Leaf residues, extraction methods

Coca paste production Coca leaves are mixed with calcium hydroxide (lime) and water. The mixture is crushed and stirred in a hydrocarbon solvent, usually kerosene. The extracted coca leaf residue is removed and the kerosene extracted with acidified water. The cocaine alkaloids are extracted into the aqueous layer and coca paste is precipitated by the addition of base. This paste contains crude cocaine as well as a mixture of inorganic salts. Alternatively, the leaves can be crushed in dilute sulfuric acid, extracted with kerosene, and the aqueous layer made alkaline with ammonia or a similar method to precipitate the alkaloids. 

Extracts of gloves, extracts of foliar dislodgeable residue and absolute foliar residues, and filters containing thiophanate-methyl were analyzed by reversed-phase HPLC and ultraviolet detection at 254 nm (Engel, 1988). The LOD was 50 mg/L for extracts of filters and gloves, and 10 mg/L for leaf samples. Recovery was > 90%, and the "between days" CV of the analytical chemical method was < 5%. 

For the assay of cocaine in Eiythroxyion coca Lam. from three locations in Peru, Turner et al.3 worked out a gas chromatographic method. The alkaloids were extracted by refluxing the powdered leaf samples (1.00 g) with ethanol (40 ml) for 15 minutes. The filtrate was evaporated to dryness under reduced pressure in a rotary evaporator, the residue dissolved in 20 ml chloroform and the alkaloids extracted into 1.5 aqueous citric acid. The pH of the solution was adjusted to 8.2 with sodium bicarbonate and the alkaloid bases extracted with chloroform. After evaporation the residue was dissolved in ethanol containing the internal standard (androst-4-ene-3,17-dione) and gas chromatographed on a packed column of 6 % OV-1 on Chromo-sorb W. A typical chromatogram is shown in Figure 9.2 and the results of the analysis in Table 9.6. 

Dislodgeable foliar pesticide residues and leaf dust were isolated by methods described in the published literature (5.6.7.8). Basically the method for the extraction of dislodgeable carbaryl... 

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