The H O monitor AL2021 from Aero-Laser has an extraordinary high sensitivity and a unique low detection limit of

100ppt (parts per trillion) for gaseous samples and 100 ng/liter (eq. 2×10 molar) for liquid samples, respectively.

The complete chemical processing, including gas stripping, is integrated into the instrument.

The detection technique is based on an enzymatic peroxidise reaction, which is not only sensitive for , but also

for other peroxides. Hence, after stripping the sample gas, the aqueous solution is separated in two channels. In

channel A the concentration of all peroxides is measured, while is selectively destroyed by the

enzyme catalase. The absolute concentration of is further calculated from the difference of the signals of both

channels. These signals are obtained by exciting the products of the peroxidase reactions with UV light and

detecting the fluorescent light by photomultipliers. With this method an extraordinary selectivity is achieved,

avoiding interferences from other substances. The AL2021 is the only instrument worldwide providing continuous

concentrations of in the range around and below 1ppb.

The AL2021 was originally developed for environmental and climate research and is employed worldwide in

atmospheric monitoring stations. Since is getting more and more important in the field of sterilisation and

decontamination, the instrument is widely used by the pharmaceutical industry for controlling of the atmosphere

inside filling systems.

2 2

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[1] A.L. Lazrus, G.L. Kok, S.N. Gitlin, J.A. Lind, S.E. McLaren,

,Anal. Chem. 57 (1985) 917