The Gastec 121TP Benzene Detector Tubes are designed for sensitive, low-level measurement of benzene (C6H6) in air using a compatible automatic air sampling pump.

The 121TP provides a quantitative measuring range of 0.1 to 14.5 ppm, with a detection limit of 0.08 ppm under the specified sampling conditions. The detecting layer produces a white-to-brown color change for visual determination of benzene concentration.

IMPORTANT: The Gastec 121TP uses two connected tubes for each measurement. Each box contains 10 tubes for a total of 5 tests.

Automatic Air Sampling Pump Required

IMPORTANT: Gastec 121TP Benzene Detector Tubes require a compatible automatic air sampling pump capable of maintaining the specified continuous sampling rates.

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

Gastec's current 121TP instructions specifically identify the GSP-501FT Automatic Air Sampling Pump as compatible with this detector tube.

The 121TP is an automatic air sampling pump detector tube and should not be treated as a standard hand-pump detector tube.

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
0.1–5 ppm	100 mL/min	1,000 mL	1	10 Minutes
5–14.5 ppm	50 mL/min	500 mL	2.9	10 Minutes

For measurements from 0.1 to 5 ppm, sample at 100 mL/min for 10 minutes, providing a total sample volume of 1,000 mL.

For measurements above 5 ppm and up to 14.5 ppm, prepare a fresh tube set 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 2.9 correction factor.

Product Specifications

Brand: Gastec
Tube Type: Benzene Detector Tube for Automatic Air Sampling Pump
Part Number: 121TP
Gas/Vapor Measured: Benzene
Chemical Formula: C6H6
Measurement Range: 0.1–14.5 ppm
Primary Measurement Range: 0.1–5 ppm
Extended Measurement Range: 5–14.5 ppm
Detection Limit: 0.08 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 2.9 depending on measurement range
Sampling Time: 10 Minutes
Color Change: White → Brown
Operating Temperature: 0–40°C (32–104°F), temperature correction not required
Operating Humidity: 0–90% RH, humidity correction not required
Relative Standard Deviation: 5% for 0.1–1 ppm; 10% for 1–5 ppm
Quantity: 10 Tubes
Tests per Box: 5 Tests
Shelf Life: 27 Months
Pump Requirement: Compatible Automatic Air Sampling Pump Required

Two-Tube Measurement System

Unlike standard single-tube measurements, the Gastec 121TP requires two detector tubes to be connected together for each test.

The system consists of a primary tube and an analyzer tube. After the required ends are broken, the marked ends are connected using rubber tubing according to Gastec's instructions.

The analyzer tube is then inserted into the automatic sampling pump with the arrow pointing toward the pump.

Because two tubes are required for each measurement, 10 tubes provide 5 complete tests.

Always follow the official Gastec 121TP instruction manual for correct tube connection, orientation, and sampling procedure.

Low-Level Benzene Measurement

The Gastec 121TP is designed for sensitive measurement of benzene (C6H6) in air.

Its quantitative measuring range extends from 0.1 to 14.5 ppm using two sampling configurations.

The 0.08 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 0.08–14.5 ppm measurement range.

During sampling, benzene passes through the primary tube and reacts within the detector system, producing a brown reaction product in the detecting layer.

Common Applications

Gastec 121TP Benzene Detector Tubes may be used for applicable benzene air-monitoring applications including:

• Industrial Hygiene & Occupational Exposure Monitoring

• Petroleum & Petrochemical Facilities

• Chemical Manufacturing & Processing

• Refineries & Fuel Handling Areas

• Solvent & Chemical Storage Areas

• Workplace Benzene Monitoring

• Environmental Atmospheric Monitoring

• Leak & Release Investigations

• Laboratory & Research Applications

• Industrial Safety & Maintenance

Operating Conditions

The Gastec 121TP can be used from 0 to 40°C (32 to 104°F) without temperature correction.

The specified operating humidity range is 0 to 90% relative humidity, and humidity correction is not required.

Atmospheric pressure correction may be required. Follow the pressure-correction procedure provided in the official Gastec 121TP instruction manual.

Possible Interferences

Certain coexisting substances may affect Gastec 121TP benzene measurements.

Ethyl Benzene: At concentrations of 7 ppm or greater, may produce positive interference and a brown color.

Ethylene: At concentrations of 200 ppm or greater, may produce positive interference. Gastec lists no independent discoloration at concentrations up to 1,000 ppm.

Xylene: At concentrations of 200 ppm or greater, may produce positive interference and a brown color.

Toluene: At concentrations of 75 ppm or greater, may produce positive interference and a brown color.

Acetone: At concentrations of 1,000 ppm or less, Gastec identifies no interference and no independent discoloration.

Hexane: At concentrations of 500 ppm or less, Gastec identifies no interference. No independent discoloration is listed at concentrations up to 1,200 ppm.

Methanol: At concentrations of 500 ppm or less, Gastec identifies no interference. No independent discoloration is listed at concentrations up to 1,000 ppm.

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

Important

A compatible automatic air sampling pump is required for correct use of the Gastec 121TP Benzene Detector Tubes.

Gastec specifically identifies the GSP-501FT Automatic Air Sampling Pump as compatible with the current 121TP measurement procedure.

For the primary 0.1–5 ppm range, sampling is performed at 100 mL/min for 10 minutes, producing a total sample volume of 1,000 mL.

For the extended 5–14.5 ppm range, prepare a fresh tube set and sample at 50 mL/min for 10 minutes, producing a total sample volume of 500 mL. Multiply the detector tube reading by the 2.9 correction factor.

Two detector tubes must be connected for each measurement. Therefore, 10 tubes provide 5 complete tests.

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

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

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

 

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