Determination of bis-(N-cyclohexyl-diazeniumdioxy)-copper in different matrices by photometer, thermal energy analyzer and HPLC
J Wittenzellner, W Hettler, M Maier
For the quantitative analysis of bis (N-cyclohexyl-diazeniumdioxy)-copper (Cu-HDO) three analytical methods are used. The employment of the different methods depends on the matrices involved. For several years now, the colorimetric determination of Cu-HDO by photometer has been applied to solutions and concentrates of wood preservatives. In principle, the technique consists of a quantitative conversion of Cu-HDO into a Fe-complex and the measurement by photometer compared to a calibration curve in a range of 20 to 220 mg Cu-HDO per liter. The colorimetric technique is unsuited to extracts of complicated materials such as soil or wood because of disturbances due to other ingredients of these matrices. Further, the method is not suitable for samples with a concentration below 10 mg Cu-HDO per liter. In the case of difficult analytical problems in the determination of Cu-HDO (e.g. soil or air from working areas) another technique, involving the detection by Thermal Energy Analyzer (TEA), is applied. In the first step of the method, Cu-HDO sets nitrogen monoxide (NO) free by a reduction reaction with NaI / acetic acid / sulphuric acid in a laboratory converter. A helium gas flow transfers the nascent NO into the TEA. There, NO is detected by chemiluminescence which originates from its reaction with ozone. The large expenditure of work and the high costs of the instrumental equipment are handicaps for a wide use of the analysis by TEA. A new technique based on the widespread analytical system HPLC was therefore developed to determine Cu-HDO in the important matrix wood. The chipped wood sample is first leached by a mixture of methanol p.a. and 0,05 M KH2PO4-solution at room temperature and the content of the active substance subsequently analysed in the filtered extract by HPLC with UV-detection. The concentration is calculated on the basis of external standard calibration. In studies carried out on impregnated pine samples (pinus sylvestris) in different laboratories, percentage recoveries for Cu-HDO of more than 80% were achieved.