Automated potentiometric analysis with selective electrodes

An automated potentiometric analyzer based on a residual-chlorine electrode has been developed that can determine chlorine concentrations of a 4–75 ppb (±2 ppb, standard deviation 0.6–1.9 ppb). A microcomputer-controlled digital buret delivers a predetermined number of aliquots of standard, and the electrode measures the potential of the test solution after each addition. An arithmetic processing unit transforms the acquired potentiometric data to the Gran (antilog) domain; the microcomputer then calculates a set of equivalence-point estimates and, using an error function criterion, selects the best estimate. The instrument includes a digital buret, 8080 microcomputer, arithmetic processing unit, real-time clock, video display, and 16-character key pad; it uses a modified version of the computer language BASIC compiled and programmed into Programmable Read-Only Memory (PROM). Although this system was designed to assay residual chlorine in water, the analyzer can also function as a digital pH (or millivolt) meter or, with minor software modifications, serve as a general-purpose instrument using any appropriate electrode system.     

A simple automatic system using the HP-85 microcomputer for programmed potentiometric titration

A simple way of constructing an automatic titration system is proposed, based on combination of a digital pH-meter and an automatic burette with an HP-85 microcomputer. An inexpensive interface unit based on a MOTOROLA 6800 has been developed, which permits communication of the computer with the pH-meter and the burette. The system constructed is very flexible and can find wide application in potentiometric titration and direct potentiometry with different kinds of ion-selective electrodes.     

Rapid automatic potentiometric method for analytical control in the manufacture of extraction phosphoric acid

A rapid automatic method for determination of free sulphuric acid in the manufacture of extraction phosphoric acid from apatite has been developed. It is based on potentiometric titration combined with the Gran approach for linearization of the titration curve. The analysis is done with an automatic potentiometric titrator controlled by an HP-85 microcomputer. BASIC software activates the system to perform the data acquisition and calculations, and the whole operation takes only 7-8 min.     

Applications of in situ detection with an auto-mated micro batch analyzer

A new batch-type microscale liquid-phase analyzer, called an automated micro batch analyzer (a.m.b.a.), is introduced. The reaction chamber, a 1500-μl capacity polypropylene microcentrifuge tube, is equipped with conductometric, potentiometric, fluorimetric and spectrophotometric sensors. The sample is loaded into a loop injector and blown into the reaction chamber by compressed gas. Various reagents are delivered to the chamber from pneumatically pressurized reservoirs equipped with inexpensive high-speed valves in the liquid-delivery lines. The valves are under microcomputer control and highly precise microliter aliquots can be delivered by controlling valve on-times. Examples illustrated include acid-base, precipitation and compleximetric titrations with the conductometric sensor; acid-base titrations with the potentiometric sensor; determination of hydrogen peroxide with the fluorimetric sensor; and acid-base titrations, studies of metal/ligand complexation, standrd addition, liquid-liquid extraction and distillation of volatile analytes with the spectrophotometric sensor.     

亚碘酰苯低聚物的结构与振动光谱18O-同位素效应的理论研究

应用LDA-PWC方法对亚碘酰苯低聚物HO-(PhIO)n-H (n＝1～10)(链末端以羟基结束)共10个模型分子进行了理论研究. 计算结果表明PhIO分子链大致呈“T”形, I—O链的两个I—O键键长非常接近, 同时发现I—O链产生扭转, 整个亚碘酰苯低聚物呈螺旋状结构. 应用B3LYP法得到HO-(PhIO)6-H更为精确的亚碘酰苯低聚物稳定构型, 平均I—O键长为0.2089 nm, 标准偏差为0.0007 nm. 理论计算表明在600～400 cm－1段, PhI18O的吸收峰向低波数方向移动, 与实验观测结果一致. 振动模式分析发现该段吸收峰均涉及氧原子, 18O同位素效应将降低各振动峰值的频率. 峰值移动最大的吸收峰为591/566 cm－1 (16O/18O), 与之对应的理论计算值为590.409/557.788 cm－1 (16O/18O), 属于对称伸缩振动ν(I—O—I). 吸收峰(443/436 cm－1)对应的理论计算值为460.627/439.158 cm－1 (16O/18O), 归属于不对称伸缩振动ν(I—O—I).     

Computerized flow injection potentiometric stripping analysis with large-volume wall-jet cell

Summary A microcomputer system for flow injection potentiometric stripping analysis is presented permitting fast digital recording of potential time-curves. A large-volume wall-jet cell simple in design has been used as detector cell. Investigations about the influence of electrode pretreatment and solution delivery mode (i.e. gravity flow, pumping) reveal the strong influence of these parameters on the magnitude and precision of stripping times. The optimized system was applied to the simultaneous determination of cadmium and lead in geological samples.

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Computerisierte Potentiometrische Stripping Analyse in einem Fließinjektionssystem mit großvolumiger Wall-jet Zelle

     

DETERM INATION OF THE STABILITY CONSTANTS OF COMPLEXES OF HISTIDINE,SOME DIPEPTIDES AND TRIGLYCINE WITH Zn(Ⅱ)AND Cd(Ⅱ)USING SMALL-SCALE PH-METRIC TITRATIONS

A potentiometric study on the complexes of His,Gly-His,ALa-His,Gly-Gly andGly—Gly—Gly with Zn(Ⅱ)and Cd(Ⅱ)has been reported.Small-scale potentiometric titrations were car-ried out to determine stabil ity constants of complexes at 25℃ with I=0.10 mol dm~(-3)(KNO_3).The com-puter programs SUPERQUAD were applied for data treatment with satisfactory results.     

Reinvestigation on the Reaction of Salicylic Chloride with Salicylic Amide and X-ray Crystal Structure of a New Macrocyclic Polyester

1 INTRODUCTION In the systematic studies on the synthesis, structure and recognition of macrocyclic phospho- ramidate containing biaryl oxadiazole[1, 2], we need to synthesize benzoxazines. Lattmann reported that the salicylic chloride reacts with salicylic amide at 170℃ to give 2-(2-hydroxyphenyl)benzo[1,3]- oxazine-4-one[3]. However, Palazzo got bisamide 1 in 90% yield under similar conditions[4]. Titherley reported that amides of type 1 underwent cycli- zation to benzoxazines if hea…     

Development of a microprocessor-based electrochemical instrument interfaced to a microcomputer system for differential-pulse stripping voltammetry in different time domains

An inexpensive, compact microprocessor-based instrument for polarographic and voltammetric analysis has been developed for use in chemically hazardous laboratories, radiation laboratories or clean laboratories. This low-cost unit controls the experiment, collects the data and can be regarded as expendable. The microprocessor-based instrumentation is interface to a microcomputer system, which is external to the laboratory and has all the required peripherals associated with larger laboratory computers. In this institution, four laboratories having the inexpensive microprocessor systems are linked to the larger microcomputer which is housed in an air-conditioned room better suited for computers. A new approach to data collection and evaluation using different time domains in differential-pulse stripping voltammetry is presented as an example of the use of such instrumentation.     

Applications,involving the iodide ion: VIII. Direct and indirect determination of mercury(I) and analysis of mixtures. Analysis of chromium(VI)-chromium (III) mixtures. Determination of hypochlorite

Mercury(I), down to 3 ppm, has been accurately determined by direct titration with iodide or by back-titrating excess of iodide with mercury (II) using silver amalgam as the indicator electrode. The direct method and additional volumetric ones were applied to the rapid analysis of various mixtures involving mercury(I) with fair accuracy and precision. Analysis of Cr(VI)-Cr(III) mixtures involved potentiometric back-titration of excess iodide and of excess EDTA separately with mercury(II). Back-titration of excess iodide was successfully applied to the determination of hypochlorite.     

The automatic interlocking system of electron absorbed dose monitoring and irradiation process control

The paper describes the real time computer control system used for monitoring and control parameters of the electron irradiation facility. The process control is achieved through the control system made up of a personal computer, three I/O boards and an ISA interface board. The improved bipartition transport theory has been applied to calculate the absorbed dose of low energy electron. The experimental results proved that the dose control precision of the system has been greatly raised, and the other performance indexes have been obviously improved. This interlocking system may be used for dose monitoring and process control in BB radiation processing.     

A dimeric titanium-containing polyoxometalate. Synthesis, characterization, and catalysis of H2O2-based thioether oxidation

The previously unknown titanium(IV)-containing mu-hydroxo dimeric heteropolytungstate (Bu4N)7[(PTiW11O39)2-OH] (TBA salt of H1) has been synthesized, starting from H5PTiW11O40, and characterized by elemental analysis, multinuclear (31P, 17O, 183W) NMR, IR, FAB-MS, cyclic voltammetry, and potentiometric titration. 31P NMR reveals that H1 (delta -12.76) readily forms in MeCN from the Keggin monomer (POM), PTiW11O40(5-) (2, delta -13.34), upon the addition of 1.5 equiv of H+, via the protonated species, P(TiOH)W11O39(4-) (H2, delta -13.44). The ratio of H1, 2, and H2, which are present in equilibrium in MeCN solution at 25 degrees C, depends on the concentration of both H+ and H2O. The Ti-O-Ti linkage readily reacts with nucleophilic reagents, such as H2O and ROH, to yield monomeric Keggin derivatives. mu-Hydroxo dimer H1 shows higher catalytic activity than 2 for thioether oxidation by hydrogen peroxide in acetonitrile. The reaction proceeds readily at room temperature and affords the corresponding sulfoxide and sulfone in ca. quantitative yield. The addition of H2O2 to H1 or H2 results in the formation of a peroxo complex, most likely the hydroperoxo complex P(TiOOH)W11O39(4-) (I), which has 31P NMR resonance at -12.43 ppm. The rate of the formation of I is higher from H2 than from H1. When H1 is used as a catalyst precursor, the rates of the thioether oxidation and peroxo complex formation increase with increasing H2O concentration, which favors the cleavage of H1 to H2. H2O2 in MeCN slowly converts 2 to another peroxotitanium complex, P(TiO2)W11O39(5-) (II), which has 31P NMR resonance at -12.98 ppm. Peroxo complexes I and II differ in their protonation state and interconvert fast on the 31P NMR time scale. Addition of 1 equiv of H+ completely converts II to I, while 1 equiv of OH- completely converts I to II. 31P NMR confirms that I is stable under turnover conditions (thioether, H2O2, MeCN). Contrary to two-phase systems such as dichloroethane/aqueous H2O2, no products resulting from the destruction of the Keggin POM were detected in MeCN in the presence of H2O2 (a 500-fold molar excess). The reactivity of I, generated in situ from II by adding 1 equiv of H+, toward organic sulfides under stoichiometric conditions was confirmed using both 31P NMR and UV-vis spectroscopy. This is a rare demonstration of the direct stoichiometric oxidation of an organic substrate by a titanium peroxo complex.     

Potentiometric Determination of Non‐Ionic Surfactants by Liquid Membrane Electrodes

It is well known that non‐ionic surfactants (NIS) influence remarkably the potentiometric measurements with liquid membrane ion selective electrodes (ISEs), interfering particularly on performance of ISEs for earth‐alkali metals, for which the loss of selectivity with regard to alkali metals has been documented. These studies indicate that such interferences are due to the extraction of surfactants within the membrane, where a competition takes place between the originally present ionophore and the surfactant which also acts as a ligand for alkali metals. The interpretation of such phenomena enabled one to exploit this interference for analytical purposes by membrane/solution extraction experiment monitored by UV measurements and by impedance FRA analysis on coated wire electrodes. Using Ca/Mg ISEs based on the neutral ionophore ETH 4030, it has been established that the logarithm of the Ca/Mg over Na potentiometric selectivity constant is linearly correlated with the concentration of NIS like Tegopren 5863 and Triton X‐100. The proposed method has been applied for the development of a new potentiometric analytical procedure for the determination of Tegopren 5863 in synthetic seawater (SSW), ranging from 0.25 to 5 ppm. Our procedure consists in the exposure of the electrode to stirred SSW containing the surfactant; the progressive extraction of Tegopren 5863 causes a growth in electrode's sensitivity to Na⁺ and K⁺, losing selectivity for Ca²⁺ and Mg²⁺. In turn this induces an increase of EMF, as all these ions are present in the studied matrix. The potential drift was monitored for 15 hours, showing that the process reaches thermodynamic equilibrium after about 12 hours of exposure. This method presents a value of 210 ppb of Tegopren 5863 as detection limit.     

Polar symmetry and intercalation of new multilayered hybrid molybdates: [M2(pzc)2(H2O)x][Mo5O16] (M = Co, Ni)

The layered molybdate [M2(pzc)2(H2O)x][Mo5O16] (I: M = Ni, x = 5.0; II: M = Co, x = 4.0; pzc = pyrazinecarboxylate) hybrid solids were synthesized via hydrothermal reactions at 160-165 degrees C. The structures were determined by single-crystal X-ray diffraction data for I (Cc, Z = 4; a = 33.217(4) A, b = 5.6416(8) A, c = 13.982(2) A, beta = 99.407(8) degrees , and V = 2585.0(6) A3) and powder X-ray diffraction data for II (C2/c, Z = 4; a = 35.42(6) A, b = 5.697(9) A, c = 14.28(2) A, beta = 114.95(4) degrees , and V = 2614(12) A3). The polar structure of I contains new [Ni2(pzc)2(H2O)5]2+ double layers that form an asymmetric pattern of hydrogen bonds and covalent bonds to stair-stepped [Mo5O16]2- sheets, inducing a net dipole moment in the latter. In II, however, the [Co2(pzc)2(H2O)4]2+ double layers have one less coordinated water and subsequently exhibit a symmetric pattern of covalent and hydrogen bonding to the [Mo5O16]2- sheets, leading to a centrosymmetric structure. Thermogravimetric analyses and powder X-ray diffraction data reveal that I can be dehydrated and rehydrated with from 0 to 6.5 water molecules per formula unit, which is coupled with a corresponding contraction/expansion of the interlayer distances. Also, the dehydrated form of I can be intercalated by approximately 4.3 H2S molecules per formula unit, but the intercalation by pyridine or methanol is limited to less than one molecule per formula unit.     

Crystal Structure of Dimeric Units Cd2（ncpo）2（phen）2（H2O）2 Constructed by Flexible Dicarboxylic Acid with Fluorescent Emission

A dimeric coordination complex Cd2（ncpo）2（phen）2（H2O）2 was constructed by a flexible dicarboxylic acid, 2-nitro-4-carboxylphenoxyacetic acid. Its crystal structure was determined by X-ray single-crystal diffraction analysis. The crystal is of monoclinic system, space group P21/n with a = 17.2616（3）, b = 12.7460（2）, c = 18.4041（3） A^°, β= 94.432（1）°, C42H30Cd2N6O16, Mr = 1099.52, V = 4037.09（12）A^°^3 Dc = 1.809 g/cm^3, F（000） = 2192, μ = 1.139 cm^-1 and Z = 4. The final R = 0.0218 and wR = 0.0703 for 8288 observed reflections with I 〉 2σ（I）. There are two crystallographically independent but structurally very similar molecules in the unit cell of the title complex. It is noticeable that the ligand ncpo^2- displays a good flexibility, demonstrating different modes from the rigid ligands. The luminescence property has been investigated, which shows photoluminescence at 465, 490 and 574 nm upon excitation at 320 nm in the solid state at room temperature.     

High-resolution photoelectron spectroscopy through deconvolution

A new iterative deconvolution algorithm for the development of very high resolution Hc(I)-excited photoelectron spectra of gases is presented. The algorithm accepts as input a medium-resolution spectrum and an instrument function obtained by scanning intrinsically narrow line (e.g. the Ar²P_3/2 line) under conditions identical to those used to acquire the medium resolution spectrum. The deconvolved partial spectrum of an O₂H₂O mixture is presented as a test case prior to presentation of results for three nitrogen lines. For comparison purposes directly obtained high-resolution spectra of the nitrogen lines are included. The shapes of the nitrogen lines are discussed within the framework of a one-center expansion theory of photoionization. The conditions under which deconvolution can be profitably applied are briefly discussed and an attempt is made to establish the deconvolution (contrary to still popular belief) is not in any way equivalent to curve fitting.     

Valgran, a program for potentiometric titrations with a versatile automatic modular system

A very flexible modular system for use with a portable IBM PC for potentiometric titrations is described. The appropriate software has been developed in order to obtain automatic end-points, and conventional, first-derivative, second-derivative and Gran curves, as well as a listing of the potentiometric points expressed in different ways. All these alternatives are selectable on menu presentations. The potentiometric system has been applied both the research and routine problems.     

Synthesis and Crystal Structure of Spiro[1-bromo-4- methoxy-5-oxa-6-oxo-bicyclo[3.1.0]hexane-2,2''-(3''- cyclohexanoxy-4''-methoxybutyrolactone]

The crystal of the title compound 6 has been prepared and determined by X-ray diffraction analysis. It belongs to the orthorhombic system, space group P212121 with a = 10.195(2), b = 11.955(2), c = 14.335(3)(A), C16H21BrO7, Mr = 405.24, V = 1747.0(6) (A)3, Z = 4, Dc = 1.541 g/cm3, μ = 2.387 mm-1, F(000) = 832, R = 0.0266 and wR = 0.0348 for 2110 observed reflections with I > 2σ(I). The crystal exhibits a characteristic spiral structure consisting of one cyclopropane and two butyrolactones with envelope configuration. The intermolecular hydrogen bond between C(16)- H(16)…O(1) and C(3)-H(3)…O(2) has been observed in the crystal lattice.     

Determination of free nitrilotriacetic acid in environmental water samples by ion chromatography with potentiometric and amperometric detection with a copper electrode

An ion-chromatographic method is described for the analysis of free nitrilotriacetic acid in water samples. Separations are achieved on a polymer-based anion-exchange column with 6 mM nitric acid as eluent. Both potentiometric and amperometric detection have been applied using metallic copper as the indicator electrode. Detection limits are at about 500 ng injected in the potentiometric mode and 100 ng in the amperometric mode. On-line sample preconcentration is possible for volumes up to 2 ml of river water samples. The response of the detector to other aminopolycarboxylic and aminopolyphosphonic acids has been investigated.     

Determination of the total acidity in soft drinks using potentiometric sequential injection titration

A potentiometric SI titration system for the determination of total acidity in soft drinks is proposed. The concept is based on the aspiration of the acid soft drink sample between two base zones into a holding coil with the volume of the first base zone twice to that of the second one and channelled by flow reversal through a reaction coil to a potentiometric sensor. A solution of 0.1 mol l⁻¹ sodium chloride is used as ionic strength adjustment buffer in the carrier stream. The system has been applied to the analysis of some South African soft drinks having a total acidity level of about 0.2–0.3% (w/v). The method has a sample frequency of 45 samples per h with a linear range of 0.1 and 0.6% (w/v). It is easy to use, fully computerised, and gives the results that are comparable to both automated batch titration and manual titration.