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GAS91D Formaldehyde Passive Dosi-Tubes 0.1 – 20ppm

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GAS91D Formaldehyde Gastec Passive Sampling Dosi Tubes (Time Weighted Average Detector Tubes)

The Dosi-Tube System allows an operator to evaluate the level of gas a worker is exposed to over a time period such as a working shift.

The Dosi-Tube is easily clipped into the dosi-tube holder (GAS710) which is worn on a garment of clothing.

Measuring Range 0.1 to 20 ppm
Sampling Hours 1 to 10 hours
Detecting Limit 0.05 ppm (10 hours)
Colour Change Yellow        Reddish Brown
Reaction Principle Formaldehyde reacts with hydroxylamine phosphate to liberate Phosphorous acid, which discolours pH indicator to reddish brown.
Coefficient of Variation 10% (for 1 to 20 ppm∙hr)
Shelf Life Up to 1 year from point of manufacture
Corrections for
temperature & humidity
Store the tubes in the refrigerator to keep at 10oC (50oF) or below.


Possible coexisting substances and their interferences


Substance Interference Change colour by itself
Aldehydes, Ketones, Acid gases Plus error Discolours reddish brown
Other substance measurable with this detector tube
Substance Correction Factor Sampling Time Measuring Range
Acetaldehyde 1.0 1 to 10 hours 0.1 to 20 ppm
Furfural 3.0 1 to 10 hours 0.3 to 60 ppm
Methyl Ethyl Ketone 1.25 1 to 10 hours 0.125 to 25 ppm
Calibration gas generation Diffusion tube method

Additional Information

Weight 0.1 kg
Multi Gas Tags


Gas Range



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