Application of a multichannel dropping dispenser in segmented continuous flow analysis.

A simple dual channel dropping dispenser has been used for the simultaneous introduction of aqueous solutions of sample and reagent directly into a continuous flow of an organic solvent. Each aqueous segment forms an enclosed reaction system, completely surrounded by a film of the organic phase, which prevents any carry over between segments. An analytical signal is measured directly on the moving segments of precisely defined volumes of the homogenized reaction mixture. The applicability of this "microbatch" technique for the determination of light-absorbing species, for sample dilution and one-standard calibration, and for providing acid-base titrations on a microlitre scale is demonstrated with simple examples.

Comparison of segmentors for liquid-liquid extraction flow-injection analysis.

The segmentation of two immiscible solvents in a continuous liquid-liquid extraction flow system has been studied with a computer-controlled photometric detection system (resolution time approximately 3 msec). The T-shaped segmentors tested were made of fluoroplastic, glass (A4-T fitting) and a modified glass (A8-T fitting). The modified A8-T fitting gave the most repeatable segmentation (rsd approximately 2%).

Studies of two-phase equilibria by liquid-liquid segmented flow extraction of dithiocarbamic acids into various solvents.

A method for the study of two-phase equilibria by extraction in liquid-liquid segmented flow is presented. The main advantage of the method is the very rapid equilibration achieved. In many cases a contact time of 5 sec is sufficient. By performing the measurements needed on-line with the extraction the total residence time of a substance studied in the system can be kept below 10 sec. This makes it possible to study two-phase equilibria of moderately unstable compounds. Other advantages are the semi-enclosed design, which minimizes contact with solvent fumes and increases the speed of operation after the system has been set up. The system has been used for a study of the two-phase equilibria of dithiocarbamic acids. The dithiocarbamates are often used for the separation and preconcentration of metals, and co-extraction of the reagent can cause severe interference in the final determination. By means of the extraction constants presented, the extraction of diethyldithiocarbamic acid and pyrrolidine-dithiocarbamic acid into Freon 113, carbon tetrachloride, methyl isobutyl ketone and chloroform can be estimated.

Polycrystalline and monocrystalline antimony, iridium and palladium as electrode material for pH-sensing electrodes.

Different ways of making pH-sensing electrodes from monocrystalline or polycrystalline antimony, iridium and palladium have been investigated. Monocrystalline antimony and iridium are superior to the polycrystalline elements with respect to reproducibility between electrodes and stability of the electrode potential over long periods of time. No good palladium/palladium oxide electrode could be obtained by electrochemical oxidation and the thermal preparation method could not take advantage of the properties of the monocrystalline palladium. Therefore, only polycrystalline palladium was used to study this type of electrodes. The different electrodes were compared with respect to the manner of preparation, the pH-response (reproducibility and time response) and the effect that different complexing ligands present in the measuring solutions may have on the electrode response. Also, the redox-response of the electrodes and the effect of different oxygen pressures on the electrode potentials were studied. The monocrystalline antimony electrodes have the best reproducibility and long-term stability but also respond to complexing ligands and to variations in the oxygen pressure. Monocrystalline iridium electrodes can be obtained by continuously cycling the potential between -0.25 and +1.25 V (SCE) in 0.5M sulphuric acid. They do not respond to the complexing ligands tested, and have fairly good long-term stability, but the reproducibility between electrodes is inferior to that of the monocrystalline antimony electrodes. Polycrystalline antimony and iridium electrodes were inferior to the monocrystalline ones. The properties of the palladium electrodes were similar to those of the iridium ones.

A photometric study of the complexation reaction between Alizarin complexan and zinc(II), nickel(II), lead(II), cobalt(II) and copper(II).

The complexation reaction between Alizarin complexan ([3-N,N-di(carboxymethyl)aminomethyl]-1,2-dihydroxyanthraquinone; H(4)L) and zinc(II), nickel(II), lead(II), cobalt(II) and copper(II) has been studied by a spectrophotometric method. All these metal ions form 1:1 complexes with HL; 2:1 metal:ligand complex were found only for Pb(II) and Cu(II). The stability constants are (ionic strength I = 0.1, 20 degrees C): Zn(2+) + HL(3-) right harpoon over left harpoon ZnHL(-) log K +/- 3sigma(log K) = 12.19 +/- 0.09 (I = 0.5) Ni(2+) + HL(3-) right harpoon over left harpoon NiHL(-) log K +/- 3sigma(log K) = 12.23 +/- 0.21 Pb(2+) + HL(3-) right harpoon over left harpoon PbHL(-) log K +/- 3sigma(log K) = 11.69 +/- 0.06 PbHL(-) + Pb(2+) right harpoon over left harpoon Pb(2)L + H(+) log K approximately -0.8 Co(2+) + HL(3-) right harpoon over left harpoon CoHL(-) log K 3sigma(log K) = 12.25 + 0.13 Cu(2+) + HL(3-) right harpoon over left harpoon CuHL(-) log K 3sigma(log K) = 14.75 +/- 0.07 Cu(2+) + CuHL(-) right harpoon over left harpoon Cu(2)L + H(+) log K approximately 3.5 The solubility and stability of both the reagent and the complexes and the closenes of the values of the stability constants make this reagent suitable for the photometric detection of several metal ions in the eluate from an ion-exchange column.

Automatic lactate determination by flow injection analysis.

Flow injection analysis has been used to determine lactate in precipitated serum samples employing the NADH-LDH method. The method is suitable for determinations in the concentration range 0.2-20 mmoles per litre of lactate. The procedure has been tested against a manual routine procedure and the results were in good agreement.

Effects of some complex-forming ligands on the potential of antimony pH-sensors.

The E vs. pH relationship for oriented monocrystalline antimony electrodes was studied in various ionic media, containing no buffer or one of several common buffer substances, and the stability of the electrode potential with time was investigated. Several makes of commercially available polycrystalline antimony electrodes were also studied. The results indicate that tris(hydroxymethyl)aminomethane may be used for calibration of antimony electrodes, but most other commonly used buffer substances, e.g., orthophosphate, yield erroneous results. Monocrystalline antimony electrodes are preferable to polycrystalline ones, especially when measurements are made in unstirred solutions. The long-term stability of monocrystalline electrodes is superior to that of polycrystalline ones.

Potentiometric studies on the complex formation between methylmercury(II) and some keto- and amino-carboxylic acids.

The protonation of pyruvic and laevulinic acid, l-serine, l-cysteine, l-methionine and l-asparagine, and their complex formation with methylmercury(II) ions, have been studied by a potentiometric method, in 1.0M sodium nitrate medium at 25 degrees . The protonation and equilibrium constants were evaluated by using the computer program LETAGROP-ETITR. The limitations of the experimental method are explained. The participation of different functional groups of the ligands in binding methylmercury(II) and the biological significance of the complex formation are discussed.

Ion-pair extraction of Na(+), K(+) and Ca(2+) with some organic counter-ions and dicyclohexyl-18-crown-6 as adduct-forming reagent.

Extraction equilibria of ion-pairs formed by the Na(+), K(+) and Ca(2+) complexes of dicyclohexyl-18-crown-6 and beta- and gamma-dinitrophenol, picric acid and dipicrylamine have been studied in the two-phase system H(2)O/CH(2)Cl(2). Extraction constants and dissociation constants for the ion-pairs in the organic phase are given and show that the efficiency of extraction increases with the hydrophobicity of the counter-ion. At the same time, the selectivity decreases.

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-III Presentation of a fully automatic titration apparatus and of results supporting the theories given in the preceding parts.

This paper forms Part III of a series in which the first two parts describe methods for evaluating titrations performed by stepwise addition of equal volumes of titrant. The great advantage of these methods is that they do not require an accurate calibration of the electrode system. This property makes the methods very suitable for routine work. e.g., in automatic analysis. An apparatus for performing such titrations automatically is presented. Further, results of titrations of monoprotic acids, a diprotic acid, an ampholyte, a mixture of an acid with its conjugate base, and mixtures of two acids with a small difference between the stability constants are given. Most of these titrations cannot be evaluated by the Gran or Hofstee methods but yield results having errors of the order of 0.1% if the methods proposed in Parts I and II of this series are employed. The advantages of the method of stepwise addition of equal volumes of titrant combined with the proposed evaluation methods, in comparison with common methods such as titration to a preset pH, are that all the data are used in the evaluation, permitting a statistical treatment and giving better possibilities for tracing systematic errors.

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-IV Photometric titration of an acid.

In Part I of this series, evaluation methods for potentiometric titrations of acids performed by stepwise addition of titrant were introduced. These methods are non-approximative and may therefore in principle be applied to titrations of acids of any strength. This paper demonstrates that photometric titrations performed by stepwise addition of titrant may also be evaluated by the proposed methods. The photometric method is compared with the potentiometric method of monitoring the course of a titration.

Acid-base titrations by stepwise additions of equal volumes of titrant with special reference to automatic titrations-I Theory, discussion of the gran functions, the hofstee method and two proposed methods for calculating equivalence volumes.

The range of acid stability constants over which the Gran functions are applicable in evaluating acid-base titrations at normal concentrations is studied and found to be quite narrow. Alternatively, the titrations can be evaluated by using non-approximative methods based upon an equation that is derived without making the simplifying assumptions leading to the Gran functions. One such method, introduced by Hofstee, is discussed and the results of a study of the effects of a systematic error in the pH-determinations upon the determination of the equivalence volume are given. Two other non-approximative methods for evaluating acid-base titrations that are particularly suitable for use in automatic titrations of many similar samples are also described. These methods yield correct values of the equivalence volume regardless of a possible systematic error in the pH-values and are particularly useful for titrations of moderately strong and very weak acids (stability constants up to 10(10)-10(11) at 0.01M concentration) where the Gran functions cannot be used.

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-II Theory of titration of mixtures of acids, polyprotic acids, acids in mixture with weak bases, and ampholytes.

A general method for evaluating titration data for mixtures of acids and for acids in mixture with weak bases is presented. Procedures are given that do not require absolute [H]-data, i.e., relative [H]-data may be used. In most cases a very rough calibration of the electrode system is enough. Further, for simple systems, very approximate values of the stability constants are sufficient. As examples, the titration of the following are treated in some detail: a mixture of two acids, a diprotic acid, an acid in presence of its conjugate base, and an ampholyte.

Analysis of chromite by cation-exchange using ethylenediaminetetra-acetic acid.

A method for the separation and determination of five major elements in chromite ore (and chrome-bearing refractories), based on complexation of the metals with EDTA is described. After removal of silica, the cations are separated into two groups by passing the solution through a cation-exchange resin (Dowex 50W-X8, in Na-form) in the presence of an excess of the complexing agent. The optimum conditions for the separation are discussed on the basis of exchange constants that were either known or determined. The first group contains Cr and Fe, which emerge in the filtrate at pH between 1.5 and 2.1, whereas A1, Mg and Ca, which are adsorbed on the resin, form another group. Complexometric titrations are used for the subsequent determination of the cations in each group. The method is simpler and more rapid and accurate for routine analysis than the current methods.

Exchange constants of Al(III) and Fe(III) on Dowex 50W-X8.

The exchange constants tor Al(3+) and Fe(3+) ions on the cation-exchange resin Dowex 50W-X8 (H(+)-form) are reported. A batch method of equilibrium at room temperature was used to determine these constants, which are Al(3+) + 3HR right harpoon over left harpoon AIR(3) + 3H(+), K = 1.66 Fe(3+) + 3HR right harpoon over left harpoon FeR(3) + 3H(+), K = 2.19 R denoting the resin.

Calculation of stability constants from photometric data.

A method originally designed for the determination of stability constants by using a wedge calorimeter has been adapted to normal photometric measuring techniques. The calculations are simple and the method is especially suitable for use when the absorptivities of the absorbing species are unavailable because these species cannot be obtained alone in solution. Results of some determinations are given.

Photometric determination of aluminium with alizarin fluorine blue.

In order to decide whether Alizarin Fluorine Blue (alizarin complexan, 3-amino-methylalizarin-N,N-diacetic acid) is a suitable reagent for the spectrophotometric determination of aluminium, values of the stability constants for some reactions of this reagent with aluminium(III) and iron(III) have been determined spectrophotometrically in a medium containing 20 % dioxan and 80 % water at ionic strength 0.1. The values of the constants that were determined are log K(Al)(AlHL) = 14.3, log K(2Al)(Al2L) = 25.3 and log K(Fe)(FeHL) = 19.6. These results were employed in the design of a method for the spectrophotometric determination of aluminium in the presence of iron and titanium. The Sandell sensitivity is 0.01 mug/cm(2) and the coefficient of variation for 34 determinations was 0.9 %.

Fluorimetric method for the determination of uranium in natural waters.

A method is described for the fluorimetric determination of uranium in natural waters. The limit of detection is 0.3 ppM. Ion-exchange is used to preconcentrate the uranium by a factor of 22 and separate it from quenching ions in the sample. The fluorescence is measured in a medium that is 1.35M in both sulphuric and phosphoric acids. The uranyl ions are excited by radiation of wavelength 280 nm and bandwidth 40 nm. The emitted signal is scanned from 470 to 510 nm. After spiking of the sample solution with a small volume of standard uranium solution, the fluorescence signal is scanned again and the uranium content of the sample calculated from the two readings. The coefficient of variation is 8.5% for determinations of U in a synthetic water sample having a uranium content of 1.9 ppM. Destruction of organic matter in the eluates gives 0.1 ppM detection limit.