สารบัญ

Maize Oil

Thai name  น้ำมันข้าวโพด (NAM-MAN KHAO PHOT)

Category  Pharmaceutic aid.

Corn Oil is the refined fixed oil obtained from the embryo of Zea mays L. (Family Poaceae).

Origin of plant  Corn Oil-yielding plant is native to Central America and Mexico.

Constituents  Corn Oil contains fatty acids, predominantly linoleic acid, oleic acid, and palmitic acid.  It also contains sterols, i.e., β-sitosterol, campesterol, and stigmasterol.   

Description  Odour mild, characteristic; taste, mild.

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

Packaging and storage  Corn Oil shall be kept in well-filled, tightly closed containers, protected from light, and stored at a temperature not exceeding 25°.

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.

Specific gravity  0.914 to 0.921 (Appendix 4.9).

Refractive index  1.472 to 1.475 (Appendix 4.7).

Water  Not more than 0.1 per cent w/w (Karl Fischer Method, Appendix 4.12). Use a mixture of equal volumes of decanol and anhydrous methanol as the solvent.

Acid value  Not more than 0.2 (Appendix 5.4).

Iodine value  103 to 130 (Iodine Monochloride Method, Appendix 5.6).

Saponification value  187 to 195 (Appendix 5.7).

Unsaponifiable matter  Not more than 1.5 per cent w/w (Appendix 5.8).

Test for alkaline  Mix 10 mL of acetone and 0.3 mL of water, and add 50 µL of bromophenol blue TS. Neutralize the solution to a green colour if necessary with 0.01 M hydrochloric acid or 0.01 M sodium hydroxide. Add 10 mL of Corn Oil, shake, and allow to stand. Titrate with 0.01 M hydrochloric acid VS. Not more than 0.1 mL of 0.01 M hydrochloric acid is required to change the colour of the upper layer to yellow.

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 Corn 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 n-heptane 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 Corn Oil taken by normalization procedure. 

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

Table 1