Stearic acid is a white flake, bead or block solid at room temperature. Almost insoluble in water (at 20°C, only 0.00029g is dissolved in 100mL water), soluble in ethanol, acetone, easily soluble in ether, chloroform, benzene, carbon tetrachloride, carbon disulfide, valeryl acetate and toluene, etc. There are two main production methods for industrial stearic acid: fractionation method and pressing method. A decomposing agent is added to the hardened oil, and then hydrolyzed to obtain crude fatty acids, which are then washed, distilled, and decolorized to obtain the finished product.
The determination method of stearic acid content is as follows:
Determination by gas chromatography (General Chapter 0M1).
Chromatographic conditions and system suitability test: Capillary column with polyethylene glycol 20M as stationary solution; starting temperature is 170°C, maintained for 2 minutes, and then heated at a rate of 10°C per minute to 240°C and maintain for several minutes until the chromatogram is recorded to 3 times the retention time of the second main peak except the solvent peak; the inlet temperature is 250°C; the detector temperature is 260°C. The separation between the methyl stearate peak and the methyl palmitate peak should be greater than 5.0.
Measurement method: Take about 0.1g of this product, weigh it accurately, place it in an Erlenmeyer flask, accurately add 5ml of methanol solution of boron trifluoride (13%~15%), and shake to dissolve. Place in a water bath to reflux for 20 minutes, let cool, transfer and wash with 10 to 15 ml of n-hexane to a separatory funnel, add 10 ml of water and 10 ml of saturated sodium chloride solution, shake and separate layers, discard the lower layer (water layer), n-hexane Add 6g of anhydrous sodium sulfate to the layer, dry and remove the water, then place it in a 25ml measuring bottle, dilute to the mark with n-hexane, shake well, and use it as the test solution; take about 50mg of the stearic acid reference substance and about 50mg of the palmitic acid reference substance. The reference solution was prepared by the same method as above. Precisely measure 1 ul each of the test solution and the reference solution and inject them into the gas chromatograph and record the chromatogram. Calculate the contents of stearic acid (C18H3602) and palmitic acid (C16h 36o2) in the test product based on the peak area using the area normalization method.
