| D. Breuer, BIA, Sankt Augustin, Germany
Water mixed metal working fluids (MWF) provide good growth conditions for micro-organisms. MWF's befallen by bacteria or fungi can cause numerous problems, beginning with the unpleasant odour of the emulsions, to difficulties for production processes, all the way to the possibility of health problems through skin contact or the inhalation of the aerosols.
Because a medicinally harmless germ concentration cannot be detected, the germ contamination in cooling lubricants should be as low as possible. In order to reduce the presence of microbes, biocides are added to the MWF's, which have a sterilising effect when used in small quantities. Yet if the biocides are added in too high a concentration, they can lead to health problems such as skin irritations by themselves.
Capillary electrophoresis is particularly suitable for determining the biocide content. Whereas a complicated sample preparation is necessary when using chromatographic methods, the cooling lubricant only needs to be diluted and filtered in water before the analysis with capillary electrophoresis.
There were 35 cooling lubricant concentrations studied. In 29 samples, one or more biocides were shown with benzotriazoles (22 samples), sodium pyrithion (7 samples), and benzoic acid derivatives (6 samples). The concentrations of the benzotriazoles generally lay in the range of 0.05¡ã% to 0.3¡ã%. In one case, a content of 9.2¡ã% was indicated ¡ª a concentration which should be seen as critical.
The method can also be used to determine the air concentration. To do this, the aerosol content that could be inhaled is collected on a quartz fibre filter. To prepare the samples, the filters are layered with water and filtered. The method fulfils the general requirements for measuring procedures in the air in work areas. | 