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In this paper, an efficient and robust technique based on reaction headspace gas chromatographic analysis for the quantification of urea in milk is presented, which is realized by measuring formed carbon dioxide from the enzymatic hydrolysis of urea under the catalysis of enzyme urease. It was observed that the headspace equilibration was finished in 40 min at 35 °C. The new technique was proved to be accurate (relative errors ≤7.17%) and precise (relative standard deviations ≤2.93%). In addition, compared with the reference spectrophotometric technique, the new technique has a higher sample throughput. The proposed approach is simple, fast and has the potential to be a practical tool for the batch analysis of urea in milk production and processing. Unlabelled Image • Quantitative analysis of urea in milk by headspace gas chromatography. • The new approach is based upon measuring formed carbon dioxide from the enzymatic hydrolysis of urea. • This approach has the potential to be used for the routine analysis of urea in milk. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is to introduce a new method for quantitatively analyzing water absorption capacity in wheat flour by a headspace gas chromatographic technique. This headspace gas chromatographic technique was based on measuring the water vapor released from a series of wheat flour samples with different contents of water addition. According to the different trends between the vapor and wheat flour phase before and after the water absorption capacity in wheat flour, a turning point (corresponding to water absorption capacity in wheat flour) can be obtained by fitting the data of the water gas chromatography peak area from different wheat flour samples. The data showed that the phase equilibrium in the vial can be achieved in 25 min at desired temperature (35°C). The relative standard deviation of the reaction headspace gas chromatographic technique in water absorption capacity determination was within 3.48%, the relative differences has been determined by comparing the water absorption capacity obtained from this new analytical technique with the data from the reference technique (i.e., the filtration method), which are less than 8.92%. The new headspace gas chromatographic method is automated, accurate and be a reliable tool for quantifying water absorption capacity in wheat flour in both laboratory research and mill applications. [ABSTRACT FROM AUTHOR]

This paper investigates a new double sealing technique for increasing the precision of the headspace gas chromatographic method. The air leakage problem caused by the high pressure in the headspace vial during the headspace sampling process has a great impact to the measurement precision in the conventional headspace analysis (i.e., single sealing technique). The results (using ethanol solution as the model sample) show that the present technique is effective to minimize such a problem. The double sealing technique has an excellent measurement precision (RSD < 0.15%) and accuracy (recovery = 99.1%–100.6%) for the ethanol quantification. The detection precision of the present method was 10–20 times higher than that in earlier HS-GC work that use conventional single sealing technique. The present double sealing technique may open up a new avenue, and also serve as a general strategy for improving the performance (i.e., accuracy and precision) of headspace analysis of various volatile compounds. [ABSTRACT FROM AUTHOR]

• Rapid determination of humic acid content in fertilizer by headspace GC. • This method is based on the oxidation of humic acid in strong acidic medium. • The CO 2 formed from the oxidation is measured by headapace GC. • This approach presents a practical tool for the humic acid estimation in fertilizer. A fast, convenient and commercially available approach for analyzing humic acid content in fertilizer using headspace gas chromatography (HS-GC) is presented in this paper. Humic acid is converted into carbon dioxide based on the oxidation of humic acid in strong acidic medium and can be measured via automatic HS-GC. Conditions for the alkaline extraction and the humic acid oxidation process are also optimized. The new technique proved to be precise (RSD ≤ 3.59%) and accurate (relative errors≤9.46% as compared with the spectrophotometric approach). The newly established technique presents a practical tool to routinely analyze humic acid content in fertilizer during the fertilizer production. [ABSTRACT FROM AUTHOR]

The purpose of this work is to introduce a rapid and practical method for quantitatively analyzing total acid number in biodiesel by a reaction headspace gas chromatography. In this method, the carbon dioxide formed by the reaction of acidic species (i.e., fatty acids) in biodiesel and sodium bicarbonate can be measured by GC. The results showed that the complete reaction can be achieved in 25 min at 75 °C. The relative standard deviation of this method in total acid number determination was within 2.93%, the relative differences has been determined by comparing the total acid number obtained from this new analytical technique with the data from the reference technique (i.e., potentiometric titration), which are less than 8.05%. The reaction HS-GC technique is automated, efficient and can be a reliable tool for quantifying the total acid number in biodiesel and related research. [ABSTRACT FROM AUTHOR]

This work investigates a new reaction headspace gas chromatographic (HS-GC) technique for efficient quantifying average valence of manganese (Mn) in manganese oxides. This method is on the basis of the oxidation reaction between manganese oxides and sodium oxalate under the acidic condition. The carbon dioxide (CO 2 ) formed from the oxidation reaction can be quantitatively analyzed by headspace gas chromatography. The data showed that the reaction in the closed headspace vial can be completed in 20 min at 80 °C. The relative standard deviation of this reaction HS-GC method in the precision testing was within 1.08%, the relative differences between the new method and the reference method (titration method) were no more than 5.71%. The new HS-GC method is automated, efficient, and can be a reliable tool for the quantitative analysis of average valence of manganese in the manganese oxide related research and applications. [ABSTRACT FROM AUTHOR]

We demonstrate a reaction headspace gas chromatographic method for quantifying anhydride groups in anhydride-based epoxy hardeners. In this method, the conversion process of anhydride groups can be realized by two steps. In the first step, anhydride groups in anhydride-based epoxy hardeners completely reacted with water to form carboxyl groups. In the second step, the carboxyl groups reacted with sodium bicarbonate solution in a closed sample vial. After the complete reaction between the carboxyl groups and sodium bicarbonate, the CO2 formed from this reaction was then measured by headspace gas chromatography. The data showed that the reaction in the closed headspace vial can be completed in 15 min at 55°C, the relative standard deviation of the reaction headspace gas chromatography method in the precision test was less than 3.94%, the relative differences between the new method and a reference method were no more than 9.38%. The present reaction method is automated, efficient and can be a reliable tool for quantifying the anhydride groups in anhydride-based epoxy hardeners and related research. [ABSTRACT FROM AUTHOR]