Spectrophotometric determination of drugs in pharmaceutical formulations withN-bromosuccinimide and celestine blue

Simple, sensitive and selective methods are proposed for the spectrophotometric determination of drugs, viz., tetracycline HCl, nifurtimox, ethionamide, propranolol HCl and isonicotinic acid hydrazide, based on their reactivity withN-bromosuccinimide (NBS). The method involves the addition of excess NBS of known concentration in the presence of 0.25M HCl and the unreacted NBS is determined by the measurement of the decrease in the absorbance of the dye celestine blue (_max 540 nm), which was found to be the most suitable of several dyes tested. This method was applied for the determination of drug contents in pharamaceutical formulations and enabled the determination of the drugs in microgram quantities (0.2 to 5 g/ml). Standard deviations were typically 0.5mg per dose (RSD 0.1–1.0%). No interferences were observed from excipients and the validity of the method was tested against reference method. Recoveries were 99.8–101.1%.     

Medium Effect of an Organic Solvent on the Activity Coefficients of HCl Consistent with Pitzer’s Electrolyte Solution Theory

This paper discusses the relationship between the medium effect as defined by Owens and Pitzers equations. Using this relationship and values of Pitzers parameters (which account for various types of short-range interactions between neutral molecules and ions, for indirect forces arising from the solvent, and for triple particle interactions), we analyzed published experimental data for {HCl + organic solvent + water} systems.     

(H2O)2和(HCl)2非线性光学性质的从头计算研究

用MP2方法及aug-cc-pVDZ,aug-cc-pVDZ+BF,aug-cc-pVTZ和aug-cc-pVTZ+BF基组对(H2O)2和(HCl)2超分子的静态偶极矩μ0,极化率α0及第一超极化率β0进行计算.采用Counterpoise方法消除基组的重叠误差(BSSE),得到上述物理性质的分子间相互作用的贡献,在此基础上研究了其中新的长程π型氢键的效应.     

O（~1D）与CF_2HCl反应的理论研究

用量子化学密度泛函理论（DFT）和G3B3方法，对为（~1D）与CF_2HCl的反应 进行了研究，在B3LYP/6-311+G(d)，B3LYP/6-311+G(2df,2pd)和G3B3计算水平上， 优化了反应热能面上各驻点的几何结构，通过内禀反应坐标（IRC）计算和振动分 析，对反应过渡态进行了确认，并确定了反应机理。     

Determination of spatial distribution of oxidation products in ultra-high molecular weight polyethylene by staining with sulphur dioxide or hydrochloric acid

Treating a sample of oxidised ultra-high molecular weight polyethylene (UHMWPE) with SO₂ will cause a reaction between SO₂ and hydroperoxides in the sample, forming a hydrosulphate group. During subsequent heat treatment the hydrosulphate group will leave as sulphuric acid, and a double bond will form in the polymer chain. During this step the sample turns brown. This browning has previously been used to determine the spatial distribution of oxidation in PP. The aim of this work was to apply this also to UHMWPE and to determine what causes the browning and how well it corresponds to the true distribution and concentration of hydroperoxides. The possible future use of the technique to determine the spatial distribution of oxidation in UHMWPE has also been evaluated.The true nature of the browning has been difficult to establish, but it seems to originate from a charge transfer complex between the double bonds and the sulphuric acid. A similar type of coloration develops in oxidised UHMWPE, when it is treated with hot hydrochloric acid. However, in that case the coloration is proportional to the carbonyl concentration and has been concluded to originate from the oxonium ion formed by protonation of ketones. The coloration of both SO₂/heat-treated samples and samples treated with hot hydrochloric acid can be used to give a qualitative picture of the spatial distribution of oxidation in UHMWPE. The techniques have been applied to study the heterogeneous oxidation in badly consolidated UHMWPE. It was found that the very good spatial resolution gave information about the heterogeneous oxidation that is not possible to obtain when using other techniques, such as FTIR mapping and imaging chemiluminescence.     

The Activity Coefficients of HCl in HCl–Na2SO4 Solutions from 0 to 50°C and Ionic Strengths Up to 6 Molal

The electromotive force of HCl−Na₂SO₄ solutions has been determined from 5 to 50°C and ionic strengths from 0.5 to 6m with a Harned type cell The results have been used to determine the activity coefficient of HCl in the mixtures. The activity coefficiencts have been analyzed with the Pitzer equations to account for the ionic interactions. The measurements were used to determine interaction coefficients (β⁰, β¹) for NaHSO₄ solutions from 5 to 50°C. The model represents the mean activity coefficients HCl in the mixtures to ±0.005 over the entire temperature and concentration range of the measurements. The results have been combined with literature data to provide parameters that are valid from 0 to 250°C for NaHSO₄ solutions.     

Application of a Validated, Stability-Indicating LC Method to Stress Degradation Studies of Ramipril and Moexipril.HCl

A stability-indicating reversed-phase liquid chromatographic (RPLC) method has been established for analysis of ramipril (RAM) and moexipril hydrochloride (MOEX.HCl) in the presence of the degradation products generated in studies of forced decomposition. The drug substances were subjected to stress by hydrolysis (0.1 m NaOH and 0.1 m HCl), oxidation (30% H₂O₂), photolysis (254 nm), and thermal treatment (80 °C). The drugs were degraded under basic and acidic conditions and by thermal treatment but were stable under other stress conditions investigated. Successful separation of the drugs from the degradation products was achieved on a cyanopropyl column with 40:60 (v/v) aqueous 0.01 m ammonium acetate buffer (pH 6)–methanol as mobile phase at a flow rate of 1 mL min⁻¹. Detection was by UV absorption at 210 nm. Response was a linear function of concentration over the range 5–50 μg mL⁻¹ (r > 0.9995), with limits of detection and quantitation (LOD and LOQ) of 0.04 and 0.09 μg mL⁻¹, respectively, for RAM and 0.014 and 0.32 μg mL⁻¹, respectively, for moexipril. The method was validated for specificity, selectivity, solution stability, accuracy, and precision. Statistical analysis proved the method enabled reproducible and selective quantification of RAM and MOEX as the bulk drug and in pharmaceutical preparations. Because the method effectively separates the drugs from their degradation products, it can be used as stability-indicating.     

Time-dependent Quantum Wave Packet Study of F+HCl and F+DCl Reactions

The F+HCl and F+DCl reactions are studied by the time-dependent quantum wave packet method, using the most recent potential energy surface reported by Deskevich et al.. Total reaction probabilities for a number of initial ro-vibrational states of HCl and DCl diatomic moiety are presented in the case of total angular momentum J=0. It is found that for both reactions the initial rotational excitation of the diatomic moiety enhances greatly the reaction probabilities but this e?ect is more signiˉcant for F+HCl system. This is mainly due to larger rotational constant of the HCl reagent. The initial vibrational excitation of the diatomic moiety has little e?ect on the reactivity for both systems except shifting down the collision energy threshold. The results indicate that the reaction coordinates for these two systems are e?ectively along rotational freedom degree. More quantum phenomena, such as tunneling and resonance, are observed in F+HCl reaction than F+DCl reaction, and for the initial states studied, the reactivity of the later is lower. Di?erent skewing angles of these two systems account for these isotopic di?erences.     

木屑焚烧过程中氯化氢排放特性研究

在小型管式炉进行了含氯垃圾(木屑)中氯化物析出试验，研究了氯析出过程中的几个因素(燃烧温度、停留时间、燃烧气氛、烟气中水蒸气含量)对反应的影响，确定了木屑反应的动力学方程式。得出如下结论：燃烧过程中Cl-HCl的转化率随燃烧温度的升高而显著增加；随停留时间的增加，HCl的析出存在两个明显的析出峰，这就清楚地说明至少有两种以上形式的氯存在于木屑中。氧化性气氛对氯化物生成影响不大，随炉内气氛由弱还原性气氛向强还原性气氛的转化，氯析出率明显降低；水蒸气的存在明显加速垃圾中氯的析出。木屑燃烧过程中，氯析出反应为零阶反应。     

水簇上次氯酸与盐酸反应的理论研究

计算表明次氯酸与盐酸通过与水分子形成环状过渡态可以极大地降低反应势垒。当环上的水分子数为三时 ,势垒最小。更多的水分子通过环外的水化作用 ,使势垒进一步降低。这表明我们提出的多分子过渡态机理可以解释次氯酸与盐酸的反应由冰表面催化的实验事实 .