Extraction is the first key step in the analysis of organic tin samples, especially for complex biological samples. Before instrumental analysis, it is necessary to selectively extract the target compounds from the matrix. Common organic tin extraction techniques include the following methods: non-polar solvent extraction, non-polar solvent extraction with acid, polar solvent extraction, solid-phase extraction, supercritical fluid extraction, alkaline or enzymatic hydrolysis, extraction using chelating agents, and the recently developed solid-phase microextraction technique.

Non-polar solvent extraction is commonly used for dry samples or water samples. Common organic solvents include hexane, benzene, dichloromethane, pentane, isooctane, toluene, etc. Parks et al. found that toluene has a better extraction efficiency than methyl isobutyl ketone (MIBK), chloroform, and n-hexane, due to the fact that MIBK can form polymers with seawater. Hexane can only extract 50% of tributyltin, and chloroform has a very low extraction efficiency for tributyltin, while toluene can provide a better recovery rate. Mixed solvent extraction can also be used for organic tin. When Matthias et al. extracted butyltin compounds from water samples with chloroform, the extraction rate for tetrabutyltin was 60%, and that for tributyltin was 95%. When sodium borohydride derivatization and dichloromethane extraction are carried out simultaneously, the response of monobutyltin and dibutyltin compounds can be increased by 50%, and the recovery rates of other butyltin compounds are also improved. Sometimes a buffer solution is added before extraction to adjust the sample pH to between 5 and 6. Common buffer systems include acetic acid-sodium acetate, citric acid-disodium hydrogen phosphate or potassium phosphate buffer. Extraction is usually carried out by shaking, mechanical agitation, stirring reflux, or ultrasonication. Soxhlet extraction is only applicable to the extraction process of volatile solvents without chelating agents. The selection of the extraction solvent needs to take into account the physicochemical properties of various organic tins. Generally speaking, for those alkyl tins and short-chain organic tins (such as methyltin) with good solubility and larger polarity, effective extraction cannot be carried out with non-polar organic solvents and ligands alone. The matrix effect is very significant, and it is often necessary to use chelating agents such as cycloheptanedione with organic solvents to increase the solubility of organic tin and carry out corresponding purification treatment. Slu et al. compared two extraction solvents when extracting organic tin chlorides from mud samples. The toluene-isobutyl acetate-cycloheptanedione mixed solution can achieve higher recovery rates for each butyltin, which are 94.4%±4.7% (tributyltin), 94.9%±2.2% (dibutyltin), and 86.3%±4.2% (monobutyltin), respectively. However, the extraction rate of the less polar dibutyltin chloride and dibutyltin chloride with a hexane-isobutyl acetate mixed solution as the extractant is only 60% to 70%, and the extraction rate of monobutyltin chloride is even lower. Chau et al. compared the most commonly used six extractants and different extraction operations. These six extractants and methods are: ① toluene; ② dichloromethane; ③ 0.5% cycloheptatrienedione-hexane solution; ④ 0.5% cycloheptanedione-dichloromethane solution; ⑤ 0.5% cycloheptatrienedione-toluene solution; ⑥ extraction with 0.5% cycloheptanedione-toluene solution after acid reflux for 2 hours. According to the recovery rate results, the extractant containing cycloheptanedione will be conducive to improving the extraction efficiency. Choosing the ⑤th extractant for extraction, each butyltin can achieve a high recovery rate of 90% to 114%. Using sodium diethyldithiocarbamate as a ligand and then extracting with hexane can also effectively extract organic tin complexes from samples.

The extraction method of non-polar solvent with acid has been widely used for non-biological or biological samples. The main purposes of sample acidification are twofold: ① to dissolve inorganic particles in the sample that affect the determination of organic tin, including carbides and sulfides; ② to convert organic tin compounds into halides that are easily extracted by organic solvents. However, the disadvantage of acidification with halides is that organic tin compounds are prone to lose organic groups after being attacked by halide hydrogen nucleophiles, thereby changing their original forms. Therefore, different acids need to be used for acidification according to different samples during analysis. Chau et al. compared the use of different acids (hydrochloric acid, hydrobromic acid solution, acetic acid, sulfuric acid) to acidify water samples in order to improve the extraction efficiency when determining methyltin and inorganic tin in water samples, and then extracted with 5mL 1% cycloheptanedione (tropolone)-benzene solution. It was found that hydrochloric acid and hydrobromic acid solution can improve the recovery rate of Sn by preventing the hydrolysis of Sn4+ and the adsorption of container walls, but they inhibit the recovery of dimethyltin and trimethyltin; acetic acid acidification can improve the recovery rate of dimethyltin and monomethyltin, but the recovery rate of dimethyltin and inorganic tin is reduced; sulfuric acid acidification cannot improve the recovery rate of these four tin compounds. Relatively speaking, the operation of adding hydrochloric acid to the sample, followed by solvent extraction after shaking or ultrasonication, is more common. In addition, HBr or HAc can enhance the ion-pair effect and effectively improve the extraction efficiency of organic tin such as monobutyltin. Vleinema et al. compared several extractants for extracting butyltin compounds from water samples. Samples acidified with hydrobromic acid solution can completely extract tributyltin and dibutyltin with benzene and chloroform, and organic solutions containing 0.05% cycloheptatrienedione can better extract tributyltin, dibutyltin, monobutyltin, and inorganic tin. Although the reports in various literatures differ in the concentration of acid added, treatment time, and shaking methods, this process is all carried out at room temperature. Recently, ultrasonication has become a common extraction method for non-biological samples, while biological samples commonly use low-energy stirring methods such as shaking and magnetic stirring. There is no consensus on the choice of solvent for extraction samples. Commonly used solvents include dichloromethane, pentane, hexane, isooctane, ethyl acetate, benzene, toluene, ether, DCM, and some people also use mixed solvents such as hexane-ethyl acetate, hexane-isobutyl acetate, toluene-isobutyl acetate, hexane-ether, pentane-ether. When benzene is used as the extractant, an excess of Grignard reagent can be added for more convenient operation. However, toluene will interfere with the determination of dimethylbutyltin, and chloroform and dichloromethane can react with Grignard reagents, so other solvents need to be used for replacement before the Grignard reaction. Solvents that reduce the polarity of the medium, such as toluene-acid (such as acetic acid), can meet the extraction efficiency of organic tin and help selectively extract organic tin from the precipitate for classical derivatization reactions. When using HCl, the salting-out effect of biological samples or the ion-pair effect of NaCl can increase the efficiency of organic tin transfer from the aqueous phase to the organic phase. Since methyltin is more easily polarized and solvated than long-chain butyltin, the addition of salt during extraction can effectively improve the recovery rate, and the salting-out effect of different amounts of sodium chloride is different. Generally speaking, adding 3.6 to 4.0g of sodium chloride to 100mL of water sample is good for the recovery rate of all methyltin and inorganic tin. Hattori et al. used hydrochloric acid to acidify various samples to convert organic tin compounds into organic tin chlorides when determining dibutyltin, dibutyltin, dipropyltin, and diphenyltin in environmental water samples and bottom mud. Although trialkyltin can be directly extracted with hexane, the extraction rate of dialkyltin with hexane alone is only 50%. This defect can be overcome by adding sodium chloride to each sample first. The extraction rate of trialkyltin and dialkyltin is 90% to 100% after the samples with added sodium chloride and hydrochloric acid are extracted with hexane. Shhora and Mastsui added 1.5