Carboxyl Groups in Wood Fibers. 1. Determination of Carboxyl Groups by Headspace Gas Chromatography

Detailed characterizations of the content of carboxyl groups in wood fibers derived from alkaline delignification of loblolly pine using various processes were conducted in this study (part 2) using the method presented in the preceding paper, part 1. It was demonstrated that the content of hexenuronic acid (HexA) groups can be used to account for the carboxyl groups associated with hemicelluloses in wood fibers. The difference between the measured contents of carboxyl and HexA groups can be used to account for the carboxyl groups associated with wood lignin. As a result, the calculated content of carboxyl groups associated with lignin correlated very well to the pulp number. An empirical correlation for predicting fiber yield with the measured contents of carboxyl and HexA groups was developed on the basis of mass conservation. Good agreement between measured and predicted fiber yield for the two wood species studied was obtained.

This paper reports an improved headspace gas chromatography (HS-GC) technique for the determination of carboxyl group content in wood fibers. The method is based on phase reaction conversion HS-GC technique developed previously [Chai et al., Ind. Eng. Chem. Res. 2003, 42, 5440−5444], but with major modifications in regard to sample preparation (i.e., sample acidification followed by water washing), reaction reagent concentration (i.e., minimization of bicarbonate decomposition), and the manner for sample addition (i.e., a direct sample addition). As a result, this technique greatly improves the measurement precision. The present method is simpler, more reliable, and more practical. It can be applied to the nonfiber samples.

Determination of acidic and basic species by headspace gas chromatography

Analysis of nonvolatile species in a complex matrix by headspace gas chromatography

Glutaraldehyde (GA) fixation of bioprosthetic tissue is a well adapted technique, with commercial products on the market for almost 40 years. Amine groups present in tissue react with GA to form different types of cross-links. An estimation of the degree of cross-linking of the tissue can be obtained by measuring the concentration of residual amine groups, which is frequently carried out with the 2,4,6 trinitrobenzene sulphonic acid (TNBS) assay. Cross-linked tissue and collagen matrices are usually further characterized by determining their physical properties (such as the shrinkage temperature), biological properties (such as resistance to enzymatic degradation), and mechanical properties before in vivo evaluation takes place. In an effort to improve the properties of cross-linked tissue and collagen, alternative cross-linking methods have been developed. One of these methods is based on the use of water soluble carbodiimides (CDI). It is generally accepted that this cross-linking method leads only to the formation of amide linkages between tissue carboxyl and amine groups. Therefore, until recently the TNBS assay was also used to determine the degree of cross-linking of CDI cross-linked tissue and collagen. However, it cannot be excluded that after activation of carboxyl groups of tissue and collagen by CDI, these groups can react with other nucleophiles (like hydroxyl groups) present in the matrix. To obtain a better insight in the degree of cross-linking of CDI cross-linked matrices a reliable assay for quantification of residual carboxyl groups is required. Up to now such an assay was not available. In this study a new assay to determine residual carboxyl groups in CDI cross-linked collagen matrices is presented. Reconstituted dermal bovine collagen matrices (RDBC) were cross-linked with a water soluble CDI and N-hydroxysuccinimide (NHS) and residual carboxyl groups were labeled using 5-bromomethyl fluorescein. Subsequently, the fluorescent label was released by mild hydrolysis and quantified with capillary zone electrophoresis. A calibration curve relating the concentration of carboxyl groups with peak intensities was obtained using Sephadex standards with known concentrations of carboxyl groups. The concentration of carboxyl groups in unprocessed RDBC as determined with this new technique was equal to the concentration of carboxyl groups measured by amino acid analysis. On the basis of the concentration of residual carboxyl groups determined for CDI/NHS cross-linked RDBC and RDBC, in which the amine groups were blocked with propionaldehyde before CDI/NHS cross-linking, it was concluded that activated carboxyl groups can also react with other groups (such as hydroxyl groups) present in the matrix. This implies that the crosslink density of RDBC matrices after treatment with CDI/NHS is higher than expected on the basis of amide bond formation only, as determined by the TNBS assay.

This paper reports on a headspace gas chromatography method (HS-GC) for efficient determination of carboxyl groups in nanofibrillated cellulose (NFC). By pretreating the NFC suspension with a strong acid cation exchange resin for 30 min, the carboxyl groups in NFC were converted to the carboxyl acids. The pretreated suspension was added into a closed headspace sample vial containing bicarbonate solution. By HS-GC measuring the CO2 produced from the reaction between carboxyl acids and bicarbonate (10 min at 60 °C), the content of carboxyl groups in NFC can be determined. The results showed that the relative standard deviation of the method in the repeatability testing was < 3.7% and the limit of quantitation was about 0.1 mmol/g. Relative differences between the HS-GC and the reference (a conductometric titration) method were within 15.0%. The present method is simple and efficient, and suitable to be used for determining the content of carboxyl groups in NFC in the related applications.

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

A reaction headspace gas chromatography (HS-GC) technique was investigated for quantitatively analyzing trichloroacetic acid in human urine. This method is based on the decomposition reaction of trichloroacetic acid under high-temperature conditions. The carbon dioxide and chloroform formed from the decomposition reaction can be respectively detected by the thermal conductivity detection HS-GC and flame ionization detection HS-GC. The reaction can be completed in 60 min at 90°C. This method was used to quantify 25 different human urine samples, which had a range of trichloroacetic acid from 0.52 to 3.47 mg/L. It also utilized two different detectors, the thermal conductivity detector and the flame ionization detector. The present reaction HS-GC method is accurate, reliable and well suitable for batch detection of trichloroacetic acid in human urine.

Efficient determination of average valence of manganese in manganese oxides by reaction headspace gas chromatography

The determination of carbonate content is the basic procedure for studies related to layer double hydroxides (LDHs). This paper reports a rapid and accurate headspace gas chromatographic (HS‐GC) technique for the determination of carbonate content in LDHs. The content of carbonate was expressed by the amount of CO 2 generated by the reaction of sulfuric acid and carbonate, which can be measured by HS‐GC technique using a thermal conductivity detector. It was found that a complete conversion of carbonate to CO 2 can be achieved at 45 °C for about 4 min and a sulfuric acid dosage of 200 μL in the headspace vial. Under optimized conditions, the limit of detection and relative standard deviation of HS‐GC method is 0.79 μmol and 1 %, respectively.

Determination of carboxyl groups in Yallourn brown coal

Determination of iodate in iodized edible salt based on a headspace gas chromatographic technique

An efficient technique was developed to monitor the emission of hydrogen and carbon dioxide from bacteria cultures by headspace gas chromatography and to investigate the efficacy of chemical antibiotics and of natural compounds with antimicrobial properties. Facultative anaerobes emit hydrogen and carbon dioxide from cultures in the closed headspace vials and obligate anaerobes too, if the air above the cultures in the vials is replaced by nitrogen. Antibiotics added to the sample cultures are apparently effective if the emission of hydrogen and carbon dioxide is suppressed. If not, either they are ineffective or the related bacteria are even resistant. The headspace technique can detect bacterial contamination in various samples, and examples are presented for food purchased from supermarkets and for medical specimens, including recognition of antibiotic resistance. However, the described technique cannot identify the related bacteria at a species or genus level, but is well suited for example for screening the bulk of food in supermarkets for microbe contamination or for the search of natural antibiotics. The samples are incubated with the proper nutrient medium in closed septum vials which remain closed during the whole process. The personnel in the lab never come into contact with pathogens, and thus, safety regulations are warranted. The described technique can be carried out with all commercially available gas chromatographs, even including simple low-cost instruments, equipped with a standard packed column and a thermal conductivity detector, up to expensive and fully automated instruments, such as used for forensic blood alcohol analysis.

This article reports on a headspace gas chromatographic (HS-GC) technique for determining the content of α-, β-, and γ-cellulose in fully delignified pulps. In this method, the pulp sample was extracted by 17.5% and 9.45% NaOH solutions (25°C), respectively, to obtain two soluble fractions; i.e., the sum of β- and γ-cellulose and γ-cellulose. By reacting with potassium dichromate in a strong-acidic medium at 100°C for 60 min in a sealed headspace sample vial, these soluble celluloses in the filtrates were quantitatively converted to carbon dioxide. With the headspace equilibration at 60°C for 7 min, the formed carbon dioxide was measured by HS-GC and thus the content of β- and γ-cellulose in the pulp samples can be determined, from which the content of α-cellulose can also be calculated. The results showed that the present method had a good measurement precision (a relative standard deviation <2.1%) and accuracy (relative differences of <10% compared to the reference); the limit of quantification (LOQ) was 1.71%. In summary, the present method is simple, practical, and is particularly suitable for use in the batch sample analysis for determining α-, β-, and γ-cellulose content in fully delignified pulps.

In our research the influence of pH on the properties of crosslinked waxy corn starch modified with acrylic monomers has been studied. These systems are characterized with the ability to absorb and hold a large quantity of water and aqueous solutions. However, due to the presence of the starch granules in their structure they are easily biodegradable. In our study, a number of cross-linked hydrogels based on waxy maize starch and acrylic acid derivatives were synthesized. Acrylic acid used in reactions was partially neutralized with NaOH. N,N\'-methylenebisacrylamide was used as the cross-linking agent. A series of polymers with different content of ionized carboxyl groups were obtained. These polymers were used for further study of their properties, in particular swelling properties and concentration of carboxyl and carboxylate groups. Presence of those hydrophilic groups is largely responsible for the high affinity of the polymer to water. A significant increase in the gelation time with increasing of sodium acrylate content was observed. As expected, the increase in content of carboxylate groups with an increase of neutralization degree of acrylic acid used in the synthesis of the polymer was observed, while content of unionized carboxyl groups decreased. A series of experiments were carried out to determine the effect of pH on the absorption of hydrogels. It should be noted that the amount of absorbed water is generally affected by the ionic strength of the solution, therefore, to compare the individual results of swelling in the range of pH 5.0-9.0 experiments were performed in buffers solution with the same ionic strength. High rate of absorption of aqueous solutions was observed. Approximately 60-70% of the maximum value is attained during the first 10 minutes. It was found that when pH of solution increases, amount of water absorbed per gram of hydrogel increases. Hydrogel composition also has a significant impact on the swelling properties of hydrogel. A minimum of water absorption was observed for polymers in which the ratio of acrylic acid to sodium acrylate was 1:1.