สารบัญ

Ground-nut Oil; Peanut Oil.

Thai name น้ำมันถั่วลิสง (NAM MAN THUA LISONG) Category Pharmaceutic aid (emollient).

Arachis Oil is the fixed oil obtained from the seeds of Arachis hypogaea L. (Family Fabaceae).

Origin of plant Arachis Oil-yielding plant is native to Bolivia.

Constituents Arachis Oil contains fatty acids predominantly oleic, linoleic acid, palmitic, stearic, and behenoic acids.

Description Clear, yellowish, viscous liquid.

Solubility Very slightly soluble in ethanol; miscible with ether, with chloroform, and with petroleum ether (boiling range, 40 to 60).

Stability On exposure to air it thickens very slowly and may become rancid.

Packaging and storage Arachis Oil shall be kept in wellfilled, tightly closed containers, protected from light, and stored at a temperature not exceeding 25º.

Identification of fixed oils by thin-layer chromatography Carry out the test as described in Appendix==.

Results The chromatogram obtained is similar to the corresponding chromatogram shown in the figure.

Composition of fatty acids Carry out the test as described in the “Gas Chromatography” (Appendix 3.4).

Standard solution Prepare an ester mixture of known composition containing the esters required in the Arachis Oil. (Nu-Chek mixture 17A® or equivalent is suitable.)

0.5 M Methanolic sodium hydroxide solution

Dissolve 2 g of sodium hydroxide in 100 mL of methanol.

Test solution (Note If fatty acids containing more than 2 double bonds are present in the sample, remove air from the flask by purging it with nitrogen for a few minutes.) Transfer about 100 mg of the sample, accurately weighed, to a 50-mL conical flask fitted with a suitable water-cooled reflux condenser and a magnetic stir bar. Add 4 mL of 0.5 M Methanolic sodium hydroxide solution, and reflux until fat globules disappear (usually 5 to 10 minutes). Add 5.0 mL of a solution prepared by dissolving 14 g of boron trifluoride in methanol to make 100 mL, swirl to mix, and reflux for 2 minutes. Add 4 mL of n-heptane for chromatography through the condenser, and reflux for 1 minute. Cool, remove the condenser, add about 15 mL of a saturated solution of sodium chloride, shake, and allow the layers to separate. Pass the nheptane layer through 100 mg of anhydrous sodium sulfate (previously washed with n-heptane for chromatography) into a suitable flask. Transfer 1.0 mL of this solution to a 10-mL volumetric flask, dilute with n-heptane for chromatography to volume, and mix.

System suitability solution Transfer about 20 mg each of stearic acid, palmitic acid, and oleic acid to a 25-mL conical flask fitted with a suitable water-cooled reflux condenser and a magnetic stir bar, and prepare as directed for Test solution beginning with “Add 5.0 mL of a solution prepared by dissolving . . . .”

Chromatographic system

DETECTOR Flame ionization.

COLUMN A fused-silica capillary column (30 m × 0.53 mm) bonded with a 1.0-µm layer of polyethylene glycol compound (Polyethylene Glycol Compound 20M®, also known as Carbowax 20M®, or equivalent.)

TEMPERATURE

Column The temperature programme is as follows:

Injection port 220.

Detector 260.

Carrier gas Helium.

Flow rate About 50 cm per second (6.6 mL per minute).

(Note The relative retention times are about 0.87, 0.99, and 1.0 for methyl palmitate, methyl stearate, and methyl oleate, respectively.)

System suitability

SAMPLE System suitability solution.

Suitability requirements

RESOLUTION Not less than 1.5 between methyl stearate and methyl oleate peaks.

RELATIVE STANDARD DEVIATION The relative standard deviation of the peak area responses for the palmitate and stearate peaks for replicate injections is not more than 6.0 per cent. The relative standard deviation of the peak area response ratio of the palmitate to stearate peaks from these replicate injections is not more than 1.0 per cent.

Procedure Separately inject equal volumes (about 1 µL) of Standard solution and Test solution into the chromatograph, and record the chromatograms. Identify the peak due to the fatty acid ester peaks in the chromatogram of the Test solution by comparing the retention times of these peaks with those in the chromatogram of the Standard solution, and measure the peak areas for all of the fatty acid ester peaks in the chromatogram from the Test solution.

Calculation Calculate the percentage content of the components of Arachis Oil taken by normalization procedure.

Limits Arachis Oil exhibits the composition profiles of fatty acids in Table 1 below.

Table 1

Acid value Not more than 0.5 (Appendix 5.4).

Peroxide value Not more than 5.0 (Appendix 5.12).

Unsaponifiable matter Not more than 1.0 per cent w/w (Appendix 5.8).

Specific gravity 0.909 to 0.916 (Appendix 4.9).

Refractive index 1.468 to 1.472, at 20º (Appendix 4.7).

Aflatoxins Not more than 20 ng per g, determined by the following method. Carry out the test as described in the Liquid Chromatography (Appendix 3.5).

[Caution: Carry out the test protected from daylight and perform manipulations in a fume cupboard whenever possible. Rinse glassware before use with a 10 per cent v/v solution of sulfuric acid and then rinse carefully with distilled water until no more acid is present.]

Diluent Prepare a mixture of 9 volumes of water and 1 volume of acetonitrile.

Aflatoxin standard stock solution Dissolve an accurately weighed quantity each of aflatoxin B1, B2, G1, G2 RS in acetonitrile to obtain a stock solution having a known concentration of about 20 µg per mL. (Note The standard stock solution is stable for 1 year at a temperature not exceeding 0º.)

Aflatoxin standard solution A Dilute 0.5 mL each of Aflatoxin standard stock solution to 20.0 mL with acetonitrile to obtain a solution having a known concentration of about 500 ng per mL. (Note The standard stock solution is stable for 1 year at a temperature not exceeding 0°)

Aflatoxin standard solution B Dilute 1 mL each of Aflatoxin standard solution A to 10.0 mL with acetonitrile to obtain a solution having a known concentration of about 50 ng per mL. (Note The standard stock solution is stable for 3 months at a temperature not exceeding 0º)

Aflatoxin standard solutions Dilute Aflatoxin standard solution B quantitatively, and stepwise with acetonitrile to obtain six solutions having known concentrations of about 0.1, 0.5, 1, 2, 2.5, and 5 ng of aflatoxin B1, B2, G1 and G2 per mL.

System suitability solution Dissolve an accurately weighed quantity of Aflatoxin RS in acetonitrile to obtain a solution having a known concentration of about 2 ng per mL.

Test solution Transfer about 2 g of Arachis Oil, accurately weighed, to a 50-mL polypropylene centrifuge tube, add 2.0 mL of water and 8.0 mL of a 0.1 percent v/v solution of formic acid in acetonitrile, mix thoroughly for 1 minute, and then shake for 30 minutes. Add 1 g of sodium chloride and 4 g of sodium sulfate, mix for 1 minute and centrifuge at 1233 ×g at 4° for 10 minutes. Pipette 6 mL of the supernatant to a 15-mL centrifuge tube with QuEChERS Mix XLVII Clean-up-Mix (Chromabond® or equivalent is suitable), mix for 1 minute, and centrifuge at 1233 ×g for 10 minutes. Pipette 4 mL of the supernatant to a vial of suitable size and pass a stream of nitrogen through at room temperature until the solvent has just evaporated. Immediately add 1.0 mL of Diluent, mix well for 30 seconds, and filter through a 0.22-µm nylon filter.

Mobile phase Prepare a mixture of 67 volumes of water, 28 volumes of methanol, and 5 volumes of acetonitrile.

Chromatographic system

DETECTOR Fluorescence 365 nm (excitation), 460 nm (emission) and Photochemical reactor UVE® 254 nm.

COLUMN A stainless steel column (25 cm × 4.6 mm), packed with octadecylsilane chemically bonded to porous silica or ceramic microparticles (5 μm).

FLOW RATE 1.2 mL per minute.

System suitability

SAMPLE System suitability solution

Suitability requirements

RELATIVE STANDARD DEVIATION Not more than 2.0 per cent.

Procedure Separately inject about 20 μL each of Aflatoxin standard solutions into the chromatograph, record the chromatograms, and measure the areas of the Aflatoxin B1, B2, G1, and G2 peaks. Plot the standard curves of the area of each Aflatoxin against their respective concentrations. Inject about 20 μL of Test solution into the chromatograph, record the chromatogram, and measure the peak areas, as with the Aflatoxin standard solution.

Calculation Calculate the contents of Aflatoxin B1, B2, G1, and G2, in a portion of the Arachis Oil taken by reference to the standard curves.