Determination of Methanol in Gasoline by Gas Chromatography A Laboratory Experiment Stanfwd L. Tacketl Indiana University of Pennsylvania. Indiana. PA 15705 Methanol is becoming a popular blending agent for gasoline. Its antiknock properties allow it t o he used a s a n effective replacement for lead alkyl compounds, and, since it is cheaper than gasoline, i t also serves a s a fuel extender.' Methanol must be blended with a higher molecular weight alcohol or it tends to combine with moisture in the gasoline and forms a separate phase. T h e separated water-methanol nhase is corrosive t o ~ l a s t i cand metal uarts in the fuel delivery system and engine, and can cause engine failure.' T h e Environmental Protection Aaencv has a ~ ~ r o v several ed blending formulations containingmeihanol and other cosolvent components for use in aasoline. A reliahle method for th; determination of methanol in gasolinc is important for moniroring the approved lewls of methanol in easoline blendsand for detectine the fraudulent representation of methanol blends as pure gasoline. A recently developed gas chromatographic method for the determination of methanol in gasoline is both simple and reli-
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T h e method reported here is fast and reliable and does not reauire snecialized e a.u i.~ m e n t .S a m.~ l . e re treatment is not required-the raw gasoline samples can he injected directly onto the chromatographic column. Experimental A Shimadzu model GC-8 APT gas chromatograph equipped with a Carbowax 20M column and a thermal conductivity detector was used. The column was 2 m long, 1' s in. in diameter and was packed with a 10%loading of Carbowan 20M (polyethylene glycol) on 801 100 mesh Chromosorh W solid support. Any gas chromatograph with temperature programming capability and a column of similar polarity should he suitable. The methanol peak is actually recorded during the isothermal portion of the run, hut temperature programming is needed to clear the column of higher hoilinggasolinecomponents. Helium carrier gas was used at a flow rate of 30 mL/min. Data were recordedmd processed an a Shimadzu Chromatopae C-R3A data station. The Shimadzu data station is especially convenient to use, hut any other datastation or stripchart recorder would suffice. Electronic integration of the methanol peak area is highly desirable, hut mechanical integration methods will give acceptable results. Simple and effective mechanical integration methods include rhe uip of a planimeter, cutting and neighing the peak, or mulr!plwn~:the peak height tinirs rhc width at me-half height. hlethand iulutiun5 drr DrrDared hv volumetric dilution of rragent-grade methanol witha gasoline that contains no methanol. A preliminary screening of the available brands and grades of gasolines in the local area is suggested. It is convenient to add the methanol by volumetric pipet to 100-mL volumetric flasks and dilute to the mark with methanol-free gasoline. It is recommended that four or five standards coveringthe range of 0-10 vol%methanol be prepared. Solutions containing more than about 5 ~ 0 1 % methanol should be freshly prepared each day since phase separation tends to occur with higher methanol concentrations. Individual samules of 1.0 uL are inieetedwith a Hamilton svrinae. Each sample is chromatographed for 3.0 min isothermally at50 c' , and then the temperature program is started. The column oven is
Anderson, E. V. Chem. Eng. News 1984, 6&29), 9-16.
* Tacken. S. L. Analyst 1987,
112,339-340.
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Gas chromatograms fw methanol/gasoline blends: (A) unleaded gasoline containing no methanol: (6) 5% methanol in unleaded gasoline; (6)10%
methanol In super unleaded gasoline. Volume 64
Number 12
December 1987
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programmed to rise from 50 O C to 150 O C at a rate of 10 "C per minute. The injection port and detector block are maintained at 190 "C.
RewHs and Dlscusslon Typical chromatograms obtained by this method are shown in the figure. Chromatogram A was recorded for an unleaded easoline s a m ~ l ethat contained no methanol. Chromatogram B was for a sample containing 5.00 \'ol 9 methanol (diluted with a methanol-free unleaded aasoline). Chromatogram C was recorded for a 10.00 vol % methanol sample (diluted with a methanol-free super unleaded gasoline). The most volatile fraction of the gasoline sample passes through the column rapidly, eluting early in the 3min isothermal portion of the run. Methanol interacts with the Carhowax 20M stationary phase and exhibits a peak with a retention time of about 2.6 min in a region that is free of other gasoline component peaks. After 3.0 min the temperature program is started, and the rest of the gasoline components elute. A total time of about 15 min is required for all measurable neaks to emeree. The qualitative determination.hf methanol in gasoline by this method is excellent. The detection limit is about 0.2%. The only other substance found to give a peak with a retention time between about 1.5 and 3.5 min is tert-butanol, which has hcen approved for coblending with methanol in Atlantic Richfields's "Oxinol50" formulation.:'lert-Rutanol is not a normal constituent of gasoline and is added only with methanol.
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Journal of Chemical Education
A calibration curve is prepared by plotting methaflol peak area versus volume percent methanol, and the unknown concentration is read from the curve. The calibration curve was found to be a straight line up to 10% methanol, which was the highest concentration measured. When a prepared sample containing 5.00 vol% methanol was analyzed by this method, a value of 5.07% was obtained. Quantitative accuracy was found to be quite high. The only small deviations noted were due to the variation of sample volumes injected with the syringe and the normal error associated with graphing. I t is suggested that local gasolines be sampled and analyzed for methanol content. ,Alternatively, standard solutions of methanol in gasoline can he prepared and issued to the students as "unknowns". Conclusion T h e results indicate that this method is useful both for rapid screening to detect the presence of methanol in gasoline and for accurate quantitation of the methanol concentration found. The method is simple and easy t o perform with readily available and inexpensive gas chromatographic equipment. Current environmental concerns coupled with the corrosion problems occurring with methanol-gasoline blended fuels make this a timely experiment as well.
Anderson, E. V. Chem. Eng. News 1986,64, (IS),18-19
