Thermometric Titrimetry Research Articles

Analysis of FFA in edible oils by catalyzed end‐point thermometric titrimetry (CETT)

AbstractA novel titrimetric procedure has been developed for the determination of FFA in edible oils using an automated thermometric titration with KOH in isopropanol as titrant. The end point is indicated by the strongly exothermic base‐catalyzed reaction between acetone and chloroform. The procedure is fast, easy to use, accurate, and highly reproducible. Analytical precisions (as one SD) in the range 0.001–0.003% w/w (as oleic acid) for new and used cooking oils were obtained. It is very suitable for the routine process and quality control of new and used oils in commercial frying operations, among other applications.

Protometric thermometric titrations of sparingly soluble compounds in water in the presence of n-octanol

Thermometric titrimetry permits titration of acido–basic compounds in water in the presence of n-octanol. n-Octanol permits the solubilization of protolytes and moreover may also displace the equilibria of the titration reactions. Hydrochlorides of highly insoluble derivatives such as phenothiazine derivatives can be titrated with satisfactory accuracy and precision by sodium hydroxide despite their high p K a values. Likewise barbiturate salts can be titrated by hydrochloric acid. In the case of some salts, the methodology may permit the sequential titration of the ion and counter ion.

Determination of the Acidity of Oils Using Paraformaldehyde as a Thermometric End-Point Indicator

The determination of the acidity of oils by catalytic thermometric titrimetry using paraformaldehyde as the thermometric end-point indicator was investigated. The sample solvent was a 1:1 (v/v) mixture of toluene and 2-propanol and the titrant was 0.1 mol L-1 aqueous sodium hydroxide. Paraformaldehyde, being insoluble in the sample solvent, does not present the inconvenience of other indicators that change the properties of the solvent due to composition changes. The titration can therefore be done effectively in the same medium as the standard potentiometric and visual titration methods. The results of the application of the method to both non-refined and refined oils are presented herein. The proposed method has advantages in relation to the potentiometric method in terms of speed and simplicity.

Quantitative assay of 3,4-diaminopyridine in water by thermometric titrimetry

Thermometric titrimetry allows the quantitative assay of pure 3,4-diaminopyridine or in pharmaceutical capsules by titration in water by hydrochloric acid. Satisfactory titrations with 99 p 100 recovery and 1 p 100 precision were obtained with amounts of about 4.5×10 −4 mol. Lactose and starch used as excipients in the capsules as well as gelatin which constitutes their matrix did not interfere in the titration.

PKa values of 3-thioxo-1,2-dithiole-4- and -5-carboxylic acids and of 3-oxo-1,2-dithiole-4- and -5-carboxylic acids in aqueous solution at 298 K

The pKa values in aqueous solution of some 3-thioxo-1,2-dithiole-5-, 3-oxo-1,2-dithiole-5-, 3-thioxo-1,2-dithiole-4- and 3-oxo-1,2-dithiole-4-carboxylic acids have been determined both by UV–VIS spectrophotometry and by potentiometry at 298 K. The 3-thioxo-1,2-dithiole- and 3-oxo-1,2-dithiole-5-carboxylic acids exhibit very low pKa values of the order of 1.20. The 1,2-dithiole-3-thione- and 1,2-dithiole-3-one-4-carboxylic acids exhibit pKa values in the range 1.8–3.2. The pKa values of 5-alkyl-4-carboxylic acids are 0.6 pH units lower than those of the corresponding unsubstituted dithiolone and dithiolethione acids. Thermodynamic ionization parameters determined by thermometric titrimetry show that: (i) for the 5-carboxylic acids, the strength is the result of an entropic effect; (ii) for the 4-carboxylic acids, the unexpected pKa values are essentially of enthalpic origin.

Determination of acetaminophen by thermometric titrimetry

A sensitive, accurate and precise thermometric titration is described for the direct determination of ⩾75 mg of acetaminophen in pure form or in pharmaceutical formulations. Titrations are performed with aqueous sodium hydroxide solution. Excipients tested (starch, talc, lactose) had no effect on the accuracy and precision.

30 years of research in thermal analysis and calorimetry

The research in thermal analysis and calorimetry, conducted by the author over the period 1964 to 1993, is summarised and concisely reviewed. The major investigations have focussed on thermal analysis studies of coordination compounds, particularly the metal dithiocarbamate complexes. A significant solution calorimetric study of some metal dithiocarbamate complexes has also been undertaken. DSC has been applied to determine the sublimation enthalpies of many metal dithiocarbamate and metal pentane-2,4-dionate complexes and solution calorimetry has been applied to study the thermochemistry of the latter group of complexes. Thermal analysis investigations of several inorganic molten salt systems have been initiated. Thermometric titrimetry has been applied to study metal-macrocyclic ligand systems in aqueous media and particularly those systems of environmental significance. Temperature calibration standards for TMA have been proposed and TMA has been applied to study the mechanical properties of several common inorganic compounds. DTA has been applied to study a wide variety of phenols and has subsequently been applied as an analytical technique to determine the components of solid state phenol mixtures. Thermometric titrimetry has been applied to determine the phenolic content of wines. A comprehensive thermal analysis study of Australian brown coal has been undertaken, involving the DSC determination of coal specific energy, a TG/DTA study of the coal pyrolysis and combustion processes and a TG/DTA and EGA study of the cation catalytic effect on the coal pyrolysis process. Thermal analysis and calorimetric techniques have been extensively publicised and promoted by the publication of specialist reviews, the presentation of symposia review papers and the oral presentation of short courses, particularly in the SE Asian region. This review essentially reveals the diversity of possible application of thermal analysis and calorimetric techniques and the primary significance of thermodynamic data in the fundamental rationalisation of chemical phenomena.

Diodes as sensors in solution thermochemistry

The advantages of using diodes as thermal sensors in solution thermochemistry are discussed and a simple, low-cost circuit for the use of diodes as temperature sensors is reported. In preliminary studies, the titration of TRIS and hydrochloric acid is used to compare the precision of thermistors and diodes in thermometric titrimetry. Several systems are assayed at various temperatures by enthalpimetric methods to illustrate the advantages of diodes as sensors for monitoring thermal methods capable of being used in quality control system.

A first estimation of the thermodynamic parameters of water/n-octanol partitioning of some tricyclic antidepressants: Similarities and differences with the values of other psychotropic drugs

Thermometric titrimetry allows the determination of the thermodynamic parameters of transfer from water to n-octanol for tricyclic antidepressants. Their transfers are both entropy and enthalpy driven, whereas those of phenothiazinic neuroleptics are solely entropy driven. The hypothesis of the folding of the lateral chain upon the tricyclic nucleus in antidepressive drugs gives a satisfactory explanation of the results. Differences and analogies of behavior during the partitioning of antidepressants and phenothiazinic compounds are also underlined.

Formalin and paraformaldehyde as end-point indicators in catalytic thermometric titrimetry

The use of formalin solution as an end-point indicator in the titration of both acids and bases in aqueous solutions was investigated. In both instances, a lowering in temperature at the end-point, due to depolymerization of poly(oxymethylene glycols), was observed. Endothermic end-points were also obtained by using paraformaldehyde as an end-point indicator in titrations of acids in aqueous solutions. The use of paraformaldehyde in the titration of very weak acids and of some sparingly soluble acids solubilized in micellar suspensions of cationic detergents was also investigated.

Twenty-five years of thermochemistry research — a personal review

The research in thermochemistry, conducted by the author over the period 1966–1991 is summarised and concisely reviewed. Significant advances have been made in the solution calorimetric determination of the standard formation enthalpies of coordination compounds, particularly metal dithiocarbamates, the application of thermometric titrimetry as an analytical technique, particularly for the determination of metals in aqueous systems of environmental significance and the rationalisation of speciation phenomena in aqueous metal-ligand systems, and the application of thermal analysis (TG, DTA, DSC, EGA and TMA) to study a wide variety of systems, particularly metal complexes. These thermal analysis studies also include the DSC determination of the sublimation enthalpies of metal complexes, the DTA study of phenols and phenol derivatives and a comprehensive TA study of Australian brown coal. This review reveals the diversity of application of calorimetric and thermal analysis techniques and the primary significance of thermodynamic data in the fundamental rationalisation of chemical phenomena.

Thermodynamic and kinetic implications involved in the titration of polyfunctional acids by catalytic thermometric titrimetry

The influence of the concentration of reactants on the results of titrations of salicylic acid in acetone with potassium and tetramethylammonium hydroxides in propan-2-ol were investigated. The titrations were performed by catalytic thermometric titrimetry using acetone as the end-point indicator and by potentiometric titrimetry. These and other results are discussed in terms of the equilibrium and kinetic aspects involved in the titrations of polyfunctional acids capable of forming intramolecular hydrogen bonds.

Titration of proteins in dimethyl sulphoxide–water mixtures

The acid–base behaviour of arginine, lysozyme and ovalbumin has been studied by potentiometric and catalytic thermometric titrimetry in a mixture of dimethyl sulphoxide–water, with acrylonitrile as the end-point indicator in the latter technique. It was observed that, with the exception of the SH groups, all the protonated groups, including the guanidine groups of lysozyme and ovalbumin, were titrated by catalytic thermometric titrimetry. By using potentiometric titrimetry, all the titratable groups of ovalbumin were determined, whereas the guanidine groups of lysozyme were not determined by this technique.

Water/n-octanol thermodynamic parameters of some phenothiazines

Abstract Thermometric titrimetry allows the determination of the water/ n -octanol transfer enthalpies of a series of phenothiazines. By combining these results with the corresponding average values of the partition coefficient determined independently, their transfer entropies can be assessed. The transfer enthalpies of the series studied are significantly more endothermic for the compounds endowed with major neuroleptic activity.

A thermometric titration study of the interaction of Al 3+, Cd 2+, Pb 2+ and Zn 2+ with ethylenediaminetetraacetic acid

The molar reaction enthalpies for the interaction of Al 3+, Cd 2+, Pb 2+ and Zn 2+ with ethylenediaminetetraacetic acid (EDTA) in aqueous solution, at pH 8.7, have been determined by thermometric titrimetry as: 48.96 ± 2.56; −40.90 ± 1.52; −45.59 ± 0.43; and −14.98 ± 0.20 kJ mol −1 respectively. A concentration range for the analytical determination of each of these metal ions is established and some rationalisation of the reactions involved is attempted. An interference study involving mixed metal-EDTA systems is interpreted in terms of the relative magnitudes of the corresponding complex stability constants involved, and supports the analytical significance of the overall enthalpy data for these systems.

Use of cumene hydroperoxide as an end-point indicator in the titration of bases by catalytic thermometric titrimetry

The use of the decomposition reaction of cumene hydroperoxide for indication of the end-point of the titration of organic bases with perchloric acid was investigated. The rise in temperature at the end-point is of the order of 25 °C. Only strong bases can be determined when the titrand solvent is acetic acid-acetic anhydride (92 + 8 v/v), but even weak bases such as caffeine can be determined in 1,2-dichloroethane. Some titration curves resulting from titration of bases with boron trifluoride (a Lewis acid) are presented.

A thermometric titrimetry study of Fe 3+/S0CN − and Ag +/SCN − systems

Thermometric titrimetry data for the Fe 3+/SCN − system show that, for a titrate concentration in the range 0.0020–0.0024 mol dm −3 and a titrant concentration of 0.1000 mol dm −3, the measured molar reaction heat corresponding to the first end-point formation is −4.42 ± 0.52 kJ mol −1 and the corresponding mean mole ratio factor, n Fe 3+ / n SCN − is 1.04 ± 0.04. However, for titrate concentrations in the range 0.0010–0.0020 mol dm −3, this factor is less than unity but progressively approaches unity as the titrant concentration nears 0.0020 mol dm −3. This phenomenon is explained in terms of a thermal bleaching effect and is demonstrated by the use of an inhibitor in these thermometric titrations. Al 3+ and Mn 2+ cause no measurable interference effect in the Fe 3+/SCN − thermometric titration. A thermometric titration with Ag + (0.0007–0.0030 mol dm −3) as titrate and SCN − (0.1000 mol dm −3) as titrant reveals one end-point-the corresponding measured molar reaction heat is −86.65 ± 3.85 kJ mol −1 and n Ag + / n SCN − is 0.97 ± 0.02. Al 3+ causes no measurable interference effect in this titration. The overall thermoanalytical data obtained for these two systems suggest that thiocyanate can be used as a reagent for the determination of Fe 3+ and Ag + in aqueous solution by thermometric titrimetry.

Structures of the borate complexes with a tetritol, pentitols and hexitols in solution. A calorimetric study

The molar heats for the reactions of borate with the polyhydroxy compounds pentaerythritol, L-arabinitol, xylitol, sorbitol and meso-inositol were determined by thermometric titrimetry. By means of the equilibrium constants, the corresponding Gibbs functions and entropies were also obtained. The results refer to aqueous medium at 25 °C and 0.1 M. The present data, together with previous data from this laboratory, lead to the conclusion that the differences in stability of these complexes are mainly determined by entropy, rather than by enthalpy factors. Unlike the other ligands (which are bidentate), pentaerythritol and meso-inositol seem to behave as tridentate ligands with borate. Nevertheless, their complexes exhibit very different stabilities, probably due to the different conformational freedoms of the two ligands in the uncomplexed form.

Phenol determination by thermometric titrimetry

Some thermometric titrimetry data are reported for the phenol, p-nitrophenol, p-methoxyphenol and pl-ienol/pentachlorophenol - thallium ethoxide interactions in benzene as solvent. These thermochemical data are interpreted in terms of the structure of the relevant phenol and ‘end-point curvature’ is rationalised in terms of a phenoxide ion interference effect. Some evidence is also reported for acid-anion complex formation at the mid-point of the thermometric titration. The method is significant in terms of analytical applications.

Rapid analysis of dosage forms of some pharmaceuticals by nonaqueous thermometric titrimetry

The use of the technique of solution thermochemistry is proposed for the rapid assay for quality control and quality assurance of dosage amounts of some ethical formulations of some antimalarial drugs. The active ingredients are chloroquine, hydroxychloroquine, dapsone, proguanil hydrochloride, and pyrimethamine.