TSI-148 - Response Factors and Molecular Weights for TSI TVOC Sensors

Sep 27, 2026

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Application note for the TSI 7585 Q-TRAK XP Indoor Air Quality Monitor explaining how Photo Ionization Detectors (PID) respond differently to individual VOC compounds when the lamp uses 10.6 eV krypton. Provides a calibration-to-actual-concentration method using Response Factors, molecular weights for converting number to mass concentration, and VOC-specific minimum detection levels for TVOC-L 801408 versus TVOC-H 801407. Includes guidance for VOC mixtures and limits on measurable gases.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Response factors and response mechanism

10.6 eV krypton lamp and PID broadband response

Calculating actual VOC concentration using RF

Minimum detection levels for TVOC-L 801408 and TVOC-H 801407

Molecular weight conversion (number to mass concentration)

Measuring VOC mixtures

Measurement limitations and notice

VOCs not measurable due to ionization energy and volatility constraints

VOC reference table

Q-TRAK™ XP INDOOR AIR QUALITY MONITOR MODEL 7585 RESPONSE FACTORS AND MOLECULAR WEIGHTS FOR TSI® TVOC SENSORS APPLICATION NOTE TSI-148 (A4) While TSI® Volatile Organic Compound (VOC) probes are calibrated using isobutylene, the probe’s Photo Ionization Detectors (PID) are broadband VOC detectors with a response that differs for each VOC compound. PID lamps can be created with a number of gasses, each of which has different photon energy. TSI®’s PID probes use Krypton gas, which has a photon energy of 10.6 eV that offers a long lamp life and responds to a wide range of gases. If you know what VOC you are measuring, then the table below will allow you to calculate the real concentration for your specific VOC that responds to a 10.6 eV (Electron Volt) lamp source. The table includes seven columns: 1. Gas/ VOC: The most common name for the VOC. 2. Formula: To assist in identifying the VOC and to determine the VOC’s molecular weight. 3. CAS No.: You can find the VOC using the CAS No. 4. Response Factor (RF): Multiply the displayed concentration by the Response Factor to calculate the actual concentration of the VOC. This value dan be programmed into the 7585. 5. Minimum Detection Level (MDL) PPB: Also called Minimum Detectable Quantity (MDQ). Typical lowest concentration that can be detected. The MDL in this column is for use with the 801408 TVOC-L sensor. Since the 801408 TVOC-L sensor has greater sensitivity than the 801407 TVOC-H sensor, the MDL for the 801408 TVOC-L sensor will be much less than the MDL for the 801407 TVOC-H sensor. 6. Minimum Detection Level (MDL) PPB: Also called Minimum Detectable Quantity (MDQ). Typical lowest concentration that can be detected. The MDL in this column is for use with the 801407 TVOC-H sensor. Since the 801407 TVOC-H sensor has less sensitivity than the 801408 TVOC-L sensor, the MDL for the 801407 TVOC-H sensor will be much more than the MDL for the 801408 TVOC-L sensor. 7. Molecular Weight: The molecular weight of the VOC is used to convert its number concentration (PPM or PPB) to mass concentration (mg/m3 ) . VOC Response Occasionally you will be measuring a mixture of VOCs. If the total concentration is within the linear range of your PID, then it is reasonable to assume that the concentrations are additive without interference between the different VOCs. If you are measuring a combination of VOCs, then accurate measurement of one of these VOCs will be difficult. Without careful data analysis, you will get only a RF averaged measurement. Be cautious when reporting actual VOC concentration if you know that there may be several VOCs present. | NOTICE | | --- | | TSI® PID sensors cannot measure all VOCs or gases. VOCs that have an electron-volt potential greater than or equal (≥) to 10.6 eV will give no response since they cannot be ionized by the 10.6 eV lamp source. Semi-Volatile Organic Compounds (SVOC) cannot be measured if the vapor pressure is too low (a few ppm at 20°C) to volatize the compound. | | Gas/VOC | Formula | CAS no. | Response Factor | MDL (ppb) TVOC-L 801408 | MDL (ppb) TVOC-H 801407 | Molecular Weight (g/mol) | | --- | --- | --- | --- | --- | --- | --- | | Acetaldehyde | C2H4O | 75-07-0 | 5.5 | 25 | 480 | 44.05 | | Acetic acid | C2H4O2 | 64-19-7 | 28 | 180 | 3615 | 60.05 | | Acetic anhydride | C4H6O3 | 108-24-7 | 4 | 20 | 400 | 102.1 | | Acetone | C3H6O | 67-64-1 | 1.17 | 5 | 70 | 58.08 | | Acrolein | C3H4O | 107-02-8 | 3.2 | 20 | 400 | 56.06 | | Acrylic Acid | C3H4O2 | 79-10-7 | 21 | 15 | 275 | 72.06 | | Allyl alcohol | C3H6O | 107-18-6 | 2.3 | 10 | 200 | 58.08 | | Allyl chloride | C3H5Cl | 107-05-1 | 4.5 | 20 | 450 | 76.53 | | Ammonia | NH3 | 7664-41-7 | 8.5 | 40 | 850 | 17.03 | | Amyl acetate | C7H14O2 | 628-63-7 | 1.8 | 10 | 180 | 130.2 | | Amyl alcohol | C5H12O | 71-41-0 | 2.6 | 15 | 320 | 88.15 | | Aniline | C6H7N | 62-53-3 | 0.5 | 3 | 50 | 93.13 | | Anisole | C7H8O | 100-66-3 | 0.59 | 2 | 50 | 108.1 | | Arsine | AsH3

FAQs

Why does a PID sensor need a compound-specific response factor?

The PID lamp is broadband, but each VOC compound responds differently. The document explains using the Response Factor (RF) to convert displayed concentration to actual concentration for the specific VOC.

What is the difference between the MDL values for TVOC-L 801408 and TVOC-H 801407?

TVOC-L 801408 has greater sensitivity, so its MDL is much lower than the MDL for TVOC-H 801407, which has less sensitivity.

How should results be handled when measuring mixtures of VOCs?

When total concentration is within the PID linear range, concentrations can be assumed additive. For combinations, accurate measurement of one target VOC becomes difficult, and without careful data analysis the result may be only an RF-averaged measurement.

Sep 27, 2026

Upload by Adam