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

The 91PL provides a quantitative measuring range of 0.01 to 0.80 ppm, with a detection limit of 0.005 ppm under the specified sampling conditions. The tube produces a pale-yellow-to-pink color change for visual determination of formaldehyde concentration.

Each box contains 10 detector tubes for 10 tests.

IMPORTANT STORAGE REQUIREMENT: Gastec 91PL detector tubes have a 12-month shelf life when stored refrigerated. Follow the storage conditions printed on the detector tube packaging.

Automatic Air Sampling Pump Required

IMPORTANT: Gastec 91PL Formaldehyde Detector Tubes require a compatible automatic air sampling pump capable of maintaining a continuous 200 mL/min sampling rate.

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

The 91PL is an automatic air sampling pump detector tube and should not be treated as a standard hand-pump detector tube. Accurate measurement depends on maintaining the specified sampling rate, sampling time, sample volume, and applicable correction factors.

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
0.01–0.20 ppm	200 mL/min	6,000 mL	1	30 Minutes
0.20–0.80 ppm	200 mL/min	2,000 mL	4	10 Minutes

For measurements from 0.01 to 0.20 ppm, sample at 200 mL/min for 30 minutes, providing a total sample volume of 6,000 mL.

For measurements above 0.20 ppm and up to 0.80 ppm, use a fresh detector tube and sample at 200 mL/min for 10 minutes, providing a total sample volume of 2,000 mL. Multiply the detector tube reading by the specified 4 correction factor.

Product Specifications

Brand: Gastec
Tube Type: Formaldehyde Detector Tube for Automatic Air Sampling Pump
Part Number: 91PL
Gas Measured: Formaldehyde (HCHO)
Measurement Range: 0.01–0.80 ppm
Primary Measurement Range: 0.01–0.20 ppm
Extended Measurement Range: 0.20–0.80 ppm
Detection Limit: 0.005 ppm at 6,000 mL (minimum detectable concentration; not part of the quantitative measuring range)
Sampling Rate: 200 mL/min
Primary Sample Volume: 6,000 mL
Extended-Range Sample Volume: 2,000 mL
Correction Factor: 1 or 4 depending on measurement range
Primary Sampling Time: 30 Minutes
Extended-Range Sampling Time: 10 Minutes
Color Change: Pale Yellow → Pink
Operating Temperature: 5–35°C (41–95°F), temperature correction required
Operating Humidity: 20–90% RH, humidity correction not required
Relative Standard Deviation: 10% for 0.01–0.06 ppm; 5% for 0.06–0.20 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

Ultra-Low-Level Formaldehyde Measurement

The Gastec 91PL is designed for particularly sensitive measurement of formaldehyde (HCHO) in environmental atmospheric conditions.

Its primary quantitative range begins at just 0.01 ppm, making the 91PL a lower-range formaldehyde tube than the Gastec 91P.

Important: The minimum scale value of 0.01 ppm is not numerically printed on the detector tube. Only the corresponding scale line is printed.

The 0.005 ppm detection limit represents the minimum concentration capable of producing a detectable reaction under the specified 6,000 mL sampling conditions. It is not part of the quantitative measuring range and should not be interpreted as a 0.005–0.80 ppm measuring range.

During sampling, formaldehyde produces a visible pale-yellow-to-pink color change.

Common Applications

Gastec 91PL Formaldehyde Detector Tubes may be used for applicable ultra-low-level formaldehyde monitoring applications including:

• Indoor Air Quality Testing

• Residential & Commercial Building Air Monitoring

• Workplace & Industrial Hygiene Monitoring

• Building & Facility Air Quality Investigations

• Formaldehyde Emission Investigations

• Chemical & Manufacturing Environments

• Laboratory & Research Applications

• Environmental Atmospheric Monitoring

• Furniture & Building Material Emission Investigations

• Ultra-Low-Level Formaldehyde Monitoring

Temperature Correction

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

Gastec provides separate temperature correction tables in the official 91PL instruction manual for the 30-minute and 10-minute measurement procedures.

The appropriate correction must be applied based on the actual sampling temperature and measurement method.

The specified relative humidity range is 20–90% RH, and humidity correction is not required within this range.

Atmospheric pressure correction may also be required according to Gastec's official measurement procedure.

Possible Interferences

Certain coexisting substances may affect or produce color changes during Gastec 91PL measurements.

Ammonia: At concentrations of 2 ppm or less, Gastec identifies no interference and no independent color change.

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

Acetaldehyde: May produce a positive interference and can independently produce a pink color change.

Acetone: At concentrations of 0.3 ppm or less, Gastec identifies no interference with the formaldehyde measurement; however, acetone may produce a pink color around the tube inlet.

Ethanol, Ethyl Acetate, p-Dichlorobenzene and Toluene: Gastec identifies these substances as producing no interference under the manufacturer's specified test conditions.

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

Refrigerated Storage Required

Gastec 91PL Formaldehyde Detector Tubes must be stored refrigerated.

The manufacturer specifies a 12-month shelf life when stored in the refrigerator.

Always follow the storage conditions and expiration information printed on the detector tube packaging.

Important

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

For the primary 0.01–0.20 ppm range, sampling is performed at 200 mL/min for 30 minutes, producing a total sample volume of 6,000 mL.

For the extended 0.20–0.80 ppm range, a fresh detector tube is sampled at 200 mL/min for 10 minutes, producing a total sample volume of 2,000 mL, and the detector tube reading is multiplied by the 4 correction factor.

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

Temperature correction must be applied according to the official Gastec 91PL 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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