Charcoal separation method limitations

Separation of DEHP from environmental samples is usually by extraction with an organic solvent such as acetonitrile, chloroform, ethyl acetate, hexane, or methylene chloride. Air samples are drawn through a solid sorbent material (e.g., charcoal or XAD-2 resin) and desorbed with carbon disulfide (NIOSH 1985b) or ether/hexane (Rudel et al. 2001). A purge and trap method might be used for separation of DEHP from the fat in foods (van Lierop and van Veen 1988). Detector options are identical to those mentioned above (Section 7.1). Detection limits for these methods are generally in the ppb range. 

Several separation and preconcentration methods for analysis of 3-MH, 3-MHA, and 4-MP, were reported (Tominaga et al., 1998 Schneider et al, 2003 Mateo-Vivaracho et al., 2007). Recently, HS-SPME-GC/MS method with limits of quantification (LOQs) of a dozen ng/L (close to the sensory thresholds of 3-MH and 3-MHA) was proposed (Fedrizzi et al., 2007b). This method does not include determination of 4-MP because the sensory threshold of this compound in wines ( 0.4 ng/L) is too low. The method has to be calibrated using a white wine pretreated with charcoal, corrected to a total S02 100 g/L, and spiked with different quantities of standard solutions. The optimized HS-SPME conditions (temperature, sampling time, solution pH) are reported in Table 5.6. 

Such a method was developed by Schwenk et al. [22] for the determination of trace amounts of carbon monoxide and dioxide in ethylene. After chromatographic separation on a column of activated charcoal the sample components were transferred in a flow of carrier gas (hydrogen) into a reactor (35 x 0.6 cm) containing a nickel catalyst (20% of nickel on Sterchamol). At 300°C carbon monoxide and dioxide were quantitatively converted in the reactor into methane, which was then detected by a flame-ionization detector. With a large sample (25 ml) the detection limit was 10 %. 

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