Organotin compounds have found two important
industrial applications. A major portion of the organotin production is used as additives in plastics (PVC-stabilizers, co-catalysts for PU-foams). The second field of application is the use as biocides (agriculture, wood preservation and antifouling paint). The latter use results in a direct environmental impact causing unintended damage to non-target biota. Their toxicity is strongly dependent on the number
and nature of organic substituents, i.e., a species sensitive analytical procedure is very important for the assessment of organotin pollution.
One of the most recent methods for the speciation of organotin is gas chromatography (GC) coupled with an atomic emission detector (AED) in which the atoms are excited by a microwave plasma (MIP). Several publications have shown the excellent aptitude of this technique for the quantification of organotin compounds (Tutschku et al., 1994); Ceulemans et al., 1993; Liu et al., 1994).
The major aim of this study was the improvement of an analytical procedure for the speciation of organotin compounds in water samples. The preparation of samples for GC analysis consists of aqueous phase ethylation with NaBEt4 and extraction into hexane. For the mesurements described only standards of ethylated organotin salts were used. They were prepared by a Grignard reaction with EtMgBr and the appropriate organotinchloride in hexane. The following componds were obtained: monomethyltintriethyl (MMT), dimethyltindiethyl (DMT), trimethyltinethyl (TMT), monobutyltintriethyl (MBT), dibutyltindiethyl (DBT) and tributyltinethyl (TBT).
The first parameter examined was the injector temperature. The emission intensity of all compounds showed a distinct increase with temperature ranging from 170 to 290°C. At higher temperatures the intensity of some compounds decreased.
Concerning the plasma conditions the helium makeup flow and hydrogen pressure have been intensively studied in literature, however only little is known about the influence of oxygen in the plasma. A systematic experiment revealed that oxygen pressure is a very sensitive parameter for emission intensity. After a careful pressure optimization an emission maximum between 1.0 and 1.25 bar was observed for all compounds.
The most intense emission line out of 12 lines investigated (224.6, 235.5, 242.9, 270.7, 284.0, 286.3, 300.9, 303.4, 317.5, 326.2, 563.2, 606.9, all in nm) was found to be at 326.2 nm. At this wavelength detection limits of at least 0.2 pg Sn (calculated as 3s) could be reached by peakheight evaluation.
The used device was a Hewlett Packard GC (HP 5890 Series II Plus, autosampler HP 7673) coupled with an AED (HP 5921 A).The following parameters can be proposed for the speciation of organotin compounds with a GC-MIP-AED:
Injection: 1 ml splitless, temp. 290°C, oven: 50°C for 3 min, heating rate 28°C/min to 250°C, transfer line and cavity temp.: 250°C, helium makeup flow: 210 ml/min, H2: 4 bar, O2: 1.1 bar, Sn 326.234 nm.
Subsequently to the analytical procedure sample preparation has to be optimized. This will be done with respect to new techniques such as the SPME (solid phase micro extraction) which has been presented by Tutschku et al. (1995) for the use in organotin analysis.
Ceulemans, M., Lobinski, R., Dirkx, W. M. R. & Adams, F. C., Fresenius J. Anal. Chem. 347, 256-262 (1993).
Liu, Y. L., Lopez-Avila, V., Alcaraz, M. & Beckert, W. F., J. High Resoln Chromatogr. 17, 527-536 (1994).
Tutschku, S., Mothes, S. & Dittrich, K., J. of Chromatogr. A 683, 269-276 (1994).
Tutschku, S. et al., Fresenius J. Anal. Chem. in press, (1995).