I have worked with a solution (specifically made of glycerol and water) that presents the hypsochromic shift in the uv spectrometer. I have "controlled" it through adding a certain volume of buffer, but it has not resulted well, do you know any other solution of this? or do you know what is the best way to quantify glycerol solutions besides TCD chromatography?
Hi Arturo,
Is there a particular molecule you are trying to quantify in glycerol/water? or are you measuring glycerol spectra in different conditions?
Typically, if chemical entities show chromicity dependent on solution environment, the best way to quantify via UV/Vis is to the use the isosbestic point for quantification. At the isosbestic point wavelength, absorption is independent of chemical or physical change and hence it is purely dependent on how much is there of the particular substance. In order to identify the isosbestic point, you will have to perform a calibration study of your samples under all the conditions you are interested in (all containing equal amount of molecule of interest) with a spectra run. After obtaining the spectra, identify the point wherein all the curves meet and that will be the isosbestic point.
Hi Rahul,
In fact, I´m measuring glycerol spectra in different conditions, mainly varying concentration, some other physical conditions and the detection of dihydroxyacetone after reaction. The point here is when I try to measure glycerol before and after the reaction this presents hypsochromic shift to very low wavelenghts (192nm), and if i use a phosphate buffer solution, the contribution of this one is so great that I can´t quantify, in a properly way, the contribution of glycerol in the spectra.
Dear Arturo!
I think there is no isodestic point in principal, since in the glycerol-water oxidation processes are possible, and the physical interaction of glycerin and its surroundings are possible too, also not excluded the complex formation.
ok, do you know what is the best way to quantify glycerol solutions?, I recently found the colorimetric method and other old ways using TCD in GC.
Dear Arturo; I think using TCD-GC is a better way than a measurement at this low wavelength.
I agree. Aqueous solutions this far into the UV transmit little of the light. Between detector sensitivity and cell thickness the GC method is far more likely to work.
Glycerol (prop-1,2,3-triol) does not have any chromophoric group that can make this compound absorb in UV/Vis region. The band at 192 nm is end-absorption typical of all types of compounds, and it should not be related to a particular one for its measurement. If you are still interested in GC, attempt silylation before injection (K. Blau and J. Halket, Handbook of Derivatives for Chromatography, John Wiley).
Simultaneous determination of free and total glycerol in biodiesel by capillary electrophoresis using multiple short-end injection
By:Spudeit, DA (Spudeit, Daniel Alfonso)[ 1 ] ; Piovezan, M (Piovezan, Marcel)[ 1 ] ; Dolzan, MD (Dolzan, Maressa D.)[ 1 ] ; Vistuba, JP (Vistuba, Jacqueline Pereira)[ 1 ] ; Azevedo, MS (Azevedo, Monia Stremel)[ 2 ] ; Vitali, L (Vitali, Luciano)[ 2 ] ; Oliveira, MAL (Leal Oliveira, Marcone Augusto)[ 3 ] ; Costa, ACO(Oliveira Costa, Ana Carolina)[ 2 ] ; Micke, GA (Micke, Gustavo Amadeu)[ 1 ]
ELECTROPHORESIS
Volume: 34
Issue: 24
Pages: 3333-3340
DOI: 10.1002/elps.201300371
Published: DEC 2013
View Journal Information
Abstract
A rapid method for the simultaneous determination of free glycerol (FG) and total glycerol (TG) in biodiesel by CE using a short-end multiple injection (SE/MI) configuration system is described. The sample preparation for FG involves the extraction of glycerol with water and for TG a saponification reaction is carried out followed by extraction as in the case of FG. The glycerol extracted in both cases is submitted to periodate oxidation and the iodate ions formed are measured on a CE-SE/MI system. The relevance of this study lies in the fact that no analytical procedure has been previously reported for the determinationof TG (or of FG and TG simultaneously) by CE. The optimum conditions for the saponification/extraction process were 1.25% KOH and 25 degrees C, with a time of only 5 min, and biodiesel mass in the range of 50.0-200.0 mg can be used. Multiple injections were performed hydrodynamically with negative pressure as follows: 50 mbar/3s (FG sample); 50 mbar/6s (electrolyte spacer); 50 mbar/3s (TG sample). The linear range obtained was 1.55-46.5 mg/L with R-2> 0.99. The LOD and LOQ were 0.16mg/L and 0.47mg/L, respectively for TG. The method provides acceptable throughput for application in quality control and monitoring biodiesel synthesis process. In addition, it offers simple sample preparation (saponification process), it can be applied to a variety biodiesel samples (soybean, castor, and waste cooking oils) and it can be used for the determination of two key parameters related to the biodiesel quality with a fast separation (less than 30 s) using an optimized CE-SE/MI system.
Eco-friendly sonoluminescent determination of free glycerol in biodiesel samples
By:Diniz, PHGD (Goncalves Dias Diniz, Paulo Henrique)[ 1 ] ; Pistonesi, MF (Fabian Pistonesi, Marcelo)[ 2 ] ; de Araujo, MCU (Ugulino de Araujo, Mario Cesar)[ 1 ] ; Band, BSF (Fernandez Band, Beatriz Susana)[ 2 ]
TALANTA
Volume: 114
Pages: 38-42
DOI: 10.1016/j.talanta.2013.04.009
Published: SEP 30 2013
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Abstract
This paper proposes a flow-batch methodology for the determination of free glycerol in biodiesel that is notably eco-friendly, since non-chemical reagents are used. Deionized water (the solvent) was used alone for glycerol (sample) extractions from the biodiesel. The same water was used to generate water-cavitation sonoluminescence signals, which were modulated by the quenching effect associated with the amount of extracted glycerol. The necessarily reproducible signal generation was achieved by using a simple and inexpensive piezoelectric device. A linear response was observed for glycerol within the 0.001-100 mg/L range, equivalent to 0.004-400 mg/kg free glycerol in biodiesel. The lowest measurable concentration of free glycerol was estimated at 1.0 mu g/L. The selectivity of the proposed method was confirmed by comparing the shape and retention of both real and calibration samples to standard solution chromatograms, presenting no peaks other than glycerol. All samples (after extraction) are greatly diluted; this minimizes (toward non-detectability) potential interference effects. The methodology was successfully applied to biodiesel analysis at a high sampling rate, with neither reagent nor solvent (other than water), and with minimum waste generation. The results agreed with the reference method (ASTM D6584-07), at a 95% confidence level. (C) 2013 Elsevier B.V. All rights reserved.
Simple enzymatic methods for glycerol analysis in commercial beverages
By:de Souza, FC (de Souza, Flavia Carvalho)[ 1 ] ; de Vasconcellos, FJ (de Vasconcellos Junior, Fabio Jorge)[ 1 ] ; Cabral, RC (Cabral, Raphael Cyriaco)[ 1 ] ;Fernandez, TL (Fernandez, Tatiana Lopez)[ 1 ] ; D'Elia, E (D'Elia, Eliane)[ 1 ]
CYTA-JOURNAL OF FOOD
Volume: 11
Issue: 3
Pages: 270-276
DOI: 10.1080/19476337.2012.732613
Published: AUG 1 2013
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Abstract
Two enzymatic methods using amperometric and colorimetric detection based on two coupled activities (glyceroquinase and glycerol-3-phosphate oxidase) were compared for the glycerol content determination. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark-type electrode and correlated with the glycerol concentration. In addition to the enzymatic-colorimetric method, there is a third enzymatic reaction that can be used to form a coloured compound; this method involves the addition of peroxidase, 4-chlorophenol and 4-aminoantipyrine. The enzymatic methods studied showed good linearity in the range of 4 to 60mol L-1 glycerol with a detection limit of 1mol L-1. Studies of glycerol recovery in fortified sugar cane liquor showed a recovery of 98 +/- 2% for the enzymatic-amperometric method and of 96 +/- 1% for the enzymatic-colorimetric method. These two methods were applied to the determination of glycerol in beverages and good correlations were found between these methods.
Why do you want to use TCD with water? Do you have access to an FID? If you don't want to (or need to use GC), why not titrate the sample as described in ASTM 7637? This works well as long as no other vicinal diols ( e.g.ethylene or propylene glycol) are present. the method is simple and robust. Glycerol by GC can be problematic because it is so polar.
The point here is that I use very low concentrations, less than 500 mM, ASTM is valid when mixtures grater than 75%, and the samples have a volume of 600 microliters. and yes, I have access to an FID, even in many articles it is reported the use of TCD.
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