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AL-2021 Hydrogen Peroxide (H2O2) in Air and Water Monitor

General Description

The Model AL-2021 is a state-of-the-art digital hydrogen peroxide (H2O2) analyzer that is available in several different application-specific configurations. Both single and dual channels models are available for air or water H2O2 measurement applications.

Features

Absolute calibrated concentrations for H2O2 and relative values for organic peroxides

Fully automated operation using internal micro controller

Automated calibration using internal H2O2 permeation source and/or liquid H2O2 standards

Liquid phase ranges: 0-30.0 m g/l

Gas phase ranges gas phase: 0-20 ppbV
0-200 ppbV

H2O2 gas phase detection limit of < 50 ppt

H2O2 liquid phase detection limit of <70 ng/l

Rugged and simple to use

RS-232 Serial interface

Applications

Plastics Production

Pharmaceuticals

Chemical Research

Ozone Drinking Water Purification

 

 

Principle of Operation

The detection of peroxides is based on the liquid phase reaction of peroxides with P-Hydroxyphenylacetic Acid catalyzed by Peroxidase. This reaction produces a fluorescent dimmer that can be excited at 326 nm (Cd-lamp) and detected between 400 and 420 nm. The technique is sensitive to all peroxides in the solution.

To distinguish between H2O2 and organic peroxides two parallel channels are used. In one channel (channel B) of the instrument, H2O2 is destroyed selectively by catalase prior to the fluorescent detection in the instrument. The amount of H2O2 is then given by the difference between the signals from the two channels - signal for total peroxide (channel A) minus the signal for total per-oxide without H2O2 (channel B) - corrected for the destruction efficiency of the catalase solution.

catalase

2 H2O2 2 H2O + O2

The above reactions are carried out in aqueous solution of peroxides and other reagents. Therefore, for the measurement of gaseous peroxides, these have to be trapped in aqueous solution first. This is achieved in a stripping coil by pumping air and a stripping solution (pH-Buffered water free of H2O2) continuously at known flow rates. The air and liquid streams are afterwards separated in a glass separator and the solution is then analyzed for peroxides.

In the instrument, capable for measuring H2O2 in air and water samples, the H2O2 mixing ratio in air is then calculated from the concentration in solution and the ratio of air and stripping solution flow rates.

The coil size and the flow rates of air and stripping solution are optimized for quantitative stripping of H2O2. Due to lower solubilities however, the stripping efficiency for other peroxides is lower than that for H2O2 and probably varies between the 60% found for Methylhydro peroxide and 100% for H2O2. As the composition of organic peroxides in air is unknown, the signal from channel A (after destroying H2O2 by catalase) gives only an approximate estimate of the concentration of organic peroxides. Therefore, the instrument cannot determine exactly the amount of organic peroxides in air but a relative measure of the concentration is indicated.

Provided the sensitivity is known for each channel, this is the case after performing an calibration cycle, the calculation of concentrations is done in two steps. In the first step the equivalent mixing ratios are calculated from signals from both channels. In the second step, the H2O2 concentration is calculated from the difference of two equivalent mixing ratios. This difference is then corrected for the transmission efficiency of the inlet tubes, for the catalase destruction efficiency, and for the efficiency of the zero trap.

Peroxides in water solutions can be measured directly. In this mode, stripping is not necessary and, consequently, either zero air has to be applied to the samples inlet or the internal zero trap has to be switched on. Model AL2021W has been designed for measuring H2O2 only in water samples. Therefore, no stripping coil is required.

Due to time response, in applications requiring two channels (such as input vs. output process checks) or simultaneous air and water measurements two analyzers are used ganged together. The fully automated nature of the system allows the system to be tailored to many configurations and on line process applications.

 

Specifications

Physical Dimensions

Length 33 cm

Width 17 cm

Height 21 cm

Weight 7.5 kg

Power Requirements

120/240VAC, 80 Watts

Operating Environment

10 - 40 C

5 - 95% Relative Humidity

Measurement Range

Liquid phase (provides calibration by liquid peroxide standard):

0 to 300 m g/l*

Gas phase (provides calibration by liquid peroxide standard if no gas phase standard is available):

0 to 100 ppbV *

Gas phase (provides calibration by gas standard. gas standard permeation rate can be determined by using liquid standard)

0 to 100.0 ppbV

Detection limit

< 50 ppt gas phase (calibration with 30 m g/l or internal H2O2 source)

< 0.07 m g/l equivalent to 2 * 10-9 M in solution (liquid phase)

Noise (each channel)

< 2% at full scale

Time constant

100 sec (10-90%), delay time 180 sec

Interference from

(e.g. 100 ppb O3 would indicate a signal of 30 ppt in presence of O3 perterber)

O3 30 ppt H2O2/100 ppb

NO 12 ppt H2O2/100 ppb

No detectable interference from

SO2, PAN, NO2, Glyoxal, Isobutane, Iso-butylene, 1-Butane, Formaldehyde, Benzene, Toluene, Methanol, Acetone, Methyl-amine, Dimethylamine, n-Butane, Cis-2-Butene, Trans-2-Butene, and Ions such as Iodide, Chloride, Nitrate, Bromide, Phosphate, Benzoate

Zeroing

internal zero trap

Signal output

Analog: 0-5 Volts FS. calibration sets automatically output to 4.0 Volt of maximum value of chosen range

Digital: via RS-232 serial interface

Maintenance Interval

1 Month (typ)

Calibration

Internal H2O2 permeation device or liquid of H2O2 standards

 

 

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This page was last updated on Monday, September 11, 2006 .