Determination of lysine content based on an in situ pretreatment and headspace gas chromatographic measurement technique.

This work reports on a simple method for the determination of lysine content by an in situ sample pretreatment and headspace gas chromatographic measurement (HS-GC) technique, based on carbon dioxide (CO2) formation from the pretreatment reaction (between lysine and ninhydrin solution) in a closed vial. It was observed that complete lysine conversion to CO2 could be achieved within 60 min at 60 °C in a phosphate buffer medium (pH = 4.0), with a minimum molar ratio of ninhydrin/lysine of 16. The results showed that the method had a good precision (RSD < 5.23%) and accuracy (within 6.80%), compared to the results measured by a reference method (ninhydrin spectroscopic method). Due to the feature of in situ sample pretreatment and headspace measurement, the present method becomes very simple and particularly suitable to be used for batch sample analysis in lysine-related research and applications. Graphical abstract The flow path of the reaction and HS-GC measurement for the lysine analysis.

Determination of 3-chloro-1,2-propanediol in polyamideamine epichlorohydrin resin solution by reaction-based headspace gas chromatography.

We report on a headspace gas chromatographic method for determining the content of 3-chloro-1,2-propanediol in polyamideamine epichlorohydrin resin solution. It was based on quantitatively converting 3-chloro-1,2-propanediol to formaldehyde by periodate oxidation in a closed headspace sample vial at a room temperature for 10 min, and then to methanol by borohydride reduction at 90°C for 40 min followed by the headspace gas chromatographic measurement. The results showed that the present method has an excellent measurement precision (relative standard deviation < 2.60%) and accuracy (recoveries from 96.4-102%) in 3-chloro-1,2-propanediol analysis. The limit of quantitation was 0.031 mg/mL. It is simple and suitable for determining the 3-chloro-1,2-propanediol content in polyamideamine epichlorohydrin resin solution.

Determination of the softening point of rosin by a simple and automated headspace gas chromatographic technique.

We report a simple and automated headspace gas chromatographic technique for the determination of the softening point of rosin. A lumpy solid of rosin is added into a headspace vial, then an automated stepwise temperature ramping and headspace sampling was performed at each temperature stage and gas chromatography measurement. By plotting the gas chromatography signal for an impurity in rosin versus the temperature, a transition point (corresponding to the rosin softening point) was determined. The results show that the present method has a good precision (<0.76%), and good accuracy (the relative differences compared to the ring and ball method was <4.0%). The present method is simple, accurate, and automated. It is practical and suitable for testing the softening of rosin and derivatives in mills.

Efficient Determination of Specific Surface Area of Shale Samples Using a Tracer-Based Headspace Gas Chromatographic Technique.

This paper reports on a novel method for determining the specific surface area (SSA) of shale via headspace gas chromatography (HS-GC). The method is based on the water adsorption on the surface of shale sample after achieving phase equilibrium at an elevated temperature (i.e., heating at 125 °C for 48 h). A mathematical model shows that the SSA can be determined from the signal of the vapor water released during HS-GC analysis. The results obtained by this method correlated well (R2 = 0.992) with data obtained by the reference BET method. Because the phase equilibrium step for multiple samples can be conducted simultaneously, and because the phase re-equilibrium step is much faster in the HS-GC measurement, the present method is more efficient for batch sample testing.

Method for improving accuracy in full evaporation headspace analysis.

We report a new headspace analytical method in which multiple headspace extraction is incorporated with the full evaporation technique. The pressure uncertainty caused by the solid content change in the samples has a great impact to the measurement accuracy in the conventional full evaporation headspace analysis. The results (using ethanol solution as the model sample) showed that the present technique is effective to minimize such a problem. The proposed full evaporation multiple headspace extraction analysis technique is also automated and practical, and which could greatly broaden the applications of the full-evaporation-based headspace analysis.

Determination of Porosity in Shale by Double Headspace Extraction GC Analysis.

This paper reports on a novel method for the rapid determination of the shale porosity by double headspace extraction gas chromatography (DHE-GC). Ground core samples of shale were placed into headspace vials and DHE-GC measurements of released methane gas were performed at a given time interval. A linear correlation between shale porosity and the ratio of consecutive GC signals was established both theoretically and experimentally by comparing with the results from the standard helium pycnometry method. The results showed that (a) the porosity of ground core samples of shale can be measured within 30 min; (b) the new method is not significantly affected by particle size of the sample; (c) the uncertainties of measured porosities of nine shale samples by the present method range from 0.31 to 0.46 p.u.; and (d) the results obtained by the DHE-GC method are in a good agreement with those from the standard helium pycnometry method. In short, the new DHE-GC method is simple, rapid, and accurate, making it a valuable tool for shale gas-related research and applications.

[A Method for Determination of Migratable Fluorescent Whitening Agents in Paper Products by Dual-Wavelength UV Spectroscopy].

The current national standard method GB/T 27741-2011, i.e., "quantitative determination of migratable fluorescent whitening agents-UV spectroscopy", overestimates the migratable fluorescent whitening agents (FWA) in the paper based products because of the spectral interference of the leached lignin from the cellulose fibers. To minimize such interference, a spectroscopic method based on dual-wavelength (305 and 348 nm) measurement was proposed. It was observed that the dual-wavelength spectroscopy can effectively subtract the spectral absorption contributed by the leached lignin in the extraction medium, thus more accurately determination of migratable FWA can be performed. The results showed that the present method has a relative standard deviation of 2.17%, the quantitative detection limit of 16.9 mg x kg(-1), and recovery of 98%-103%. Compared with the current alternative standard-HPLC method, the present method possesses advantages of low operation and maintenance costs, simple, and practical in application. Therefore, it is more suitable for the rapid determination of migratable FWA in the product quality control in the production process and sample examination in the commercial market.

[A triple-wavelength visible spectroscopic method for determination of iron content in lignocellulosic materials].

The present paper described a triple-wavelength visible spectroscopic method for the determination of iron content in lignocellulosic materials. After the sample was pretreated with acidic hydrolysis method under selected conditions, the color agent, 1, 10-phenanthroline monohydrate, was added in the filtrate and then measured by a triple-wavelength spectroscopic method at wavelengths of 416, 510 and 700 nm, from which the iron contents of the sample can be calculated. The results showed that this method can efficiently deduct the influences of acidic soluble lignin and furfural compounds generated during the sample pretreatment and baseline drift caused by the tiny particles in the filtrates. It not only has a good measurement precision but also is accurate, in which the relative differences of the results obtained by the present method and ICP-OES method is less than 5%. The method is simple and practical, and suitable for industrial applications.

[Rapid determination of silicon content in black liquor of straw fibrous material].

The present paper reports a novel method for the determination of silicon content in straw fibrous material black liquor based on alpha-Si--Mo heteropoly acid spectrophotometry. The selected conditions were as follows: detection wavelength 360 nm, pH 4.0, and reaction time 10 min. It was found that the acidic soluble lignin in the sample liquor was the major interference species in the silicon content determination. The interference of acidic soluble lignin can be eliminated by hydrogen peroxide-nitric acid digestion method. The present method is not only simple, rapid, stable and less interferential, but also of good measurement precision and accuracy, with the relative standard deviations of 0.9%, and recoveries of 99.0%-102%. It is suitable for use in high silicon content of black liquor routine rapid analyses.

Determination of methanol partition coefficient in octanol/water system by a three-phase ratio variation headspace gas chromatographic method.

Determining the methanol partition coefficient (Kow) in octanol/water system is important to assess the risk of its impact to humans and the environment. In this paper, we report a novel method for the determination of the Kow of methanol with headspace gas chromatography (HS-GC), using a three-phase equilibrium-based phase ratio variation approach. Three headspace vials with different phase ratios [(1) 0.2 mL of water plus 3 mL of octanol, (2) 1 mL of water plus 3 mL of octanol and (3) 1 mL of water plus 10 mL of octanol] were used in the experiment. After pre-standing at 25 °C for > 10 h and equilibrating in the headspace oven at a temperature of interest for additional 25 min, the methanol signals of the vapor phase (i.e., the headspace) in these vials were measured by HS-GC, from which the Kow of methanol can be calculated based on the established equations. The results showed that the method has good precision (within 0.06 log unit in standard deviation) and acceptable accuracy (with method error within 0.5 log unit). A correlation between the Kow of methanol and temperature extrapolated the Kow values in a temperature range of interest. The present method represents a simple and in-situ approach for the determination of the Kow of methanol and is also suitable to be applied to other volatile compounds.

Preparation of coated paper reinforced by a blend of anionic-starch-based nanocellulose/chitosan and its properties.

Carboxylated cellulose nanocrystal whisker (C-CNC) and chitosan (CTS) were used to blend and reinforce anionic starch (AS) to prepare a paper-coating agent, AS-CNC-CTS, which was coated on one side of the surface of offset paper and kraft paper. Scanning electron microscopy (SEM) showed that the AS-CNC-CTS coating agent can form a layer of dense film on the paper surface and fill the surface pores. And also, owing to the irregular pore structure of the paper, the coating agent penetrated the pores to different degrees. The structure and mechanical properties of the coated paper were analyzed using a Fourier infrared spectrometer, computer-controlled paper-tearing tester and paper tensile strength test machine. Peptide bonding interaction between C-CNC and CTS, hydrogen bonding between C-CNC and CTS, C-CNC and AS, C-CNC and paper fibers, as well as electrostatic attraction between acidified CTS and AS were found. Moreover, the coating agent also had good antibacterial properties, and no mold spots formed throughout the observation period (60d). The gas-barrier properties and oil resistance of the coated paper were further studied using a paper and paperboard air permeability tester and a paper oil-permeability tester. Results showed that the coating agent can significantly enhance the gas-barrier properties and oil resistance of paper. Furthermore, with increased C-CNC content in the coating agent, its barrier properties gradually increased. This finding indicated that the coating preparation had no effect on the crystal region of C-CNC.

[A dual-wavelength spectroscopic method for the low chemical oxygen demand determination].

The present paper reports a dual wavelength spectroscopic method for the determination of chemical oxygen demand (COD) of low content samples, based on the absorption measurement at 440 and 560 nm. Since the absorptivities of Cr3+ at these two wavelengths are the same, a net absorption from dichromate ions can be determined by subtracting the absorption at 560 nm (only contributed by Cr3+) from the absorption at 440 nm The results showed that the detection limit of quantification is 8.6 mg x L(-1) and the relative standard deviations are in the 2%-15% range for the low COD standard samples (< or = 100 mg x L(-1)) in this proposed method. Further more, the method does not require calibration based on the standard samples. The present method is simple, reliable, and accurate; it is suitable for the application in a mass testing for low COD samples.

Simultaneous Determination of Amphiphobicities of Material Surface by A Dual-Indicator Headspace Gas Chromatography.

This paper reports on a new method for simultaneously determining the amphiphobicities of material surface by a dual-indicator assisted headspace gas chromatography. After adding 40 µL of both methanol-water and toluene-oil droplets on the sample surface for 20 s, the sample was turned vertically (to remove water and oil) and then placed in a headspace vial. The amount of methanol and toluene in the residual water and oil adhered to material surface was quantified using headspace gas chromatography. The results showed that the method has good measurement precision (RSD < 4.58%). It can be an effective tool for simultaneously determining the amphiphobicities of material surface.

Determination of water content in municipal sludge by multiple headspace extraction gas chromatography.

This paper reports a new method for the determination of sludge water content by a multiple headspace extraction gas chromatographic (MHE-GC) method. It is based on measuring the GC signals for the water vapor in a sample vial from the first five headspace extractions, from which the water content in the sludge sample can be extrapolated according to the established calculation equation. The results show that the method has a good repeatability (the relative standard deviation is less than 1%) and accuracy. The maximum relative difference is less than 16% compared to the reference method. The present method is very simple and efficient, and suitable for rapid sample testing in related applications.

Determination of activity of denitrifying enzyme in soil samples by a headspace gas chromatographic technique.

This paper reported a headspace gas chromatography (HS-GC) for the determination of denitrifying enzyme activity in soil samples. It was based on measuring the NO2 signal in a set of closed/air-free vials containing soil samples that incubated at the designated conditions. The results showed that the method has a good measurement precision (RSD < 5.0%) and reasonable accuracy for determining the denitrifying enzyme activity in soil samples. It is simple and efficient, and very suitable to be used in batch sample analysis.

[Rapid method for determination of furfural and 5-hydroxymethyl furfural in pre-extraction stream of biomass using UV spectroscopy].

The present paper reports a rapid method for the determination of furfural (F) and 5-hydroxymethyl furfural (HMF) in pre-extraction liquors of lignocellulosic biomass based on UV spectroscopy. In a concentrated acetic acid medium, F and HMF have an isosbestic point at 276 nm. It was found that the acidic soluble lignin in the pre-extraction sample is the major interference species in the F and HMF spectroscopic quantification However, only acidic soluble lignins have the absorption at the wavelengths above 325 nm. Based on the absorption of the acidic soluble lignins at 325 nm, their absorptions at either F or HMF absorbed wavelengths can be determined. Thus, with a simple triple-wavelength technique, both F and HMF in the pre-extraction liquors of lignocellulosic biomass can be quantified based on the spectroscopic measurement at the isosbestic point wavelength (276 nm), maximum absorption wavelength of F (272 nm) and the acid soluble lignin absorbed wavelength (325 nm). The present method does not require the hazardous organic compounds (such as phenolic compounds etc.) acting as a color reagent in the experiment. It is not only simple and rapid, but also has a good measurement precision and accuracy, with the relative standard deviations of 3.02% and 2.72%, and recoveries of 95%-107% and 96%-101%, respectively, in the F and HMF quantification. The present method is suitable for use in the research on pre-extraction hemicellulose of the lignocellulosic biomass in bio-refinery area in order to achieve a high selective sugar conversion.

[Rapid determination of sugars in hemicellulose extraction liquor by dual-wavelength spectrophotometry].

The traditional Douglas colorimetric method (phloroglucinol - glacial acetic acid colorimetry) could only be used to measure all forms of five-carbon sugars, including mono-, oligo- and poly- saccharides. Relative improvement is done on this method to achieve simultaneous determination of pentosan, hexosan and their monosaccharides, by the dual-wavelength method. Results indicate that 425 nm is the equal molar absorption wavelength of pentose and hexose, while 553 nm is the maximum absorption wavelength of pentoses. So the calculating formula has been greatly simplified based on the absorbance at 425 and 553 nm. The research results of interfering substances in the extraction liquor show that the lignin and glucuronic acid has no significant influence on the determination of pentoses or hexoses. It is concluded that this improved method has high precision and accuracy, and its recovery range is from 97.4% to 101.9%. Therefore, as a simple and rapid method, it is quite appropriate for measuring mixed sugars of pentoses and hexoses in the extraction liquor from hardwood or gra minaceous plant.

In-situ determination of the observed yield coefficient of aerobic activated sludge by headspace gas chromatography.

This paper describes a headspace gas chromatographic (HS-GC) method for the in-situ determination of the observed yield coefficient (Yobs) of aerobic activated sludge from domestic wastewater treatment plants. It is based on the measurement of oxygen and carbon dioxide in samples that have been incubated in headspace vials for relatively short periods of time. The method has good precision (the relative standard deviation < 5.46%) and accuracy (the relative differences < 9.23% when compared with the data from the reference method). The new method is much simpler and more efficient than the reference methods and should greatly facilitate the testing in aerobic activated sludge related applications, such as system design, operation and management.

Determination of water distribution in sludge by a multiple headspace extraction analytical technique.

This paper reported a new method for the determination of the water distribution in sludge. It was based on a multiple headspace extraction (MHE) procedure to step-wise remove the water vapor from a closed vial containing a sludge sample, followed by a gas chromatographic measurement (GC). By plotting the GC signal of water vapor vs. the headspace extraction number, three different trend lines from the profile can be observed. From which two transition points can be determined and thus the stages for the free water, capillary water, and adsorption water release can be divided. Based on the sum of GC peak areas ate each stage, the content of these water types in the sludge can be calculated through a method calibration. The results showed that the MHE-GC method has a better measurement repeatability (RSD < 18.6%) and sensitivity (limit of quantitation = 0.028%) than the thermal drying method (used as a reference method). There was also a good agreement between the MHE-GC and the reference method on the free water and capillary water analysis. Moreover, the results on the adsorption water and bound water testing by the present method is more justifiable than the reference method.

Rapid determination of ethanol in fermentation liquor by full evaporation headspace gas chromatography.

This paper reports a full evaporation (FE) headspace gas chromatographic (GC) method for rapid determination of ethanol in fermentation liquor. The data show that ethanol in the fermentation liquor was transferred to the vapor phase (headspace) almost completely within 3 min at a temperature of 105 degrees C when a very small volume (< 50 microL) of sample was directly added to a sealed headspace sample vial (20 mL). The ethanol in the vapor phase was then measured by headspace GC using a flame ionization detector. The results show that the present method has an excellent measurement precision (RSD=1.62%) and accuracy (recovery=98.1 (+/-1.76%)) for the ethanol quantification in fermentation liquors. The method requires no sample pretreatment and is very simple and rapid.