National Standard Interpretation: GB/T 46434-2025 has officially come into effect, marking a new phase in the determination of methanol purity and trace organic impurities.

　　Methanol is an important basic chemical feedstock, widely used in coal‑chemicals, fine chemicals, new materials, fuels, and downstream synthesis applications. As quality‑control requirements for methanol continue to tighten, the accurate identification and quantitative analysis of trace organic impurities—beyond the main methanol content—are receiving increasing attention from manufacturers, quality‑inspection agencies, and downstream users.

　　On October 31, 2025, the State Administration for Market Regulation and the National Standardization Management Committee issued GB/T 46434-2025, “Determination of Methanol Purity and Trace Organic Impurities—Gas Chromatographic Method,” which entered into force on May 1, 2026.
　　The implementation of this standard provides a unified gas chromatographic analytical method for the determination of trace organic impurities—such as alcohols, ketones, and esters—in methanol products, while also setting more stringent requirements for laboratory instrument configuration, method development, detection sensitivity, and data rigor.

　　 I. Which samples are covered by the new national standard?
　　According to GB/T 46434-2025, this method is applicable for the determination of methanol products with a mass fraction of not less than 99.0%.
　　The standard is primarily used for the determination of: methanol purity; alcohol impurities; ketone impurities; ester impurities;
　　Carbonate impurities; trace organic impurities such as ethylene glycol methyl ether.
　　Unlike the traditional approach, which focuses solely on methanol’s main component, the new standard places greater emphasis on the systematic detection of trace organic impurities, enabling enterprises to conduct a more comprehensive assessment of methanol product quality.

　　 II. What testing methods are used in the standard?
　　GB/T 46434-2025 employs gas chromatography.
　　Its basic principle is:
　　Under the selected chromatographic conditions, the individual components in methanol are separated on a capillary column and detected using a hydrogen flame ionization detector (FID), with quantification performed by either the internal standard method or the corrected area normalization method.
　　The standard explicitly stipulates that the gas chromatograph shall be equipped with:
　　Hydrogen flame ionization detector, FID;
　　Injection split device;
　　Chromatography workstation;
　　The standard stipulates that the gas chromatograph used for analysis shall meet the following requirements in terms of stability, limit of detection, and linear range:
　　The overall machine stability complies with the relevant provisions of GB/T 9722.
　　Use a spare chromatographic column, set the column temperature to 80°C, and appropriately select the carrier gas flow rate. Within 10 minutes, the instrument’s baseline drift shall not exceed the baseline drift requirement specified in JJG 700 (i.e., ≤3 pA).
　　The peak height of the impurity at the lowest detectable concentration shall be at least three times the noise level.
　　The instrument’s linear range shall meet the requirements for quantitative analysis; specifically, it must cover a linear range that satisfies quantitative criteria. Furthermore, the peak height generated by impurities at the minimum detectable concentration specified in the standard shall be at least three times greater than the noise level.
　　This means that, during the implementation of the new national standard, laboratories must not only ensure that peaks can be detected, but also pay close attention to instrument sensitivity, baseline stability, repeatability, and the ability to detect low‑level impurities.

　　 III. Two recommended chromatographic conditions—how should the laboratory choose?
　　GB/T 46434-2025 provides two sets of recommended chromatographic conditions.
　　 Condition 1: Polyethylene glycol stationary phase
　　Condition 1: A polyethylene glycol–based capillary column was used, with the following specifications: 60 m × 0.32 mm × 0.5 μm.
　　Under these conditions:
　　• The detection limit for dimethyl carbonate is 4 mg/kg;
　　• The detection limit for other organic impurities is 2 mg/kg.
　　The standard also notes that Condition 1 cannot separate butanone from methanol, but its detection sensitivity for other impurities is superior to that of Condition 2.
　　Therefore, if the laboratory focuses on low‑level organic impurities other than methyl ethyl ketone, Condition 1 offers a distinct advantage in sensitivity.
　　 Condition 2: 100% polydimethylsiloxane stationary phase
　　Condition 2 employs a capillary column with a 100% polydimethylsiloxane stationary phase, having the following specifications: 60 m × 0.32 mm × 5 μm.
　　Under these conditions:
　　• The detection limit for ethylene glycol methyl ether is 12 mg/kg;
　　• The detection limits for methyl formate and dimethyl carbonate are 8 mg/kg;
　　• The detection limit for other organic impurities is 5 mg/kg.
　　The advantage of Condition 2 is its ability to cover the separation and detection of a wide range of typical organic impurities in methanol, making it well suited for routine quality control and multi-component analysis.

　　 IV. What key issues should laboratories focus on under the new national standard?
　　From the perspective of the standard’s content, when implementing GB/T 46434-2025, laboratories are advised to focus on the following key aspects.
　　1. FID Sensitivity and Stability
　　Methanol contains low levels of trace organic impurities, requiring detection limits at the mg/kg level. The noise, drift, and response stability of the FID directly affect the identification and quantification of these low‑concentration impurities.
　　2. Chromatographic Column Selection and Method Compatibility
　　The standard provides two sets of recommended chromatographic conditions. Different stationary phases exhibit varying retention behaviors toward impurities such as methanol, esters, ketones, and alcohols; laboratories should select appropriate method parameters based on the specific analytical objectives.
　　3. Preparation of Standard Solutions and Determination of Calibration Factors
　　The standard specifies that quantification may be performed using either the internal standard method or the corrected area normalization method. n-Heptane can serve as either an internal standard or a reference compound. Accurate determination of the correction factor is a critical prerequisite for obtaining reliable quantitative results.
　　4. Validation of the ability to detect low-concentration impurities
　　The standard provides clear specifications for the limit of detection under various conditions. Therefore, before a method is put into routine use, laboratories should conduct validation of the limit of detection, repeatability, and stability, taking into account the target impurity.
　　5. Presentation of Data Results
　　The standard stipulates that the arithmetic mean of two parallel determinations shall be taken as the test result. The methanol purity is reported to two decimal places, while the impurity levels are reported to four decimal places or 1 mg/kg.

　　 V. Case Study on the Application of Domestic Gas Chromatographs in the Analysis of Methanol under the New National Standard
　　To better meet the new national‑standard testing needs of methanol producers, we conducted application validation for the detection of trace organic impurities in methanol using the GS2010‑IIF gas chromatograph. During on‑site commissioning at the Shanxi Coking Methanol Testing Laboratory, the GS2010‑IIF was equipped with an FID detector and a DB‑01 capillary column, with polydimethylsiloxane as the stationary phase, measuring 60 m × 0.32 mm × 5 μm.
　　This column is equivalent to the 100% dimethylsiloxane stationary phase, 60 m × 0.32 mm × 5 μm chromatographic column recommended in Condition 2 of GB/T 46434-2025, and is suitable for the separation and detection of various trace organic impurities in methanol.

　　 VI. On-Site Commissioning Results
　　During on-site commissioning, the instrument was validated with respect to FID performance, repeatability, and the ability to detect typical impurities in methanol.
　　1. FID detection limit
　　Customer requirement: FID minimum detection limit < 3 pg carbon/s, calculated using n-tridecane.
　　Field measurement results: The FID detection limit is 0.267 pg carbon/s.
　　This result exceeds the customer’s requirements, demonstrating that the instrument exhibits excellent sensitivity for the analysis of low-concentration components.
　　2. Repetitive Performance
　　Seven consecutive injections were performed, and the results for n-tridecane are as follows:
　　Retention time repeatability RSD: 0.096%
　　Peak area repeatability RSD: 1.466%
　　Retention time and peak area repeatability are key indicators of the stability of gas chromatographic methods. Excellent repeatability helps ensure the reliability of both qualitative and quantitative results for trace impurities.
　　3. Baseline Noise and Drift
　　Field test results show:
　　FID baseline noise: 0.022 pA/min
　　FID baseline drift: 0.1 pA/30 min
　　Although this parameter meets the requirements of the national standards GB/T 9722 and JJG‑700, it still falls short of Kairui Chromatography’s internal corporate standard. On-site notes indicate that the carrier gas purity did not reach 99.999%; further improving the carrier gas purity could potentially lead to additional reductions in baseline noise. This also underscores that, when implementing the new national standard, laboratories should recognize that, in addition to instrument performance, the purity of the gas supply, the cleanliness of the gas delivery system, and routine system maintenance all significantly influence the final analytical results.
　　4. Detection capability for trace impurities in methanol
　　In the verification of the limit of detection for impurities in methanol, a manual gravimetric method was employed on-site to prepare the test solutions, and the results are as follows:

　　The aforementioned targets correspond to the relevant detection limit requirements specified in Condition 2 of GB/T 46434-2025: under Condition 2, the detection limit for ethylene glycol methyl ether is 12 mg/kg, for methyl formate and dimethyl carbonate it is 8 mg/kg, and for other organic impurities it is 5 mg/kg.
　　Field validation results demonstrate that the GS2010‑IIF gas chromatograph meets the customer’s requirements for detecting typical trace organic impurities in methanol in this application scenario.

　　 VII. From standard methods to stable operation, both instrument and method validation are indispensable.
　　The implementation of GB/T 46434-2025 provides a unified and standardized gas chromatographic method for the analysis of methanol purity and trace organic impurities. However, for laboratories to achieve reliable and consistent data output, it is also essential to pay close attention to the method’s practical application, including:
　　Appropriate chromatographic column configuration;
　　Stable FID detector;
　　The purity of the gas source meets the requirements;
　　Reasonable split injection conditions;
　　Standard and calibration factor management;
　　Method detection limit verification;
　　Monitoring of repeatability and quality control samples.
　　The GS2010‑IIF gas chromatograph has been validated through field application cases, providing a domestically developed instrument solution that can serve as a reference for methanol producers, coal‑chemical enterprises, and third‑party testing laboratories in implementing the new national standard methods.