GAS91D Formaldehyde Passive Dosi-Tubes 0.1 - 20ppm


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Shelf Life - a1-cbiss will never dispatch detector tubes with less than 3 months remaining before expiry. a1-cbiss employ a stock rotation policy of first in, first out. Specific shelf life requirements must be identified at the point of order placement (use the comment box in the checkout process). The expiry date is printed clearly on the front of the detector tube packet.

Excl. VAT: £36.75 Incl. VAT: £44.10
Excl. VAT: £36.75 Incl. VAT: £44.10

Product Description


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





Change colour by itself

Aldehydes, Ketones, Acid gases

Plus error

Discolours reddish brown


Other substance measurable with this detector tube



Correction Factor

Sampling Time

Measuring Range



1 to 10 hours

0.1 to 20 ppm



1 to 10 hours

0.3 to 60 ppm

Methyl Ethyl Ketone


1 to 10 hours

0.125 to 25 ppm


Calibration gas generation

Diffusion tube method


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Product Downloads

View FileGAS91D Formaldehyde Datasheet
View FileGastec Detector Tube List 25th Edition & Manual
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