No abstract

Total tin determinations can be accomplished at trace levels (10–25 ppb) by a continuous on-line hydride generation (HY), followed by direct current plasma (DCP) emission spectroscopy (HY-DCP). This approach is applicable for organotin compounds such as mono-, di-, and trimethyltin chloride, as well as stannous and stannic cations. HY-DCP methods of total tin analysis have been applied to a number of spiked and actual samples. Detection limits, calibration plots, sensitivities, and related analytical parameters have been evaluated. Organotin analysis and speciation can be accomplished by the interfacing of this HY-DCP step with high-performance liquid chromatography (HPLC), with the use of a polymeric PRP-1 type column with an acidic, ionic mobile phase, usually containing a suitable ion-pairing reagent. The overall speciation approach, HPLC-HY-DCP, has been evaluated with regard to separation conditions; detection limits; sensitivities; calibration plots; and applications to spiked water, clam juice, seawater, and tuna fish samples. The results suggest the suitability and reliability of this HPLC-HY-DCP approach for individual tin species. Other metal species capable of forming a hydride derivative on-line, in a continuous fashion, may also be suitable for speciation by HPLC-HY-DCP.

Gas chromatography (GC) has been interfaced very simply and inexpensively with a direct current plasma (DCP) atomic emission spectrometer in order to perform highly specific and selective determinations of methylmercury (MeHg) in fish samples. A simple, isothermal, low-cost GC was constructed which could be dedicated to the DCP, allowing routine qualitative and quantitative determinations of organomercury species in complex food matrices. Optimisation of the GC -DCP interface was accomplished, followed by a determination of the detection limits, the linearity of the calibration graph and comparison of the results with those obtained by GCelectron-capture detection (ECD) and total mercury by cold-vapour atomic absorption spectrometry. In most instances, qualitative and quantitative results for incurred and spiked levels did not agree for the GC -DCP and GC -ECD approaches. An additional extraction procedure has also been developed for MeHg from fish samples involving extraction with an organic solvent, concentration and injection on to the GC column. Depending on the particular organic solvent employed, artifact formation of MeHg can occur as a result of the extraction -GC conditions. Methods to avoid an artifact situation are suggested, and the possible implications of this for the currently accepted AOAC method involving GC -ECD.

A collaborative study on the determination of indole in shrimp was conducted in which a high pressure liquid chromatographic (HPLC) method and a spectrofluorometric method were compared with the AOAC gas-liquid chromatographic (GLC) method (18.075–18.078,13th ed.). In the HPLC method, 10 g shrimp was blended with methanol, an internal standard was added, and the extract was filtered. Indole was separated on an octadecylsilane reverse phase column, using 60% MeOH-H2O, and quantitated with a fluorescence detector (excitation 280 nm, emission 330 nm) by comparing the indole peak height with that of an internal standard, 2-methylindole. Recoveries at a 25 μg/100 g level averaged 104% with a range of 90–127%, and at a level of 35 μg/100 g averaged 102% with a range of 93–112%. In the spectrofluorometric method, 25 g shrimp was extracted with 2% EtOAc-hexane. After several washes, indole was partitioned into a saturated NaCl-MeOH solution and its fluorescence was measured (excitation 280 nm, emission 332 nm). Recoveries at a 25 μg/100 g level averaged 93% with a range of 0–255% and at a level of 35 μg/100 g averaged 64% with a range of 0–107%. Recoveries obtained by the AOAC-GLC method at a level of 25 μg/100 g averaged 96% with a range of 81–116% and at a level of 35 μg/100 g averaged 101% with a range of 81–119%. The coefficients of variation were 20,10, and 64% at a 25 μg/100 g level for the GLC method, the HPLC method, and the spectrofluorometric method, respectively. The HPLC method was adopted as official first action for indole levels in shrimp exceeding 1 μg/100 g.