyceride may partly hydrolyse to ricinoleic acid and glycerol.
1 Scope and field of application
This part of ISO 6225 specifies a thin layer chromatogrephic method for the determination of the castor oil and castor oil glycerides content of raw rubber.
It is applicable to all grades of natural rubber.
The lower limit of detection is approximately 0,05 % of castor oil glycerides.
NOTE — ISO 622.5/2 specifies a method for the determiriaton of total ridnoteic acid content of raw rubber
2 References
ISO 1407, Rubber — Determination of solvent extract.
ISO 1795, Raw rubber In bales — Sampling.
ISO 1796, Rubber, raw — Sample preparation.
ISO 6225/2. Rubber, raw, natural — Determination of castor oil content — Part 2: Detei’minatibn of total nc/no/a/c acid content — Gas chromatographic method.
3 Principle
Extraction of a test portion with acetone, separation of the castor oil glycerides from other extractables by thin layer
chromatography, development of the castor oil glycerides spots with phosphornolybdic acid or anisaldehyde, and visual or spectrometric evaluation.
4 Reagents
All recognized health and safety precautions shall be taken when carrying out the procedure specified In this part of ISO 6225.
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity.
4.1 Silica gel, TLC grade.
4.2 Developing solvent.
Prepare a mixture of light petroleum (boiling range 40 to 60 °C). diethyl ether and glacial acetic acid, in the proportions, by volume, of 50 : 50: 1, respectively.
4.3 Spray reagents.
4.3.1 Phosphomolybdlc acid, ethanolic solution. Dissolve 15 g of phosphoniolybdic acid in 100 cm3 of 95 %
(V/V) ethanol.
4.3.2 Anisaldehyde. solution.
Mix 10 cm3 of ethanol, 0,5 cm3 of sulfuric acid
= 184 Mg/rn3) and 0,5 cm3 of anisaldehyde.
4.4 Solvents.
4.4.1 Acetone, redistilled.
4.4.2 Dichloromethane.
4.5 Standard castor oil solutions.
4.5.1 Weigh accurately 0,5 ± 0,01 g of castor oil (pharmaceutical grades have been found satisfactory) and prepare a stock solution by diluting to 100 cm3 with dichioromethane (4.4.2) in a one-mark volumetric flask (5.8).
4.5.2 DIlute 2; 4; 6; 8; and 10 cm3 aliquot portions of the stock solution (4.5.1) to 10 cm3 with dichioromethane (4.4.2) in one-mark volumetric flasks to gIve solutions corresponding to 02; 0,4; 06; 0,8; and 1,0 % (rn/rn) of castor oil, based on the rubber, when 5g of rubber is taken for analysis.
5 Apparatu&
Usual laboratory equipment, and
5.1 Extraction unit, all-glass (see figure 1 or figure 2 of
ISO 1407).
5.2 Water-bath, or electric heating mantle.
5.3 ThIn layer chromatography (TLC) plate, of dimensions 200 mm x 200 mm, coated with a layer approximately 025 mm thick of the silica gel (4.1). Commercial plates may also be used.
5.4 Thin layer applicator.
5.5 Developing tank, of sufficient size to hold the TLC plate
(5.3).
5.6 Spray apparatus, for the spray reagent (4.3).
5.7 Oven, capable of being maintained at 100 ± 5 °C.
5.8 One-mark volumetric flasks, of capacity 5; 10; and
100 cm3.
5.9 Spectrometer, capable of accurate measurement
(± 1 % total absorbance at 700 ± 1 nm), equipped with cells
of optical path length 10 mm.
Operate the spectrometer according to the manufacturer’s instructions for optimum performance.
6 Preparation of test sample
Take a piece of rubber, weighing at least 10 g, from the bale and cut it into small pieces (about 1 mm x 3 mm).
if there is an excess of castor oil, the surface of the bale is liable to feel oily. In this case, select a sufficient number of pieces. each of at least 10 g, to provide adequate representation. Prepare and analyse each piece separately, making sure that cross-contamination does not occur during the preparation.
NOTE As there could be a high concentration of castor oil on the surface of a piece, some of which might be lost it the rubber is milled, the homogenization procedure describod in ISO 1796 cannot be used.
7 Procedure
7.1 Test portion
Weigh accurately 5 ± 0,1 g of the test sample and place it in the extraction thimble of the extraction unit (5.1). If the sample Is sheeted out, roll it into a cylinder between filter paper or cloth to prevent sticking.
7.2 DetermInation
7.2.1 Introduce the thimble into the syphon cup and, using
100 cm3 of the acetone (4.4.1) in the extraction flask, extract the test portion for 16 h using the water-bath or electric heating mantle (5.2) to maintain a temperature sufficient to reflux the acetone and fill the extraction cup 10 to 20 times per hour.
7.2.2 Evaporate the acetone from the extract in the extraction flask, for example by distillation over a water-bath, until about 2 cm3 remains.
7.2.3 Transfer the extract to a 10 cm3 one-mark volumetric flask (5.8). rinse with dichioromethane and make up to the mark with the dichloromethane (4.4.2).
7.2.4 Spot 5 p1 of the test solution (723) and 5 p1 of each of the diluted standard castor oil solutions (4.5.2) on to the TLC plate (5.3).
7.2.5 Develop the TLC plate to a height of 100 mm in the developing tank using the developing solvent (4.2).
7.2.6 Remove the plate, allow to air dry and spray with either the phosphomolybdic acid solution (4.3.1) or the anisaldehyde solution (4.3.2). Bake in the oven (5.7) until the spots have developed colour on a pale background. This takes about 10 ryin.
NOTE — Phosphoniolybdic acid is adequate for relatively “cleanrubbet-s (i.e. those having low contents of extractables); however, in some less “clean” rubbers, the main castor oil spot is overlapped by another one, which also g)ves a blue coloration. Interference can be avoided by spraying with the anisaldehyde solution (4.3.2) which g.ves spots which are initially mauve and soon turn green.
8.2.2 Measure the absorbance (optical density) at 700 nm of each solution (see 8.2.1) using the spectrometer (5.9). Use water as the reference liquid.
8.2.3 Construct a calibration curve of absorbance against the castor oil content, expressed as a percentage by mass, using the values from the spots from the standard solutions.
8.2.4 From the calibration curve read the castor oil content, expressed as a percentage by mass, of the test portion.
8.3 Report the result to the nearest 0,05 % (in/in).
9 Test report
The test report shall include the following information
a) a reference to this part of ISO 6225;
b) identification of the sample;
c) the results obtained and the method of evaluation used;
d) any unusual features which may have affected the results;
e) the date of test.