粮食、饲料中尿素酶活性测量结果不确定度的评定

对粮食、饲料中尿素酶活性测量结果的不确定度进行了评定。使用酸度计，利用pH增值法，以pH增量表示尿素酶活性。通过对影响样品测试过程的不确定度分量的分析和量化，求得尿素酶活性测量结果的标准不确定度和扩展不确定度分别为0．019、0．04，并对测量结果进行了表述。     

A ratiometric approach for pH optosensing with a single fluorophore indicator

A new fiber-optic prototype of luminometer has been designed in order to perform ratiometric-based measurements for optical sensing purposes. The coupling of a pH-selective sensing phase to the fiber-optic prototype has been evaluated for robust pH optosensing in drinking water. The pH-sensitive material has been synthesized by entrapping a pH-sensitive luminescent indicator (mercurochrome) in a sol-gel inorganic matrix. The pH optosensing is based on the detection of pH-induced reversible changes in the mercurochrome fluorescent emission and in the light reflected by the sensing phase.The instrument has been constructed using low-cost and simple optoelectronic components. The active phase was excited by means of a visible 470 nm high intensity light emitting diode (LED). The radiant power of the LED was modulated using a sinusoidal function so that scattered light due to light sources of different frequency than the modulating signal (e.g. sunlight) can be easily removed by adequate electronic filtering of the emission signal. Both the fluorescence emission from the dye and the sensing phase reflected light were collected in a bifurcated fiber-optic to allow the ratiometric measurement.Two different ratiometric approaches have been evaluated. The analytical performance of the pH optrode using both measurement methods have been compared, between them and with simple fluorescence intensity measurements, in terms of sensitivity, measurement range, response time, repeatability and insensitivity to changes in excitation light intensity.The applicability of the developed pH optrode and methods has been tested for pH analysis in tap and bottled still mineral water samples. The results obtained showed good agreement with the corresponding pH values provided by a commercial glass electrode.In this work, pH was selected as a model analyte to evaluate the performance of the proposed methodology, although other optical sensors for different applications/analytes could benefit of this approach.     

Spectrophotometric pH measurements of freshwater

The use of cresol red (CR) indicator for determination of freshwater pH is evaluated. Ionic strength effects and indicator pH perturbation are discussed and quantified using theoretical and empirical approaches. Spectrophotometric and potentiometric methods are directly compared by repeated analyses of a low ionic strength pH buffer. The mean and standard deviation of the two methods were 7.618±0.008 (spectrophotometric) and 7.484±0.040 (potentiometric) (N=18) with systematic errors of 0.003 and 0.137 pH units relative to the true pH (7.621). Field data from an alkaline river (pH∼7.8-8.8) show that measurement reproducibility is better than 0.01 pH units, making it possible to resolve very small spatial and temporal changes in riverine pH. Uncertainty in the indicator apparent dissociation constant limits the accuracy of the pH measurement to ∼0.05 pH units. An alternative method for estimating the dissociation constant, based on calculation of pH from two other carbonate parameters, is proposed.     

Performance Test of Vitamin B6 Test Kit Candidate

Vitamin B6 test kit was designed as an alternative, affordable and user-friendly analysis tool for small and medium enterprises which process bananas. Its performance was evaluated twice with 70 respondents and the measurements considered satisfying when the results were laid in the range of one square deviation from the real value that determined by spectrophotometer. Performance tests results then compared to pH measurement using pH indicator, the more familiar test kit that also rely on human ability to distinguish color. The first performance test to respondents that closely related to chemical measurement got 33 success results and 29 respondents gave satisfying results which was comparable to pH measurement that gave 31 of 33 satisfying results. The second performance test was conducted by 70 respondents which involving respondents with background that unrelated to chemical measurement. As much as 34 success results for both measurements from the related group but only 32 and 27 success measurements for pH measurement and Vitamin B6 measurement using kit, respectively, from the unrelated group. The second performance test results for pH measurement did not give significant difference with the second one, 34 of 35 satisfying results from closely related group and 27 of 32 from unrelated group. Second performance test results for Vitamin B6 was significantly different from the first one since the respondents required to conduct the measurement twice and the results were reported as average values. Vitamin B6 kit gave 23 of 61 satisfying results with 15 of 34 were from the closely related group and 8 of 27 from the unrelated group. Data from closely related group from second performance test were further analyzed by considered as two separated measurements and compared to the results from the first performance test. It was found that measurement conducted first gave only 2 of 34 satisfying results compared to 22 of 34 from measurement conducted at second. The results were also recapitulated and analyzed based on background and gender. Closely related group gave 44.12%, 29.41%, 26.47% satisfying, query and unsatisfied measurement results, respectively. These results were better compare to the unrelated group that only gave 29.63%, 25.93% and 44.44%. Female respondents gave 36.36%, 36.36%, 27.27% satisfying, query and unsatisfied measurement results, respectively, which better than male respondents that gave 41.18%, 5.88% and 52.94%. Vitamin B6 kit had good performance as a test kit candidate but still required many improvements so the measurement results doesn’t affected by gender, user background and number of conducted measurement. Better design of color chart was a proposed improvement to reduce the fatigue of eye's conical cell that will be conducted in the next study.     

Effect of pH on the properties of nanocrystalline CuO thin films deposited by sol-gel process

Nanocrystalline cupric oxide thin films were prepared using the sol-gel method. Three sols with different pH were performed in order to evaluate the pH effect on the morphology and optical properties of the films. XRD pattern confirmed the nanocrystalline monoclinic CuO phase formation. The influences of pH on surface morphology of films were investigated by scanning electron microscopy (SEM). It was observed that grains size increases by increasing the pH of the sol. UV-Vis spectrum measurement showed low transparency of the films in the visible region. Optical constants such as extinction coefficient, refractive index and optical band gap were evaluated from these spectra by using the Pointwise Unconstrained Minimization Approach (PUMA). The band gap of the films varies from 2.20 to 1.98 eV for various pH of sol.     

Electrochemical Deposition and Spectroelectrochemical Response of Bromophenol Blue Films on Gold

Bromophenol blue (BPB) was electropolymerized onto a Au substrate. The effects of voltammetric cycle number, BPB concentration, and pH on film thickness, density, optical absorption, and electrochemical susceptibility were evaluated, and favorable deposition conditions were identified. Quantitative measurement of the film mass via quartz crystal microbalance enabled determination of the molar volume and revealed a strong dependence of film density with deposition pH. Finally, electrochemical control of the optical properties of BPB films was demonstrated via in situ spectroelectrochemistry. We believe this is the first demonstration of electropolymerization of pure BPB on Au, and thus the first demonstration of poly(BPB) as an electrochemically switchable optical coating.     

基于光度法的高精度海水pH值测量系统

基于光度法的海水pH值自动测量系统测定速度快,精密度高,是海洋酸化和碳循环研究急需的测量装置.本研究以光度法和流动注射分析技术为基础,通过整合泵阀流路体系、LED光源、流通池和光谱仪,研发了海水pH值自动测量系统.本系统在分析过程中不易产生气泡,利用指示剂在样品中的浓度变化校正指示剂的加入带来的测量偏差,操作简单方便,测量一个样品用时约为1.5 min,精密度为0.0013,准确度为0.0059,可在实验室或调查船中对所采集的海水快速地进行高精度pH值测量.     

Estimation of uncertainty in routine pH measurement

A procedure for estimation of measurement uncertainty of routine pH measurement (pH meter with two-point calibration, with or without automatic temperature compensation, combination glass electrode) based on the ISO method is presented. It is based on a mathematical model of pH measurement that involves nine input parameters. Altogether 14 components of uncertainty are identified and quantified. No single uncertainty estimate can be ascribed to a pH measurement procedure: the uncertainty of pH strongly depends on changes in experimental details and on the pH value itself. The uncertainty is the lowest near the isopotential point and in the center of the calibration line and can increase by a factor of 2 (depending on the details of the measurement procedure) when moving from around pH 7 to around pH 2 or 11. Therefore it is necessary to estimate the uncertainty separately for each measurement. For routine pH measurement the uncertainty cannot be significantly reduced by using more accurate standard solutions than ±0.02 pH units – the uncertainty improvement is small. A major problem in estimating the uncertainty of pH is the residual junction potential, which is almost impossible to take rigorously into account in the framework of a routine pH measurement.¹ Received: 11 August 2001 Accepted: 22 February 2002     

在线酸度仪校准装置的研制

为了提高在线酸度监测仪表的计量精度,使计量校准实现动态测量,研究了在线式酸度监测仪的校准方法,并根据校准方法研制了一种在线动态计量检定校准装置,该装置利用国家一级标准物质进行量值传递。整套装置模拟了在线酸度仪的工作状态,工作流速30－250mL／min,校准结果的不确定度为0．01pH,满足校准的要求。     

Development of an enzymatic fiber-optic biosensor for detection of halogenated hydrocarbons

An enzyme-based biosensor was developed by co-immobilization of purified enzyme haloalkane dehalogenase (EC 3.8.1.5) and a fluorescence pH indicator on the tip of an optical fiber. Haloalkane dehalogenase catalyzes hydrolytic dehalogenation of halogenated aliphatic hydrocarbons, which is accompanied by a pH change influencing the fluorescence of the indicator. The pH sensitivity of several fluorescent dyes was evaluated. The selected indicator 5(6)-carboxyfluorescein was conjugated with bovine serum albumin and its reaction was tested under different immobilization conditions. The biosensor was prepared by cross-linking of the conjugate in tandem with haloalkane dehalogenase using glutaraldehyde vapor. The biosensor, stored for 24 h in 50 mM phosphate buffer (pH 7.5) prior to measurement, was used after 15 min of equilibration, the halogenated compound was added, and the response was monitored for 30 min. Calibration of the biosensor with 1,2-dibromoethane and 3-chloro-2-(chloromethyl)-1-propene showed an excellent linear dependence, with detection limits of 0.133 and 0.014 mM, respectively. This biosensor provides a new tool for continuous in situ monitoring of halogenated environmental pollutants.     

Development of metrology for pH measurement in Thailand

It has not been long that metrology is well accepted as an important part in analytical chemistry since it helps the chemists to receive the best measurement and accurate results with traceability. The National Institute of Metrology Thailand (NIMT), which is a public agency under the supervision of the Ministry of Science and Technology, not only focuses on physical standards but also provides and maintains standards in chemical field. pH measurement is one of the most widely used in the laboratories including industries and medical area in Thailand. The chemical laboratory starts working on the project with the objective of disseminating an accurate result in routine pH measurement. In 2002, the laboratory provided a service in calibration of pH meter and organized the first local interlaboratory comparison program (NIMT–C-ILC-1: pH buffer) in pH measurement. There were three buffer solution samples in the range of acid, neutral, and base. A total of 44 laboratories participated in this program. The NIMT chemical laboratory also participated in the proficiency testing program that was conducted by PSB Corporation Testing Group in Singapore. In 2003, NIMT started research in preparation of secondary buffers by using highly accurate pH meters with glass electrode systems. The laboratory produced three secondary buffers, which were pH 4.01, 6.86, and 9.18 with uncertainty 0.020 pH at 25°C. The competence of the laboratory was shown by the measurement results of the pilot study (APMP.QM-P06), which was organized by the APMP electrochemical analysis working group (EAWG/TCQM) in 2005. The title of this study was “pH determination of two phosphate buffers by Harned cell method and glass electrode method”. NIMT aims to achieve for establishment of the primary method for pH measurement in the near future. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA     

An Evaluat Ion of the Performance of the Nitrate-Selective Electrode

Abstract

The performance of the Orion nitrate-selective electrode has been evaluated with respect to its working range, accuracy, precision, response time, and memory. The effects of temperature, type of reference electrode, and mode of operation have also been considered. The device makes possible the measurement of free nitrate activity with about the same accuracy as standard colorimetric methods, but with about the same ease as a pH measurement.     

Improved reliability of pH measurements

Measurements of pH are performed on a large scale at laboratory level, and in industry. To meet the quality-control requirements and other technical specifications there is a need for traceability in measurement results.The prerequisite for the international acceptance of analytical data is reliability. To measure means to compare. Comparability entails use of recognised references to which the standard buffer solutions used for calibration of pH meter-electrode assemblies can be traced.The new recommendation on the measurement of pH recently published as a provisional document by the International Union on Pure and Applied Chemistry (IUPAC) enables traceability for measured pH values to a conventional reference frame which is recognised world-wide. The primary method for pH will be described.If analytical data are to be accepted internationally it is necessary to demonstrate the equivalence of the national traceability structures, including national measurement standards. For the first time key comparisons for pH have been performed by the Consultative Committee for Amount of Substance (CCQM, set up by the International Bureau of Weights and Measures, BIPM) to assess the equivalence of the national measurement procedures used to determine the pH of primary standard buffer solutions. The results of the first key comparison on pH CCQM-K9, and other international initiatives to improve the consistency of the results of measurement for pH, are reported.     

Determination of Hg from Cu concentrates by X-ray fluorescence through preconcentration on polyurethane foam

A methodology was developed for the separation and determination of microamounts of mercury from copper concentrate samples by wavelength dispersive X-ray fluorescence (WDXRF) after solid-phase extraction of mercury from iodide medium using polyurethane foam (PUF). The best sorption conditions for the Hg-KI-PUF system were settled using X-ray fluorescence technique after collection of ground PUF on a filter paper by vacuum filtration and direct measurement of the intensity signal of the sorbed mercury on PUF. The main parameters of sorption such as iodide concentration, pH, shaking time and sample dilution effect were studied. The system shows rapid kinetic sorption and maximum X-ray intensity signal was achieved after shaking for 2 min a 0.01 mol l⁻¹ iodide solution containing microamounts of mercury in the pH range from 1.0 to 9.0. Effective sorption up to a volume of 0.9 l allows preconcentration of mercury. A linear fit up to 50 μg mercury was obtained by the plot of the initial mercury mass in the bulk solution (0.5 l) vs. its respective XRF intensity signal measurement on ground PUF after the sorption process. The calibration sensitivity, quantification and detection limits found were 9.09 CPS μg⁻¹, 9.0 and 2.7 μg, respectively. The sorption of many elements was also evaluated under the best conditions. High concentrations of Cu(II) and Fe(III) interfere seriously. Mercury-selective separation could be achieved using citrate or EDTA as masking agent; no interference due to copper matrix samples was observed in citrate medium. This methodology was evaluated by recovery for mercury determination in copper concentrate ore samples supplied by a mining industry and copper sulfate salts; the results were between 98% and 106%.     

Neutron activation analysis of water and waste

The neutron activation method has been applied to the determination of Ag, Cd, Co, Cr, Cu, Fe, Hg, Mo, Se and Zn in waters and wastes. The method involves decomposition of organic substances by ozonation, preconcentration of elements to be determined by coprecipitation with thionalide at pH 9 or sorption on Dowes 1×2 loaded with 8-hydroxyquinoline-5-sulfonic acid at pH 7, irradiation of the concentrate, radiochemical separation of the respective radioisotopes and gamma spectrometric measurement of the activity. Accuracy and precision of the determination have been evaluated.     

Improving the quality of potentiometric pH measurements

Like all experimentally determined physical and chemical properties, pH measurements are affected by the limited precision and accuracy of the measurement procedures. Fundamental studies of pH standards, based on measurement of the potential of an electrochemical cell without transference, known as the Harned cell, containing a platinum–hydrogen electrode and a silver–silver chloride reference electrode, indicate that vapour condensation phenomena on potentiometric cell walls not immersed in the thermostatic bath are a major source of error in assessment of pH values. In this work a study was conducted on phthalate buffer, 0.05 mol kg⁻¹ KHPhth, and results are reported for the effect of this phenomenon on the assignment of pH values and on their corresponding uncertainties. Identification and quantification of this effect constitute an original contribution to improvement of the primary method of pH measurement and, therefore, more rigorous pH (PS) values.     

Determination of the pH of binary mobile phases for reversed-phase liquid chromatography

The measurement of pH in chromatographic mobile phases has been a constant subject of discussion during many years. The pH of the mobile phase is an important parameter that determines the chromatographic retention of many analytes with acid-base properties. In many instances a proper pH measurement is needed to assure the accuracy of retention-pH relationships or the reproducibility of chromatographic procedures. Three different methods are common in pH measurement of mobile phases: measurement of pH in the aqueous buffer before addition of the organic modifier, measurement of pH in the mobile phase prepared by mixing aqueous buffer and organic modifier after pH calibration with standard solutions prepared in the same mobile phase solvent, and measurement of pH in the mobile phase prepared by mixing aqueous buffer and organic modifier after pH calibration with aqueous standard solutions. This review discusses the different pH measurement and calibration procedures in terms of the theoretical and operational definitions of the different pH scales that can be applied to water-organic solvent mixtures. The advantages and disadvantages of each procedure are also presented through chromatographic examples. Finally, practical recommendations to select the most appropriate pH measurement procedure for particular chromatographic problems are given.     

Adsorptive potentiometric stripping analysis of trace tamoxifen at a glassy carbon electrode

A highly sensitive adsorptive stripping procedure for trace measurement of the anticancer drug tamoxifen is described. The method is based on controlled adsorptive accumulation of the drug at an electrochemically treated glassy carbon electrode, followed by chronopotentiometric measurement of the surface species. The chronopotentiometric operation effectively addresses the large background contribution inherent to the glassy carbon electrode to yield a detection limit of 4 x 10(-10) M after 4 min preconcentration. The adsorptive stripping response is evaluated with respect to electrode type and conditioning, accumulation potential and time, stripping current, pH, drug concentration, potential interferences, and other variables. Applicability to urine samples is illustrated.     

Effects of dissolved state of aminoalkyl methacrylate copolymer E/HCl on solubility enhancement effect for poorly water-soluble drugs

Eudragit® E/HCl salt (E–SD) displays a good antireprecipitation effect on solid dispersion formulations of poorly water-soluble drugs. To elucidate the mechanism underlying the antireprecipitation effect of E–SD, a study on supersaturation was conducted using a dissolution test method with test fluids at varying pH and ionic strength values. Both pH and ionic strength of the test fluid were shown to influence the antireprecipitation effect of E–SD; a strong antireprecipitation effect was observed at a neutral pH (pH?6～7) and an ionic strength of 0.1 to 1.0. To investigate E–SD in its dissolved state in each test fluid, fluorescence measurement using pyrene as a probe molecule and dynamic light-scattering (DLS) measurement were conducted. The total fluorescence intensity of pyrene increased with increasing E–SD concentrations. Further, small nanoparticles were observed using DLS measurement. These results suggest that E–SD may form a micelle-like structure in the dissolved test fluid.     

Medium-throughput pKa screening pharmaceuticals by pressure-assisted capillary electrophoresis

A fast screening method for the determination of the dissociation constants (pKa) of acidic, basic, and multivalent compounds was developed by using pressure-assisted capillary electrophoresis (PACE). External air pressure was applied to shorten the analysis time. The separation efficiency decreases as air pressure increases. However, it was found that air pressure does not affect the measurement of electrophoretic mobility and pKa significantly when it is less than 2 psi. The method was evaluated in terms of accuracy, precision, and ruggedness by using a set of 48 compounds with literature pKa values ranging from 2 to 10. The difference between the measured pKa values and literature values is less than 0.2 units. The throughput is approximately 20 compounds per day with a 12-point measurement ranging from pH 2.5 to 11. It was demonstrated that this method is applicable for pKa screening of pharmaceuticals with diverse chemical structures.