Solid phase extraction and its application in food analysis · Overview · In food analysis, the pretreatment of the tested sample is an extremely important step.
At present, the commonly used extraction and separation methods for food analysis and pretreatment in China are still liquid-liquid extraction, gas-liquid extraction, Soxhlet extraction, oscillating extraction, ultrasonic wave and other traditional technologies. The above methods have different characteristics and can solve the problem of pretreatment of certain samples. However, there are different levels of limitations, such as large sample demand, cumbersome steps, long extraction time, large consumption of organic solvents, and low separation efficiency.
Since the introduction of Solid Phase Extraction (SPE) technology in the late 1970s, due to its low solvent usage, simple operation, high selectivity, and good reproducibility, it has developed into the separation and concentration of traces in various samples. A powerful tool for quantitative analysis of substances [1], widely used in food inspection, environmental monitoring, medicine and health, biochemistry and other fields [2 ~ 5]
It shows good development prospects in food analysis applications.
1 Basic principle of solid phase extraction technology The separation mode of solid phase extraction is the same as that of liquid chromatography, which can be regarded as a simple chromatographic process [6]. Solid phase extraction uses a solid adsorbent to adsorb the target compound in the liquid sample, separating it from the sample matrix and interfering compounds, and then eluting with the eluent, or heating and desorption to achieve the purpose of separating and enriching the target compound.
2 Brief process of solid phase extraction Typical offline solid phase extraction is generally divided into four steps: activating adsorbent, loading, washing and eluting. Before extracting the sample, the solid phase extraction column should be rinsed with a suitable solvent to eliminate the impurities adsorbed on the adsorbent and its interference with the target compound, and activate the activity of the active groups on the surface of the stationary phase. Activation usually uses two steps. First, the solvent with strong elution ability is used to elute the remaining interferences in the column to activate the stationary phase; then the solvent with weak elution ability is used to rinse the column to make it compatible with the loading solvent. Match [7]. Loading: Pour the liquid or dissolved solid sample into the activated solid phase extraction column. Washing and elution: After the sample enters the adsorbent and the target compound is adsorbed, the weak retention interfering compound can be washed away with a weaker solvent, and then the target compound can be eluted with a stronger solvent and collected.
3 Types of solid-phase extraction columns Common types of solid-phase extraction columns include polar columns, non-polar columns, cation exchange columns, anion exchange columns, and covalent columns. Polar columns: CN, NH, PSA, COH, Si, etc., non-polar columns: C18, C8, C2, CH, CN, pH, etc., cation exchange columns: SCX, PRS, CBA, etc., anion exchange columns: SAX, PSA, NH2, etc., covalent column: PBA, etc. Select the appropriate solid phase extraction column and eluent according to the target compound properties and sample type.
4 Influencing factors of solid phase extraction column The main factors affecting the effect of solid phase extraction are: the type and amount of adsorbent, the volume of water sample, the type of eluent, etc. Try to choose an adsorbent that is similar in polarity to the target compound. Normal phase adsorbents retain polar organics, reverse phase adsorbents retain non-polar organics or weakly polar organics, and anion exchange resins are suitable for ionic organics. The volume of eluent should be based on complete elution, and the smallest volume is the best [8]. The pH value in the sample solution also affects the adsorption efficiency [9]. Under the selected conditions of adsorbent and eluent, the recovery rate increases with the increase of the adsorbent dose; the effect of the water sample flow rate on the recovery rate is not obvious [10].
5 Application of solid phase extraction technology in food analysis 5.1 Combination of solid phase extraction technology and gas chromatography Literature [11] reported the application of solid phase extraction technology in the analysis of the purification of pentachloronitrobenzene residues in food. The solid phase extraction column used was a PT-silicon magnesium adsorbent pretreatment cartridge, and the solid phase extraction technology was compared with traditional liquid-liquid extraction. The results show that the solid phase extraction purification technology is much better than the liquid-liquid extraction purification method, using fewer reagents (solid phase extraction 7ml, liquid-liquid extraction 48ml), saving time (solid phase extraction 1min, liquid-liquid extraction 30min), and gas chromatography Combined determination of pentachloronitrobenzene residue in food, the minimum detection limit is 5 × 19-9mg. Long Su et al. [12] used activated carbon columns to purify samples, and established a solid phase extraction microchemical gas chromatography method for simultaneous determination of methamidophos, dichlorvos, and dimethoate residues in organophosphorus pesticides in rice. The linear relationship between the proposed method and The recovery rate is good, the peak shape of the chromatogram is stable, the precision and accuracy are high, the operation is simple, and the practicability is strong. Su Shaoming [13] took the C18 cartridge and placed it in the DL-1 solid phase extractor to purify the sample, and analyzed the tetramine in water by GC / NPD method. The qualitative and quantitative results were consistent with the liquid-liquid extraction GC / MS method. Zhang Xiaohui [14] selected ENVI- Florisil cartridges for pesticide residues, whose packing is magnesium silicate, which has good selectivity for polar compounds and pesticides, adsorbs and extracts six six six and DDT in water, and is determined by gas chromatography, the lowest The detected concentration was 0.018μg / L ~ 0.16μg / L, and the relative standard deviation was 1.4% ~ 5.6%. Mass spectrometers have a good qualitative effect on the substances to be tested, and are often used in conjunction with gas chromatographs to qualitatively and quantitatively analyze organic substances. At present, the literature reports that the SPE-GC-MS method is widely used. Angelica et al. [15] used the polystyrene-divinylbenzene (PS-DVB) solid phase extraction material AccuBondⅡENV cartridge to extract the phenolic compounds in drinking water, combined with gas chromatography-mass spectrometry to analyze traces (10μg / L) in water ) Phenolic compounds. The recovery rate exceeds 90%, and the CV is less than 5%. The previous treatment method greatly shortened the drying time (currently only 2min, compared with the previous 20min). Angelica et al. Also believe that for more polar compounds, polymer resins such as polystyrene-divinylbenzene have a particularly low background, which is better than the solid phase extraction adsorbents commonly used in octadecyl and similar silica gel matrix. Lin Ji et al [16] solid-phase extraction GC / MS qualitative and quantitative analysis of brucine in poisoning liquor, the detection limit was 39ng, and the average recovery was 93.2%. The SPE method for extracting alkaloids requires a small sample volume of only 1 to 2 ml. The extraction efficiency is high, and the eluent sample volume is small, only 1 to 2 ml. Liu Yizi et al. [7] conducted a systematic study on the purification and enrichment methods of bee samples, and found that the recovery rate of chloramphenicol at different concentrations on silica gel columns and C18 columns was more than 90%, combined with gas chromatography-mass spectrometry to determine honey The minimum detection concentration of chloramphenicol is 0.139μg / kg, relative standard deviation solid phase extraction and its application in food analysis. Song Yingchun, Tan Hongtao, review Hu Guoliang, reviewing the Chinese Library Classification No. R155.5 C Article No. 1008- 0023 (2005) 06- 0583- 03 Author unit: 330029 Nanchang, Jiangxi Provincial Center for Disease Control and Prevention · 583 · Jiangxi J. Med Lab Sci. December 2005, Vol 23, No6 is 7.2% ~ 18.2%.
5.2 The combination of solid phase extraction technology and liquid chromatography Lu Jie et al. [8] used solid phase extraction as a pretreatment method. The solid phase extraction column was Oasis HLB 3cc, combined with high performance liquid chromatography to determine tablets, capsules, vitamins The minimum detection concentration of vitamin B12 in health foods such as Teng tablets is 0.2mg / kg, and the linear range is 0.334 ～ 167μg / L. Kang Li et al [9] reported the determination of clenbuterol hydrochloride in meat by solid phase extraction-high performance liquid chromatography, with a detection limit of 1.7 ng, CV values ​​of 1.37% (low concentration) and 0.76% (high concentration), The recovery rate is 81.0% ～ 91.4%. Liu Yafeng et al [17] used Waters Oasis HLB solid phase extraction column to purify the sample solution, HPLC method was used to detect the residual amount of natamycin in meat products, the detection limit of the method was 0.05mg / kg, and the precision (CV) was 0.48% ～ 2.50%, the recovery rate is 86.0% ~ 95.7%. Yang Fang et al. [18] used high-performance liquid chromatography to detect mebendazole residues in animal foods. The sample was purified by NH2 SPE column. The packing of the small column was amorphous silica gel bonded with amino group. The eluents were methanol and formic acid. The elution efficiency can reach 95.1%, the sensitivity is high, and the detection limit of the method is 0.4ng. Lin Haidan et al. [7] determined the residues of four sulfonamides in animal-derived foods by high-performance liquid chromatography. The sample preparation used liquid-liquid partitioning combined with solid-phase extraction technology. The solid-phase extraction column was Waters Oasis HLB ( Divinylbenzene-N-vinylpyrrolidone copolymer), to ensure that there is no sample matrix interference during the measurement, the detection limit of the method is 0.010 × 10-6 ～ 0.020 × 10-6 (w), and the recovery rate is 71% ～ 83%. Yang Yaling et al [20] studied solid phase extraction enrichment and pre-separation, high-performance liquid chromatography determination of seven kinds of carotene in wolfberry. The solid phase extraction column is Waters Xterra TM RP18, the eluent is tetrahydrofuran, the recovery rate is high (95% ~ 103%), and the detection limit is between 25-40ng / ml. Lin Weixuan et al [21] studied high-performance liquid chromatography to determine the residue of rice carbamate pesticides. They used florisil and C18 double-column solid-phase extraction purification columns to purify the samples, simplifying the purification operation, and improving the detection sensitivity and detection. The lower limits (mg / kg) are: carbamazepine 0.005, metoprolol 0.01, aldicarb 0.005, anti-budavir 0.005, candicarb 0.0025, phenoxavir 0.0025, carbaryl 0.005, sulbutarol 0.01, recycling The rates are all above 80%. Luo Xiaoyan et al. [22] successfully conducted a study on simultaneous determination of four antibiotic residues such as chloramphenicol in aquatic products by SPE-HPLC method. After purification and concentration of the ZORBAX SPE C18 column, the impurity peaks were less and the sensitivity was increased by 10 Times, the recovery rate is 93% ～ 101%. Yan Haoying et al. [23] used Sep-Pak C18 column for sample purification and concentration, and then determined the residual amount of wheatgrass herbicide in whole wheat and flour by high performance liquid chromatography. The detection limit was 0.05 mg / kg, and the recovery rate was 84.5% ～ 92.4%. Jia Wei et al. [24] extracted and purified four tetracycline drugs in milk using a C18 micro-purification enrichment column, optimized the eluent, and used liquid chromatography-mass spectrometry to determine the amount of drug residues. As a result, tetracycline in milk , The detection limit of oxytetracycline and metacycline can reach 0.05μg / L, the detection limit of chlortetracycline is 0.1μg / L, and the recovery rate is above 90%. Literature [25] established a method for the determination of basic rose essence in dyed shrimp by HPLC method. SPE-HLB column solid phase extraction was used to purify and enrich the alkaline rose essence in the extract, which achieved a high sensitivity and the lowest detection. Limit 2μg / kg, average recovery rate 84.92%. Lin Haidan et al [26] extracted benzimidazole residues in milk powder with basic ethyl acetate, purified by Waters Oasis HLB solid phase extraction column, determined by HPLC, detection limit 0.020mg / kg, recovery rate 71% ～ 90%. The activated carbon solid phase extraction and HPLC analysis method for trace acrylamide in water established by Chen Ling et al. [27] is easy to operate and also meets the control requirements of WHO 0.5 μg / L.
5.3 Combination of solid-phase extraction technology and other methods In addition to being used with chromatograph, solid-phase extraction can also be used with other instrumental methods for compound analysis. Li Ligeng et al. [28] used C18-SPE for pre-test pretreatment, because the components to be tested were difficult to adsorb (more polar glycosides) and interfered with impurities (less polar aglycon and other impurities). To achieve the purpose of removing impurities, the content of rutin in the medicinal Sophora japonica was successfully determined by spectrophotometry, and the recovery rate was as high as 99.98%. Literature [29] reported the use of Waters Porapak Sep-Park solid-phase extraction cartridges to extract the complex formed by copper ions and reagents, which achieved a high multiple concentration of trace copper in the sample, and spectrophotometric determination of copper in drinking water. The detection limit can reach 0.5μg / L. Yan Fangfang [30] used C18 Cartaidge for solid phase extraction to effectively remove sucrose that interfered with the determination. The colorimetric method was used to determine the content of Gynostemma pentaphyllum in Jianzhibao oral solution with high accuracy and an average recovery rate of 99.5%. Yang Yuan et al. [31] used cation exchange resin LC-SCX cartridges (with sulfonic acid functional groups) for solid-phase extraction of trace beryllium, cadmium, and lead ions in water, and ICP-AES detection. The sensitivity was greatly improved and detected. The limit is 1.4ng / L for beryllium, 5.5ng / L for cadmium, and 49ng / L for lead. Guo Mei et al. [32] studied the extraction of organochlorine pesticides in samples by subcritical water extraction-solid phase extraction, using activated carbon fiber as a solid phase extractant to purify subcritical water extracts, hexachlorocyclohexane The extraction recovery rate of (HCH) four isomers is between 70% and 95%.
6 Existing problems and prospects Solid-phase extraction technology is a sample pretreatment technology with broad application prospects, and has achieved good application results. With the efforts of the majority of scientific and technological workers, new types of adsorbents are constantly emerging, and the scope of application is also increasing, but they cannot fully meet the actual needs. The scope of application needs to be expanded. At present, the measurement items are mainly organic substances, and there are few reports on the measurement of inorganic substances. Solid-phase microextraction (SPME), developed on the basis of solid-phase extraction, is economical, simple, time-saving, labor-saving, and requires no solvents.In recent years, it has been widely used in the research of volatile or semi-volatile compounds in food. High-selection, high-efficiency adsorbents and widening the application range of samples are important directions for the research of solid phase extraction technology. The combination of SPE with multiple instruments online and the combination of analysis technology are also waiting for us to carry out more research and development and promotion work.
references
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[12] Long Su, Zhou Yigang, Wang Xiaochun, et al. Determination of various organophosphorus pesticide residues in rice by solid phase extraction gas chromatography [J]. Practical Preventive Medicine, 2001, 8 (5): 341 ～ 342.
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[14] Zhang Xiaohui. Determination of six six six and six DDT in water by solid phase extraction gas chromatography [J]. Strait Journal of Preventive Medicine, 2004, 10 (6): 38 ～ 39.
[15] Angelica A Reese, Harry Prest. Application Notes of Solid Phase Extraction and Gas Chromatography-Mass Spectrometry for Analysis of Phenolic Compounds [J]. Environmental Chemistry, 2003, 22 (2): 196 ～ 199.
[16] Lin Ji, Lu Shoufang. Qualitative and Quantitative Analysis of Brucine in Poisoned Liquor by Solid Phase Extraction GC / MS [J]. Chinese Journal of Sanitary Inspection, 2003, 13 (3): 299 ～ 300.
[17] Liu Yafeng, Liu Zhaohui, Yang Jizhou. Solid phase extraction-liquid chromatography detection of natamycin residues in meat products [J]. Inspection and Quarantine, 2002, 21 (3): 181 ～ 183.
[18] Yang Fang, Li Yaoping, Li Xiaojing. Determination of mebendazole residues in animal foods by high-performance liquid chromatography [J]. Chinese Journal of Sanitary Inspection, 2004, 14 (5): 545 ～ 546.
[19] Lin Haidan, Xie Shouxin, Feng Dexiong, et al. Determination of sulfonamides residues in foods of animal origin by solid-phase extraction-high performance liquid chromatography [J]. Journal of Analysis and Testing, 2003, 22 (1): 94 ～ 96 .
[20] Yang Yaling, Zhao Yulin, Lin Qiang, et al. Determination of carotenoids in wolfberry by solid phase extraction-high performance liquid chromatography [J]. Analytical Laboratory, 2004, 23 (6): 25 ～ 27.
[21] Lin Weixuan, Tian Miao, Li Jiye, et al. Study on the determination of residues of rice carbamate pesticides by high performance liquid chromatography with double-column solid phase extraction [J]. Chinese Journal of Cereals and Oils, 2003, 18 (2): 79 ～ 84.
[22] Luo Xiaoyan, Lin Yuna, Liu Lizhi. Study on simultaneous determination of four antibiotic residues in aquatic products by SPE-HPLC method [J]. Modern Preventive Medicine, 2005, 32 (3): 198 ～ 199.
[23] Yan Haoying, Lu Changhao. High performance liquid chromatography determination of wheatgrass herbicide residues in whole wheat and flour [J]. China Public Health, 1995, 11 (9): 422 ～ 423.
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[26] Lin Haidan, Xie Shouxin, Wu Yingxuan. Determination of benzimidazole residues in milk powder by solid phase extraction and high performance liquid chromatography [J]. Analytical Laboratory, 2005, 24 (1): 27 ～ 29.
[27] Chen Ling, Chen Hao. Solid phase extraction-high performance liquid chromatography combined analysis of trace acrylamide in water [J]. Chromatography, 2003, 21 (5): 534.
[28] Li Gengeng, Li Zuoping, Huo Changhong. Study on the determination of rutin content in the medicinal rice Huai Mi by solid phase extraction-spectrophotometry [J]. Chinese Patent Medicine, 2003, 25 (8): 673 ～ 674.
[29] Li Yang, Liu Shixi, Yi Jiayuan. Study on 2- (4-antipyrine azo) -5-dimethylaminoaniline solid phase extraction spectrophotometric determination of copper in drinking water [J]. Hygiene Research, 2002, 31 (3): 203 ～ 204.
[30] Yan Fangfang. Colorimetric determination of the total saponin of Gynostemma pentaphyllum in Jianzhibao oral solution [J]. Guangdong Pharmaceutical, 2001, 11 (4): 14 ～ 16.
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[32] Guo Mei, Huang Weihong, Lu Xiaohua, et al. Subcritical water extraction-solid phase extraction combined technology for extraction of organochlorine pesticides in sediments [J]. Journal of Analytical Science, 2004, 20 (3): 257 ～ 259. In addition, it can completely eliminate the interference of jaundice [3].
2.3 The hemolysis specimen interferes significantly with the determination of TPR. There are two reasons. First, the hemoglobin after the destruction of red blood cells is divided into oxyhemoglobin, reduced hemoglobin, carboxyhemoglobin, and methemoglobin, forming alkalized hemoglobin under alkaline conditions, with an absorption peak at 520nm [4], so the total protein of the original method The measurement has a large interference, and after using these two reagents to add the blank reagent (reagent 1), the instrument automatically deducts this part of the interference. Second, the globin in hemoglobin reacts with the biuret reagent. This reaction cannot be eliminated by either single or double reagents. In this paper, a normal-looking serum was selected to determine that the total protein was 70.3g / L, the red blood cells were artificially destroyed, and the Hb was calibrated to 14g / L. The original method was used to determine Tpr as 110.2g / L, which was 83.3g / L. The original method Hb 1g / L increased TPr by 2.85g / L [(110.3-70.3) ÷ 14 = 2.85], and this method Hb1g / L increased TPR by 0.93g / L [(83.3-70.3) ÷ 14 = 0.93]. The original method and the literature report that each increase of Hg by 1g / L can increase the single reagent TPR by 3% [5]. This method can greatly reduce the interference of hemolysis specimens in the determination of TPR.
2.4 Select 30 serums with normal appearance and use two methods to determine TPr. The results showed no significant difference. Original method: 72.6 ± 0.92g / L, this method: 72.3 ± 0.91g / L, t = 1.27, P> 0.05.
2.5 When preparing Reagent 2, Reagent 1 should be prepared first, and then copper sulfate is added to dissolve. The effect is better, there is only a little precipitation, and it is filtered twice with filter paper for use. If it is prepared according to the "National Clinical Inspection Operation Rules", there will be more precipitation, and the effect is not good. It may be that the added copper sulfate is four times the original method. In short, this method changes the original biuret single reagent to a dual reagent, without changing the reaction principle of the original method and ensuring the advantages of the original method, it can better eliminate the interference of lipid blood, jaundice, and hemolysis on TPR determination. , And set R1: R2 to 3: 1, which is conducive to the simultaneous addition of reagents in the automatic analyzer. Therefore, it is recommended that a laboratory with a fully automatic analyzer should use a two-agent method to determine serum TPR, which is conducive to improving the accuracy of the results.
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