Formaldehyde HCHO NO.91L
91L


Performance

Measuring Range

0.1 to 5 ppm

5 to 40 ppm

Number of Pump Strokes

5

1

Correction Factor

1

8

Sampling Time

1.5 minutes per pump stroke

Detecting Limit

0.05 ppm (n=5)

Color Change

Yellow Reddish Brown

Reaction Principle

Formaldehyde reacts with hydroxylamine phosphate to librate
phosphorous acid, which discolors pH indicator to reddish brown
3HCHO + (NH2OH)3H3PO4 H3PO4
H3PO4 + Base Phosphate
Coefficient of Variation

10% (for 0.1 to 0.5 ppm), 5% (for 0.5 to 5 ppm)
Shelf Life 3 Years
Corrections for
temperature & humidity		 Temperature correction is necessary
Store the tubes in the refrigerator to keep at 10oC (50oF) or below.


Possible coexisting substances and their interferences (NOTE)

Substance

Concentration

Interference

Change color by itself

Aldehydes

 -

Plus error

Produce reddish brown stain

Ketones

 -

Plus error

Produce reddish brown stain

Acid Gases

 -

Plus error

Produce red stain

Organic acids

 -

No effect

No stain by themselves


Other substance measurable with this detector tube

Substance

Correction Factor

No. of Pump strokes

Measuring range

Diisobutyl ketone

5.8

4

0.58 to 29 ppm

Methaldehyde

0.65

3

0.065 to 3.25ppm

Propionaldehyde

7.6

1

0.76 to 38 ppm


91L Tube Reading (n=1)

0.2

0.5

1

2

3

4

5

Benzaldehyde (ppm)

2

4

9

22

40

63

92

91L Tube Reading (n=1/2)

0.2

0.5

1

2

3

4

5

Cyclohexanone (ppm)

10

30

60

130

220

330

470


Calibration gas generation Diffusion tube method


TLV-TWA TLV-STEL Explosive range
- C 0.3ppm 7.0 to 73%

Copyright(c) 2001 GASTEC CORPORATION. All rights reserved.