This study reports on a rapid method for the determination of levulinic acid (LA) and 5-hydroxymethylfurfural (HMF) in acid hydrolyze system of glucose based on UV spectroscopy. It was found that HMF and LA have a maximum absorption at the wavelengths of 284 nm and 266 nm, respectively, in a water medium, and the absorptions of HMF and LA at 284 nm and 266 nm follow Beer’s law very well. However, it was found that a major spectral interference species will arise in the quantification of HMF and LA; nonetheless, this interference can be eliminated through the absorption treatment of charcoal. Therefore, both HMF and LA can be quantified with a double-wavelength technique. The repeatability of the method had a relative standard deviation of less than 4.47% for HMF and 2.25% for LA; the limit of quantification (LOQ) was 0.017 mmol/L for HMF and 4.68 mmol/L for LA, and the recovery ranged from 88% to 116% for HMF and from 94% to 105% for LA. The present method is simple, rapid, and accurate. It is suitable to use in the research of the preparation of HMF and LA in biorefinery area.
Levulinic acid (LA) can be used as a new platform chemical for the production of a wide range of value-added products through salification, esterification, hydrogenation, condensation, oxidation and halogenation reaction [
The traditional quantitative analysis for HMF included thiobarbi acid method [
In this work, we have developed a UV spectroscopic method for the simultaneous determination of HMF and LA. The present method is simple, rapid, and accurate and has the potential for online process monitoring.
All chemicals used in the experiments were from commercial sources. Five HMF solutions (the concentration range is from 0 to 0.1 mmol/L) and LA solutions (the concentration range is from 0 to 65 mmol/L), analytica1 grade, were used as the standard for calibration. A 5 wt% of H2SO4 solution was used to hydrolyze glucose.
Seven stream samples were collected from the H2SO4 solution hydrolyze system of glucose in the laboratory using a reaction kettle. The process conditions of acid hydrolyze system experiments were as follows: 3 g of glucose was used, 50 mL of H2SO4 solution (5 wt%) was poured into the reaction kettle, the reactor was placed in the electricity bath and heated to 180°C, and time was recorded from the set-value temperature. The reaction was stopped after 2 h from the start of the reaction and cooled to room temperature.
A UV-Vis spectrophotometer (S-3100, Shinco, Korea) equipped with a 1 cm path length flow cell was used for the experiments.
Calibration was conducted by preparing a set of standard solutions, that is, 0.019, 0.037, 0.056, 0.075, and 0.093 mmol/L of HMF and 20.25, 29.80, 39.00, 47.86, and 64.66 mmol/L of LA. The absorption spectrum for each solution was measured at wavelength of 284 nm and 266 nm, respectively.
For a typical UV analysis of glucose hydrolysate, 5 mL of filtrate for glucose hydrolysate and 0.5 g of activated charcoal were added to a 10 mL of colorimetric tube. The solution was boiled for 1 min; then, the reaction solution was filtrated by filter paper, and the filtrate was measured at the wavelength of 284 nm and 266 nm after filtration.
UV light can be absorbed by HMF and LA. Therefore, HMF and LA can be determined by spectroscopy as long as there is no spectral interference. As shown in Figure
Spectra of HMF and LA.
As shown in Figure
Calibration curves for HMF and LA.
Being calculated by (
For HMF and LA determination in hot acid hydrolysis solution of glucose or fructose, the major spectral interference species are produced by byproducts which are generated by subsidiary reactions during the hot acid hydrolysis. As shown in Figure
Spectra of HMF, LA, and sample.
The spectral difference of a sample before and after it was treated by charcoal was shown in Figure
Spectra of the sample before and after it was treated by charcoal.
The dosage of charcoal can affect the adsorption ratio of byproducts. So, it will influence the spectra of the sample after adsorption treatment by charcoal. As shown in Figure
Effect of charcoal dosage on the spectra of a sample.
The absorption intensity at wavelengths of 400 nm as a function of charcoal dosage, which indicated that complete interference was eliminated when the dosage of charcoal achieved 0.1 g/mL sample (Figure
Effect of charcoal dosage on the absorbance at 400 nm of a sample.
During the charcoal absorption treatment of the hot acid hydrolysis solution, not only the byproducts were absorbed, but also HMF and LA would be absorbed at a certain extent. Figure
Effect of charcoal absorption on the absorbance of LA and HMF.
In this paper, we developed a dual-wavelength spectrophotometric method to determine the contents of HMF and LA at the same time. As Figure
So, the content of LA and HMF in the hot acid hydrolysis solution of glucose can be calculated:
The repeatability tests of the present method were conducted by adding some standard solutions of LA and HMF to a hot acid hydrolysis sample. The sample was measured by the present method, and the coefficients of recoveries of LA and HMF were calculated. The results are listed in Table
Recovery test of the method.
Sample | Weight, |
|||||
---|---|---|---|---|---|---|
Added | Measured | Recovery, % | ||||
LA | HMF | LA | HMF | LA | HMF | |
1 | 34 | 148 | 32 | 130 | 94 | 88 |
2 | 50 | 123 | 49 | 144 | 98 | 116 |
3 | 78 | 165 | 84 | 173 | 108 | 104 |
4 | 97 | 200 | 102 | 188 | 105 | 94 |
According to the present method, seven samples were measured to determine the contents of LA and HMF, and the results were listed in Table
Contents of LA and HMF in the sample.
Reaction time, min | 20 | 24 | 26 | 29 | 40 | 49 | 66 |
---|---|---|---|---|---|---|---|
LA, g | 0.32 | 1.39 | 1.40 | 2.00 | 1.80 | 1.87 | 1.49 |
HMF, g | 0.27 | 1.06 | 0.38 | 0.46 | 0.17 | 0.11 | 0.05 |
A very simple and rapid spectroscopic method to determine HMF and LA in hot acid hydrolysis solution of glucose had been developed. In this method, a sample was absorbed by charcoal, and direct UV absorption of the filtrate is then measured. The contents of HMF and LA can be calculated using a dual-wavelength (at 266 nm and 284 nm) spectroscopic technique. The present method is simple, rapid, and accurate and has the potential for online process monitoring.
The authors are grateful to the financial support from Science and Technology Program from Science Technology Department of Zhejiang Provincial of China (2012C322080), Science and Technology Planning Program from Zhejiang Environmental Protection Bureau of China (2012B008), 521 Talent Cultivation Plan of Zhejiang Sci-Tech University, and the open fund of Key Lab. of Biomass Energy and Material of China (JSBEM201303).