Water-mixed cooling lubricants, or metalworking fluids, provide excellent environments for microorganisms to grow. Numerous studies over the last few decades have shown that the conditions for the growth of microorganisms are quite good in cooling lubricants. Diverse species of bacteria, yeasts, and fungi have been isolated in cooling lubricant emulsions. Aerobic bacteria can grow in the ventilated parts of a cooling lubricant circulation system. Anaerobic microorganisms are also often found growing on inner surfaces and in undisturbed areas within machines. Cooling lubricants contaminated with bacteria or fungi can cause numerous problems, beginning with the unpleasant smell of these emulsions (commonly known as "Monday odour" in metalworking industries in Germany), to production difficulties and health hazards resulting from skin contact or inhalation of the associated aerosols. Because it is not possible to designate an entirely harmless concentration of biological contamination, the microbial content in cooling lubricants should be as low as possible. Biocides with germ-killing effects at low quantities are added to metalworking fluids to reduce the microbial presence. If the biocides are added to the cooling lubricants in concentrations that are too high, these compounds themselves can also lead to health risks including skin inflammation and respiratory irritation. Substances employed as biocides often utilize the germ-killing effects of nitrogen-oxygen and/or nitrogen-sulphur aromatic heterocycles. Non-aromatics such as bismorpholinomethane (BMM) or hexahydrotriazine (HHT), which react to produce formaldehyde, are also used. Most of the analytical methods for determining these substances use high-performance liquid chromatography (HPLC) as the measurement technology, but HPLC often has the disadvantage of requiring complicated sample preparation procedures. A large number of these biocide compounds can be successfully analyzed using capillary electrophoresis (CE) under the proper conditions. The advantages of CE lie mostly in the ease of sample preparation, low consumption of reagents, high separation performance, and very short periods of analysis. The devices currently available are very robust and simple to automate. However, there are some disadvantages to CE, such as the use of a diode array detector (DAD) as a standard detector; to date, commercial CE instruments interfaced with mass spectral detectors have technical difficulties. Also, there are strict requirements on buffer composition used for CE. Additionally, because of the very small diameters of the capillaries used for separation, CE is often not suited for trace analysis.
Dr. Dietmar Breuer, BIA, Alte Heerstraße 111, D-53757 Sankt, Augustin, Germany