Improvement of Pulse Amperometric Detection Integrated Automated Flow Injection Analysis of Ethylenethiourea Determination

Improvement of pulse amperometric detection (PAD) method is demonstrated in determination of ethylenethiourea (imidazolidine‐2‐thione, ETU). The anodic detection of ETU will produce polymeric film on an electrode leading to an inactive electrode surface. Here, the PAD method was used to remove the polymeric film formed on the electrode surface between ETU detection. Further, the scheme was integrated with automated flow injection analysis (AFIA) for determining ETU. The operational parameters of PAD in the AFIA system were discussed thoroughly. The analytical characteristics of the system were evaluated at optimum conditions. The linear range of calibration plot was between 20 to 300 μM (the correlative coefficient, r = 0.999) and the detection limit was 0.9 μM (S/N = 3). The relative standard deviations of detection of 50 μM ETU were 0.82% with and 9.07% without PAD scheme. The results indicate the system is a very promising tool for ETU determination. Finally, the matrix effects of two water samples that were collected from a campus and a farm show good recoveries of 92% and 96%.     

Determination of cysteine in a pharmaceutical formulation by flow injection analysis with a chemiluminescence detector

A simple and convenient flow injection-chemiluminescence (FI-CL) method for the determination of cysteine is reported, based on a fast and strong CL in a basic luminol-cysteine-NaIO₄ solution. The linear range was 1.0×10⁻⁸ to 1.0×10⁻⁶ M with a detection limit (3s) of 5×10⁻⁹ M, which was 100 times more sensitive than previously reported CL methods. Singlet oxygen, hydroxyl radical and hydrogen peroxide were suggested to be produced in this reaction and were responsible for the CL of cysteine. This simple method has been successfully applied for the determination of cysteine in a pharmaceutical formulation.     

不同硬段含量溶液聚合和RIM嵌段聚脲热性质和动态力学性质的研究

用溶液聚合法和RIM制备了软段为胺端基聚环氧丙烷,硬段为4,4′-二苯甲烷二异氰酸酯(含量为30％,50％,70％)经二乙基甲苯二胺扩链的热塑性嵌段聚脲。用动态力学温度谱(DMS)和示差扫描量热计法(DSC)对比研究了这些聚脲的性质。结果表明,溶液聚脲比RIM聚脲的枢分离情况好。DMS和DSC均未观察到聚脲中硬段的玻璃化转变。     

Large volume sample introduction using temperature programmable injectors: Implications of liner diameter

Temperature programmable injectors with liner diameters ranging from 1 to 3.5 mm are evaluated and compared for solvent split injection of large volumes in capillary gas chromatography. The liner dimensions determine whether a large sample volume can be introduced rapidly or has to be introduced in a speed controlled manner. The effect of the injection technique used on the recovery of n-alkanes is evaluated. Furthermore the influence of the liner diameter on the occurrence of thermal degradation during splitless transfer to the analytical column is studied. Guidelines are given for the selection of the PTV liner internal diameter best suited for specific applications.     

微孔膜气体扩散分离流动注射光度法测定废水中氰化物

研究了利用吡啶-巴比妥酸显色体系反应的中间产物,采用微孔膜气体扩散分离流动注射分析技术测定工业废水中氰化物,该法具有简便、快速并能消除某些干扰的特点。进样频率为65个样/h,检出限为0.02μg/ml,取氰化物2.5μg/ml时测量的相对标准偏差为0.3％(n=20),测定实际样品结果令人满意。     

Cold on-column – solvent split injection with a three-way press-fit device

In a previous paper we described the possibilities of cold on-column – sample split injection achieved by means of an inexpensive and simple three way press-fit device [1]. The same arrangement is proposed here for cold on-column – solvent split injection in which specific elimination of the solvent, without loss of any other sample components, is achieved by opening the splitting tube (or better, in this case, the early solvent vapor exit) during solvent elution, and then closing it during elution of the sample's other components. Discrimination between solvent and other sample components is achieved by means of a retention gap, a retaining precolumn, and an early vapor exit. The technique enables both selective enrichment of a sample, in order to record satisfactory mass and infrared spectra of minor components, and injection of large volumes (up to 100 μl) of dilute solutions which cannot be concentrated because of component volatility. Details of the assembly and tuning the system are given, together with some examples.     

An automated large volume on-column injection technique for capillary gas chromatography

Automated large volume (25-200 μl) on-column injections into a gas chromatograph with a capillary column were successfully performed by coupling a retention gap technique with an air actuated rotary valve. The linearity, injection precision, and carryover were evaluated. Slight boiling point discrimination was observed. This technique is compatible with commonly used chromatographic detectors (FID, ECD, MS) and conditions, while requiring very little instrument modification. The work is directed at the eventual reduction of manpower and turnaround time for sample collection and extraction, and Kuderna-Danish concentration when dealing with methods similar to EPA 625.     

Conditions for accurate split injection of samples with wide boiling point range

The effect of injection temperature, carrier gas flow rate, geometry of the glass insert, and column temperature program on the precision and accuracy of split injections was measured. Three types of injection techniques were compared: injection into a hot isothermal injector, isothermal injection with the injector at the solvent boiling point temperature, and programmed injection temperature. The last of these techniques produced the best accuracy and precision of analysis. Conditions for complete sample trapping at the beginning of programmed temperature analysis are described.     

Sequential multiple analyses of atmospheric nitrous acid and nitrogen oxides

Sequential injection analysis (SIA) was applied to multi-gas monitoring for atmospheric analysis. HONO, NO₂ or NO was collected in an individual diffusion scrubber in which the channel array was filled with either HCl or triethanolamine solution. All analytes were collected in the form of nitrite ions in the scrubber, and were transferred via a 12-port selection valve into a 2.5-ml syringe. The reagent, 3-amino-1,5-naphthalenedisulfonic acid (C-acid) solution was subsequently introduced into the syringe, and inter-mixed with the nitrite sample, whereafter the mixed solution was transferred to a heated reactor and held for 3 min at 100 °C. After that, the sample/reagent solution was returned to the syringe and alkalinized. Then, the final solution was analyzed using a homemade fluorescence detector. Atmospheric HONO, NO₂ and NO were successfully monitored 3 or 4 times/h. The limits of detection were 0.22, 0.28 and 0.35 ppbv for HONO, NO₂ and NO, respectively. It was demonstrated for the first time that SIA is a good tool for multi-gas atmospheric analysis. These nitrogen-oxygen compounds are interconvertible, and the simultaneous measurement of these gases is important. Especially, HONO is a source of OH radicals which contribute greatly to atmospheric pollution, and indeed atmospheric chemistry. This method allows the three gases to be measured using one system. The NO₂ and NO data obtained by SIA was compared with those obtained using chemiluminescence instrument. SIA has been successfully applied to atmospheric measurements. Interestingly, it was observed that HONO levels rose toward the end of periods of rain.