Determination of Methanol in Gasoline and Ethanol Fuels by High-Performance Liquid Chromatography

Dias, Gabriella P.; Santos, Rafael C. dos; Carvalho, Renato C.; Souza, Cristiane G. de; Santos, Amanda P. F. dos; Andrade, Débora F. de; d’Avila, Luiz A.

doi:10.21577/0103-5053.20190272

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Article • J. Braz. Chem. Soc. 31 (5) • May 2020 • https://doi.org/10.21577/0103-5053.20190272 linkcopy

Determination of Methanol in Gasoline and Ethanol Fuels by High-Performance Liquid Chromatography

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Gasoline and ethanol fuels have been adulterated with methanol in Brazil. Methanol is not permitted in concentrations greater than 0.5 vol% due its toxicity but its lower price stimulates the adulteration. A new approach for quantitative analysis of methanol in gasoline and ethanol fuels is reported employing high-performance liquid chromatography coupled with refractive index (RI) detector on C18 column (250 × 4.6 mm, 5 µm) using deionized water as mobile phase (0.6 mL min⁻¹). The method showed good analytical performance in terms of linearity for methanol concentration ranging from 0.5 to 4.5 vol% (coefficient of determination (R²) = 0.999) and from 4.0 to 12.0 vol% (R² = 0.998). The recoveries (accuracy) values ranged from 98.6 to 103.2%. The results indicated that the developed method is accurate and suitable for the determination of methanol in gasoline with ethanol and ethanol fuel as an alternative procedure to gas chromatography (GC)-based techniques.

Keywords:
liquid chromatography; adulterant; ethanol fuel; methanol; gasoline; refractive index

Parameter	Lowest concentrations	Highest concentrations
Linearity range (n = 5) / vol%	0.5-4.5	4.0-12.0
Regression equation	$y = 1.0462 x - 0.0376$ a	$y = 1.1238 x - 0.4191$ a
Determination coefficient (R²)	0.9999	0.9988
LOD / vol%	0.0053	0.0048
LOQ / vol%	0.016	0.014
Repeatability (RSD)b / %
Lower	0.354	0.039
Middle	0.288	0.044
Higher	0.308	0.051
Recoveryb / %
Lower	99.07 ± 0.01	103.26 ± 0.09
Middle	100.60 ± 0.01	98.61 ± 0.08
Higher	100.09 ± 0.01	100.46 ± 0.04

Sample	Methanol content ± SD / vol%
Sample	HPLC-RI	GC
1	0.487 ± 0.001	0.70 ± 0.02a
2	0.704 ± 0.004	0.60 ± 0.02a
3	0.934 ± 0.001	0.80 ± 0.02a
4	1.190 ± 0.002	1.20 ± 0.02a
5	1.258 ± 0.001	1.30 ± 0.02a
6	1.508 ± 0.003	1.30 ± 0.02a
7	1.562 ± 0.006	1.50 ± 0.02a
8	1.855 ± 0.004	2.00 ± 0.02a
9	2.191 ± 0.017	2.00 ± 0.02a
10	2.350 ± 0.003	2.70 ± 0.02a
11	2.721 ± 0.002	2.80 ± 0.02a
12	2.763 ± 0.002	3.10 ± 0.65b
13	3.594 ± 0.011	3.60 ± 0.65b
14	5.472 ± 0.009	5.50 ± 0.65b
15	6.317 ± 0.034	6.00 ± 0.65b
16	7.051 ± 0.018	7.10 ± 0.65b
17	7.909 ± 0.030	8.20 ± 0.65b
18	7.980 ± 0.086	8.10 ± 0.65b
19	9.245 ± 0.027	9.40 ± 0.65b
20	9.607 ± 0.016	9.50 ± 0.65b

Sample	Methanol content ± SD / vol%
Sample	HPLC-RI	GC
1	< LOQ	< 0.07 ± 0.02a
2	0.50 ± 0.01	0.50 ± 0.02a
3	2.60 ± 0.01	2.90 ± 0.02a
4	4.90 ± 0.07	5.00 ± 0.65b
5	5.80 ± 0.01	5.60 ± 0.65b
6	6.30 ± 0.01	6.60 ± 0.65b
7	7.30 ± 0.02	7.60 ± 0.65b
8	11.30 ± 0.08	11.90 ± 0.65b

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[TFN1] ^a
y stands for the peak area (µRIU min) and x for the methanol concentration (vol%);

[TFN2] ^b
repeatability and recovery values were determined in three different concentrations (lower, middle and higher), in triplicate, for each analytical curve. Lower, middle and higher concentrations were 0.5, 2.5 and 4.5 vol% for the first calibration curve and 4.0, 8.0 and 12.0 vol% for the second curve. HPLC-RI: high-performance liquid chromatography and refractive index detector; LOD: limit of detection; LOQ: limit of quantification, RSD: relative standard deviation.