Abstract
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).
Highlights
Glycerol (1,2,3-propanotriol) is a chemical compound widely employed in cosmetics, pharmaceuticals, detergents, and foods as well as in the manufacture of resins, additives, explosives, papers, and paints.[1,2,3] Due to this variety of applications, it is important that new, reliable, fast, and lowcost techniques are being developed to quantify glycerol.The emollient, moisturizing and conditioning action of glycerol makes this compound used mainly in the formulation of cosmetics such as soaps, shower gels, toothpaste, and cream hair
The AOAC 942.22 standard method[36] is recommended to analyze glycerol in a cosmetic, from which it is separated by partition with acidified water/ chloroform
The monitoring of the sodium periodate solutions over time revealed that when exposed to the environment, until nine hours after their preparations, the iodate concentration does not decrease enough to influence the determination of glycerol (Figure 1)
Summary
Glycerol (1,2,3-propanotriol) is a chemical compound widely employed in cosmetics, pharmaceuticals, detergents, and foods as well as in the manufacture of resins, additives, explosives, papers, and paints.[1,2,3] Due to this variety of applications, it is important that new, reliable, fast, and lowcost techniques are being developed to quantify glycerol. The high excess of periodate used in the Malaprade reaction, and the low quantity of iodate produced (due to low glycerol content) can cause a situation in which the difference between the volumes of titrant becomes very small, fact which magnifies the relative titration error To increase this difference, the ABNT NBR 15771 standard method[50] recommends the use of a large-scale sample. Periodate ions react with water producing iodate ions which react with sodium thiosulfate causing a systematic error in the analysis, unless the volume of titrant spent on the blank titration is taken into account.[56,57] Even though from a thermodynamic point of view they are unstable, periodate solutions have been reported[56] to be kinetically stable, regardless of the pH value, as they oxidize water very slowly. In order to investigate the effect of storage conditions, two groups of periodate solutions, used in this study, were stored in different conditions: (i) in closed flasks protected from light and from the environment; (ii) in open flasks unprotected from light and exposed to the environment
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