NB/SH/T 0663-2014 Determination of alcohols and ethers in gasoline by gas chromatography

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: NB/SH/T 0663-2014
• Chinese title: Determination of alcohols and ethers in gasoline by gas chromatography
• English title: Standard test method for determination of alcohols and ethers in gasoline by gas chromatography
• Replacement relationship: replaces SH/T 0663—1998 "Determination of certain alcohols and ethers in gasoline (gas chromatography)"
• Adoption relationship: modified adoption using the redrafting method of ASTM D4815—09
• Publication/implementation: published on 2014-06-29, implemented on 2014-11-01
• Custodianship: Subcommittee on Petroleum Fuels and Lubricants of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC280/SC1)
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafter: Jin Ke
• Main technical changes compared with SH/T 0663—1998 (original foreword):
  • The scope clause 1.2 was modified, and the lower measurement limits for various alcohols and ethers were changed from 0.1% to 0.2% (see Chapter 1, 1998 edition, 1.2)
  • Figure 1 and Figure 2 were modified
  • Deleted the relevant content in the 1998 edition concerning the capillary pre-cut column 1 and the analytical column of length 30 m and internal diameter 0.35 mm (see Chapter 6 of the 1998 edition)
  • Removed the relative density at 15.56 ℃ in Table 1 of the 1998 edition and in the formula for calculating the volume concentration of oxygen-containing compounds (20)
  • Added an informative annex on hydrocarbon interference (see Annex A)
• Main differences compared with ASTM D4815—09 (original foreword):
  • The standard title was changed to "Determination of alcohols and ethers in gasoline by gas chromatography"
  • Chapter 2 adopts the corresponding national standards and industry standards of our country
  • Changed the relative density of each component 15.56 ℃ in Table 1 of ASTM D4815-09 to density at 20 ℃; supplemented the density of water at 20 ℃ according to ISO 3838:1983
  • Replaced helium with nitrogen as the carrier gas

2. Scope of application and non-applicability

• Applicable: determination of ethers and alcohols in gasoline by gas chromatography.
• Specific components determined: methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), methyl tert-amyl ether (TAME), diisopropyl ether (DIPE), methanol, ethanol, isopropanol, n-propanol, isobutanol, tert-butanol, sec-butanol, n-butanol, and tert-amyl alcohol.
• Measurement range: single ether mass fraction 0.20% to 20.0%; single alcohol mass fraction 0.20% to 12.0%.
• Provides calculation formulas for converting each component to oxygen mass fraction and volume fraction.
• When the mass fraction is less than 0.20%, hydrocarbons may interfere with certain ethers and alcohols. For gasoline with an olefin content not greater than 10% (volume fraction), the detection limit is 0.20% (mass fraction); for gasoline with an olefin content greater than 10% (volume fraction), hydrocarbon interference may be greater than 0.20% (mass fraction). Annex A shows a chromatogram of hydrocarbon interference for gasoline with an olefin content of 10% (volume fraction).
• Not applicable: alcohol-based fuels, such as M-85, E-85, MTBE products, ethanol products, and denatured alcohol.
• Benzene can be detected simultaneously by this standard but cannot be quantified and requires analysis by another method (see test method SH/T 0713).

3. Method principle

• 4.1 Add an appropriate internal standard, dimethoxyethane (ethylene glycol dimethyl ether DME), to the sample, then introduce this sample into a gas chromatograph equipped with two columns and a valve. The sample first passes through a polar TCEP pre-cut column, which first flushes light hydrocarbons to vent and retains oxygen-containing compounds and heavier hydrocarbon components.
• 4.2 After methylcyclopentane but before DIPE and MTBE elute from the pre-cut column, switch the valve to the backflush position to allow the oxygen-containing compounds to enter the nonpolar WCOT analytical column. Before any heavy hydrocarbon components elute, the alcohols and ethers elute from the analytical column in order of boiling point.
• 4.3 After benzene and TAME elute from the analytical column, switch the column switching valve back to the starting position in order to backflush the heavy hydrocarbon components.
• 4.4 Detect the eluting components by a flame ionization detector (FID) or thermal conductivity detector (TCD). Record the detector response proportional to the component concentration, measure the peak area, and calculate the concentration of each component with reference to the internal standard.

4. Reagents and materials (purity / preparation)

• 7.1 Carrier gas: use a carrier gas suitable for the detector type, such as high-purity helium or nitrogen. Helium has been used successfully. The minimum purity of the carrier gas used should be 99.95% (mole fraction).
• 7.2 Qualitative and quantitative standard samples: standard samples including all analyzed components and the internal standard are required so as to apply retention time for qualitative analysis and quantitative measurement calibration. These substances should have known purity and contain no other components to be determined. Warning: these substances are all flammable, and if ingested or inhaled by humans may be harmful or fatal.
• 7.3 Dichloromethane: used for chromatographic column preparation. Analytical reagent grade, no volatile residue. Warning: harmful if inhaled. High concentrations can cause coma or death.
• 8 Preparation of column packing (TCEP column packing):
  • 8.1 Any preparation method for chromatographic column packing that can retain and separate alcohols of the same boiling point range C1 to C4 and ethers MTBE, ETBE, DIPE, and TAME from gasoline hydrocarbon compounds may be used.
  • 8.2 Completely dissolve 10 g TCEP in 100 mL dichloromethane. To this solution add 40 g of Chromosorb P (AW) 180 μm to 250 μm support. Quickly transfer the mixture to a culture dish in a fume hood; there is no need to specially collect the residue in the container. Stir the coating slightly and constantly until the solvent has completely evaporated. This column packing can be used immediately for TCEP micropacked column preparation.
• 12.2.2 Before preparing standard samples, the purity of the oxygen-containing compound reagents shall be determined, and corrections shall be made for any impurities found. Use substances with a purity of at least 99.9% (mass fraction) whenever possible. Correct the purity of the components using the water content determined according to SH/T 0246.
• 12.2.3 In order to reduce volatilization of light components, cool all chemical reagents and gasoline used to prepare standard samples.
• 12.2.5 Dilute each standard sample to 100 mL with oxygenate-free gasoline or a hydrocarbon mixture, such as isooctane/xylene (volume ratio) of about 63/37. All oxygen-containing compounds, including the added internal standard, shall not exceed 30% (volume fraction). When not analyzing, store the calibration standard samples sealed at 5 ℃.

5. Instruments and equipment

• 6.1 Chromatograph
  • 6.1.1 Any gas chromatography system capable of separating the various ethers and alcohols shown in Table 1 may be used for this analysis. A gas chromatograph equivalent to that shown in Figure 1 is suitable for the analysis of this standard; it can operate under the conditions given in Table 2 and has a set of column switching and backflush systems. The carrier gas flow controller should be able to precisely control the required low flow rates (Table 2). The pressure control device and pressure gauge should be able to accurately control the required typical pressure range.
  • 6.1.2 Detector: either a flame ionization detector or a thermal conductivity detector may be used. The system should have sufficient sensitivity and stability so that for a sample with an oxygen-containing compound concentration of 0.5% (volume fraction), the component ... (the original text here is source-text extraction incomplete, requires confirmation against the source standard (source-text extraction)) ... recorder full scale at least 20.
  • 6.1.3 Switching backflush valve: installed in the gas chromatographic column oven, having the function described in Chapter 11 and Figure 1. This valve should have a small internal bore volume and have no significant adverse effect on chromatographic separation.
    • 6.1.3.1 Valco Model No. A4 C10WP ten-port valve: has 1.6 mm (1/16 in.) column connections. This special valve was used for most of the analytical research work in Chapter 15.
    • 6.1.3.2 Valco Model No. C10W ten-port valve: has 0.8 mm (1/32 in.) column connections. This valve is recommended for chromatographic columns with an internal diameter of 0.32 mm and below.
    • 6.1.3.3 Some gas chromatographs are equipped with an auxiliary column oven that can accommodate a valve and a polar column (pre-cut column). In such a configuration, the nonpolar column (analytical column) is installed in the main column oven, and both column oven temperatures can be adjusted to obtain optimal separation of oxygen-containing compounds. An automatic valve switching device should be used to ensure repeatability of switching times. This device should be synchronized with the injection time and data collection time.
  • 6.1.5 Injection system: if a capillary column and flame ionization detector are used, the chromatograph should be equipped with split injection equipment. In order to keep the actual chromatographic sample amount within the column load and the detector optimum efficiency and linear range, split injection should be used.
    • 6.1.5.1 Some gas chromatographs are equipped with an on-column injector and an autosampler capable of injecting small sample amounts. This injection system can be used to provide a sample amount within the column load and the detector optimum efficiency and linear range.
    • 6.1.5.2 In order to introduce a representative sample into the gas chromatograph inlet, a microsyringe, autosampler, and liquid injection valve may all be used.
• 6.2 Data display and calculation
  • 6.2.1 Recorder: use a recorder or equivalent equipment with a full scale of 5 mV or less to monitor the detector signal. Its full-scale response time should be less than 1 s, while having sufficient sensitivity and stability to meet the requirements of 6.1.2.
  • 6.2.2 Integrator or computer: a means of measuring the detector response should be provided. Peak height or peak area can be measured by computer, electronic integrator, or manual techniques.
• 6.3 Two types of chromatographic columns
  • 6.3.1 Polar column: This column performs the pre-separation of oxygenated compounds from volatile hydrocarbons in the same boiling point range. The oxygenated compounds and the remaining hydrocarbons are backflushed onto the non-polar column in 6.3.2. Any column having chromatographic efficiency and selectivity equivalent to or better than that described in 6.3.1.1 may be used. Unless it is placed in an auxiliary oven such as 6.1.3.3, the column should be operated at the same temperature as required for the chromatographic column in 6.3.2.
    • 6.3.1.1 TCEP Micro-packed column: length 560 mm, 1.6 mm outer diameter, and 0.76 mm inner diameter stainless steel tubing, packed with 0.14 g to 0.15 g 20% TCEP/Chromosorb P (AW) 180 μm to 250 μm stationary phase.
  • 6.3.2 Non-polar (analytical) column: Any column having chromatographic efficiency and selectivity equivalent to or better than those described in 6.3.2.1 and Figure 2 may be used.
    • 6.3.2.1 WCOT Methyl silicone column: length 30 m, inner diameter 0.53 mm, cross-linked methyl silicone elastic quartz capillary WCOT column coated with a film thickness of 2.6 μm.

6. Recommended operating conditions

Table 2 Chromatographic operating conditions (original table 2):

Note: *The sample amount should be adjusted so that the mass fraction of alcohol eluting from the column is within 0.20% to 12.0%, and the mass fraction of ether is within 0.20% to 20.0%, and so that it is within the linear range of the detector. In most cases, a sample volume of 1.0 μL is injected.

(Note: Table 2 is unclear in the source text due to source-text extraction serial, and the correspondence between some rows and condition columns is doubtful, requires confirmation against the source standard (source-text extraction).)

Table 1 Physical constants and retention characteristics related to the column setting conditions of TCEP/WCOT (original table 1, source-text extraction is noisy, the following is the identifiable content, doubtful points are marked as requires confirmation against the source standard (source-text extraction)):

Note: M relative retention time with MTBE as 1; D relative retention time with DME as 1.

7. Sampling and test sample preparation

• 9.1 Sampling should be carried out in accordance with GB/T 4756 or other equivalent methods.
• 9.2 From the time the sample is received in the laboratory, before completing any subsampling, the container holding the original sample should be cooled to 0 ℃ to 5 ℃ for storage.
• 9.3 If necessary, transfer the cooled sample to a pressure-sealed container and store at 0 ℃ to 5 ℃ until analysis is required.
• 13.1 Test sample preparation: Using a pipette, transfer 0.5 mL internal standard to a dry and weighed 10 mL volumetric flask. Weigh the volumetric flask with the cap on, to the nearest 0.1 mg. Record the net mass of internal standard added (W.). Fill the volumetric flask to volume 10 mL with sample, cap the flask, weigh the flask, and record the net mass of sample added (W), weighed to 0.1 mg. Mix the solution thoroughly and inject a sample into the gas chromatograph. If an autosampler is used, transfer a portion of the solution to a GC glass vial for gas chromatography. Seal the GC glass vial with an aluminum cap with a polytetrafluoroethylene liner. If the sample is not analyzed immediately, it should be stored below 5 ℃.

8. Analysis procedure

• 10 TCEP Preparation of micro-packed column
  • 10.1 Clean a stainless steel tube of 560 mm, outer diameter 1.6 mm (inner diameter 0.76 mm) with methanol, and dry it with compressed nitrogen or air.
  • 10.2 Place a plug made of 6 strands to 12 strands of silver wire bundle, fine mesh partition, or stainless steel mesh at one end of the stainless steel column. Slowly add 0.14 g to 0.15 g of TCEP packing from the other end of the column. Pack the column packing tightly by gently vibrating. Add a plug at the loading end. When silver wire bundle or stainless steel mesh plugs are used to retain the column packing, occupy about 1 cm of the column space at each end of the column. (The original text here source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • 10.3 Column aging: Before use, both the TCEP and WCOT columns should be briefly aged. Connect the column to the valve of the chromatographic oven (see 11.1), adjust the carrier gas flow according to 11.3, and turn the valve to the reset position. After a few minutes, raise the column oven temperature to 120 ℃, and maintain these conditions for 5 min/10 min. Set the column to below 60 ℃... (The original text here source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
• 11 Instrument preparation and establishment of conditions
  • 11.1 Assembly: Connect the WCOT column to the valve system using small-volume fittings and small-bore stainless steel tubing. It is important to minimize the volume of the chromatographic system that contacts the sample; otherwise, peak broadening will occur.
  • 11.2 Leak detection: Adjust the operating conditions as listed in Table 2, but do not turn on the detector circuitry. The system should be leak-tested before proceeding.
  • 11.2 (original text continues): If columns of different polarity and non-polarity, capillary columns of smaller inner diameter, or both are used, it may be necessary to use different flow rates and temperatures. (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • 11.3 Flow ratio adjustment
    • 11.3.1 Connect a flow measuring device to the pre-cut column vent, leave the valve in the reset position, then adjust the inlet pressure to give a flow of 5.0 mL/min. For this purpose, a soap film flowmeter may be used for measurement.
    • 11.3.2 Connect the flow measurement device to the split injector vent, and use the A gas line flow controller and back pressure regulator to adjust this flow to 70 mL/min. Recheck the column outlet flow as in 11.3.1. Adjust repeatedly until the required flow is reached.
    • 11.3.3 Switch the valve to the backflush position, and repeatedly adjust the resistance valve so as to reach the pre-cut column vent flow set in 11.3.1, that is, make the resistance of the resistance valve the same as the resistance of the pre-cut column. This is necessary to reduce flow changes when the valve switches and to obtain a stable chromatographic baseline.
    • 11.3.4 Switch the valve to the reset position, and adjust the tail gas line flow controller so as to obtain a flow of 3.0 mL/min to 3.2 mL/min at the detector outlet. When using a specific instrument, adjust the makeup gas flow and the switching gas flow of TCD so that the total flow at the detector outlet reaches... (the source text here source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • 11.4 Detector: when using a thermal conductivity detector, turn on the electrical system to equilibrate it. When using a flame ionization detector, adjust the hydrogen and air flows and ignite.
  • 11.5 Determination of backflush time: the backflush time varies slightly for each column system and should be determined by the following experiment. The start time of the integrator and the valve timer should be synchronized with injection so that the backflush time can be accurately repeated.
    • 11.5.1 Initially set the valve backflush time to 0.23 min. Place the valve in the reset position, inject 1 μL～3 μL a mixture in which the concentration of each oxygenated compound is at least 0.5% (mass fraction), and at the same time start the analysis timing. At 0.23 min switch the valve to the backflush position and keep it there until TAME has completely flowed out. Record this time as... (the source text here source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... the reset time, that is, the time when the valve returns to the reset position. After all retained hydrocarbons have been backflushed out, the signal will return to a stable baseline, and the system will be ready for another analysis. The displayed chromatogram should be similar to Figure 2.
    • 11.5.1.1 (the source numbering is as such) It should be ensured that there is sufficient retention time to quantitatively transfer higher concentrations of alcohols, especially to allow MTBE to enter the analytical column.
    • 11.5.3 (the source numbering is as such) It is necessary to select the valve switching time by analyzing a standard mixture of oxygenated compounds. Preset the valve switching time between 0.20 min～0.35 min, and determine the exact backflush time experimentally. When the valve switches too early, C5 and lighter hydrocarbons are backflushed and elute in the same chromatogram segment as the alcohols; when the valve switches too late, part or all of the ether components (MTBE, ETBE or TAME) are vented, causing incorrect determination results.
    • 11.5.2 (the source numbering is as such) DIPE may require a slightly shorter backflush time than the other ethers. If DIPE needs to be analyzed, the system may need to reselect the optimum conditions.
    • 11.5.3 (the source numbering is as such) In order to determine the backflush time, that is, in Table 1... (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... connected through a narrow inner diameter line to another detector (TCD or FID), then use an oxygenated compound standard containing some ethers to test its time through the pre-cut column. After subtracting the time for the oxygenated compound to pass through the external connecting line, the backflush time can be determined.
• 13.2 Chromatography: using the same technique and sample amount as used for calibration, introduce a representative sample, including the internal standard, together into the chromatograph. When the split ratio is 15:1, an injection amount of 1.0 μL～3.0 μL is preferable. The start of the recording and integration device should be synchronized with the introduction of the sample. Obtain a spectrum or peak integration report, or rely on... (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... a report of the retention times and integration areas of the detected component peaks.
• 13.3 Interpretation of spectra: compare the component retention times obtained from sample analysis with those from calibration analysis results to qualitatively identify the oxygenated compounds present.

9. Qualitative and quantitative determination and calculation formulas

• 12.1 Qualitative: determine the retention time of each component by separately injecting a small amount of pure compound or a known mixture sample, or by comparison with the relative retention times in Table 1.
  • 12.1.1 In order to ensure that interference from hydrocarbon compounds is minimized, it is recommended to first perform a chromatographic determination of oxygenate-free gasoline in order to determine the level of hydrocarbon interference.
• 12.2 Preparation of calibration samples: prepare multi-component oxygenated compound calibration standards according to the principle of accurately weighing and mixing reagents in order from low to high volatility.
  • 12.2.1 For each oxygenated compound, prepare at least 5 calibration standards to cover the concentration range of the oxygenated compounds in the sample. For example, for full-range calibration, concentrations of each oxygenated compound with mass fractions of 0.1%, 0.5%, 2%, 5%, 10%, 15% and 20% may be used.
  • 12.2.4 Using a pipette or dropper [for volumes less than 1% (volume fraction)], transfer fixed volumes of the oxygenated compounds as follows into 100 mL volumetric flasks or small vials with septum caps to prepare standards. Cap and record the mass of the empty volumetric flask or vial, weighing to 0.1 mg. Open the cap and carefully add the oxygenated compound to the volumetric flask or vial. Do not let the sample contaminate the part of the volumetric flask or vial that contacts the cap. Cap it and record the mass of the oxygenated compound added (W), weighing to 0.1 mg. Repeat this addition and weighing process for each required oxygenated compound. Similarly, add 5 mL internal standard (DME), and record its net mass (W.), weighing to 0.1 mg.
• 12.3 Quantitative calibration
  • 12.3.1 Run the calibration standards and establish a calibration curve for each oxygenated compound. Plot the calibration curve for each oxygenated compound with the response ratio (rsp) as the y axis and the corresponding mass ratio (amt) as the x axis. The response ratio (rsp) and mass ratio (amt) are calculated according to formula (2) and formula (3), respectively:
    • Response ratio rsp = (A/A.)... (2)
      • Where: A—— area of oxygenated compound i; A.—— area of the internal standard.
    • Corresponding mass ratio amt = (W/W.)... (3)
      • Where: W—— mass of oxygenated compound i, in grams (g); W.—— mass of the internal standard, in grams (g).
  • Check the correlation coefficient value r of each oxygenated compound calibration curve; the r value should be at least 0.99 or better. r is calculated according to formula (4), formula (5), and formula (6):
    • r = (Σxy)² / [(Σx²)(Σy²)]... (4)
    • Where: x = X - X̄... (5); y = Y - Ȳ... (6)
    • Where: X—— mass ratio (amt) data point; X̄ — average of all (amt) data points; Y—— response ratio (rsp) data point; Ȳ — average of all (rsp) data points.
  • Table 3 gives an example of calculating r based on an ideal data set X and Y (the source table 3, source-text extraction has relatively large noise, requires confirmation against the source standard (source-text extraction)).
  • 12.3.3 For each oxygenated compound i calibration data set, a linear least squares fitting equation can be obtained as in formula (7):
    • rsp = (m) (amt) + b... (7)
    • Where: rsp—— response ratio of oxygenated compound i (y axis); m—— slope of the linear equation for oxygenated compound i; amt—— mass ratio of oxygenated compound i (x axis); b——y axis intercept.
  • 12.3.4 The values of m and b are calculated according to formula (8) and formula (9), respectively:
    • m = Σxy / Σx²... (8)
    • b = ȳ - m x̄... (9)
  • 12.3.5 Taking the data in Table 3 as an example: formula (10), formula (11) and formula (12) should be derived:
    • m = 5/10 = 0.5... (10)
    • b = ȳ - m x̄ = 1.5 - 0.5×3 = 0... (11)
    • Note: generally the value of b is not 0, but may be positive or negative. Figure 3 gives an example of MTBE linear least squares fitting, and the resulting equation has the same form as equation (7) above.
    • Taking MTBE as an example: rsp = 1.83(amt) - 0.015, r² = 1.000 (Figure 3)
    • Therefore, the least squares fitting equation for the example in Table 3 above is: rsp = 0.5 amt + 0... (12)
  • 12.3.6 In order to obtain the best calibration... (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... (mass fraction), A approaches... (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... the distance can be expressed by the following formula... (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... the mass percentage of oxygenated compound i or... (source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))... the equation is simplified to formula (13):
    • ω = (b/m)×(W./W)× 100%... (13)
    • Where: ω—— the mass fraction of oxygenates i, %. Here ω ≤ 0.1% (mass fraction); W.—— the mass of internal standard added to gasoline, in grams (g); W—— the mass of gasoline... (the original text here source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Note: based on actual... (source-text extraction incomplete, requires confirmation against the source standard (source-text extraction))... it is not easy to accurately... (source-text extraction incomplete, requires confirmation against the source standard (source-text extraction))... therefore an average value is used.
  • 12.3.7 An example is given below using the measured intercept (b) to calculate the concentration of oxygenates (MTBE). For MTBE, b = 0.015 and m = 1.83, and from 13.1 it can be known that the internal standard and typical sample preparation may contain approximately W. = 0.4 g (0.5 mL) and W = 7.5 g (9.5 mL) of gasoline. Substituting these values into equation (13) gives equation (14):
    • ω = (0.015/1.83) × (0.4/7.5) × 100% = 0.05% (mass fraction)... (14)
  • 12.3.8 Because ω is less than 0.1% (mass fraction), therefore for MTBE, the intercept is as true... (source-text extraction incomplete, requires confirmation against the source standard (source-text extraction))... an acceptable value. Similarly, the ω of all other oxygenates can be determined. For all oxygenates ω should be less than 0.1% (mass fraction). If any ω value is greater than 0.1% (mass fraction), the calibration process for oxygenates i must be redone, or the instrument parameters and hardware checked, or the hydrocarbons checked... (source-text extraction incomplete, requires confirmation against the source standard (source-text extraction))
• 14 Calculation and reporting
  • 14.1 Mass fraction of oxygenates: after qualitative identification of the various oxygenates, measure the area of each oxygenate peak and the internal standard peak. From the corresponding least-squares fitted calibration curve, as shown in the example of MTBE in Figure 3, use the response ratio of the oxygenate area to the internal standard area (rsp) to calculate the mass of each oxygenate in the gasoline sample (in... (source-text extraction incomplete, requires confirmation against the source standard (source-text extraction))... calculated according to equation (15), equation (16) or equation (17), equation (18):
    • ... (15) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Where: m—— the slope of the linear fit; ... the defined mass ratio.
    • Or ... (16) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Or ... (17) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • ... (18) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • The mass fraction (ω) result for each oxygenate can be obtained: ... (19) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Where: W—— the mass of the gasoline sample, in grams (g).
  • 14.2 The mass fraction of each oxygenate reported, accurate to 0.01%, concentrations less than or equal to 0.20% are reported as "not detected".
  • 14.3 Volume fraction of oxygenates: if it is desired to determine the volume fraction of each oxygenate... (20) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Where: ω—— the mass fraction of oxygenate i calculated by equation (19); ρ—— the relative density of each oxygenate found in Table 1 at 20 ℃; ρ gasoline—the relative density of the relevant gasoline measured according to GB/T 1884 or SH/T 0604 at 20 ℃.
  • 14.4 Report the volume fraction of each oxygenate, accurate to 0.01%.
  • 14.5 Mass fraction of oxygen: in order to determine the total oxygen content of gasoline ω oxygen % (mass fraction), convert and sum the oxygen content of all oxygenate components according to equation (21) or equation (22):
    • ... (21) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Or ... (22) (the original formula source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
    • Where: ω—— the mass fraction of oxygenate i determined by equation (13), %; M—— the relative molecular mass of the oxygenate given in Table 1; 16.0—— the relative atomic mass of oxygen; N—— the number of oxygen atoms in the oxygenate molecule.
  • 14.6 Report the total mass fraction of oxygen in gasoline (%), accurate to 0.01%.

10. Precision

• 15.1 Precision: judge the reliability of test results according to the following provisions (95% confidence level).
  • 15.1.1 Repeatability: the difference between two repeat results obtained by the same operator using the same instrument on the same sample shall not exceed the values in Table 4 or Table 5.
  • 15.1.2 Reproducibility: the difference between two single and independent test results obtained in different laboratories by different operators using different instruments on the same sample shall not exceed the values in Table 4 or Table 5.
• Table 4 Precision (original table 4, source-text extraction noisy, the following is the identifiable content, doubtful points marked requires confirmation against the source standard (source-text extraction)):