Determination of Inorganic Anions in Biobutanol Samples by I

1 Introduction
Into the 21st century, the rapid development of the world economy, natural resources are consumed at a frantic speed. Some important resources such as oil and even the danger of depletion, the world is aware of the seriousness of the problem, have to study the product can be replaced. The current gasoline fuel alternatives to bio-butanol research and production of the most popular. Biobutanol is considered a better fuel additive for alternative ethanol because it has a lower vapor pressure than ethanol, a higher energy density, and can be mixed with a very high proportion of gasoline. Especially the butanol octane number and gasoline closer [1]. Compared with fossil fuels, bio-butanol has a stronger renewable energy characteristics.
Early bio-butanol is from corn and barley and other cereal crops produced. Now the use of straw and wood fiber fermentation to produce butanol is the industry's main development direction [2]. With the bio-butanol fermentation and related separation technology is increasingly perfect, the price of its products will also be reduced.
Different fermentation materials, require biological butanol production process is different. In order to ensure the quality of the product, the impurities must be routinely tested. The excess inorganic insoluble salts contain inorganic anions that may corrode the engine of the motor vehicle, and the exhaust gas that will emit will also affect the quality of the atmosphere [3-5].
At present, the standard method for the determination of inorganic anions in alcohols is generally based on ion selective electrode method, colorimetric method and precipitation titration. The method has the advantages of complicated operation, large matrix interference and low accuracy [6]. The existing literature shows that ion chromatography has the advantages of simple operation, no matrix interference, high accuracy and good reproducibility such as Cl3-, NO3- and SO42- in alcoholic substances [7-10] But generally the use of expensive imported equipment. For the application of domestic ion chromatography, determination of domestic inorganic butanol in the concentration of inorganic anions, the author has not been published in the literature. It can be considered that the determination of inorganic anions such as sulfate and chloride ions is an important index of biobutanol quality inspection.
In this paper, a method for the determination of inorganic anions such as Cl- in biological butanol was established by using domestic ion chromatograph. The detection limits were as follows: 0.5-2.0mg / L (S / N = 3), recovery range: 96.8% - 102.2 %, Reproducibility range: 0.59% - 0.84%. Compared with the imported instrumentation method, no butanol matrix interference, reproducibility of the results for the biological butanol in the determination of inorganic anions to provide a reliable method.
2, the experimental part
2.1 Instruments and reagents
Instrument: PIC-10A type ion chromatograph, Qingdao Pu Ren Instrument Co., Ltd.;
Adjustable million electric furnace, Longkou City electric furnace factory;
Reagents: Na2CO3 (reference reagent), NaHCO3 (analytical grade), Shanghai Optoelectronics Reagent Co., Ltd.;
Clin, NO3-, H2PO4-, SO42-standard solution (1000mg / L), National Standard Material Research Center;
30% H2O2, Yantai Sanhe Chemical Reagent Co., Ltd .;
Ultra pure water (resistivity greater than 18.2MΩ.cm), Millipore;
Sample: a biological butanol production units of the pilot products.
2.2 chromatographic conditions
Column: PR-SA-10A Anion exchange column (250 mm x 4.6 mm), eluent: 1.8 mM Na2CO3 + 1.7 mM NaHCO3, flow rate: 1.0 mL / min, injection volume: 200 mL
2.3 Sample pretreatment
Add 10 mL of sample to a 50 mL beaker and mix with 2 mL of H2O2 for about 5 min. Place the beaker in the low temperature range of the electric furnace (in the fume hood) to allow the liquid sample to evaporate slowly. When the sample close to dry (volume of about 1mL), stop heating, so that the sample naturally cooled 5min. Add 80mL of deionized water, heat dissolve the tidal salt, and then cool to room temperature. Transfer the sample to a 100 mL volumetric flask. The samples were analyzed by post-0.22 mm filter.
3. Results and discussion
3.1 Selection of chromatographic conditions
9, 10], if the use of spontaneous inhibition mode, both leaching methods are matrix interference. While the use of additional acid suppression mode is no matrix interference. Taking into account the pretreatment method has been removed butanol, and OH- in the domestic ion chromatography column elution ability is weak, this paper uses Na2CO3 + NaHCO3 eluent.
    In order to analyze the inorganic anions in the alcoholic substances, the imported instruments are generally used in the presence of carbonate eluents or KOH eluents [
3.2 Anion spectra in samples
 
 

Figure 1 shows that inorganic anions such as Cl- (3.786mg / L), NO3- (2.146mg / L), H2PO4- (2.719mg / L) and SO42- (3.517mg / L) are mainly present in n-butanol. There is no butanol matrix interference after pretreatment. Thermo Fisher Scientific [7] used direct injection method to determine the chromatographic pure methanol in the Cl- and SO42-, the method of methanol matrix interference, the Cl- quantitative production have a certain impact. In the literature [10] mentioned that the methanol matrix will even cover the Cl-peak, can not detect Cl-, therefore, remove the sample alcohol matrix is necessary.
2.2 Standard curve and detection limit

A series of standard solutions were arranged and the minimum detection limit was calculated at 3 times the signal-to-noise ratio (S / N = 3) under sequential chromatographic conditions. The linear equations, correlation coefficients and minimum detection limits of the four ions (n = 3) are shown in Table 1.
Table 1 Cl-, NO3-, H2PO4-, SO42- linear equation, correlation coefficient and minimum detection limit

   It can be seen from Table 1 that the method has high sensitivity and that the minimum detection limit of the four ions is even lower than that of the imported instrument, which may be related to the large volume of the injection (200ml). The imported instrument generally adopts 25ml Sample volume. Figure 2 shows the linear superposition spectra of the four anions.
2.3 spiked recovery rate
A known amount of four ions was added to the sample obtained in 1.3, and the calibration was carried out under the determined ion chromatographic conditions. The samples were measured three times in parallel. The experimental results are shown in Table 2.
Table 2 Sample spiked recovery

2.3 Reproducibility test
The n-butanol sample was treated in parallel 5 times according to the treatment method of 1.3. The reproducibility of the retention time and peak area of the ions in 5 samples is shown in Table 3.

Table 3 Retention results and peak area reproducibility results

Note: a for 1.0mg / L continuous injection of 10 times the reproducibility, b is 10.0 mg / L continuous injection 10 times the reproducibility
It can be seen from Table 2 that the method is stable and reliable, and the recovery rate is better. As can be seen from Table 3, the method described herein has a high reproducibility both in terms of retention time and peak area, and the results are comparable to those of imported instruments. In the method provided by Thermo Fisher Scientific [7], due to the limited solubility of SO42- in methanol, 10 mg / L SO42- is gradually lost, resulting in poor reproducibility of peak area (n = 10, RSD% = 1.90). The reproducible overlay spectrum is shown in Fig.
3. Conclusion
   The inorganic anions in biobutanol (pilot products) were detected by PIC-10 ion chromatography. The recovery range was 96.8% - 102.2%, and the reproducibility range was 0.59% - 0.84%. The recoveries were as follows: 0.5-2.0 mg / L (S / N = 3) The method has no butanol matrix interference, high sensitivity, reproducible results and imported equipment for the biological butanol industry, conventional quality inspection.
I solemnly recommend that this method can be applied to biological butanol development industry routine testing.
In this study, oxygen bomb combustion experiments will be carried out on sample processing, which will further accelerate the rate of sample handling.
    The four inorganic anions of chloride ion and sulfate in the pilot sample are obviously visible in the spectrum. Compared with the higher level of contact with the author, nitrates and other high signs [11]. It is suggested to further optimize the extraction process of bio-butanol.
4. References

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[2].   Green, E. M., Fermentative production of butanol—the industrial perspective.[J].Current Opinion in Biotechnology.2011, 22: (3), 337-343.

[3].   S. Y. Lee, J. H. P., S. H. Jang, et al, Fermentative butanol production by clostridia. [J]. Bio-technology and Bioengineering .2008, 101: (2), 209-228.

[4], 39-41. [J]. Natural Gas Chemical Industry: C1 Chemical and Chemical Industry .2011, 36: (1), 39-41. [J]. Natural Gas Chemical Industry:

[5]. Yan Yongliang, Liu Hongjuan, Zhang Jianan, metabolic engineering in bio-butanol production and research progress. [J]. Modern Chemical .2012, 32: (4), 25-30.
[6] .Chen He, Lin Yifei, Liu Jingjing, Determination of Inorganic Anions in Ethanol by Ion Chromatography [J]. Physical Testing (Chemistry) .2012, 01.
[7]. Determination of Chloride and Sulfate in Methanol Using Ion Chromatography. Dionex Application Note 201.
[8]. Kirk Chassaniol, D. T., Determination of Chloride and Sulfate in Ethanol Using Ion Chromatography; Dionex Application Update 161; LPN 1920. Sunnyvale, CA.2007.
[J] .Chinese Journal of Analytical Chemistry 2005, 33: (2), 187-190. Determination of trace anions in organic solvents by ion chromatography [J] .Chinese Journal of Analytical Chemistry 2005, 33: (2), 187-190.
[10]. Guo Yingying, Zhang Jiajie, Shi Qinghong, Determination of Trace Anions in Water Soluble Organic Solvents by Ion Chromatography and Its Mechanism [J]. Journal of Zhejiang University (Natural Science Edition) .2005, 32: (2), 194-197.
[11] GB / T6027-1998 National Standard of the People's Republic of China --- Industrial Butanol.

THE DETERMINATION OF INORGANIC ANIONS IN BIO-BUTANOL SAMPLE WITH ION CHROMATOGRAPHY

Hou Qianhui 1 Wang Cunjin1 Du Xiaolei1 Yu Jijin2

（1. QingDao Puren Instrument. Com.Ltd, Qingdao 266043    2. QingDao University，Qingdao 266071）

Abstract：Cl- and some inorganic anionsin butanol sample were determined with China’s ion chromatography. The detection limits（S/N=3）, recovery and reproducibility were in the range of 0.5 – 2.0 mg/L, 96.8% - 102.2% and 0.59% - 0.84% respectively. The method showed short analytical period(in 14 min), no butanol matrix interference, higher sensitivity, and the reproducibility is as good as imported instrument.

Key Words：Bio-butanol, ion chromatography, conductivity detection, matrix