SH/T 1550-2012 Determination of purity and impurities of methyl tert-butyl ether (MTBE) for industrial use — Gas chromatography

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Card type: Test method

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

• Standard number: SH/T 1550-2012 (on the cover source-text extraction there appears “SHVT 1550-2012”, suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction))
• Chinese title: Determination of purity and impurities of methyl tert-butyl ether (MTBE) for industrial use — Gas chromatography
• English title (original text source-text extraction): Methnyl tert - loutyl ether (MITBE)for ind ustrial use—Determinatiom of purity amd impurities—Gas Chromatographic metinod (multiple spellings suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction))
• Replacement relationship: replaces SH/T 1550-2000 “Determination of purity and hydrocarbon impurities of methyl tert-butyl ether (MTBE) for industrial use — Gas chromatography”
• Previous versions: SH/T 1550—93, SH/T 1550—2000
• Adoption relationship: not equivalent to ASTM D5441-98 (2008)
• Publication/implementation: published on 2012-05-24, implemented on 2012-11-01
• Record number: 36919-2012

2. Scope of application and non-applicability

• This standard specifies a gas chromatographic method for the determination of the purity and impurities of methyl tert-butyl ether (MTBE) for industrial use.
• It is applicable to the determination of the purity of MTBE, and also to the determination of impurities in MTBE, such as C4 to C.in hydrocarbons (original text as such, suspected to be something like C4 to C10, requires confirmation against the source standard (source-text extraction)), methanol, isopropanol (original text source-text extraction writes “[garbled alcohol name]”, requires confirmation against the source standard (source-text extraction)), tert-butanol and sec-butanol, methyl sec-butyl ether and methyl tert-amyl ether, acetone, and methyl ethyl ketone.
• Minimum detectable concentration:
  • Polymethylsiloxane column analysis method: minimum detectable concentration of impurities 0.02% (mass fraction).
  • 624 column and heart-cutting analysis method: minimum detectable concentration of impurities 0.002% (mass fraction).
• Not applicable: no explicit “not applicable” clause is provided in the available source. The original text indicates that water and other impurities that cannot be determined by this standard must be determined by corresponding standard methods, and the results obtained shall be normalized.

3. Method principle

3.1 Single-column (polymethylsiloxane column and 624 column) analysis method

Under the conditions specified in this standard, an appropriate amount of sample is injected into a gas chromatograph equipped with a flame ionization detector (FID) for analysis. The peak areas of each impurity and the main component are measured, and the mass percentage of each component is calculated by the corrected area normalization method. The correction factors are determined by analyzing standard samples with concentrations similar to those in the sample to be tested.

3.2 Heart-cutting analysis method

Under the conditions specified in this standard, an appropriate amount of sample is injected into a gas chromatograph equipped with a heart-cutting device and dual FID detectors. The sample first passes through a polymethylsiloxane column, and the components are separated according to boiling point. Based on the elution times of the difficult-to-separate substances, the time period for heart-cutting is determined, and they are cut to a polyethylene glycol capillary column so that the difficult-to-separate substances are effectively separated. The peak areas of each impurity and the main component are measured, and the mass percentage of each component is calculated by the corrected area normalization method. The correction factors are determined by analyzing standard samples with concentrations similar to those in the sample to be tested.

Water and other impurities that cannot be determined by this standard must be determined by corresponding standard methods, and the results obtained shall be normalized.

4. Reagents and materials (purity / preparation)

Warning: The reagents and materials involved in this chapter are all high-pressure compressed or flammable gases and flammable, toxic liquids, and should be used with attention to safety.

• 4.1 Carrier gas: helium or nitrogen, purity ≥99.99% (volume fraction) (original text source-text extraction writes “≥99 [garbled purity/unit text])”, requires confirmation against the source standard (source-text extraction)).
• 4.2 Combustion gas: hydrogen, purity ≥99.99% (volume fraction) (original text source-text extraction writes “≥99 [garbled volume-fraction text])”, requires confirmation against the source standard (source-text extraction)).
• 4.3 Auxiliary gas: nitrogen, purity ≥99.99% (volume fraction).
• 4.4 Combustion support: air, none (original text source-text extraction writes “air, none”, the rest is not provided in the available source, requires confirmation against the source standard (source-text extraction)).
• 4.5 Reference materials (original text source-text extraction numbers and names are disordered; the following are listed according to the discernible content of the original text, numbers require confirmation against the source standard (source-text extraction)):
  • Used for preparing standard samples and determining correction factors, wherein the purity of methyl tert-butyl ether shall be greater than 99.7% (mass fraction), and the purity of other substances shall be greater than 99.0% (mass fraction).
  • Methyl tert-amyl ether;
  • Methanol;
  • Isopropanol (original text source-text extraction writes “alcohol [incomplete name];”, requires confirmation against the source standard (source-text extraction));
  • Sec-butanol (original text source-text extraction writes “alcohol [incomplete name];”, requires confirmation against the source standard (source-text extraction));
  • Methyl sec-butyl ether;
  • 4,4- dimethyl-2- neopentyl-1- pentene (original text source-text extraction writes “4, 4- dimethyl-2- neopentyl”, requires confirmation against the source standard (source-text extraction));
  • Isooctane (original text source-text extraction writes “[garbled hydrocarbon name]”, requires confirmation against the source standard (source-text extraction));
  • n-Heptane (original text source-text extraction writes “[garbled alcohol name]” “n-heptane”, requires confirmation against the source standard (source-text extraction));
  • 2- methyl-2- butene (original text source-text extraction writes “[garbled substituent]-2-butene”, requires confirmation against the source standard (source-text extraction));
  • Methyl tert-butyl ether: used as the base liquid for preparing standard samples and determining correction factors;
  • 2,2,4,6,6- pentamethyl-3- heptene (original text source-text extraction writes “4,6,6- pentamethyl-3 heptene”, requires confirmation against the source standard (source-text extraction));
  • Pentene (specific isomer not provided in the available source, requires confirmation against the source standard (source-text extraction));
  • 2- pentene (original text source-text extraction writes “[garbled prefix]2[garbled alkene name]”, requires confirmation against the source standard (source-text extraction));
  • Trimethyl-pentene (specific isomer not provided in the available source, requires confirmation against the source standard (source-text extraction));
  • 2- pentene (original text source-text extraction writes “:2-pentene”, requires confirmation against the source standard (source-text extraction));
  • n-Heptane.
• 4.6 Preparation of calibration mixture: prepare a calibration mixture of high-purity MTBE, the impurities to be measured, and the reference substance n-heptane by the weighing method. The weighing of each component shall be accurate to 0.0001 g, and the content calculation shall be accurate to 0.0001% (mass fraction). The impurity concentration of the calibration mixture shall be similar to the impurity concentration in the sample to be tested.

5. Instruments and equipment

• 5.1 Gas chromatograph
  • 5.1.1 Single-column analysis method: a gas chromatograph equipped with a hydrogen flame ionization detector (FID) and capable of operating under the conditions recommended in Table 1. The peak height produced by the instrument for impurities at the minimum determination concentration specified in this standard shall be at least greater than twice the noise.
  • 5.1.2 Heart-cutting analysis method: a gas chromatograph equipped with a heart-cutting device and dual FID detectors and capable of operating under the conditions recommended in Table 1. The peak height produced by the instrument for impurities at the minimum determination concentration specified in this standard shall be at least greater than twice the noise. The gas path connection system is shown in Figure 1. Its default state is generally off: at this time, each component in the sample flows through the main analytical column and the damping column and is detected by detector A. When further separation of the co-eluting components flowing through the main analytical column is required, the analysis system is switched to state on for heart-cutting, so that the co-eluting components flowing through the main analytical column enter the auxiliary analytical column for further separation and are then detected by detector B. Other flow path control systems that satisfy the separation and quantification effects of this standard may also be used.
  • Figure 1 Schematic diagram of the gas path connection for the heart-cutting analysis method (state off: pre-separation state; state on: heart-cutting state).
• 5.2 Injection device: microsyringe (1 μL, original text source-text extraction writes “(1Mk,”, requires confirmation against the source standard (source-text extraction)) or autosampler.
• 5.3 Chromatographic column: This standard uses fused silica capillary columns as shown in Table 1. Other chromatographic columns and analysis conditions that can give equivalent separation and quantification effects may also be used.
• 5.4 Recording device: electronic integrator or chromatographic workstation.

6. Recommended operating conditions

Table 1 Recommended chromatographic columns and typical operating conditions (original table source-text extraction is misaligned; the following is organized according to the discernible content, with doubtful points marked as requiring confirmation against the source standard (source-text extraction)):

Note: The three sets of switching times listed in the table respectively correspond to the heart-cutting times for the three pairs of difficult-to-separate substances: methanol and butene, tert-butanol and 2-pentene, and methyl sec-butyl ether and sec-butanol.

7. Sampling and Test Sample Preparation

• Take the sample in accordance with the provisions of GB/T 4756.
• The sample may be stored in the glass pressure-resistant sampling bottle shown in Figure 2, and kept at a low temperature of about 4℃ until the sample measurement is carried out.
• Figure 2 Schematic diagram of the glass pressure-resistant sampling bottle (unit: mm; 1— hard glass bottle body; 2— stainless steel or brass screw connection; 3— silicone rubber gasket; 4— stainless steel or brass compression nut; the dimensions in the figure source-text extraction are given as “80, 25, -3, d2”, requires confirmation against the source standard (source-text extraction)).
• Test sample preparation: no separate “test sample preparation” clause is provided in the available source; for preparation of the calibration mixture, see 8.2.

8. Analytical Procedure

7 Instrument Preparation (original numbering is 7)

• 7.1 Installation and aging of the chromatographic column: install and age the chromatographic column according to the instructions in the instrument manual. After aging, connect the column outlet to the inlet of the flame ionization detector, and check the system for leaks.
• 7.2 Adjustment of gas chromatograph operating conditions: adjust the operating conditions of the gas chromatograph to comply with the parameters shown in Table 1.
• 7.3 Determination of the cutting time for the heart-cutting analysis method: with the electromagnetic switching valve in the preseparation state shown in Figure 1 (off), inject the prepared standard test sample into the gas chromatograph injection port. After the components to be measured are preseparated by the main analytical column, they pass through the damping column and enter detector A, and the start and end times of the peaks of the difficult-to-separate substance pairs (methanol and butene, tert-butanol and 2-pentene, methyl sec-butyl ether and sec-butanol) are determined. Because the residence time of the sample components on the damping column is less than 0.01 min, the start and end times of the peaks of the difficult-to-separate substance pairs on detector A are the valve switching times for the electromagnetic switching valve to switch from the preseparation state to the heart-cutting state (from state off to state on) and to switch back to the preseparation state (from state on back to state off). When the retention times of the cut components and the components before and after them are relatively far apart, the cutting time may be appropriately relaxed. Fine-tune the valve switching time to ensure that the difficult-to-separate substance pairs are completely cut into the auxiliary analytical column.
• 7.4 Determination of linear range: before carrying out sample testing, it must be verified whether the injected sample amount will cause signal saturation of FID. A standard sample with a concentration within the expected range may be used to construct a “concentration—peak area” curve for MTBE, so as to determine the injection volume range that satisfies linearity.

8 Measurement Procedure (original numbering is 8)

• 8.1 Qualitative identification of components: the qualitative identification of the component peaks obtained from sample analysis is determined by comparing their retention times with the retention times of reference materials under the same conditions. The typical retention times of common impurities in MTBE product are shown in Table 2. The typical chromatograms of common impurities in MTBE product on a polymethylsiloxane column, a 624 column, and by the heart-cutting analysis method are shown in Figure 3, Figure 4, and Figure 5, respectively.
• 8.2 Preparation of calibration mixture: see Section 4 4.6.
• 8.3 Determination of correction factors: according to the recommended operating conditions in Table 1, after the instrument has been running stably, accurately draw the same volume of the calibration mixture and methyl tert-butyl ether base liquid and inject them successively into the chromatograph. After repeated measurements, measure the areas of the chromatographic peaks. Based on the obtained chromatographic peak areas and the contents of each impurity component, calculate the correction factor of each component. The calculation of the mass correction factor is shown in formula (1). Typical relative mass correction factors are shown in Table 2.
  • Formula (1): f = (A₀ × mᵢ) / ((Aᵢ - A₀) × m₀) (the original source-text extraction formula is garbled, requires confirmation against the source standard (source-text extraction))
  • Where: f— component i relative mass correction factor relative to n-heptane; A₀—peak area of n-heptane in the calibration mixture; mᵢ—mass of component i in the calibration mixture, in milligrams (mg); Aᵢ—peak area of component i in the calibration mixture (the original source-text extraction is given as “peak area of component in the calibration mixture”, requires confirmation against the source standard (source-text extraction)); m₀—mass of n-heptane in the calibration mixture, in milligrams (mg). (The original source-text extraction also contains “average value of the peak areas of component i in the methyl tert-butyl ether base liquid from three determinations”, whose attribution requires confirmation against the source standard (source-text extraction))
• 8.4 Sample measurement
  • 8.4.1 When the gas chromatograph has not been used for more than 24 h, the column temperature should be raised to the maximum allowable operating temperature specified for the chromatographic column and maintained for more than 20 min to remove contaminants from the column. After a stable baseline is obtained, lower the column temperature to the initial temperature.
  • 8.4.2 Perform appropriate baseline compensation so that any component not lower than the method minimum detection concentration can be detected, integrated, and reported.
  • 8.4.3 Adjust the operating conditions of the gas chromatograph according to the parameters shown in Table 1, inject an appropriate amount of test sample, and the injection volume should ensure that the FID signal is not saturated, while recording the chromatogram.

Table 2 MTBE Typical retention times, relative mass correction factors, and densities of samples in different analytical methods

(The original table source-text extraction is severely misaligned; only identifiable component names are listed below; retention times, correction factors, and density values cannot be reliably matched due to the misalignment and are all marked as requires confirmation against the source standard (source-text extraction))

Identifiable component names: isobutane, methanol, isobutene + 1-butene, 1-butene, n-butane, trans-2-butene, cis-2-butene, 3-methyl-1-butene, acetone, isopentane, 2-propanol, 1-pentene, 2-methyl-1-butene, n-pentane, trans-2-pentene, tert-butanol, cis-2-pentene, 2-methyl-2-butene, cyclopentene, methyl tert-butyl ether, 2,3-dimethyl-1-butene, 4-methyl-cis-2-pentene, 2-methyl-pentane, methyl ethyl ketone, 3-methylpentane, methyl sec-butyl ether, sec-butanol, ethyl tert-butyl ether, methyl-2-butenyl ether, isooctane, methyl tert-amyl ether, 3,5-dimethyl-1-hexene, 2,4,4-trimethyl-1-pentene, 2,4,4-trimethyl-2-pentene, 3,4,4-trimethyl-trans-2-pentene, 2,3,4-trimethyl-2-pentene, 4,4-dimethyl-2-neopentyl-1-pentene, 2,2,4,6,6-pentamethyl-3-heptene.

Notes to Table 2 (identifiable in the original):

• Note 1: Under the recommended conditions, methanol elutes simultaneously with isobutane on the polymethylsiloxane column, but can be completely separated on the 624 column; under the heart-cutting analysis method, methanol and isobutane are cut onto the polyethylene glycol column and can be completely separated.
• Note 2: Isobutene and 1-butene elute simultaneously under the recommended column temperature in all three methods (polymethylsiloxane column, 624 column, and heart-cutting), but can be separated at a column temperature below room temperature.
• Note 3: Sec-butanol and methyl sec-butyl ether cannot be separated on the polymethylsiloxane column under the recommended conditions, but can be completely separated on the 624 column and by the heart-cutting analysis method.
• Note 4: Under the recommended conditions on the polymethylsiloxane column, trans-2-pentene elutes before tert-butanol, and cis-2-pentene elutes after tert-butanol, but both are shoulder peaks; however, on the 624 column and by the heart-cutting analysis method, the above components can be separated.
• Note 5: In the heart-cutting analysis method, those not marked with a detector are all measurement results on detector FID A.
• Note 6: Although this standard separates most impurities in MTBE, some components still cannot be separated. For example, it has been found that cyclopentane and 2,3-dimethylbutane (the original source-text extraction is given as “2, 3-dimethylbut”, requires confirmation against the source standard (source-text extraction)) elute simultaneously with MTBE on the polymethylsiloxane column, but these two impurities are usually not present in MTBE. Therefore, attention should be paid to identification during use.

9. Qualitative and Quantitative Determination and Calculation Formulas

9.1 Calculation of Mass Content

The mass content wᵢ of each component is expressed as a mass fraction, with the value expressed in %, and is calculated according to formula (2):

wᵢ = (Aᵢ × fᵢ) / Σ(Aᵢ × fᵢ) × (100 - w) (the original source-text extraction formula is garbled, requires confirmation against the source standard (source-text extraction))

Where:

• wᵢ—content of component i, % (mass fraction);
• Aᵢ—peak area of component i;
• fᵢ—relative mass correction factor of component i relative to n-heptane;
• Σ(Aᵢ × fᵢ)—sum of the corrected peak areas of all components;
• w— impurity content in the test sample measured according to GB/T 6283 and other methods, % (mass fraction).

For the few impurity components for which correction factors cannot be obtained, their relative mass correction factor fᵢ may be set to 1.00.

9.2 Calculation of Volume Content

If it is necessary to report the volume content Vᵢ of each component, expressed as a volume fraction, with the value expressed in %, conversion may be carried out according to formula (3):

Vᵢ = wᵢ × ρ / ρᵢ (the original source-text extraction formula is garbled, requires confirmation against the source standard (source-text extraction))

Where:

• Vᵢ—volume content of component i, % (volume fraction);
• wᵢ—mass content of component i calculated from formula (2), % (mass fraction);
• ρ— density of the test sample at 20℃, in grams per milliliter (g/mL);
• ρᵢ—density of component i found from Table 2, in grams per milliliter (g/mL).

10. Precision

11 Repeatability (original number is 11)

In the same laboratory, by the same operator using the same equipment, according to the same test method, and within a short period of time, the absolute difference between two independent test results obtained from mutually independent tests on the same test object shall not exceed the repeatability limit listed in Table 3 (r), on the premise that the cases exceeding the repeatability limit do not exceed 5%.

Table 3 Repeatability requirements

Note: The original foreword states that "a self-determined repeatability limit (r) was adopted, and the typical data for reproducibility were deleted", therefore the reproducibility is not provided in the available source.

11. Report

The report includes the following contents:

• a) All information about the sample, such as sample name, batch number, sampling date, sampling location, sampling time, etc.;
• b) The number of this standard;
• c) Analysis results;
• d) Details and explanations of any abnormal phenomena observed during the determination process;
• e) Name of the analyst;
• f) Date of analysis.

12. Normative references

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756—1998, Neq ISO 3170:1988)
• GB/T 6283 Determination of water content in chemical products—Karl Fischer method (general method)
• GB/T 8170 Rules for rounding off numerical values and expression and judgment of limiting values
• GB/T 1.1—2009 (mentioned in the foreword, as the drafting basis)
• ASTM D5441-98 (2008) "Standard Test Method for Analysis of Methyl Tert-Butyl Ether (MTBE) by Gas Chromatography" (not equivalently adopted)

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A reference