Direct fluorescent detection of chromatographically separated amino-acids by means of 9-isothiocyanatoacridines.

A new method is presented for fluorescent detection of amino-acids separated on silica gel R plates, by spraying with a 0.1% solution of 9-isothiocyanatoacridine derivatives in dichloromethane or benzene, heating and examining in ultraviolet light at 254 and 336 nm. This method is useful for routine analysis owing to its selectivity and sensitivity.

On the confidence interval of the equivalence point in linear titrations.

As the point of intersection in linear-branch titration curves results from two optimized linear regressions, calculated by least-squares from n(1) and n(2) pairs of values of the signal y as a function of the added volume of titrant upsilon, the value of the equivalence volume V(e) has the character of an estimated average V (e) hence a confidence interval is associated with it. If the point of intersection V (e) belongs concomitantly to both regressions then the same value of y (e) should correspond to the two extreme values V'(e) and V'(e) of the confidence interval as to V (e) itself. Consequently, the two segments of the confidence interval are obtained by averaging each of the two unequal segments of the separate confidence intervals. Alternatively, considering that multiple estimates of V (e) can be obtained, the confidence interval can be calculated from the normally distributed random variables Deltaa' and Deltab' of the two linear regressions.

Conductometric titration with indicating resistance--IV: the use of membranes with some organic and inorganic acids as active components, for HCl titration in a highly conducting medium.

Membranes consisting of a methyl polymethacrylate or collodion support containing sparingly soluble inorganic or organic acids can be used for end-point detection in acid-base titrations in high-conductivity media. The collodion + Na(3)[As(Mo(3)O(10))(4)].nH(2)O + Na-Alassion CS membrane is a very good conductometric sensor if given preliminary treatment to form molybdic acid. The conductivity jump with this membrane starts at pH approximately 7 and permits titration of strong acid down to 10(-4)M concentration in highly conducting medium. Similar membranes containing some organic acids such as benzoic, o-chlorobenzoic, and o-phthalic also behave as conductometric sensors, giving a conductivity change at a ph which depends on the dissociation constant of the organic acid used and on the way it interacts with the support and the conducting medium used.

Redox-sensitive membrane-electrode based on the organic free radical octachlorophenothiazinyl.

An electrode based on an organic free radical and sensitive to redox systems is described.

A statistical approach by serial correlation to assessment of stability of analytical systems.

The functional instability of infrared spectrometers can result in serious errors of analysis. This work shows that the stability can be tested by means of the serial correlation method, and the various causes of unstable conditions and equipment faults identified. Drift and large oscillations present separately or together can be detected by new statistics developed from the serial correlation method.

Utilization of an Hg(2+)-sensitive membrane-electrode in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+).

The paper reports the results obtained in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+) by using an Hg(2+)-sensitive membrane-electrode for the end-point indication. The determination of Bi(3+) and Fe(3+) is performed after addition of mercuric complexonate from which these cations release Hg(2+) by means of which the electrode senses the equivalence point. In the case of Cr(3+) an excess of complexone is added and the surplus is titrated with a standard solution of Hg(2+) in the presence of the Hg(2+)-sensitive membrane-electrode.

Pretreated bright palladium electrode in potentiometric redox titrations Titration of Cr(2)O(7)(2-) and Ce(4+) with Fe(2+).

The behaviour of the bright palladium electrode toward the redox systems Cr(2)O(7)(2-)/Fe(2+) and Ce(4+)/Fe(2+) (in potentiometric titration) has been investigated as a function of pretreatment of the electrode. Anodization of the electrode at potentials higher than 800 mV increases DeltaE at the equivalence point by 300-400 mV for the dichromate titration. The sharp change in potential is due to the reaction between PdO(2) and Fe(2+). The equivalence point corresponds to the beginning of the potential drop, rather than the inflexion point, especially for dilute solutions. If the electrode is ignited before use the surface oxide PdO is oxidized to PdO(2) by Cr(V), the potential increases during the titration and DeltaE is 200 mV bigger than when an untreated electrode is used. In the titration of Ce(4+) with Fe(2+) the DeltaE is largest with untreated electrodes, and if the anodized electrode is used, the titration curves clearly show the reaction between PdO(2) and Fe(2+).

Niederschlagsbildung-III Kristallwachstum und einfluss der fremdionenkonzentration in der bariumsulfatfällung.

The influence of foreign ions on the particle size of barium sulphate precipitates has been investigated by sedimentation experiments, establishing that NaCl, NaNO(3), KBr, KNO(3), and other salts at high concentrations powerfully hinder the growth of the crystals even at high supersaturation. The linear growth rate has been measured as a function of BaSO(4) concentration, foreign ion concentration and [BaCl(2)]/[K(2)SO(4)] ratio. Because the growth is already diffusion controlled at a fivefold supersaturation, the BaSO(4) precipitates will not undergo Ostwald ripening. A suitable apparatus has been devised for the investigations.

Studies on the polymer + plasticizer membrane-electrode-VIII Use of the PVC + tricresyl phosphate membrane as indicating electrode in potentiometric precipitation titration.

Results obtained by use of the PVC + tricresyl phosphate membrane-electrode in potentiometric precipitation titration of some halides and pseudohalides are given. Solutions of Ag(+), Tl(+) and Hg(2)(2+) were used as titrants, to which the membrane is responsive. The fast response to Ag(+) ions allowed the determination of iodide by automatic recording of the potentiometric curve (or its derivative).

Use of membranes for equivalence point indication-VIII Electrochemical characterization of BaSO(4)-parchment membrane-electrode.

Some new aspects of the electrochemical characterization of the BaSO(4)-parchment membrane-electrode are discussed. The electrode function E vs. pH is strongly affected by the ionic strength of the external solution. The electrode is mainly selective for hydrogen, and without interference from sodium ions. The basis of operation of the electrode is selective diffusion. This conclusion is supported by the temperature coefficient, the response rate, and the impedance measurements.

Conductometric titration with indicating resistance-III Mechanism of the PVC + Alassion CS (Cationite R-H) + dioctyl phthalate (plasticizer) membrane as indicating resistance.

The problem of conductometric acid-base titration in a highly-conducting medium (5M sodium chloride) has been solved by introducing a PVC + Alassion CS + dioctyl phthalate membrane between the two electrodes. The equivalence point is marked by a sudden decrease in conductivity. The membrane (obtained by plasticization at 175 degrees ) functions through the phthalic acid dissolved in the PVC membrane, this acid being formed by decomposition of the dioctyl phthalate by the sulphonic acid groups of the cation-exchanger. In this process the sulphonic acid groups are esterified, but hydrolyse on being treated for 2-3 hr with NaOH, and then increase the conductivity in the membrane.

Characterization of ceramic ion-selective membrane-electrodes-I The Ag(2)S electrode.

The behaviour of a new type of electrode, made from ceramic Ag(2)S, has been investigated. The electrode response is Nernstian for Ag(+) over the range 10(-6)-2M and for Hg(2+) in the concentration range 10(-6)-10(-2)M, both at constant ionic strength (0.1M). The electrode is Ag(+)-selective, with maximum interference from Hg(2+). It can be used for acid-base potentiometric titration and for potentiometric Ag(+) and Hg(2+) precipitation titrations.

Liquid-liquid interfaces as potentiometric ion-sensors-I The n-butanol-water interface as indicating sensor for the potentiometric titration of some acids and bases.

The property that liquid-liquid interfaces modify their electrical charge as a function of the composition of the two phases in contact has been used to detect the end-points in a series of acid-base titrations in the aqueous phase. Although the titration curves are not classical in shape, the equivalence points can be located if the solutions are not too dilute. Good results for concentrations down to 10(-3)N have been obtained. The electrode has a fast response. The influence of surface-active substances on the titration has also been investigated.

[Not Available]. / L'utilisation des membranes pour l'indication du point d'équivalence-VI La membrane de papier-parchemin imprégnée de BaSO(4) pour des titrages acido-basiques en milieu non aqueux.

A first attempt to apply inorganic membranes made from parchment paper impregnated with alkaline earth precipitates, as indicating electrodes for potentiometric acid-base titrations in nonaqueous media, is presented. Mixtures of acids can be titrated and the course of the titration is a function of the nature of the solvent and the titrant.

[Not Available]. / Etude sur les électrodes-membranes polymére + plastifiant-II L'utilization de l'électrode-membrane PVC et tricrésylphosphate dans le titrage potentioméque de HCl par NaOH.

A membrane-electrode made from PVC plasticized with tricresyl phosphate has been tested for use in the potentiometric titration of hydrochloric acid with sodium hydroxide. The influence of factors such as temperature, the method of making the membrane, concentration of the titrated acid, of electrolytes and of ethanol, on the accuracy and precision of the titration has been studied.

[Not Available]. / Thermochromatographie sur papier-XIII Considérations sur l'efficacité de la séparation en chromatographie à gradient de température.

Some problems concerning the efficiency of temperature gradient chromatography as compared to that of isothermal chromatography have been investigated. The following expression has been derived for temperature-gradient chromatography: where beta is the separation coefficient, alpha(1) and alpha(2), are the partition coefficients of two substances to be separated, R(f)(1) is the retardation factor for the substance with alpha(1)v is the volume of the eluent in the column, Deltav is the Supplementary volume of the eluent passing through the column owing to evaporation caused by the temperature-gradient, A(M). is the cross-sectional area of the mobile phase and d is the distance between the mid-points of the spots on the chromatogram. It has been shown that under the influence of the temperature gradient Deltav can be large enough for separation of two substances with an alpha(1)/alpha(2), ratio very close to 1. For this reason temperature-gradient chromatography with an open column is the most efficient means of separation so far known.