Assessment of polycrystalline graphites as sorbents for solid-phase microextraction of nonionic surfactants.

Two polycrystalline graphites (pencil lead and glassy carbon) were used as sorbents for solid-phase microextraction of a nonionic alkylphenol ethoxylate surfactant (Triton X-100). Analyses were performed by reversed-phase HPLC-fluorescence detection. The presence of the benzene ring in the congeners of Triton X-100 also allowed their direct detection at lambda(ex) = 230 nm and lambda(em) = 310 nm. Variables such as time of adsorption, time of desorption and concentration of surfactant in water were evaluated. The method limit of detection was found to be 0.5 microg/l for Triton X-100, with a linear dynamic range of 0.5-150 microg/l. Results were compared to those obtained using polymeric fibers such as PDMS/DVB and Carbowax/TPR. The chemical resistance and low cost of the polycrystalline graphites are advantageous over commercially available SPME fibers.

Sonication of aqueous solutions of chlorobenzene.

Sonication at two frequencies (20 and 900 kHz) was carried out on dilute (220 ppm) aqueous solutions of chlorobenzene. The formation of chloride ions was followed using ion chromatography. The solutions became more colored with time; the absorbance maximum was around 270 nm. Some of the compounds remaining in the solution could be identified; they were chlorinated phenols, chloronaphthalene, mono and dichlorobiphenyls, etc. At the same acoustic power, the rate of chloride formation with 20 kHz ultrasound was greater when a probe with a larger tip area was used, but significantly less than the rate with 900 kHz. The use of ultrasound for conversion of chlorine in organic compounds in water to chloride can thus be performed more efficiently using a higher frequency and with a lower intensity (power per area). There is, however, a possibility that the toxicity of the aqueous solution is increased by such treatment.