40 CFR § 1065.845 - Response factor determination.
Since FID analyzers generally have an incomplete response to alcohols and carbonyls, determine each FID analyzer's alcohol/carbonyl response factor (RFOHCi[THC-FID]) after FID optimization to subtract those responses from the FID reading. Use the most recently determined alcohol/carbonyl response factors to compensate for alcohol/carbonyl response. You are not required to determine the response factor for a compound unless you will subtract its response to compensate for a response.
(a) You may generate response factors as described in paragraph (b) of this section, or you may use the following default response factors, consistent with good engineering judgment:
Table 1 of § 1065.845 - Default Values for THC FID Response Factor Relative to Propane on a C1-Equivalent Basis
(b) Determine the alcohol/carbonyl response factors as follows:
(1) Select a C3H8 span gas that meets the specifications of § 1065.750. Note that FID zero and span balance gases may be any combination of purified air or purified nitrogen that meets the specifications of § 1065.750. We recommend FID analyzer zero and span gases that contain approximately the flow-weighted mean concentration of O2 expected during testing. Record the C3H8 concentration of the gas.
(2) Select or prepare an alcohol/carbonyl calibration gas that meets the specifications of § 1065.750 and has a concentration typical of the peak concentration expected at the hydrocarbon standard. Record the calibration concentration of the gas.
(3) Start and operate the FID analyzer according to the manufacturer's instructions.
(4) Confirm that the FID analyzer has been calibrated using C3H8. Calibrate on a carbon number basis of one (C1). For example, if you use a C3H8 span gas of concentration 200 µmol/mol, span the FID to respond with a value of 600 µmol/mol.
(5) Zero the FID. Note that FID zero and span balance gases may be any combination of purified air or purified nitrogen that meets the specifications of § 1065.750. We recommend FID analyzer zero and span gases that contain approximately the flow-weighted mean concentration of O2 expected during testing.
(6) Span the FID with the C3H8 span gas that you selected under paragraph (a)(1) of this section.
(7) Introduce at the inlet of the FID analyzer the alcohol/carbonyl calibration gas that you selected under paragraph (a)(2) of this section.
(8) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the analyzer and to account for its response.
(9) While the analyzer measures the alcohol/carbonyl concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these values.
(10) Divide the mean measured concentration by the recorded span concentration of the alcohol/carbonyl calibration gas on a C1-equivalent basis. The result is the FID analyzer's response factor for alcohol/carbonyl, RFOHCi[THC-FID] on a C1-equivalent basis.
(c) Alcohol/carbonyl calibration gases must remain within ±2% of the labeled concentration. You must demonstrate the stability based on a quarterly measurement procedure with a precision of ±2% percent or another method that we approve. Your measurement procedure may incorporate multiple measurements. If the true concentration of the gas changes deviates by more than ±2%, but less than ±10%, the gas may be relabeled with the new concentration.