Rapid Determination of HAAs Formation Potential of the Reaction of Humic Acid with Chlorine or Chlorine Dioxide

On the basis of gas chromatography(GC) coupled with a short capillary column and an electron capture detector(ECD), a simple and rapid method for the determination of five haloacetic acids(HAAs) in drinking water was developed by the optimization of derivation conditions and the modification of gas chromatographic program. HAAs formation potential(HAAFP) of the reaction of humic acid with chlorine was determined via this method. The major advantages of the method are the simplicity of chromatographic temperature program and the short run time of GC. Dichloroacetic acid(DCAA) and Trichloroacetic acid(TCAA), which were detected in the determination of HAAFP, were rapidly formed in the first 72 h of the reaction of humic acid with chlorine. HAAFP of the reaction of humic acid with chlorine increased with the increase in the concentrations of humic acid and chlorine. The average HAAFP of the reaction of humic acid with chlorine was 39.9 μg/mg TOC under the experimental conditions. When the concentration of humic acid was 4 mg/L, the concentration of HAAs, which were produced in the reaction of humic acid with chorine, may exceed MCL of 60 μg/L HAAs as the water quality standards for urban water supply of China and the first stage of US EPA disinfection/disinfection by-products(D/DBP) rule; when the concentration of humic acid was 2 mg/L, the concentration of HAAs may exceed MCL of 30 μg/L HAAs for the second stage of US EPA D/DBP rule. When humic acid was reacted with chlorine dioxide, only DCAA was detected with a maximum concentration of 3.3 μg/L at a humic acid content of 6 mg/L. It was demonstrated that the substitution of chlorine dioxide for chorine may entirely or partly control the formation of HAAs and effectively reduce the health risk associated with disinfected drinking water.     

HPLC柱切换技术在临床药物分析中的应用

综述了近十年来高效液相色谱柱切换技术在药物分析中的应用情况，主要介绍了柱切换技术在生物样品纯化，富集和手性分离方面的实际应用，该技术可用于直接进样分析，特别适用于临床药物分析，可和于药代动力学，生物利用度等研究。     

Large diameter open tubular columns in gas chromatographic analysis

Large diameter open tubular columns provide the packed column chromatographer with a simple route to higher resolution gas chromatography. They can be operated in a high-flow (lower resolution) mode that permits their direct substitution for a packed column, or they can be operated in a low-flow (higher resolution) mode that maximizes separation at the cost of longer analysis times. Inlet design and column installation can influence both the chromatographic results and quantiative reliability. Make-up gas is not required in the high-flow mode, and its benefits in the low-flow mode are restricted to enhanced detector sensitivity, provided the outlet end of the column resides in the detector jet (FID). The columns seem fully compatible with all common modes of detection.     

二维毛细管柱气相法测定大气中的挥发性烃类

 用二维毛细管柱气相法测定了大气中的挥发性烃类 (VHCs)C3 ～C10 共 5 7种化合物。采用吸附 /两级热解吸预富集样品。采用双柱 (PLOT柱 :5 0m× 0 32mmi d × 8μm ,Al2 O3 /Na2 SO4 ;HP 1柱 :5 0m× 0 2 2mmi d × 0 5 μm ,methylsilicone) /双FID系统进行样品分析。方法的定性稳定性好 ,峰面积的相对标准偏差小于 2 0 % ,用外标法定量 ,线性相关系数r2 分别为 0 9990和 0 9997。分析周期为 48min。通过对江苏常熟生态站 182个农田大气样品中VHCs的含量测定 ,表明方法准确 ,快速 ,可取得满意的结果。     

The use of microparticulate guard columns in reverse-phase high-performance liquid chromatography

Summary The use of mciroparticulate guard columns in conjunction with high efficiency reverse-phase columns has been evaluated in terms of system efficiency and peak symmetry using three standard test mixtures. The effects of linking tube dimensions, particle size of guard column packing and the use of low or zero dead volume couplings have been investigated. Both valve and stopped-flow injection techniques have been used. Recommendations are given for the most efficient use of guard columns.     

Computer comparisons of variables in capillary gas chromatography

A series of computer-constructed van Deemter curves that permits evaluation of a number of variables in capillary gas chromatography is presented. The graphs permit the comparison of inter-related parameters, including the choice of carrier gas (hydrogen vs helium vs nitrogen), column length (10-100 m), column diameter (0.20, 0.25, 0.32, 0.4 mm), solute partition ratios (0-10), and liquid phase film thickness (0.1, 0.25, 0.5, 1.0 μm). The curves are evaluated, both in terms of the relative magnitude of the optimum average linear carrier gas velocity, and in terms of the significance of the sharpness of the curve.     

Prediction of molecular structures of aza-arenes by retention indices and fluorescence spectra

Two methods are described for predicting the molecular structures of aza-arenes eluted from a capillary column. The first is based on a combination of retention indexes (RI) and a post-column reaction. The RI of an aza-arene is calculated by using the incremental contributions of some atomic groups to RI. Once the molecular weight is determined by the mass spectrum, the possible compounds are picked up, based on comparison of the observed RI with the calculated RI values and information about the intramolecular environment around the nitrogen atom obtained from the degree of peak shift resulting from interaction with Ni(II). The second is due to combination of information from fluorescence spectrometry and TLC fractionation. The fluorescence spectrum allows the identification of the fused ring system.     

Capiliary columns with immobilized stationary phases. Part 5: Determination of column bleeding; re-silylation

The bleeding of apolar high temperature columns may well be the critical factor limiting their applicability for GC/MS-coupling, and for high temperature analyses. Therefore, a bleeding determination procedure has been designed as a basis for a systematic approach to the production of low-bleed columns. Re-silylation is a traditional method of reducing column bleeding. Increased efficiency of re-silylation becomes feasible with immoblized coatings. Experience gained so far shows that resilylation of immoblized coatings may indeed result in the expected strongly reduced bleed rates and in improved overall column quality. Re-silylation may also contribute to column washing by enhancing the solubility of adsorbed contaminants.     

The effect of make-up flow on detector time variance in micro column liquid chromatography

Summary Time variance is better suited than volume variance to compare performances of columns of different diameters but of same length and working at the same linear velocity of the mobile phase. When a make-up flow is used at the detector inlet, only column and detector time variances remain additive. Make-up flow enables reduction of the detector contribution to the total variance. However, in some practical cases, the dispersion effects of the detector inlet tubing or electronic time constant can prevail over that of the flow cell. Owing to their different flow dependence, the decrease in detector variance due to make-up is often much lower than expected. Theoretical equations and curves are given for a rapid evaluation of make-up flow.     

Effects of slight variations in nutrient loadings on pore plugging in soil columns

The high nutrient concentrations that would exist near the nutrient injection well during the application of cometabolicin situ bioremediation may lead to the development of significant quantities of biomass at this point in the subsurface. This biomass can decrease the porosity of the soil to such an extent that nutrient injection is no longer possible. In this work, experiments were conducted using a porous media biofilm reactor, operated under constant substrate loading conditions, such that the pressure drop across the reactor was allowed to increase to maintain a constant volumetric flow rate through the reactor. Results suggest that biomass production, and hence biofilm thickness, near the injection feed port is highly sensitive to substrate loading. In addition, these variations in biofilm thickness produce dramatic differences in the pressure drop that is attained across the reactor. Use of the Kozeny-Carman equation can be used to predict that once a critical depth has been exceeded, the pressure drop across the bed will increase exponentially within biofilm depth. This result means that pressure is not a reliable indicator of the onset of pore plugging.