The Gastec 91TP Formaldehyde Detector Tubes are designed for sensitive, low-level measurement of formaldehyde (HCHO) in air using a compatible automatic air sampling pump.

The 91TP provides a quantitative measuring range of 0.01 to 1.75 ppm, with a detection limit of 0.005 ppm under the specified sampling conditions. The tube produces a yellow-to-pale orange color change for visual determination of formaldehyde concentration.

Each box contains 10 detector tubes for 10 tests.

IMPORTANT STORAGE REQUIREMENT: Gastec 91TP detector tubes require refrigerated storage and have a manufacturer-specified shelf life of 12 months when refrigerated.

Automatic Air Sampling Pump Required

IMPORTANT: Gastec 91TP Formaldehyde Detector Tubes require a compatible automatic air sampling pump capable of maintaining the specified continuous sampling rate.

Compatible Pump: Gastec GSP-501FT Automatic Air Sampling Pump

The 91TP is an automatic air sampling pump detector tube and should not be treated as a standard hand-pump detector tube.

For the primary measuring range, the pump must maintain 100 mL/min for 10 minutes. For the extended measuring range, sampling is performed at 50 mL/min for 10 minutes.

Do not substitute a standard manual Gastec detector tube pump for the required automatic sampling method.

Measurement & Sampling Specifications

Measurement Range	Sampling Rate	Sample Volume	Correction Factor	Sampling Time
0.01–0.50 ppm	100 mL/min	1,000 mL	1	10 Minutes
0.50–1.75 ppm	50 mL/min	500 mL	3.5	10 Minutes

For measurements from 0.01 to 0.50 ppm, sample at 100 mL/min for 10 minutes, providing a total sample volume of 1,000 mL. The correction factor is 1.

For measurements above 0.50 ppm and up to 1.75 ppm, use a fresh detector tube and sample at 50 mL/min for 10 minutes, providing a total sample volume of 500 mL. Multiply the detector tube reading by the specified 3.5 correction factor.

Product Specifications

Brand: Gastec
Tube Type: Formaldehyde Detector Tube for Automatic Air Sampling Pump
Part Number: 91TP
Gas Measured: Formaldehyde (HCHO)
Measurement Range: 0.01–1.75 ppm
Primary Measurement Range: 0.01–0.50 ppm
Extended Measurement Range: 0.50–1.75 ppm
Detection Limit: 0.005 ppm at 1,000 mL (minimum detectable concentration; not part of the quantitative measuring range)
Primary Sampling Rate: 100 mL/min
Extended-Range Sampling Rate: 50 mL/min
Primary Sample Volume: 1,000 mL
Extended-Range Sample Volume: 500 mL
Correction Factor: 1 or 3.5 depending on measurement range
Sampling Time: 10 Minutes
Color Change: Yellow → Pale Orange
Operating Temperature: 5–35°C (41–95°F), temperature correction required
Operating Humidity: 0–80% RH, humidity correction not required
Relative Standard Deviation: 10% for 0.01–0.10 ppm; 5% for 0.10–0.50 ppm
Quantity: 10 Tubes
Tests per Box: 10 Tests
Shelf Life: 12 Months When Refrigerated
Storage: Refrigerated
Pump Requirement: Compatible Automatic Air Sampling Pump Required

Low-Level Formaldehyde Measurement

The Gastec 91TP is designed for sensitive measurement of formaldehyde (HCHO) in air, industrial areas, and environmental atmospheric conditions.

Its quantitative measuring range extends from 0.01 to 1.75 ppm using two sampling configurations.

The 0.005 ppm detection limit represents the minimum concentration capable of producing a detectable reaction under the specified 1,000 mL sampling conditions. It is not part of the quantitative measuring range and should not be interpreted as a 0.005–1.75 ppm measuring range.

During sampling, formaldehyde reacts with the detector tube reagent to produce a visible yellow-to-pale orange color change.

Common Applications

Gastec 91TP Formaldehyde Detector Tubes may be used for applicable formaldehyde air-monitoring applications including:

• Indoor Air Quality Testing

• Industrial Hygiene & Occupational Exposure Monitoring

• Residential & Commercial Building Air Monitoring

• Building & Facility Air Quality Investigations

• Formaldehyde Emission Investigations

• Chemical & Manufacturing Environments

• Furniture & Building Material Emission Investigations

• Laboratory & Research Applications

• Environmental Atmospheric Monitoring

• Low-Level Formaldehyde Monitoring

Temperature Correction

The Gastec 91TP is designed for use between 5 and 35°C (41–95°F) and requires temperature correction.

Gastec provides the following temperature correction factors:

Temperature	Correction Factor
5°C (41°F)	1.60
10°C (50°F)	1.30
15°C (59°F)	1.05
20°C (68°F)	1.00
25°C (77°F)	0.90
30°C (86°F)	0.70
35°C (95°F)	0.55

Apply the appropriate temperature correction factor to the detector tube reading according to Gastec's instructions.

No humidity correction is required within the specified 0–80% RH operating range.

Atmospheric pressure correction may also be required according to the official Gastec 91TP instruction manual.

Possible Interferences

Certain coexisting substances may affect Gastec 91TP measurements.

Acetaldehyde: Produces a positive interference and may independently produce a pale orange color.

Acetone: Produces a positive interference and may independently produce a pale orange color.

Ethanol: At approximately 0.15%, may produce a negative interference and a yellow color.

Xylene: At 50 ppm, Gastec identifies no interference and no independent color change.

Ammonia: At concentrations of 1 ppm or greater, may produce a negative interference and a yellow color.

Nitrogen Dioxide: At concentrations of 1 ppm or less, Gastec identifies no interference and no independent color change.

Coexisting gases and vapors should always be considered when interpreting detector tube results.

Refrigerated Storage Required

Gastec 91TP Formaldehyde Detector Tubes must be stored refrigerated.

The manufacturer specifies a 12-month shelf life when stored in the refrigerator. Gastec's instructions specify storing the tubes refrigerated at 10°C (50°F) or below.

Always follow the storage requirements and expiration date printed on the detector tube packaging.

Important

A compatible automatic air sampling pump is required for correct use of the Gastec 91TP Formaldehyde Detector Tubes.

For the primary 0.01–0.50 ppm range, sampling is performed at 100 mL/min for 10 minutes, producing a total sample volume of 1,000 mL.

For the extended 0.50–1.75 ppm range, use a fresh detector tube and sample at 50 mL/min for 10 minutes, producing a total sample volume of 500 mL. Multiply the detector tube reading by the 3.5 correction factor.

Do not use a standard manual detector tube pump in place of the required automatic sampling method.

Temperature and atmospheric pressure corrections must be applied when required according to Gastec's official 91TP instructions.

Always follow Gastec's official instructions for sampling rate, sampling time, sample volume, correction factors, environmental conditions, refrigerated storage, possible interferences, and interpretation of results.

Compatible Pump: Gastec GSP-501FT Automatic Air Sampling Pump

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