In situ, rapid, and temporally resolved measurements of cellulase adsorption onto lignocellulosic substrates by UV-vis spectrophotometry.

This study demonstrated two in situ UV-vis spectrophotometric methods for rapid and temporally resolved measurements of cellulase adsorption onto cellulosic and lignocellulosic substrates during enzymatic hydrolysis. The cellulase protein absorption peak at 280 nm was used for quantification. The spectral interferences from light scattering by small fibers (fines) and particulates and from absorptions by lignin leached from lignocelluloses were corrected using a dual-wavelength technique. Wavelengths of 500 and 255 nm were used as secondary wavelengths for correcting spectral interferences from light scattering and absorption of leached lignin. Spectral interferences can also be eliminated by taking the second derivative of the measured spectra of enzymatic hydrolysate of cellulose or lignocelluloses. The in situ measured cellulase adsorptions in cellulose and lignocellulose suspensions by these two spectrophotometric methods showed general agreement with batch sampling assayed by the Bradford method. The in situ methods not only eliminated tedious batch sampling but also can resolve the kinetics of the initial adsorption process. The measured time-dependent cellulase adsorptions were found to follow pseudo-second-order kinetics.

Corrosion problem in headspace gas chromatography with phase reaction conversion technique.

This paper reports a corrosion problem in the headspace sampling needle when using a phase reaction conversion headspace gas chromatographic method in Agilent headspace auto-sampler. The examination by microscopy shows that corrosion mainly takes place on the surface of the outer wall of the needle that is exposed to the air during each headspace sampling. Since it was proven that the helium flushing is effective in minimizing the pit type of corrosion on the stainless needle material, a custom-made surface flushing device was proposed for corrosion inhibition.

Novel headspace gas chromatographic method for determination of oxalate in oxygen delignification liquor.

A novel headspace gas chromatographic (HS-GC) method is demonstrated for an indirect determination of oxalate in oxygen delignification liquors. A small volume (50-100 microL) of liquor sample is introduced into a sampling vial that contains 1.0 mL of 2 mol/L sulfuric acid. After removal of carbon dioxide (generated from carbonate in the acidic medium) by heating, the sample was mixed with a 0.5 mL of 0.02 mol/L potassium permanganate solution in a closed testing vial. At an elevated temperature (70 degrees C), the oxalate in the sample is rapidly converted to carbon dioxide by reacting with permanganate. The carbon dioxide in the headspace can be measured by gas chromatography with a thermal conductive detector. Using a multiple headspace extraction (MHE) measurement technique, the kinetics of formation of the carbon dioxide from the other organic species in the sample can be determined, and thus a correction can be made for minimizing the interferences. The present method is simple, accurate and can be easily automated.

Determination of microstickies in recycled whitewater by headspace gas chromatography.

This study proposed a novel headspace gas chromatographic (HS-GC) method for determination of adhesive contaminants (microstickies) in recycled whitewater, a fiber containing process stream, in the paper mill. It is based on the adsorption behavior of toluene (as a tracer) on the hydrophobic surface of microstickies, which affects the apparent vapor-liquid equilibration partitioning of toluene. It was found that the equilibrium concentration of toluene in the vapor phase is inversely proportional to the apparent effective surface area of microstickies that remain in the corresponding solution. Thus, the amount of microsticky materials in the recycled whitewater can be quantified by HS-GC via indirect measurement of the toluene content in the vapor phase of the sample without any pretreatment. The presented method is simple, rapid and automated.

Determination of acidic and basic species by headspace gas chromatography.

This paper reported a novel headspace gas chromatographic (GC) technique on quantification of acidic and basic species. It is based on an acid-base reaction between the measured species and bicarbonate in an aqueous solution, which generates carbon dioxide in a closed headspace sample vial. By operating at 60 degrees C, carbon dioxide is completely released to the headspace and thus can be measured by GC with a thermal conductivity detector. Bicarbonate concentrations of 0.030 and 0.0025 mol/L are recommended for general applications and very small species content, respectively. This method is able to accurately measure small sample sizes (down to few milligrams or microliters). The present method is simple, accurate, and automatic.

Simplified multiple headspace extraction gas chromatographic technique for determination of monomer solubility in water.

This paper reports an improved headspace gas chromatographic (GC) technique for determination of monomer solubilities in water. The method is based on a multiple headspace extraction GC technique developed previously [X.S. Chai, Q.X. Hou, F.J. Schork, J. Appl. Polym. Sci., in press], but with the major modification in the method calibration technique. As a result, only a few iterations of headspace extraction and GC measurement are required, which avoids the "exhaustive" headspace extraction, and thus the experimental time for each analysis. For highly insoluble monomers, effort must be made to minimize adsorption in the headspace sampling channel, transportation conduit and capillary column by using higher operating temperature and a short capillary column in the headspace sampler and GC system. For highly water soluble monomers, a new calibration method is proposed. The combinations of these technique modifications results in a method that is simple, rapid and automated. While the current focus of the authors is on the determination of monomer solubility in aqueous solutions, the method should be applicable to determination of solubility of any organic in water.

Determination of residual monomer in polymer latex by full evaporation headspace gas chromatography.

This study demonstrated a full evaporation (FE) headspace gas chromatographic technique for the determination of residual monomer in methyl methacrylate (MMA) polymer latex. A very small amount (approximately 10-30 mg) of latex was added to a sealed headspace sample vial (20 ml). A near-complete monomer mass transfer from both liquid (aqueous phase) and solid phase (polymer particles) to the vapor phase (headspace) is achieved within 5 min at a temperature of 110 degrees C. The method eliminates sample pretreatment procedures such as the solvent extraction. Thus, it avoids the risk of polymer deposition on the GC system caused by a directly injection of extraction solvent in the conventional GC monomer analysis. The present method is simple, rapid, and accurate.

Determination of the solubility of inorganic salts by headspace gas chromatography.

This work reports a novel method for determination of salt solubility using headspace gas chromatography. A very small amount of volatile compound (such as methanol) is added in the studied solution. Due to the molecular interaction in the solution, the vapor-liquid equilibrium (VLE) partitioning coefficient of the volatile species will change with different salt contents in the solution. Therefore, the concentration of volatile species in the vapor phase is proportional to the salt concentration in the liquid phase, which can be easily determined by headspace gas chromatography. Until the salt concentration in the solution is saturated, the concentration of volatile compound in the vapor phase will continue to increase further and a breakpoint will appear on the VLE curve. The solubility of the salts can be determined by the identification of the breakpoint. It was found that the measured solubility of sodium carbonate and sodium sulfate in aqueous solutions is slightly higher (about 6-7%) than those reported in the literature method. The present method can be easily applied to industrial solution systems.

Quantification and reduction of organic sulfur compound formation in a commercial wood pulping process.

This study experimentally quantified the formation of organic sulfur compounds in a commercial SuperBatch kraft pulping process using a laboratory pilot-scale digester. The results indicate that wood chips not only can adsorb HS- but also methyl mercaptan (MM) in the black liquor used for pretreatment during the two pretreatment stages. The absorption rate of MM is much faster than that of HS-. In the third stage of SuperBatch pulping, the rate of formation of MM and dimethyl sulfide (DMS) is very similar to that found in conventional batch kraft pulping processes. The study examined the applicability of the phase transition cooking (PTC) concept for reducing organic sulfur compounds in pulping, previously developed in laboratory batch pulping using a bomb-type digester, in a SuperBatch process. It was confirmed that there is a phase transition point (PTP) corresponding to PTC in SuperBatch pulping beyond which further delignification significantly increases the formation of volatile organic sulfur compounds. The results indicate that a 40% reduction of TRS formation can be achieved by using PTC.

Multiple headspace extraction-gas chromatographic method for the study of process kinetics.

A multiple headspace extraction gas chromatographic technique to automate the study of process kinetics that involves volatile species was developed in this study. The technique was demonstrated by using it to study methanol formation in kraft black liquor samples under an isothermal temperature of 70 degrees C. The results indicate that methanol formation in kraft black liquors under isothermal conditions follows an exponential decay function. The present method is very simple, efficient and fully automated. It can be easily applied to study slow kinetic processes, such as reaction or adsorption and desorption, involving volatile species in any environmental and industrial samples with complicated matrices.

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

This study developed a phase reaction conversion (PRC) headspace gas chromatographic (HS-GC) technique for the measurements of nonvolatile species in liquid or solid samples. The technique is demonstrated by the measurements of carbonate in aqueous carbonate solutions and in kraft pulp mill liquor samples. A very small amount of sulfuric acid (volume of 0.5 ml, concentration of 2 mol/l) is used to acidify a sample of less than 300 microl in volume and convert the dissolved carbonate into carbon dioxide (gas) in a sample vial (reactor) that is analyzed by thermal conductivity detection through a headspace sampler. The carbonate concentrations measured by PRC-HS-GC in seven kraft liquor samples agree very well with those measured using a coulometric and a titrametric method. Simultaneous analysis of multiple species was also conducted to demonstrate the versatility of the method. The present method is very simple, rapid, reliable, accurate, and fully automated. It can be applied to analyze other nonvolatile species in various industrial and environmental samples.

[Effect of electrical stimulation of afferent renal nerve on arterial blood pressure, heart rate and vasopressin in rabbits].

The effect of electrical stimulation of afferent renal nerve (ARN) on cardiovascular response, the synthesis and release of vasopressin were studied in rabbits. During the course of the experiment, the pathway of ARN to central nerve system was also analyzed. The results showed that electrical stimulation of ARN elicited significantly decrease of mean arteral blood pressure and heart rate as well as inhibition of cervical sympathetic nerve activity. In the event of the above physiological changes, the AVP concentration in supraoptic nucleus (SON), paraventricular nucleus (PVN) and plasma was increased, but that in hypophysis was decreased. Injection of sodium nitropruside (SNP) or AVPa indicated that increase of AVP release was due directly to stimulation of ARN. Nodose ganglionectomy or transversal section of spinal cord at different levels suggested that the main afferent pathway of ARN to higher level of central nerve system entered into spinal cord at T5-L2.

Efficacy of tablet huperzine-A on memory, cognition, and behavior in Alzheimer's disease.

AIM: To evaluate the efficacy and safety of tablet huperzine-A (Hup) in patients with Alzheimer's disease. METHODS: Using multicenter, prospective, double-blind, parallel, placebo controlled and randomized method, 50 patients were administered orally 0.2 mg (4 tablets) Hup and 53 patients were given po 4 tablets of placebo bid for 8 wk. All patients were evaluated with Wechsler memory scale, Hasegawa dementia scale, mini-mental state examination scale, activity of daily living scale, treatment emergency symptom scale, and measured with BP, HR, ECG, EEG, ALT, AKP, BUN, Cr, Hb, WBC, and urine routine. RESULTS: About 58% (29/50) of patients treated with Hup showed improvements in their memory (P < 0.01), cognitive (P < 0.01), and behavioral (P < 0.01 functions. The efficacy of Hup was better than placebo (36%, 19/53) (P < 0.05). No severe side effect was found. CONCLUSION: Hup is a promising drug for symptomatic treatment of Alzheimer's disease.

[Effects of puerarin on cat vascular smooth muscle in vitro].

Puerarin is an isoflavone compound isolated from Pueraria lobata (Wild). This study characterized the vascular action of puerarin in order to more clearly elucidate its pharmacological activities. Helically cut strips of cat femoral veins and renal arteries were suspended in an organ chamber filled with Krebs bicarbonate solution for measurement of isometric force development. In the cases of femoral veins and renal arteries isoproterenol (0.01 mumol.L-1 -0.1 mmol.L-1) caused relaxation of methoxamine-induced contraction (0.01 mmol.L-1) in a concentration-related manner. Puerarin (0.01-0.1 mmol.L-1) inhibited the relaxation response to isoproterenol in a concentration-response fashion. Propranolol (0.1-1 mumol.L-1) inhibited the isoproterenol-induced relaxation too. Puerarin (0.1mmol.L-1) did not alter the relaxation response to nitroglycerin (1 mumol.L-1). These results indicated that puerarin acted as a beta-adrenoreceptor antagonist in isolated arteries and veins.

[Effect of electrical stimulation of the area postrema on plasma renin activity and renal sympathetic nerve activity in rabbits].

68 urethan-anesthetized rabbits were prepared for registration of changes of respiration, arterial blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) due to stimulation of area postrema (AP) by rectangular pulse trains each lasting for 4 s for every 30 s. During 40 min of such a stimulation paradigm the venous blood samples were collected for radioimmunoassay of plasma renin activity (PRA) (both pre- and post-stimulation), RSNA registered and processed by a computer. Animals were divided into three groups: (1) with AP stimulation only (n = 47); (2) AP stimulation after bilateral renal denervation (n = 13); (3) AP stimulation after propranolol injection (n = 8). In Group I, a 91% increase in PRA, an augmentation of RSNA, a rise of BP and a decrease of HR were observed, while respiration did not show obvious change. In Group II, hemodynamic and RSNA response was similar to that in Group I, but PRA was not changed significantly. In Group III, the effects on BP, HR, respiration and RSNA showed no remarkable changes compared with Group I, but significant inhibition of the response of PRA [from 0.65 +/- 0.07 ng/(ml.h-1) to 0.72 +/- 0.10 ng/(ml.h-1), P > 0.05] was observed. The results mentioned above suggested that electrical stimulation of AP may induce an increase in renin release and renal sympathetic nerve activity and hemodynamic changes in rabbits.