---
kind: "section"
citation: "40 C.F.R. § 1065.845"
title: "40"
number: "1065.845"
heading: "Response factor determination."
url: "https://uscodex.org/cfr/40/1065.845"
---

# §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)](#b) of this section, or you may use the following default response factors, consistent with good engineering judgment:
- (b) **Determine the alcohol/carbonyl response factors as follows—**
  - (1) Select a C3H8 span gas that meets the specifications of [§ 1065.750](/cfr/40/1065.750.md). 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](/cfr/40/1065.750.md). 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](/cfr/40/1065.750.md) 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 C<I>3</I>H<I>8</I>.** 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](/cfr/40/1065.750.md). 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.

## Notes

### Amendments

[79 FR 23812, Apr. 28, 2014, as amended at 79 FR 36658, June 30, 2014]

### Authority

Authority: 42 U.S.C. 7401-7671q.

### Source

Source: 70 FR 40516, July 13, 2005, unless otherwise noted.

### Amendments

[79 FR 23812, Apr. 28, 2014, as amended at 79 FR 36658, June 30, 2014]