Solid-phase extraction is compared with solid-phase micro-extraction.

Related TopicsSolid Phase Extraction (SPE) - Versatile sample pre-processing technologyOne Solid Phase ExtractionSolid Phase Extraction (SPE) is a sample pre-treatment technology based on liquid-solid separation extraction developed by column phase
chromatography
technology. Since the late 1970s, SPE technology has developed rapidly in many fields, such as environment, due to its advantages of high efficiency, reliability and low solvent consumption. In foreign countries has gradually replaced the traditional liquid-liquid extraction and become a reliable and effective method of sample pre-treatment..SPE technology is based on the principle of liquid chromatography and can be approximated as a simple chromatography process. The adsorbent acts as a fixed phase, while the flow phase is a water sample during extraction. When the flow phase comes into contact with the fixed phase, some of the trace substances (targets) remain in the fixed phase. At this time with a small amount of selective solvent washed away, you can get the rich and purified target. Solid-phase extraction can be divided into online extraction line extraction of the former extraction and chromatography analysis completed simultaneously, while the latter extraction and chromatography analysis step-by-step completion, the two are consistent in principle.general solid-phase extraction procedures include the selection of solid-phase extraction columns (i.e. adsorbents), column pre-treatment, sample, wash, and enchantment. The factors to be considered in the experimental process are as follows: 1) The selection of adsorbents a. traditional adsorbents the most commonly used in environmental analysis of introspective adsorbents is more suitable for the collection and purification of non-polar to medium polar organic matter in water samples. Among them are the representative bonded silicone C18 and bonded silicone C8 and so on. The adsorbent mainly retains the target object by producing non-polar Van der Waal force or dispersion force through the hydrocarbon bond of the target object and the function group on the silicone surface.positive phase adsorbents include magnesium silicate, amino, cyanide, biol-bonded silicone and alumina, etc., mainly through the polar function group of the target object and the polar function group of the adsorbent surface polar interaction (hydrogen bonding, etc.) to retain the polar compounds dissolved in the non-polar medium. Because of its special principle of operation, it is often used in environmental analysis in association with other types of adsorption columns, adsorption to remove interference, and to achieve sample purification.ion exchange adsorbent mainly includes strong cation and strong anion exchange resin, the skeleton of these resins is usually styrene-dylethylene styrene co-polymer, mainly through the target of the charged group and bonded silicone on the charged group of electrostration attract each other to achieve adsorption.b.
antibody
bonded adsorbents (Immunosorbents-IS)are new adsorbents that take full advantage of the high sensitivity and selectivity between bioimmune
antigens
-antibodies, especially for the abundance and separation of trace organic matter in water. Its characteristics are, because the vast majority of organic pollutants are low molecular weight substances, can not cause immune response in animals, so it is required to bond the pending pollutants to the biomogluent vector of bovine
serum
albumin, so that it has immunoantigen activity, and then injected into the purebred animal body (such as rabbits or sheep), to produce antibodies, by hybrid tumor technology to produce a monoclonal antibody corresponding to the organic pollutant. By bonding the antibody to the silicone surface or polymer surface of the inverse adsorbent (e.g. C18 fixed phase), an antibody bonding adsorbent can be produced and can be used to isolate and collect specific contaminants. Research and development of monoclonal antibodies or polyclonal antibodies that can specifically detect various priority pollutants has become a frontier research field of SPE technology.antibody bonded adsorbent can generally be used 20% to 80% methanol-water solution, this kind of adsorbent can be stored by refrigeration can be used many times. The appropriate adsorbent should be selected according to the nature of the target object when carrying out SPE operation. Table 1 - 1 gives in addition to the commonly used adsorbent types and their associated separation processes, the properties of the enchantment and the nature of the parts to be tested.the amount of adsorbent is directly related to the properties of the target object (polarity, volatility) and its concentration in the water sample. In general, increasing the amount of adsorbent can increase the retention of the target object, by drawing the adsorption curve to determine the amount of adsorbent.2) Bar pre-processing .The purpose of resuming is to create an environment compatible with the sample solvent and remove impurities from the column. Two solvents are usually required to complete the task, the first solvent (primary solvent) for purifying the fixed phase and the other solvent (final solvent) for technology to create a suitable fixed phase environment for the sample adesthon to be properly retained. The amount of each active solvent is approximately 1 to 2 mL/100 mg fixed phase.solvent should not be stronger than the sample solvent, if the use of too strong solvent, will reduce the recovery rate. There is usually no problem with a solvent that is weaker than the sample solution. It is important to note that during and at the end of the reification process, the fixed phase cannot be dried, as this will lead to cracks in the filler bed, resulting in a low recovery rate and re-ability, and the sample has not been properly purified. If cracks appear in the column bed during the process of reification, the above-mentioned resuscing steps must be repeated.3) on the .The sample is added to the solid phase extraction column and the sample solution is forced to pass through the fixed phase, so that the adlyte and some sample interference remain on the fixed phase. In order to retain the adesthon, the solvent that dissolves the sample must be weak. If it is too strong, the admission will not be retained and the recovery rate will be very low, a phenomenon known as a leak. Using the weakest sample solvent possible allows the solute to be the strongest preserved or narrowest spectral band. As long as there is no leakage, a large volume of samples (0.5 to 1L) is allowed.sometimes a fixed sample must be extracted with a strong solvent, and such an extract cannot be directly sampled. Therefore, the extraction solution should be diluted with a weak solvent to obtain a suitable total solvent strength for sampling. For example, a soil sample is extracted from 50% methanol, 2 mL extract is obtained, diluted with 8 mL water, and 10% of methanol solution is obtained, so that the column can be extracted directly on the inverse solid phase without leakage.4) Wash .After the analyt is retained, it is usually necessary to wash the fixed phase to wash off the unwanted sample parts, the wash solvent is slightly stronger than or equal to the sample solvent. Washing solvents must be as strong as possible to wash off as many interfering parts as possible, but not strong enough to wash away any one adable. Solvent volume can be 0.5 to 0.8 mL/100 g fixed phase.should not use too strong solvent when washing, too strong solvent will be strong retained impurities washed down. Using too weak a solvent can increase the volume of the wash. It can be replaced by a mixture of strong and weak solvents, but the solvents used before and after mixing must be mutually soluble.5) Wash away .After washing, the adlyses are washed away from the fixed phase, and the amount of the washed solvent is generally 0.5 to 0.8 mL/100 g fixed phase. The solvent must be carefully selected, the solvent is too strong, some of the more retained unnecessary parts will be washed out;should also pay attention to the solvent's solubility when choosing to dissolute the solvent. The solvent flowing through the column bed must be mutually soluble with the previous solvent, a solvent that is not mutually soluble with the residual solvent in the column can not fully function with the fixation, of course, there will be no proper liquid solid distribution, resulting in poor recovery rate and undesirable purification effect. If it is difficult to use mutually soluble solvents, it is necessary to
dyress
the column bed;, solid-phase extraction technology is simple and easy to use, which can significantly improve chromatography separation, extend the life of
-chromatography column
, and reduce the detection limit of the method. Compared with traditional liquid-liquid extraction methods, SPE solid-phase extraction has significant advantages in: increasing sample handling yield, greatly reducing solvent consumption and waste generation, high recovery rate, good reproducible, very low impurity interference, no emulsification, multiple separation mode selection, and easy automation. However, the price of the consumables solid-phase extraction column used in the experiment is high, and the cost of the experiment can not be ignored.-phase micro-extractionSolid-Phase Microextraction (SPME) is a new test sample analysis pre-processing technology that has emerged internationally in recent years. Developed on the basis of solid-phase extraction, it retains all its advantages, discards the disadvantages of its need for column fillers and the use of solvents for de-absorption, as long as a solid-phase micro-extraction device similar to the sampler can complete all pre-treatment and sample work.Solid phase micro-extraction is mainly for the analysis of organic matter, according to the principle of "similar dissolving" between organic matter and solvent, using the chromatography of quartz fiber surface to fix the adsorption of relative analysis of the ingredients, the ingredients extracted from the sample substation, and gradually rich, complete the pre-sample process. In the process of inlet, using the high temperature of gas chromatography sampler, the flow phase of liquid chromatography and capillary electrophoresis de-absorbs the absorbent parts from the fixed phase and is analyzed by the chromatography instrument..The choice of SPME extraction method is mainly related to the volatility of the object to be measured, the substation and the nature of the probe fixed phase coating. SPME has three different extraction methods: top-empty extraction, air extraction, and direct extraction. Samples with particularly high volatility can be extracted by overhead or air, and direct extraction should be used for semi-volatile and non-volatile samples. many factors affect the efficiency of SPME extraction, mainly to optimize the factors that interfere with the adsorption and analysis of admins. The main parameters affecting the adsorption of the adlyss are fiber surface fixation phase type, extraction time, ion strength, pH, temperature, sample size and stirring. For SPME-GC, analysis is related to time and temperature, while for SPME-HPLC, analysis is mainly related to solvent type, volume and time. In the course of the experiment, the main factors of extraction effect are as follows: 1) fiber surface fixed phase type when choosing fixed phase should generally be considered from two aspects: (i) the polarity of the admin and fixed phase match, that is, the distribution coefficient, polarity and boiling point of the analytical parts in each phase should be taken into account, according to the principle of "similar dissolving", select the most suitable fixed phase of the analysis of the fixed phase; 2) Extraction time . The extraction time is the time required to contact the adsorption balance from quartz fibers and samples. In order to ensure that the experimental results are reproducible, the extraction time should be kept in the experiment. There are many factors that affect the extraction time, such as distribution coefficient, diffusion speed of the sample, sample size, container volume, substation of the sample itself, temperature, etc. In the initial stage of extraction, the analytical parts are easily collected into the fixed phase of quartz fiber, with the extension of time, the rate of accumulation is more and more slow, close to the equilibrium state even if the time extension is meaningless to the rich, so in groping the experimental method must do the rich-time curve, from the curve to find the best extraction point of time, that is, the curve close to the minimum time of flat. The general extraction time is between 15 and 180 min. 3) ion strength . Adding a small amount of sodium chloride, sodium sulfate and other inorganic salts to the liquid sample can enhance ion strength, reduce the solubility of polar organic matter in water, that is, play a salt analysis role, so that quartz fiber fixed phase can absorb more analytical parts. In general, extraction efficiency can be effectively improved, but not necessarily applicable to any components, such as Boyd-Boland in the test of 22 nitrogen-containing insecticides found that the use of most components after adding sodium chloride will significantly improve the extraction effect, but the evil grass, ethyl fluoroform ether and other pesticides are not effective; Fisher and others added inorganic salts to the analysis of pollutants in wine 25% higher than the results of the analysis. The amount of inorance salt added needs to be determined according to the specific sample and analysis parts. 4) pH . Changing the pH can change the distribution coefficient between the analytical components and the sample medium and fixed phase, which is beneficial to improve the adsorption of the analytical components in the sample. Because the fixed phase is a non-ionized polymer, it is more effective for adsorption-neutral forms of adlyses. Adjusting the pH of the liquid sample prevents the analysis group from separating the sub-groups and improves the ability to be absorbed by the fixed phase. For acidic compounds, the extraction efficiency is improved with the decrease of pH, and at low pH, the acid-alkali balance of acidic compounds shifts to neutralization and material, which is more conducive to the adversary being fixed phase adsorption. In contrast, for alkaline compounds, the pH decreases, the compound ionizes, and the extraction efficiency decreases. In the actual test, it was found that the pH changed between 4 and 11, which had no effect on the extraction efficiency of triamcinolone, nitrobenzene, substitute urethane, thioesteramide,
chloroacetalamide, diphenyl ether, amino compounds and oxygenated diazole
. However, at pH 2, the extraction efficiency of phphenyl ether and dinitrophenylamine is improved. 5) Temperature . The equilibrium time at which an adable enters a fixed phase is related to the extraction temperature, so it is necessary to select the appropriate extraction temperature to achieve satisfactory sensitivity within a reasonable time range. For immersive SPMEs, an appropriate temperature increase speeds up molecular motion and accelerates molecular diffusion, thus reducing the balancing time between extraction/water phases. Its optimal extraction temperature for triglycerides and thioesterethanes is between 55 and 60 degrees C. For overhead SPME, an appropriate increase in temperature can increase the concentration of gas on the liquid, thus increasing the sensitivity of the analysis. Its optimal extraction temperature for triage herbicides in human blood and urine is between 90.