Sequential spectrofluorimetric determination of free and total glycerol in biodiesel in a multicommuted flow system |
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Authors: | Silva Sidnei G Morales-Rubio Angel de La Guardia Miguel Rocha Fábio R P |
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Institution: | (1) Instituto de Qu?mica, Universidade de S?o Paulo, P.O. Box 26077, 05513-970 S?o Paulo-SP, Brazil;(2) Department of Analytical Chemistry, Universidad de Valencia, C/Dr. Moliner 50, 46100, Burjassot, Valencia, Spain;(3) Centro de Energia Nuclear na Agricultura, Universidade de S?o Paulo, P.O. Box 96, 13400-970 Piracicaba- SP, Brazil; |
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Abstract: | A new procedure for spectrofluorimetric determination of free and total glycerol in biodiesel samples is presented. It is
based on the oxidation of glycerol by periodate, forming formaldehyde, which reacts with acetylacetone, producing the luminescent
3,5-diacetyl-1,4-dihydrolutidine. A flow system with solenoid micro-pumps is proposed for solution handling. Free glycerol
was extracted off-line from biodiesel samples with water, and total glycerol was converted to free glycerol by saponification
with sodium ethylate under sonication. For free glycerol, a linear response was observed from 5 to 70 mg L−1 with a detection limit of 0.5 mg L−1, which corresponds to 2 mg kg−1 in biodiesel. The coefficient of variation was 0.9% (20 mg L−1, n = 10). For total glycerol, samples were diluted on-line, and the linear response range was 25 to 300 mg L−1. The detection limit was 1.4 mg L−1 (2.8 mg kg−1 in biodiesel) with a coefficient of variation of 1.4% (200 mg L−1, n = 10). The sampling rate was ca. 35 samples h−1 and the procedure was applied to determination of free and total glycerol in biodiesel samples from soybean, cottonseed,
and castor beans. |
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