(a) General component requirements. We recommend that you use an analyzer that meets the specifications in Table 1 of § 1065.205. Note that your system must meet the linearity verification in § 1065.307.
(b) Instrument types. You may use any of the following analyzers to measure N2O:
(1) Nondispersive infrared (NDIR) analyzer.
(2) Fourier transform infrared (FTIR) analyzer. Use appropriate analytical procedures for interpretation of infrared spectra. For example, EPA Test Method 320 (see § 1065.266(b)) and ASTM D6348 (incorporated by reference in § 1065.1010) are considered valid methods for spectral interpretation.
(3) Laser infrared analyzer. Examples of laser infrared analyzers are pulsed-mode high-resolution narrow band mid-infrared analyzers, and modulated continuous wave high-resolution narrow band mid-infrared analyzers.
(4) Photoacoustic analyzer. Use an optical wheel configuration that gives analytical priority to measurement of the least stable components in the sample. Select a sample integration time of at least 5 seconds. Take into account sample chamber and sample line volumes when determining flush times for your instrument.
(5) Gas chromatograph analyzer. You may use a gas chromatograph with an electron-capture detector (GC-ECD) to measure N2O concentrations of diluted exhaust for batch sampling.
(i) You may use a packed or porous layer open tubular (PLOT) column phase of suitable polarity and length to achieve adequate resolution of the N2O peak for analysis. Examples of acceptable columns are a PLOT column consisting of bonded polystyrene-divinylbenzene or a Porapack Q packed column. Take the column temperature profile and carrier gas selection into consideration when setting up your method to achieve adequate N2O peak resolution.
(ii) Use good engineering judgment to zero your instrument and correct for drift. You do not need to follow the specific procedures in §§ 1065.530 and 1065.550(b) that would otherwise apply. For example, you may perform a span gas measurement before and after sample analysis without zeroing and use the average area counts of the pre-span and post-span measurements to generate a response factor (area counts/span gas concentration), which you then multiply by the area counts from your sample to generate the sample concentration.
(c) Interference verification. Perform interference verification for NDIR, FTIR, laser infrared analyzers, and photoacoustic analyzers using the procedures of § 1065.375. Interference verification is not required for GC-ECD. Certain interference gases can positively interfere with NDIR, FTIR, and photoacoustic analyzers by causing a response similar to N2O. When running the interference verification for these analyzers, use interference gases as follows:
(1) The interference gases for NDIR analyzers are CO, CO2, H2O, CH4, and SO2. Note that interference species, with the exception of H2O, are dependent on the N2O infrared absorption band chosen by the instrument manufacturer. For each analyzer determine the N2O infrared absorption band. For each N2O infrared absorption band, use good engineering judgment to determine which interference gases to use in the verification.
(2) Use good engineering judgment to determine interference gases for FTIR, and laser infrared analyzers. Note that interference species, with the exception of H2O, are dependent on the N2O infrared absorption band chosen by the instrument manufacturer. For each analyzer determine the N2O infrared absorption band. For each N2O infrared absorption band, use good engineering judgment to determine interference gases to use in the verification.
(3) The interference gases for photoacoustic analyzers are CO, CO2, and H2O.
[74 FR 56512, Oct. 30, 2009, as amended at 76 FR 57443, Sept. 15, 2011; 78 FR 36398, June 17, 2013;79 FR 23761, Apr. 28, 2014; 81 FR 74163, Oct. 25, 2016; 86 FR 34536, June 29, 2021]