Determination of Traces of Mercury (II) and Phenylmercury by Direct Polyurethane foam Thin-Layer Spectrophotometry

Abstract

The determination of mercury and phenylmercury in the ppb concentration range using polyurethane foam (PUF) thin-layer spectrophotometry has been described. Sorption of mercury and phenylmercury into foam parallepiped loaded with diphenylthiocarbazone (dithizone) contributed to considerable improvement in the absorbance value of the colored species, being concentrated about 140 times.

The method allowed the achievement of satisfactory results, the detection limits are 5 and 10 μg per litre for mercury and phenylmercury, respectively, for 100ml sample volume. The average recovery from tap water amounts to 100% for mercury and 96.6% for phenylmercury.     

陈爱敏,魏海英*

室温下,硒(IV)与邻苯二胺配位生成黄色配合物,用环己烷萃取后,在最大吸收波长330nm处测定其吸光度。实验结果表明：硒含量在4～20 μg/mL内线性关系良好,线性方程Y=0.1999C-0.0011(R=0.9995)。最优化条件下测定硒盐中硒的含量取得满意结果。该法操作简单,设备和药品价格低廉,准确度高,稳定性好,适宜于基层实验室对食品中微量元素硒的检验。     

双波长分光光度法同时测定载硫酸长春新碱/姜黄素聚合物纳米粒中两种药物的含量

以聚乙二醇单甲醚-聚乳酸-乙醇酸共聚物（m PEG-PLGA）为载体材料,制备同时载带硫酸长春新碱（VCR）和与之具有协同抗肿瘤作用的姜黄素（Cur）的m PEG-PLGA纳米粒（VCR/Cur-m PEG-PLGA-NP）。建立了以等吸收双波长紫外分光光度法同时测定纳米粒中VCR和Cur含量的方法,研究显示,VCR测定波长296.5nm,等吸收波长462nm;Cur测定波长414nm;VCR在4.0—36.0μg.mL-1范围内,浓度C与差值吸光度ΔA呈良好线性相关;Cur在0.5—8.0μg.mL-1范围内,浓度C与吸光度A具有良好的线性关系。该方法简便迅速,结果准确可靠,适用于VCR/Cur-m PEG-PLGA-NP中药物含量的同时测定。     

一种快速测定过氧化氢浓度的方法

建立一种利用分光光度法快速测定过氧化氢溶液浓度的方法。本方法基于在酸性条件下硫酸铈能够与过氧化氢发生氧化还原反应,橙黄色的四价铈被还原为无色的三价铈,从而导致其溶液的吸光度值发生变化,根据溶液中硫酸铈和过氧化氢的反应定量关系,可计算得到过氧化氢的浓度。本方法选择的测定波长为480nm,硫酸浓度为0.5mol·L-1,反应时间为3.0min。研究结果表明,该方法具有较高的精度和准确度,其重现性实验的相对标准偏差(RSD)为0.31%,而准确度实验的RSDs≤0.91%。该方法具有操作简单、快速,检测灵敏度高,实验成本较低等优点,适用于工业快速分析。     

Development of a Simple and Inexpensive Optical Absorption One‐Shot Sensor Membrane for Detection and Determination of Cyanide Ions in Water Samples

A new one‐shot optical cyanide ion sensor is proposed for determination of cyanide ions. The sensor was constructed by immobilizing crystal violet (CV) on triacetylcellulose membrane. The sensing mechanism involves reaction between cyanide ions and the immobilized CV at pH = 5.4, which results in a decrease in absorbance of the membrane at 600 nm. The sensor shows sufficient repeatability, reproducibility, operational lifetime of 3 weeks, and a response of less then 10 min under the optimum conditions and response time of 8 min. Cyanide can be determined in the concentration range of 50.0‐800 μg mL^‐1 with a detection limit of 5.0 μg mL^‐1. Most ions do not interfere with the determination of cyanide ions. The proposed sensor was successfully applied to the determination of cyanide in spiked water samples.     

A spectrophotometric flow procedure for the determination of cationic surfactants in natural waters using a solenoid micro-pump for fluid propulsion

An automatic flow-analysis procedure for spectrophotometric determination of cationic surfactants in surface water using a solenoid micro-pump for propelling solutions of reagents and sample is described. The proposed method is based on a ternary formation complex between chromazurol S, the Fe(III) ion, and the cationic surfactant. The flow network comprised four solenoid micro-pumps controlled by a microcomputer, which performed the sampling step by loading a reaction coil with sample and reagent solutions and displacing the sample zone through the analytical path. The system is simple, easy to operate, and very flexible, with sufficient sensitivity to determine cationic surfactants in water without any pre-concentration or separation step. After determining the best operational conditions, favourable features such as a linear response between 0.34 and 10.2?mg?L^?1 of surfactant (R?=?0.999), a relative standard deviation of 0.6% (n?=?11) for a sample containing 3.4?mg?L^?1 of surfactant, a detection limit of 0.035?mg?L^?1 of surfactant, and a sampling throughput of 72 determinations per hour were achieved. The system was used to determine cationic surfactant in river-water samples, and recovery values between 91 and 106% were achieved.     

Chemical equilibria and sequential extractive spectrophotometric determination of selenium(IV) and (VI) using the chromogenic reagent 4,4′-dichlorodithizone

The chromogenic reagent 4,4′-dichloro(3-mercapto-1,5-diphenylformazan), Cl₂H₂D _Z , forms a yellow–red-coloured complex with selenium(IV). The produced complex species was extracted quantitatively into n-hexane, and its absorbance was measured at 416?nm. The chemical composition of the extracted selenium(IV)-Cl₂H₂D _Z chelate and the molar absorptivity at 416?nm were found to be [SeO (Cl₂HD _Z )₂] and 9?×?10⁴?L?mol^?1?cm^?1, respectively. The values of the extraction constants (K _D, K _ex, β) enable a convenient application of the proposed system for the liquid–liquid extraction procedure and sequential spectrophotometric determination of traces of inorganic selenium(IV) and/or selenium(VI) after reduction of the later to selenium(IV) with HCl (6?M). Beer's law and Ringbom's plots were obeyed in the concentration range 0.01–20 and 0.5–19?µg?mL^?1 of selenium(IV), respectively, with a relative standard deviation of 2.2%. The proposed method has been successfully applied to the determination of selenium(IV) or (VI) and total inorganic selenium(IV) and (VI) in tap and freshwater samples.     

Hydrogen Halide-Catalyzed Thermal Decomposition of Poly(vinyl Chloride)

The thermal decomposition of solid PVC was studied in the presence of added hydrogen chloride and hydrogen bromide over the temperature range 170–210°C. Under certain conditions the decomposition was shown to be dependent in a first-order manner on the hydrogen halide pressure. These gases acted as catalysts, increasing the rate of HCl evolution and the degree of discoloration but not producing longer polyene sequences. Activation energy for the HCl-catalyzed process was found to be similar to that of the uncatalyzed decomposition of PVC. A unified mechanism is presented for an overall process consisting of three steps: random generation of a single carbon-carbon double bond in the cis configuration; 1,4-elimination of HCl via a six-centered transition state yielding a polyene; HCl- or HBr-catalyzed isomerization of the polyene formed by HC1 elimination to regenerate the initial structure. Hydrogen chloride catalysis is seen as an integral part of the overall process.     

Ultraviolet emissions from Gd ions excited by energy transfer from Ho ions

Ultraviolet (UV) upconversion (UC) emissions of Gd³⁺ ion were investigated in Y_1.838−xGd_xYb_0.16Ho_0.002O₃ (x=0, 0.16, 0.4, 1, 1.4) bulk ceramics under 976 nm laser diode (LD) excitation. The UC emissions centered at 309 and 315 nm are assigned to the transition of ⁶P_5/2→⁸S_7/2 (Gd) and ⁶P_7/2→⁸S_7/2 (Gd). The ⁶P_J levels of Gd³⁺ ions are populated by an energy transfer (ET) process from ⁸S_7/2 (Gd)+(³P₁, ³L₈, ³M₁₀) (Ho)→⁶P_J (Gd)+⁵I₈ (Ho). A four-photon ET UC process was confirmed by the dependence of the ⁶P_7/2 level emission intensity on the pumping power. We found that the intensity of the UC emissions increased with Gd³⁺ ion concentration and peaked at 8 mol%, then starts to decrease until the Gd³⁺ ion concentration reached 70 mol%. The variation in the UV emission intensity is the result of the competition between the ET process and concentration quenching effect. Theoretical calculations based on steady-state equations validated the proposed UC mechanisms.     

Excitation and quenching of ultraviolet nitrogen bands in the mixture of N2 and O2 molecules

Total quenching rate coefficients of three singlet and three triplet states of molecular nitrogen in the collisions with O₂ molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of N₂^? molecules are compared with the available experimental data. An influence of collisional processes on vibrational populations of electronically excited N₂(a¹Π_g) and N₂(A³Σ_u⁺) molecules is studied for conditions of laboratory discharge in N₂ and O₂ at admixtures of molecular oxygen 0%-20% for the pressures 1-1000 Pa. It is indicated that molecular collisions cause changes in relative populations of vibrational levels of these states and intensity relations of ultraviolet bands of N₂ with rise in the pressure and the O₂ admixture.