关于酱油中氯化钠的检测

酱油标准中规定以硝酸银溶液为滴定剂,以铬酸钾溶液为指示剂,用直接沉淀滴定法测定酱油中氯化钠的含量;用电位滴定法测酱油中的氯化钠以硝酸银溶液为滴定剂,以硝酸溶液和丙酮为溶剂,用玻璃电极和银电极来测定酱油中氯化钠的含量。直接沉淀滴定法会因酱油本身的颜色增加终点判定的难度,也会造成判定终点的视觉误差,从而影响其测定结果的准确度;电位滴定法则根据电位的"突跃"确定滴定终点,可提高对酱油中氯化钠检测的准确度。     

硫酸亚铁电位滴定法测定硝化棉氮量及不确定度评估

用硫酸亚铁作滴定剂,电位滴定仪指示滴定终点测定硝化棉含氮量,对硝化棉氮含量测定过程和标定过程中的不确定度的来源进行了分析,确定了含氮量测量过程中不确定度的主要来源为:重复性、样品质量、体积.对引入不确定度的各个不确定分量,用统计方法及所获得的各种信息,逐个进行不确定度的量化.通过测量和计算得到硝化棉含氮量测量结果为(12.97±0.05)％.     

石油产品碱值测定法(高氯酸电位滴定法)不确定度分析

一、测量方法简述（根据ＳＨ／Ｔ０２５１ -１９９３《石油产品碱值测定法》）在规定条件下 ,用标准滴定溶液１ｇ试样所用的高氯酸量 ,以ｍｇＫＯＨ／ｇ为单位表示 ,这称为碱值。测量方法分为正滴定法和反滴定法 ,两种滴定法效果相同（本单位使用正滴定法）。每种方法又分为Ａ法和Ｂ法 ,我们以仲裁试验Ａ法为例 ,分析其不确定度。二、测量数学模型正滴定法 :试样溶解于滴定溶剂中 ,以高氯酸冰乙酸标准滴定液为滴定剂 ,以玻璃电极为指标电极 ,甘汞电极为参比电极。进行电位滴定 ,用电位滴定曲线的电位突跃判断终点。试样碱值的计算公式如下 :…     

塑料复合膜、袋溶剂残留量不确定度评估

目的为提高包装用塑料复合膜、袋中溶剂残留的检测水平,建立溶剂残留测定结果的不确定度评定方法模型。方法以GB/T 10004—2008《包装用塑料复合膜、袋干法复合、挤出复合》中溶剂残留的检测方法为基础,参考相关标准和文献系统分析该法测量结果的不确定度来源,并对不确定度各个分量进行评估和合成。结果样品中溶剂残留总量的测定结果可表示为(22.40+1.421)mg/m2,k=2,P=95%。样品中苯系物残留量的测定结果可表示为(1.748+0.090 06)mg/m2,k=2,P=95%。最小二乘法得到的拟合校准工作曲线是溶剂残留结果测量不确定度的主要来源。结论溶剂残留测量结果的不确定度可作为表征测量结果准确度的指标之一。     

盐酸滴定液浓度测量的不确定度评定

对盐酸滴定液(0.1mol/L)浓度的不确定度进行了计算.不确定来源主要为重复测定引入的不确定度,基准物质称量引入的不确定度,基准物质纯度引入的不确定度,滴定液的体积测量引入的不确定度,滴定度引入的不确定度.当盐酸滴定液浓度为0.1022 moi/L时,测定结果的扩展不确定度为0.0003mol/L.     

硝酸银电位滴定法测定外加剂中氯离子含量的不确定评定

依据JJF 1059-1999测量不确定度评定与表示,从试剂纯度、摩尔质量、电子天平称量、容量瓶、滴定管、移液管、酸度计、重复性测试等影响因素引入的不确定度分量,对以硝酸银溶液用电位滴定法测定外加剂中氯离子含量进行不确定度评估。分析了测定过程中不确定度来源,量化不确定度分量,求出了合成不确定度和扩展不确定度,给出了测定结果的表示式为(5.43±0.30)%,k=2。     

基于紫外可见分光光度法的富勒烯纯度测量不确定度评定北大核心CSCD

富勒烯纯度影响了其力学、热学等性能及其在润滑、超导等领域的应用。紫外可见分光光度法仪器简单、操作简便,适用于富勒烯纯度的快速测量。然而,目前紫外可见分光光度法对富勒烯纯度测量的相关文献中,尚未有对测量影响因素的系统分析。因此,基于紫外可见分光光度法,建立了C 60富勒烯纯度测量的数学模型,通过分析紫外可见分光光度法测量富勒烯纯度的不确定度来源,进行不确定度评定。结果表明:电弧法合成的C 60富勒烯纯度为(74±7)%,k=2;燃烧法合成的C 60富勒烯纯度为(99±9)%,k=2。同时,通过不确定度评定,分析最大不确定度分量主要来源于标准曲线的拟合和标准系列溶液的配制,为后续基于紫外可见分光光度法的富勒烯纯度测量降低不确定度、提高测量准确性提供了技术依据。     

银量分析浅谈

银量分析测定对于乳剂和胶片都是非常重要的,如何在实验中快速准确测出乳剂和胶片的含银量呢?我们在实践中所采用的测定银量的方法是电位滴定法。电位滴定法对滴定终点的确定方法有三种:绘制E-V曲线法;绘制ΔE/ΔV-V曲线法;以及二级微商法。在实践中我们认为使用绘制E-V曲线法比较简单易行。绘制E     

碳酸钠标准滴定液两种不确定度评定法的比较

碳酸钠标准滴定液的配制引用GB/T 601—2016标准中4. 4. 2的规定,碳酸钠标准滴定液浓度有直接计算和标定计算两种方法,由此与之对应就有两种不确定度的评定方法。本文通过数据分析得出直接计算法浓度c1=(0. 4986±0. 0003) mol/L,k=2,相对扩展不确定度0. 06%;标定计算法浓度c2=(0. 4986±0. 0016) mol/L,k=2,相对扩展不确定度0. 31%。两种不确定度评定方法得出的结果相差甚大,结论为碳酸钠标准滴定液的配制直接计算法优于标定计算法。     

电位滴定法测定润滑油酸值不确定度评估

利用电位滴定法测定润滑油中酸值,建立了电位滴定法测定酸值的数学模型,分析了不确定度来源,评定了电位滴定法测定润滑油酸值的不确定度。通过重复性试验,测定齿轮油酸值为0.706 mg/g,对该结果进行了A类和B类不确定度评定,当包含因子为k=2置信水平为95%时, 扩展不确定度为0.010 mg/g。     

Tracer monitored titrations: measurement of total alkalinity

We introduce a new titration methodology, tracer monitored titration (TMT), in which analyses are free of volumetric and gravimetric measurements and insensitive to pump precision and reproducibility. Spectrophotometric monitoring of titrant dilution, rather than volume increment, lays the burden of analytical performance solely on the spectrophotometer. In the method described here, the titrant is a standardized mixture of acid-base indicator and strong acid. Dilution of a pulse of titrant in a titration vessel is tracked using the total indicator concentration measured spectrophotometrically. The concentrations of reacted and unreacted indicator species, derived from Beer's law, are used to calculate the relative proportions of titrant and sample in addition to the equilibrium position (pH) of the titration mixture. Because the method does not require volumetric or gravimetric additions of titrant, simple low-precision pumps can be used. Here, we demonstrate application of TMT for analysis of total alkalinity (A(T)). High-precision, high-accuracy seawater A(T) measurements are crucial for understanding, for example, the marine CaCO3 budget and saturation state, anthropogenic CO2 penetration into the oceans, calcareous phytoplankton blooms, and coral reef dynamics. We present data from 286 titrations on three types of total alkalinity standards: Na2CO3 in 0.7 mol kg x soln(-1) NaCl, NaOH in 0.7 mol kg x soln(-1) NaCl, and a seawater Certified Reference Material (CRM). Based on Na2CO3 standards, the accuracy and precision are +/-0.2 and +/-0.1% (4 and 2 micromol kg x soln(-1) for A(T) approximately 2100-2500 micromol kg x soln(-1), n = 242), using low-precision solenoid pumps to introduce sample and titrant. Similar accuracy and precision were found for analyses run 42 days after the initial experiments. Excellent performance is achieved by optimizing the spectrophotometric detection system and relying upon basic chemical thermodynamics for calculating the equivalence point. Although applied to acid-base titrations in this paper, the approach should be generally applicable to other types of titrations.     

Continuous on-line true titrations by feedback-based flow ratiometry. The principle of compensating errors

We introduce a new concept for continuous on-line titrations based on feedback-controlled flow ratiometry and the principle of compensating errors. The system has been thoroughly tested by applying it to acid-base neutralization titrations with indicator-based end point detection. In a typical case, the total flow (FT, consisting of the sample and the titrant flows) is held constant while the titrant (e.g., a standard base containing an indicator) flow FB varies linearly in response to a controller output voltage. The sample (e.g., an acidic solution to be titrated) flow FA constitutes the makeup and thus also varies (FA = FT - FB). The status of the indicator color in the mixed stream is monitored by an optical detector and used either for governing the controller output or for interpreting the results of the titration. Three methods (PID based control, fixed triangular wave control, and feedback-based triangular wave control implemented on a PC) were examined. In the last and the most successful approach, the titrant flow is initially ramped upward linearly. At the instant a change in the color is sensed by the detector, the titrant flow rate FH is higher than the true equivalence flow rate FE because of the lag time between the first compositional change and its detection. The sensing of the change in color causes the system output to immediately reverse its ramp direction such that the titrant flow now goes down linearly at the same rate. At the instant a change in color, in the opposite direction this time, is again sensed, the titrant flow rate FL is lower than FE by exactly the same amount that FH was higher than FE. This principle of compensating errors (FE = (FH + FL)/2) allows true titrations with excellent reproducibility and speed (0.6% RSD at 3 s/titration and 0.2% RSD at 10 s/titration) and titrant volume consumption as little as 12 microL/titration and solves an old conceptual problem in flow based titrations.     

Direct electrochemistry and electrocatalytic activity of cytochrome c covalently immobilized on a boron-doped nanocrystalline diamond electrode

Cytochrome c (Cyt c) was covalently immobilized on a boron-doped nanocrystalline diamond (BDND) electrode via surface functionalization with undecylenic acid methyl ester and subsequent removal of the protecting ester groups to produce a carboxyl-terminated surface. Cyt c-modified BDND electrode exhibited a pair of quasi-reversible and well-defined redox peaks with a formal potential (E(0)) of 0.061 V (vs Ag/AgCl) in 0.1 M phosphate buffer solution (pH 7.0) and a surface-controlled process with a high electron transfer constant (ks) of 5.2 +/- 0.6 s(-1). The electrochemical properties of as-deposited and Cyt c-modified boron-doped microcrystalline diamond (BDMD) electrodes were also studied for comparison. Investigation of the electrocatalytic activity of the Cyt c-modified BDND electrode toward hydrogen peroxide (H2O2) revealed a rapid amperometric response (5 s). The linear range of response to H2O2 concentration was from 1 to 450 microM, and the detection limit was 0.7 microM at a signal-to-noise ratio of 3. The stability of the Cyt c-modified BDND electrode, in comparison with that of the BDMD and glassy carbon counterpart electrodes, was also evaluated.     

Titration without Mixing or Dilution: Sequential Injection of Chemical Sensing Membranes

A novel, miniaturized titration was developed using beads 35 μm in diameter as semisolid aqueous titrant retained in a nonaqueous sample stream. Agarose beads with internally bound pH indicator served as a pH sensing membrane material swollen with aqueous NaOH titrant. The indicator monitored the remaining titrant within the agarose beads during perfusion with H(2)SO(4) in 1-butanol samples. Irreversible reaction of 2 mg bead layers was made possible by automated packing and disposal in a flow cell. This strategy substituted membrane advantages for the burdens of mixing and unnecessary dilution under laminar flow conditions. The agarose environment was conditioned with NaCl to tolerate dissolved salt in the sample. Transmittance measurements were made via fiber optics through FEP PTFE optical windows. A simple inverse relationship held between endpoint volume and acid concentration so that calibration curves were linear, R(2) = 0.9980.     

Lead (II) ion selective electrodes based ondiphenylmethyl-N-phenylhydroxamic acid ionophore in cyanocopolymermatrix

A Pb²⁺ ion selective electrode has been prepared using diphenylmethyl-N-phenylhydroxamic acid (DPNINPRA) as ionophore and cyanocopolymer as new membrane matrix. The electrode (Membrane-2) exhibited a Nernstian slope of 36.75±0.001 mV decade^-1 activity of Pb²⁺ ions on varying the Pb²⁺ ions activity from 7.41×10^-8 to 3.68×10^-1 mol dm^-3. The electrode has exhibited a response time of 13.0±s at 1.0×10^-3 mol dm^-3 activity of Pb²⁺ ions and also revealed an improved selectivity in presence of various interfering ions. The high dipolar property of the selected cyanocopolymer has reduced significantly the anions interference and shown potential response independent to the activity of sodium tetraphenylborate (NaTPB). The electrode has shown isothermal point of 30°C as determined from a hysteresis curve. Sensitivity of the electrode has shown a significant variation with thickness of the membrane. The electrode has shown a constant response on continuous use for a period of six months without any drift in potential and has been also found to be useful as indicator electrode for potentiometric titration of Pb²⁺ ions     

Automatic potentiometric determination of uranium in the presence of organic solvents

Redox potentiometric titration of small amounts of uranium in mixed systems aqueous H₃PO₄ solutionorganic solvent using an automatic titrator was studied. The accuracy of the U determination strongly depends on the kind and concentration of the solvent. In determination of 0.1–0.2 mg of U in mixed phosphoric acid-organic solvent systems using ammonium vanadate as titrant, the determination accuracy decreases in the order acetone ? acetonitrile > nitromethane > ethanol. In the presence of acetone, 0.1 mg of U can be determined with high accuracy, which was impossible when using aqueous H₃PO₄ solutions. With all the organic components tested, the metrological characteristics are improved with an increase in the organic solvent content from 10 to 37 vol %.     

Porous CS monoliths and their adsorption ability for heavy metal ions

Highly porous chitosan (CS) monoliths were prepared by a unidirectional freeze-drying method and the adsorption performance of the monoliths for metal ions in aqueous solution was evaluated. The porous CS monoliths have excellent adsorption for a range of metal ions. The effect of the amount of porous CS monoliths, the pH, the adsorption time, the amount of the cross-linking agent, and the amount of disodium ethylenediamine tetraacetate (EDTA) on the saturated adsorption efficiency (Ade) were determined. The pH had the greatest influence on the adsorption behavior. Under optimal conditions (C(CU2?) = 800 mg/L, pH 6, and cross-linking agent = 0.15%) for the CS monoliths, the Ade for Cu(2+) exceeded 99%, and the saturated adsorption capacity (Q(s)) reached a value of 141.8 mg/g (2.23 mmol/g) in 4h. Moreover, the addition of EDTA can both increase the Q(s) and shorten the time that achieved the level. If EDTA was added, this level was achieved in 2h. The porous CS monoliths can be regenerated by soaking them in acid and their Ade is maintained.     

Electrochemically mediated reduction of horseradish peroxidase by 1,1'-ferrocenedimethanol in organic solvents

Cyclic voltammetry is an efficient means of analyzing the catalytic reduction of H2O2 at immobilized horseradish peroxidase (HRP)-Eastman AQ 55 electrodes in the presence of 1,1'-ferrocenedimethanol as a one-electron reversible cosubstrate. This system was employed to study the kinetics of the reduction of compound II of HRP in a number of organic solvents. An electrocatalytic response was detected in methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, 2-butanone, 1,2-propanediol, acetonitrile, ethyl acetate, and ethylene glycol. Unusual bell-shaped variations of the peak or plateau catalytic current with the substrate concentration were observed in all solvents tested. The results obtained in methanol, acetonitrile, and 1-propanol were analyzed using the model developed by Saveant (Limoges, B.; Saveant, J.-M.; Yazidi, D. J. Am. Chem. Soc. 2003, 125, 9192-9203). The values of k3Gamma0 and K3,M, where k3 = k3,1k3,2/(k3,-1 + k3,2), Gamma0 is the surface concentration of active enzyme, and K3,M = (k3,-1 + k3,2)/k3,1, were determined. The values of k3Gamma0 for the mediated reduction of compound II of HRP in methanol, 1-propanol, and acetonitrile (in the presence of 5% aqueous buffer) were not affected by the solvent dielectric constant but decreased with solvent hydrophobicity. The value of K3,M obtained in methanol was similar to that obtained for [Os(bpy)2pyCl]2+ in aqueous buffer.     

Spectrophotometric and Differential Pulse Polarographic Methods of Analysis for Ketotifen Hydrogen Fumarate

Spectrophotometric and differential pulse polarographic methods have been proposed for the assay of ketotifen hydrogen fumarate in authentic powder and in capsule dosage forms (Zaditen^(R)), using acetate buffer of pH 5.0 as a solvent as well as a supporting electrolyte. Ketotifen hydrogen fumarate exhibits relatively strong absorption in the ultraviolet region with maximum absorption at 300 nm; the molar absorptivity, $eP_max, and specific absorbance, A (1 per cent, 1 cm), being 1.38 × ⁴ L mole^-1 cm^-1 and 325 respectively. Beer's Law was verified; the absorbance, (A_max), was found to be linearly related to concentration, C, over the range 2 to 30 ug ml^-1. The mean percentages of recovery for ketotifen hydrogen fumarate powder and in capsule form obtained spectrophotometrically were 100.85 $pM 0.56 and 99.75 $pM 0.85 respectively.

Differential pulse polarograms were recorded at room temperature under constant pulse amplitude of 50 mV superimposed on a linearly increasing DC-voltage ramp. The peak current, i, of the polarogram was measured at the peak potential of -1.06 V on the dropping mercury electrode, (dme), versus Ag/AgCl reference electrode. A linear relationship between the peak current and concentration, C, was observed over the range 5 to 70 ugm^-1 The mean percentages of recovery obtained polarographi-cally for ketotifen hydrogen fumarate in bulk and in capsule form were 99.33 $pM 1.12 and 101.15 $pM 0.70 respectively.

The purity of authentic ketotifen hydrogen fumarate was checked by nonaqueous potentiometric titration using 0.1 N - perchloric acid.     

Molecular Heteroconjugation Equilibria in (n-Butylamine + Acetic Acid) Systems in Binary (Dimethyl Sulfoxide + 1,4-Dioxane) Solvent Mixtures

The acidity constants of molecular acid, K _a (HA), cationic acid, K _a (BH⁺), as well as the equilibrium constants of anionic homoconjugation, , cationic homoconjugation, , and molecular heteroconjugation, K_AHB, have been determined in (n-butylamine + acetic acid) systems without proton transfer in binary [dimethyl sulfoxide (DMSO) + 1,4-dioxane (D)] solvent mixtures. The constants were determined by using the potentiometric titration method at a fixed ionic strength. It is concluded that the molecular heteroconjugation constants in the mixed solvent systems studied are linearly related to the 1,4-dioxane content. Furthermore, in the (acid + base) systems without proton transfer, the direction of titration (direct B + HA or reverse HA + B) has been found to affect the precision of determination of reliable values of molecular heteroconjugation constants. Moreover, it has been found that the relative dielectric constants of the solvent mixtures studied change linearly as a function of solvent composition, as well as solvent components do not show interactions of solvent–solvent type.