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Gas chromatography method to determine the degree of rapeseed biodiesel synthesis reaction. In recent years, biodiesel, as an alternative energy source, has attracted attention and praise from countries around the world for its good renewable nature and environmental friendliness. Currently, the bottleneck issue in the development of biodiesel is the raw material issue J, that is, the scale and price of raw materials. Rapeseed is my country's dominant oil crop. It has many advantages such as a short planting cycle, no competition for land with grain and cotton, a large marginal land area suitable for planting, and similar fatty acid composition to petrochemical diesel molecules. It has become the most potential and ideal biodiesel raw material for the development of biodiesel in southern my country. Therefore, the rapeseed biodiesel project has attracted the attention of relevant experts and scholars. Rapeseed biodiesel is synthesized from rapeseed oil and methanol through an ester-alcohol exchange reaction. The main component is fatty acid methyl ester, and the by-products are glycerol, monoglyceride and diglyceride. In order to optimize production conditions and monitor product quality, it is necessary to judge the degree of reaction in a timely manner. Although the glycerol cold oxidation titration method and glycerol copper colorimetric method reported in the literature can determine the degree of reaction by measuring the glycerol production, the processing of the sample to be tested is cumbersome and the measured reaction degree is low. ； Although there are already * * Standard gas chromatography method lL6 can determine the degree of reaction by measuring the content of fatty acid methyl esters in the product. However, due to the different fatty acid compositions and properties of different raw oils and fats, the gas chromatography conditions and methods required for measurement are also different. Guo Dengfeng et al. used gas chromatography to determine the content of mixed fatty acid methyl esters in soybean biodiesel. Fang Fang et al. used gas chromatography to determine the content of fatty acid methyl esters in camellia seed biodiesel. However, research on the gas chromatographic analysis method of fatty acid methyl esters in rapeseed biodiesel has not yet been reported. Received date: 2006-02-08 ； Repair date: 2006-03-10 Fund Project: Hunan Provincial Science and Technology Plan Project (No.: 05SK3085) About the author: Wu Suxi (1965), male, associate professor/Ph.D. candidate ； Mainly engaged in the development and research of rapeseed bioenergy. Correspondence contact: Guan Chunyun, academician, professor, and doctoral supervisor of the Chinese Academy of Engineering. This paper uses methyl tridecanoate as the internal standard to first establish a gas chromatography method for determining the content of main fatty acid methyl esters in rapeseed biodiesel, and then uses it to determine the degree of synthesis reaction of rapeseed biodiesel. It has a wide linear range, high accuracy, good precision, easy and fast operation, and provides an effective analytical testing method for the research, development and production of rapeseed biodiesel. 1 Materials and methods 1.1 Experimental materials and reagents Rapeseed oil I (Hunan Jinjian Rice Industry Co., Ltd.), rapeseed oil II (Hunan Yueyang Daodao Whole Oil Company) ； Methyl tridecanoate, methyl palmitate, methyl oleate, methyl linoleate, methyl linolenate, methyl arachidate and methyl erucate were all chromatographically pure (Sigma), and other reagents were all analytical grade. 1.2 Experimental instruments SP-6890 gas chromatograph, FID detector, N3000 chromatography workstation HP-innowax capillary chromatography column (30 m × 0.25 mm × 0.25 m) ； AL204 electronic balance. 1.3 Chromatographic conditions and sample analysis methods: The vaporization chamber temperature is 280°C, and the detector temperature is 280°C.℃ ； Column temperature adopts programmed heating: The initial temperature is 170°C, maintained for 0.5 min, raised to 200°C at a heating rate of 5°C/min, then raised to 240°C at a heating rate of 15°C/min, and held for 5 min. ； carrier gas: N,, column head pressure 60 kPa ； hydrogen: 32mL/min ； Air: 320mL/min ； Injection volume: 1.0L. The internal standard method is used. The specific method is:: Take a small amount of the sample to be tested (g) in a 1 mL volumetric flask, add 0.25 mL of methyl tridecanoate with a concentration of 20 mg/mL, dilute it with n-hexane to a constant volume, and perform gas chromatography analysis. Multiply the sum of the fatty acid methyl ester concentrations (mg/mL) found on the standard working curve by the dilution factor of the sample and divide it by the sample amount (g) to obtain the VIP information of fatty acid methyl esters in the sample to be tested. http://www.cqvip.com China Fats and Oils, Volume 31, Issue 8, 2006 Content A (mg/g). 1.4 Preparation of standard series solutions Weigh a certain amount of standard samples of methyl palmitate, methyl oleate, methyl linoleate, methyl linolenate, methyl arachidate and methyl erucate, and use n-hexane as the solvent to prepare a standard stock solution of mixed fatty acid methyl esters. Then dilute it into 10 mixed fatty acid methyl ester standard solutions with different concentrations. Then take 0.75 mL of the above mixed standard solution into a 1 mL volumetric flask, add 0.25 mL of methyl tridecanoate with a concentration of 20 mg/mL as the internal standard, and mix evenly to obtain a standard series of solutions for later use. In this standard series of mixed solutions, the concentrations of methyl palmitate, methyl oleate and methyl linoleate are 1.50 3 00, 4.50 6.00 7.50 9 00 10 5 12.0, 13.5, 15.0 mg/mL, the concentrations of methyl linolenate, methyl arachidate and methyl erucate are 0.75, 1.50, 2.25, 3.00, 3.75, 4.50, 5.25, 6.00, 6.75, 7.50 mg/mL. 1.5 Preparation and measurement of biodiesel synthesis reaction samples Weigh rapeseed oil I or rapeseed oil II, methanol and organic solvent in a certain proportion into a 150 mL Erlenmeyer flask, add an appropriate amount of a certain catalyst, place the Erlenmeyer flask in a 40 cc constant temperature water bath oscillator, start the reaction and record the time. After a certain period of time, the layers are statically separated, and the solvent and methanol are distilled off from the upper layer to obtain a biodiesel synthesis reaction sample. Determine the total amount of fatty acid methyl ester A (mg/g) according to the gas chromatography internal standard method in 1.3. 1.6 Preparation and determination of complete methyl esterification sample Take an appropriate amount of raw material rapeseed oil, and follow the * * Standard Method 9 Preparation of Completely Methyl Esterified Biodiesel Samples. Determine the total amount of fatty acid methyl esters B (mg/g) O according to the gas chromatography internal standard method in 1.3. 1.7 Calculation of the degree of synthesis reaction degree of reaction (%) = A/B × 100% 2 Results and discussion 2.1 Chromatographic separation and qualitative analysis of fatty acid methyl esters Since the fatty acid composition of rapeseed oil is mainly palmitic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid and erucic acid [1 , therefore this article selected these fatty acid methyl ester mixtures as standard samples for chromatographic separation and qualitative analysis. The chromatographic separation diagrams of mixed fatty acid methyl ester standard solution and rapeseed biodiesel sample are shown in Figure 1 and Figure 2 respectively. Chromatographic peaks 1, 2, 3, 4, 5, 6 and 7 in Figure 1 are methyl tridecanoate, methyl palmitate, methyl oleate, methyl linoleate, methyl linolenate, methyl arachidate and methyl erucate respectively. As can be seen from Figure 2, the six fatty acid methyl esters are clearly separated and have good peak shapes. 2.2 Standard working curve and regression analysis The standard series solutions prepared in 1.4 were analyzed by gas chromatography respectively, and the standard working curve between the peak area ratio y and the concentration ratio of each fatty acid methyl ester and the internal standard was obtained. The linear regression analysis results are shown in Table 1. It can be seen that the built regression equation has a significant linear correlation. Figure 1 Gas chromatogram of the standard solution - 12 Ⅱl BU l1 4 . ,—^l． 'JI. ^-4 6 Retention time (min) Figure 2 Gas chromatogram of rapeseed biodiesel 2.3 The total amount of fatty acid methyl esters in the completely methyl esterified sample B Rapeseed oil I is 949.1 mg/g ； Rapeseed oil II is 924.3 mg/g. There is a difference between the two total amounts. The reason is that the non-oil component content of rapeseed oil from different manufacturers is not exactly the same. 2.4 Recovery rate measurement: Put a certain amount of biodiesel synthesis reaction sample with known content of each fatty acid methyl ester into a 1 mL volumetric flask, add 0.25 mL of methyl tridecanoate with a concentration of 20 mg/mL and a certain amount of methyl palmitate, methyl oleate, methyl linoleate, methyl linolenate, methyl arachidate and methyl erucate standard samples. After diluting to volume with n-hexane, conduct 5 parallel gas chromatography analyses. The results are shown in Table 2. 2.5 Sample determination and precision experiment: Take a certain amount of 5 biodiesel synthesis reaction samples prepared with rapeseed oil I as raw material, place them in 1 mL volumetric flasks, add 0.25 mL of methyl tridecanoate with a concentration of 20 mg/mL, and dilute to volume with n-hexane, then perform gas chromatography analysis. The results are shown in Table 3. 3 Conclusion Methyl palmitate, methyl oleate, methyl linoleate, methyl linolenate, methyl arachidate and methyl erucate in rapeseed biodiesel can be separated well under the given gas chromatography conditions. The quantitative determination using the internal standard method is fast and accurate (sample analysis can be completed in 10 minutes) and has good reproducibility. Its linear correlation coefficient is r≥0.9963, and the average recovery rate is between 97.59% and 101.42%. , the relative standard deviation is between 1.32% and 2.89%. By measuring the total content of fatty acid methyl esters in the sample and comparing it with the total content of methyl esters in the complete methyl esterified product of raw oil and fat, VIP Information http://www.cqvip.com 2006 Volume 31 Issue 8 China Oils and Fats 69 Table 1 Samples of linear regression analysis results. actual. Measured amount of fatty acid methyl ester added (mg/mL) Added amount - Average recovery rate (mg/mL) 1 2 3 4 5 (%) Methyl palmitate, methyl oleate, methyl linoleate, methyl linolenate, methyl arachidate, methyl erucate, methyl ester Total amount A Reaction degree (%) 63.0l 62, l8 6l. 69 66.29 64. 14 341.1 338.3 336.5 326.5 330.5 203.5 204.3 l99.3 2l2.9 208.0 92.93 94.37 92.58 91.29 94.0l 60.48 65.30 63.80 62.27 63.04 175.7 l83.9 l85.1 174.6 177.8 936.7 948.4 939.0 933.9 937.5 98.7 99.9 98.9 98.4 98.8 63.46 334.6 205.5 93.04 62.98 179, 0 939.1 98.9 2.89 1.78 2.49 1.32 2.84 2.67 The degree of biodiesel synthesis reaction can be accurately judged. Therefore, the gas chromatography method established in this article can be popularized and applied in the research and development, production process control and product purity detection of biodiesel.