[Determination of formaldehyde concentration in a low-pressure sterilizer]

Two methods are described in determining the concentration of Formaldehyde in the sterilisation chamber of a regular commercial sterilizer. The measurement and flow of the concentration is ascertained during a routine sterilization procedure. With regard to the biological efficiency test of the examined apparatus the stability of the active Formaldehyde concentration is controlled. The difficulty in the determination of the Formaldehyde in such sterilizers is due to the fact that samples must be taken at a reduced pressure of 200 mbar. We have developed two different sampling methods. By employing the first continual collection method Formaldehyde gas is drawn out of the sterilization chamber with a high vacuum pump and conveyed with hydrogen into a nickel catalysator, whereby Methane is formed. The determination of Methane is carried out with a flame ionisation detector (F.I.D.). The results of the F.I.D. method are between 10.1-10.8 mg Formaldehyde per litre of gas. It is possible to detect a slight, even reduction in the Formaldehyde concentration throughout a period of 90 min. With the second discontinual method of determination vacuum tubes are employed which are furnished with external magnetic valves for control. By opening the magnetic valves briefly during the pre-vacuum therewith causing loss of pressure, Formaldehyde gas can be collected in the vacuum tubes throughout the sterilization procedure. The determination of the samples extracted by the discontinual method is carried out spectrophotometrically using the p-Rosanilin method after Miksch et al. The second method of determination shows values of 9.0-9.8 mg/l (Sx = 0.8 mg/l). These results lie somewhat lower than those of the F.I.D. determination. The flow of the concentration during 90 min. shows an average reduction of 7.4% and matches exactly the curve which was obtained by the F.I.D. method. By measuring the Formaldehyde concentrations which goods are subjected to in normal sterilization procedure it is possible to examine the efficacy of Formaldehyde sterilizers under regular conditions. Only by quotation of the Formaldehyde concentration present is it possible to reproduce details on sterilization times of treated articles.