A Simple, Rapid, and Reliable Titrimetric Method for the Determination of Glycerol at Low Concentration

Santos, Luana O.; Rocha, Sheisi F. L. S.; Barra, Cristina M.; Tubino, Matthieu; Rocha Junior, José G.

doi:10.21577/0103-5053.20220004

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Article • J. Braz. Chem. Soc. 33 (06) • 2022 • https://doi.org/10.21577/0103-5053.20220004 copy

A Simple, Rapid, and Reliable Titrimetric Method for the Determination of Glycerol at Low Concentration

Authorship SCIMAGO INSTITUTIONS RANKINGS

Glycerol can be determined in several products by various analytical techniques. Titrimetric ones have stood out for their low cost, being recommended as standards. However, reliable, simple, fast, and green methods with low quantification limits are still needed. Titration of glycerol is based on its oxidation by periodate (Malaprade reaction) producing formic acid, formic aldehyde, and iodate. Iodate and periodate are iodometrically titrated, but mutual interference between these ions has produced methods with some drawbacks. Here is proposed to mask periodate with molybdate, to eliminate interference, determining the glycerol content through iodate, employing iodometric titration. Solutions containing from 10 to 1000 µg of glycerol were analyzed (error < 3.4%). The method was successfully applied for the determination of glycerol in biodiesels from different raw materials. Recoveries were from 92.9 ± 0.4 to 111 ± 3%. Semi-micro extraction was done, providing a fast procedure for determining free glycerol in biodiesel (< 10 min).

Keywords:
glycerol; periodate; molybdate; Malaprade; biodiesel

Concentration range / (mg L^-1)	Nominal content / (mg L^-1)	Volume of titrant / mL	Experimental content / (mg L^-1)	Coefficient of variation / %	Error / %	t value^a a t critical value = 3.18 (degree of freedom = 3; α = 0.05);
100-1000^b b 20 mmol L-1 Na2S2O3 solution and 10 mL burette;	997	6.44 ± 0.05	995 ± 6	0.6	-0.2	0.23
	798	5.26 ± 0.05	785 ± 5	0.6	-1.6	1.26
	598	3.77 ± 0.04	595 ± 10	1.7	-0.50	0.15
	391	2.58 ± 0.07	385 ± 10	2.8	-1.5	0.27
	195	1.29 ± 0.05	193 ± 7	3.6	-1.0	0.17
	99.7	0.648^c c the blank was discounted, according to equation 7; ± 0.010	96.3 ± 1.4	1.5	-3.4	1.2
10-100^d d 5 mmol L-1 Na2S2O3 solution and 5 mL burette.	97.7	2.388 ± 0.010	97.93 ± 0.10	0.1	0.24	0.23
	78.2	1.946 ± 0.005	79.8 ± 0.2	0.3	2.1	4.15
	58.6	1.471 ± 0.006	60.3 ± 0.3	0.5	2.9	3.29
	40.2	1.04^c c the blank was discounted, according to equation 7; ± 0.04	40.0 ± 1.6	4.0	-0.5	0.05
	20.1	0.522^c c the blank was discounted, according to equation 7; ± 0.010	20.0 ± 0.4	2.0	-0.5	0.06
	10.0	0.27^c c the blank was discounted, according to equation 7; ± 0.02	10.3 ± 0.8	8.0	3.0	0.13

Principle	Sample	Mass of glycerol	Oxidant agent/mass	time for Malaprade reaction / min	Agent for periodate elimination	time for periodate elimination / min	Blank	Titrant	Previous steps^a a Procedures for extracting the analyte or for pH adjustments, due to the intrinsic characteristics of the extraction solution, were disregarded; / estimated time^b b 3 min were considered for titration procedures;	Reference
Iodometric	biodiesel	4 mg	H₅IO₆/ 67.5 mg	30-90	none	-	yes	Na₂S₂O₃	none	⁵⁰50 ABNT NBR 15771: Biodiesel - Determinação de Glicerina Livre - Método Volumétrico, Brazil, 2009.
	vanishing cream	30-40 mg	KIO₄/ 230 mg	60	none	-	yes	H₃AsO₃	none	³⁶36 AOAC 942.22: Cosmetics - Vanishing Cream - Glycerol, Washington, DC, USA, 1990.
	fats and oils	600 µg	NaIO₄/ 275 mg	10	NaHCO₃	immediately	yes	NaAsO₂	none	⁵⁸58 Dantas, M. B.: Obtenção, Caracterização e Estudo Termoanalítico de Biodiesel de Milho (Zea mays L); MSc Dissertation, Universidade Federal da Paraíba, João Pessoa, Brazil, 2006, avalilable at https://www.ufpb.br/ppgq/contents/documentos/teses-e-dissertacoes/dissertacoes/2006/Dissertacao_Manoel_B_Dantas.pdf/view, accessed in December 2021. https://www.ufpb.br/ppgq/contents/docume... ^c c adapted from the AOCS Ca 14-56 standard;51dbased on the AOCS Ca 14-56 standard;51ebased on the IRAM 5571 standard;66faccording to the authors;
	fats and oils	15 µg	HIO₄/not reported	30	none	-	yes	Na₂S₂O₃	none	⁵⁹59 Rosas, J. C. F.: Produção de Biodiesel Metílico Utilizando Óleo Residual de Fritura via Ultrassom; MSc Dissertation, Universidade Federal do Pará, Belém, Brazil, 2011, available at https://ppgeq.propesp.ufpa.br/ARQUIVOS/dissertacoes/J%C3%BAlio%20C%C3%A9sar%20Freitas%20Rosas.pdf, accessed in August 2021. https://ppgeq.propesp.ufpa.br/ARQUIVOS/d... ^d
	water	30 mg	KIO₄/ 350 mg	5	KAsO₂^e	10	yes	chloramine-T	none	⁶⁰60 Hartman, L.; J. Appl. Chem. 1953, 3, 308.
Potentiometric	fats and oils	43-208 mg	NaIO₄/2.5 g	1	ethylene glycol	5	no	NaOH	pH adjustments/ 3 min	⁶¹61 Naviglio, D.; Romano, R.; Pizzolongo, F.; Santini, A.; De Vito, A.; Schiavo, L.; Nota, G.; Musso, S. S.; Food Chem. 2007, 102, 399.
Potentiometric	commercial glycerin	150 mg	H₅IO₆/1 g	60	none	-	yes	NaOH	pH adjustments/ 3 min	⁶²62 Bradford, P.; Pohle, W. D.; Gunther, J. K.; Mehlenbacher, V. C.; Oil Soap 1942, 19, 189.
Alkalimetric	water	400 mg	NaIO₄/3 g	30	ethylene glycol	20	yes	NaOH	evaluation of NaIO₄ solution/ 38 min	⁴⁰40 ASTM D7637: Standard Test Method for Determination of Glycerin Assay by Titration (Sodium Meta Periodate), West Conshohocken, PA, 2015.
	vanishing cream	30-40 mg	KIO₄/ 230 mg	60	propylene glycol	10	no	NaOH	none	³⁶36 AOAC 942.22: Cosmetics - Vanishing Cream - Glycerol, Washington, DC, USA, 1990.
	resin solutions	19-26 mg	HIO₄/ 550 mg	50-70	none	-	yes	NaOH	pH adjustments/ 3 min	⁶³63 ASTM D1615: Standard Test Methods for Glycerol, Ethylene Glycol, and Pentaerythritol in Alkyd Resins (Withdrawn 2004), West Conshohocken, PA, 1995.
	glycerol	100-120 mg	KIO₄/1.4 g	5	propylene glycol	few minutes^f	yes	NaOH	pH adjustments/ 3 min	⁵⁸58 Dantas, M. B.: Obtenção, Caracterização e Estudo Termoanalítico de Biodiesel de Milho (Zea mays L); MSc Dissertation, Universidade Federal da Paraíba, João Pessoa, Brazil, 2006, avalilable at https://www.ufpb.br/ppgq/contents/documentos/teses-e-dissertacoes/dissertacoes/2006/Dissertacao_Manoel_B_Dantas.pdf/view, accessed in December 2021. https://www.ufpb.br/ppgq/contents/docume...
	biodiesel	5-20 mg	NaIO₄/ 900 mg	30	ethylene glycol	20	no	NaOH	pH adjustments; boiling for CO₂ removal; cooling/ 15 min	³⁸38 Pisarello, M. L.; Costa, B. O. D.; Veizaga, N. S.; Querini, C. A.; Ind. Eng. Chem. Res. 2010, 49, 8935.
	biodiesel/ diesel blends	0.25-5 mg	NaIO₄/ 900 mg	30	ethylene glycol	20	yes	NaOH	pH adjustments; boiling for CO₂ removal; cooling/ 15 min	⁴³43 Pisarello, M. L.; Maquirriain, M. A.; Querini, C. A.; Energy Fuels 2018, 32, 8431.
	soaps and glycerin	150 mg	NaIO₄/ 900 mg	30	ethylene glycol	20	sometimes	NaOH	pH adjustments; boiling for CO₂ removal; cooling/ 15 min	⁶⁴64 NP 16 018 05: Combustibles. Biodiesel Puro (B100). Requisitos Generales, Paraguay, 2011.
	fermented glycerol broth	150-250 mg	NaIO₄/not reported	30	ethylene glycol	20	yes	NaOH	pH adjustments/ 3 min	⁶⁵65 Sanchez, D. L. R.: Butanol Production from Glycerol by Clostridium pasteurianum in Defined Culture Media - a Phenotypic Approach; MSc Dissertation, University of Maryland, College Park, USA, 2009, available at https://drum.lib.umd.edu/bitstream/handle/1903/9665/RamosSanchez_umd_0117N_10727.pdf?sequence=1&isAllowed=y, accessed in December 2021. https://drum.lib.umd.edu/bitstream/handl... ^g g based on the AOCS Ea 6-51 standard;47husing freshly prepared NaIO4 solution.
Iodometric	water	10-1000 µg	NaIO₄/ 1.07-10.7 mg	3	sodium molybdate	immediately	no^h	Na₂S₂O₃	none	proposed work

Biodiesel	Free glycerol content / (g per 100 g)	Added glycerol / (g per 100 g)	Found glycerol / (g per 100 g)	Recovery / %
Soybean	0.0268 ± 0.0017	0.031 ± 0.002	0.058 ± 0.003	100 ± 5
		0.062 ± 0.002	0.086 ± 0.003	97 ± 3
		0.131 ± 0.002	0.149 ± 0.006	93 ± 5
Palm kernel	0.011 ± 0.003	0.0306 ± 0.0003	0.040 ± 0.002	95 ± 5
		0.0617 ± 0.0013	0.071 ± 0.002	96 ± 4
		0.1281 ± 0.0011	0.1304 ± 0.0010	92.9 ± 0.4
Macauba kernel	0.052 ± 0.006	0.0305 ± 0.0004	0.085 ± 0.014	102 ± 6
		0.0631 ± 0.0010	0.115 ± 0.002	97 ± 4
		0.127 ± 0.003	0.182 ± 0.003	98 ± 8
Disposed frying oil	0.018 ± 0.003	0.0305 ± 0.0004	0.049 ± 0.002	111 ± 3
		0.0631 ± 0.0010	0.075 ± 0.009	101 ± 3
		0.125 ± 0.004	0.14 ± 0.03	102 ± 4

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