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AL-4021 Formaldehyde (HCHO) in Air and Water Monitor

General Description

The Model AL-4021 is a state-of-the-art digital formaldehyde (HCHO) analyzer that is available in several different application-specific configurations. Models are available for air or water HCHO measurement applications.


Provides absolute concentrations for HCHO (formaldehyde)

Simple to use, fully automatic operation

Automated calibration using internal HCHO permeation source or liquid HCHO standards

Liquid phase ranges: 0 to 30.0 m g/l
(user programmable) 0 to 300 m g/l
0 to 1.5 mg/l

Gas phase ranges: 0 to 20.0 ppbV
(user programmable) 0 to 200 ppbV
0 to 2.0 ppmV

HCHO gas phase detection limit of < 50 ppt

HCHO liquid phase detection limit of < 100 ng/l

Rugged design

RS232 serial interface and PC user software


Chemical Research

Pharmaceutical Production

Plastics Production and Quality Control

Environmental Quality Control

Standards Laboratories



Principle of Operation

The detection of formaldehyde is based on the so-called "Hantzsch"-reaction. The technique is sensitive to formaldehyde in aqueous solutions. Therefore, for the measurement of gaseous formaldehyde, 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 HCHO) continuously, at known flow rates. The air and liquid streams are afterwards separated in a glass separator and the solution is then analyzed for formaldehyde.

The Model AL4021 is capable of measuring HCHO in air and water samples, the HCHO mixing ratio in air is then calculated from the concentration in solution and the ratio of air and stripping solution flow rates.

Formaldehydes 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 sample inlet or the internal zero trap must be switched on.

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



Physical Dimensions

Length 49.6 cm

Weight 48.8 cm

Height 13 cm

Weight 20 kg

Power Requirements

120/240VAC, 80 Watts

Measurement Range (liquid calibration for can be user defined within the given ranges)

Measuring range 1: 0-30.0 m g/l or 1 10-6 molar

Measuring range 2: 0-300.0 m g/l

or 1 10-5 molar

Measuring range 3: 0-1.50 mg/l

or 5 10-5 molar

Measurement Range (gas phase provides calibration by liquid formaldehyde standard, if gas phase standards are unavailable)

Measuring range 1: 0-20.0 ppbV*

Measuring range 2: 0-200.0 ppbV*

Measuring range 3: 0-2.00 ppmV*

* These ranges depend on the flow rate of stripping solution and air flow which are user determined from time to time or after replacement of pump tubing and replacement of flow controller.

Measurement Range (provides calibration by gas standard gas standard permeation rate can be determined by using liquid standard)

Measuring range 1: 0-20.0 ppbV

Measuring range 2: 0-100.0 ppbV

This mode also allows measurement in liquid phase from 0-30 m g/l and
0-150 m g/l





Detection limit

equivalent to:

< 50 ppt gas phase**
< 100 ng/l

2 * 10-9 M (liquid phase)


< 2% at full scale

Time constant

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

Interference from

(e.g. 1:20,000 ppb indicates that a measurement signal of 1 ppb in the presence of a 20,000 ppb concentration of the perterber)

Benzaldehyde < 1 : 20,000

Acetaldehyde < 1 : 10,000

Acrolein < 1 : 10,000

Propanal < 1 : 20,000

Glyoxal < 1 : 123

Methanol < 1 : 50,000

H2O2 < 1 : 100

O3 < 1 : 3,000

No detectable interference from

Acetone, SO2, NO2, Isobutane


Internal zero trap

Signal output

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

Digital: via RS 232 interface

Maintenance Interval

1 Month (typ)


Distilled Water, Acetyl Acetone, Acetic Acid, Ammonium Acetate, H2SO4 and Zero-Trap


Internal permeation device using KIN-TEK permeation tubes



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