Distillation, analyte recovery

The first step in using SPE is to condition the sorbent with an appropriate solvent. This prewetting increases the capacity of the bonded surfaces by opening up the hydrocarbon chain of the bonded-phase sorbents [31]. For nonploar sorbents, such as C,8) and for the ion exchangers, one column volume of methanol followed by one column volume of distilled water is required. Excessive washing with water will reduce analyte recovery [32]. Polar sorbents such as diol, cyano, amino, and silica should be rinsed with one column volume of a nonpolar solvent such as methylene chloride. Aternate cleanup methods may have to be developed if the analyte is sensi-... 

The fluoride amount recovery by Willard-Winter distillation process using a mixture of mineral acids (50 % v/v) was 3.2 0.1 % F. The new analytical conditions using H SO obtained from the chemometric study gave the result of3.3 0.2%F. 

The same analytical methods as for liquid sodium have been applied. Distillation separates and concentrates the impurities prior to analysis. Amalgamation has poor recovery value for oxygen compared to distillation (Table 1). ... 

An analytical sample may be prepared by quick distillation (or Kugelrohr distillation) at 117-120°C (15 mm), but there is significant loss of material because of decomposition in the distillation pot. From 1 g of product, 0.72 g of pure material is obtained in this way, and recovery decreases as scale of distillation increases. 

During sampling cruises 3-5, 20 L of sample from the ultrafilter was preserved with chloroform, shipped back to an analytical laboratory, and vacuum-evaporated to 500 mL before being passed through a 500-mL column of XAD-8 resin (27). This revised procedure should have increased the recovery of DOM because of a 10-fold increase in the resin water ratio. In addition, hydrophilic organic solutes that did not adsorb on the XAD-8 resin were isolated by a vacuum-evaporation procedure whereby water is distilled from acetic acid and inorganic salts precipitate in the acetic acid (28). Recoveries of DOC by the two procedures are presented in Table IV. 

A second portion of soil, or the soil fraction from the dichloromethane extraction (after drying in a fume cupboard for approximately lh), is extracted with distilled, deionized water in the manner described above for the dichloromethane extract. Usually, sonication is avoided because it may reduce recoveries of the polar CWC-related chemicals by creating new active sites for analytes in the soil. The extracts are centrifuged, filtered, and combined and the pH is determined. 

Many investigations have been carried ont of procednres for improving the analytical qnality of GC methods by changing the matrix, increasing the concentration of the pertinent analytes and redncing the interference of other componnds present in the sample. Preconcentration by LLE, before or after derivatization, is most freqnently apphed in GC trace analysis however, other techniqnes, snch as SPE, sample stacking (see Section V.A.l) and some of their modifications, snch as simnltaneons distillation and extraction (SDE) and SPME, are also mentioned. Application of microwave-assisted processes (MAP) dnring sample preparation seems to improve recoveries. 

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