Determination of methanol content

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5. Determination of trace methanol in gases or liquids – Chromatographic method 1 Scope of application: This method is suitable for determining the methanol content at the ppm level in gases, as well as the trace amounts of methanol in wastewater. 2 Instruments 2.1 Gas chromatograph equipped with a hydrogen flame ionization detector (FID). 2.2 Microsyringe: 1.0µL or 2.0µL. 2.3 Pipettes, volumetric flasks, etc. 2.4 Balance: 0.1mg3 Operating conditions 3.1 The chromatography column is a stainless steel column with a diameter of Φ4mm and a length of 2m, filled with TDX-01. 3.2 The carrier gas is pure nitrogen, with a pressure of 0.150 MPa. 3.3 The fuel gas is pure hydrogen, at a pressure of 0.03 MPa. 3.4 The assist gas is air, with a pressure of 0.134 MPa. 3.5 Column temperature: 115°C. 3.6 Vaporization chamber temperature: 140°C. 3.7 Amplifier range: 10–114. Operating steps: 4.1 Steps for turning on the gas chromatograph equipped with a hydrogen flame ionization detector (FID). 4.1.1 Turn on each gas source and adjust it to the desired pressure. 4.1.2 Turn on the power switch and set the column temperature and vaporization chamber temperature to the specified values. 4.1.3 Sampling and analysis can be carried out after the baseline is adjusted and stabilized. 4.2 Shutdown procedure: The power supply must be turned off first, followed by the gas supply. During shutdown, the temperature should be reduced; the column temperature and the vaporization chamber temperature should both be lowered to 30°C before shutting down the system. 4.3 Calibration of the coefficient 4.3.1 Take a 50 mL brown volumetric flask, wash it, dry it, cool it, then weigh it on a balance with a precision of one ten-thousandth, and record its mass m1 ； Add about 45 mL of distilled water, weigh it, and record its mass m2 ； Using a syringe, about 1.5 mL of anhydrous methanol was drawn up and injected into a volumetric flask; its mass was measured and recorded in mg. This solution was designated as Solution 1. 4.3.2 Thoroughly mix the solution in the aforementioned volumetric flask. Transfer 1.0 mL of this solution into a 100 mL volumetric flask containing approximately 95 mL of distilled water, then dilute to the mark with distilled water and shake well. This solution is designated as Solution 2. 4.3.3 Use a micropipette to draw 0.8 µL of Solution 2 for analysis, and measure the peak height. 4.3.4 Calculate the peak height concentration correction factor f_liquid for the methanol content in the liquid. In the formula: f: peak height of methanol – concentration correction factor, wtppm/mm; h: peak height, mm ； m1: Mass of the volumetric flask, in g; m2: Mass of the volumetric flask and water, in g; m3: Mass of the volumetric flask, water, and methanol, in g. 4.3.5 Calculation of the peak height-concentration correction factor for methanol in the gas: f_gas. Here, f_gas is the peak height-concentration correction factor for methanol, expressed as VPPm/mmHg; peak height is in mm. m1: Mass of the volumetric flask, in g; m2: Mass of the volumetric flask and water, in g; m3: Mass of the volumetric flask, water, and methanol, in g. 0.8: Injection volume of Solution 2, in µL; 32: Molecular weight of methanol; 22.4: Volume of 1.0 millimole of methanol vapor under standard conditions, in mL. 4.4 Testing of samples: The injection volume for liquid samples is 0.8 µL, while the injection volume for gas samples is 2 mL. 4.4.1 When analyzing gas samples, fully displace the volumetric tube with sample gas, then rotate the six-way valve to introduce the sample for analysis and measure its peak height h. The methanol content in the gas is calculated using the following formula: C = 1/2f. Where: C is the methanol content in the gas, in Vppm; f is the concentration correction factor for the peak height of methanol, in Vppm/mm; and h is the peak height, in mm. 4.4.2 When analyzing the methanol content in water, if the sample is contaminated, it must be filtered using filter paper or absorbent cotton. Afterwards, 0.8 µL of the sample should be taken using a micropipette for analysis, and its peak height h should be recorded. The methanol content in the liquid is calculated using the following formula: C = f_liquid · h. Where: C is the methanol content in the liquid, in wtppm; f_liquid is the peak height of methanol; the concentration correction factor, in wtppm/mm; and h is the peak height, in mm