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

Designed for sampling hazardous air pollutants, the 121P provides a quantitative measuring range of 250 to 3,000 µg/m³, with a detection limit of 100 µg/m³ under the specified sampling conditions. The detector system produces a white-to-brown color change for visual determination of benzene concentration.

IMPORTANT: The Gastec 121P 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 121P Benzene Detector Tubes require a compatible automatic air sampling pump capable of maintaining a continuous 50 mL/min sampling rate for the full 60-minute sampling period.

Compatible Pump: Gastec GSP Series Automatic Air Sampling Pump

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

Accurate measurement requires drawing 3,000 mL of air through the connected detector tube system at 50 mL/min for 60 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
250–3,000 µg/m³	50 mL/min	3,000 mL	1	60 Minutes

The Gastec 121P requires a continuous sampling rate of 50 mL/min for 60 minutes, producing a total sample volume of 3,000 mL.

The correction factor is 1 under the specified sampling conditions.

Product Specifications

Brand: Gastec
Tube Type: Benzene Detector Tube for Automatic Air Sampling Pump
Part Number: 121P
Gas/Vapor Measured: Benzene
Chemical Formula: C6H6
Measurement Range: 250–3,000 µg/m³
Detection Limit: 100 µg/m³ at 3,000 mL (minimum detectable concentration; not part of the quantitative measuring range)
Sampling Rate: 50 mL/min
Sample Volume: 3,000 mL
Correction Factor: 1
Sampling Time: 60 Minutes
Color Change: White → Brown
Operating Temperature: 0–35°C (32–95°F), temperature correction not required
Operating Humidity: 0–85% RH, humidity correction not required
Relative Standard Deviation: 10% for 250–1,000 µg/m³; 5% for 1,000–3,000 µg/m³
Quantity: 10 Tubes
Tests per Box: 5 Tests
Shelf Life: 30 Months
Pump Requirement: Compatible Automatic Air Sampling Pump Required

Two-Tube Measurement System

The Gastec 121P requires two tubes to be connected together during each measurement.

The primary and analyzer tubes must be prepared and connected according to Gastec's instructions before the detector tube assembly is connected to the automatic air sampling pump.

Because two tubes are consumed during each measurement, a box containing 10 tubes provides 5 complete tests.

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

Ultra-Low-Level Benzene Measurement

The Gastec 121P is specifically designed for sensitive benzene measurement in the µg/m³ concentration range.

Its quantitative measuring range extends from 250 to 3,000 µg/m³.

Important: The minimum measuring value of 250 µg/m³ is represented by a scale line on the detector tube but the number “250” itself is not printed on the tube.

The 100 µg/m³ detection limit represents the minimum concentration capable of producing a detectable reaction under the specified 3,000 mL sampling conditions. It is not part of the quantitative measuring range and should not be interpreted as a 100–3,000 µg/m³ measurement range.

During sampling, benzene reacts within the detector system and produces a visible white-to-brown color change.

Common Applications

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

• Hazardous Air Pollutant Sampling

• Environmental Air Monitoring

• Low-Level Benzene Monitoring

• Industrial Hygiene Investigations

• Petroleum & Petrochemical Facilities

• Chemical Manufacturing & Processing

• Refineries & Fuel Handling Areas

• Environmental Atmospheric Investigations

• Laboratory & Research Applications

• Benzene Emission & Release Investigations

Operating Conditions

The Gastec 121P can be used from 0 to 35°C (32 to 95°F) without temperature correction.

The specified operating humidity range is 0 to 85% relative humidity, and humidity correction is not required.

Atmospheric pressure correction may be required according to the official Gastec 121P measurement procedure.

Possible Interferences

Gastec identifies the following coexisting substances at the stated concentrations as producing no interference and no independent discoloration:

Toluene: 500 µg/m³
Xylene: 500 µg/m³
n-Hexane: 500 µg/m³

Other substances not listed by Gastec may potentially affect detector tube results. Coexisting gases and vapors should always be considered when interpreting measurements.

Important

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

Sampling is performed at 50 mL/min for 60 minutes, producing a total sample volume of 3,000 mL.

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, atmospheric pressure correction, environmental conditions, possible interferences, and interpretation of results.

Choose Instrument Depot for dependable Gastec 121P Benzene Detector Tubes, C6H6 detector tubes, low-level benzene testing, hazardous air pollutant sampling, environmental benzene monitoring, automatic air sampling pumps, industrial hygiene air monitoring, benzene vapor testing, gas detector tubes, and industrial gas detection equipment.