Walter Selig

Micro and semimicro determination of sulfur in organic compounds by potentiometric titration with lead perchlorate

SummaryA method for the micro- and semimicro-determination of sulfur in organic compounds is described. After combustion in an oxygen-flask, the sulfur-containing species are oxidized to sulfate with sodium nitrite. The sulfate is titrated potentiometrically with 0.01M lead perchlorate in a 60% 1,4-dioxane solution at pH 4 to 6.5. A lead ion-specific electrode is used in conjunction with an expanded-scale pH meter to monitor the emf. Results are within the ±0.3% absolute limits considered acceptable for microanalysis. Halogens do not interfere. The interference of fluoride is eliminated by complexation with boric acid. If, in addition to sulfur, both fluorineand chlorine are present, the former is removed by acidification with perchloric acid. Phosphorus interferes and must be separated prior to sulfur analysis.ZusammenfassungEin Verfahren zur Mikro- und Halbmikrobestimmung von Schwefel in organischen Verbindungen wurde beschrieben. Nach Verbrennung im Schöniger-Kolben wird mit Natriumnitrit zu Sulfat oxydiert. Dieses wird mit 0,01-m Bleiperchlorat potentiometrisch in 60%iger Dioxanlösung bei pH 4 bis 6,5 titriert. Eine für Blei spezifische Elektrode wird in Verbindung mit einem pH-Meter mit gedehnter Skala zur Messung der E. M. K. verwendet. Die Resultate sind mit einer absoluten Fehlerbreite von ±0,3% für mikroanalytische Zwecke akzeptabel. Halogene stören nicht. Fluor wird mit Borsäure maskiert. Wenn außer Schwefel auch Fluorund Chlor anwesend sind, entfernt man Fluor mit Perchlorsäure. Phosphor stört und muß daher vor der Schwefelbestimmung entfernt werden.

Potentiometric titration of thallium(I) with sodium tetraphenylborate, using ion-selective electrodes.

Thallium(I) has been determined by potentiometric titration with sodium tetraphenylborate. The titrations were monitored with a double-junction reference electrode and various liquid-membrane and solid-state ion-selective electrodes. The largest end-point breaks were obtained with the liquid-membrane fluoroborate and nitrate electrodes. The cyanide electrode yielded the largest break of the solid-state electrodes tested. Although the magnitude of the end-point break for the cyanide electrode is considerably less than for the above-mentioned liquid-membrane electrodes, routine use of this electrode is preferred because no conditioning is required for the solid-state electrodes. Precision was satisfactory for all electrodes investigated. Thallium(I) can be titrated with tetraphenylborate at any pH from 1.3 to at least 10.2. Other cations that can be precipitated with tetraphenylborate interfere.

Potentiometric micro- and semimicro-determination of fluorine in organic compounds

ZusammenfassungNach Verbrennung der Substanz im Sauerstoffkolben wird das Fluorid potentiometrisch mit 0,02 M Lanthan(III)-lösung bei pH 5–7 titriert. Hierbei wird eine fluoridspezifische Elektrode in Verbindung mit einem pH-Meter mit Skalendehnung verwendet. Der absolute Fehler ist kleiner als ±0,3%. Störender Schwefel wird als Bariumsulfat gefällt; Filtration ist nicht erforderlich. Phosphor muß vor der Bestimmung abgetrennt werden.SummaryA method for the potentiometric micro- and semimicro-determination of fluorine in organic compounds is described. After combustion in a Vycor oxygen-flask, the fluoride is titrated potentiometrically with 0.02 M lanthanum (III) in an aqueous solution at pH 5–7. A fluoride ion-indicating electrode is used in conjunction with an expanded-scale pH meter. Results are within the ±0.3% absolute limits considered acceptable for microchemical analysis. The interference of sulfur is eliminated by its precipitation as barium sulfate. Filtration of the precipitate is not necessary. Phosphorus interferes and must be separated prior to fluorine analysis.

Microtitration of various anions with quaternary ammonium halides using solid-state electrodes☆☆☆

Many solid-state electrodes were found to respond as endpoint detectors in the potentiometric titration of large inorganic and organic anions with quaternary ammonium halides. The best response was obtained with the iodide and cyanide electrodes although practically any electrode can function as endpoint sensor. The titrants were hexadecylpyridinium chloride and hexadecyltrimethylammonium chloride; hexadecyltrimethylammonium bromide and Hyamine 1622 may also be used. Some inorganic anions thus titratable are perrhenate, persulfate, ferricyanide, hexafluorophosphate, and hexachloroplatinate. Examples of organic anions titratable are nitroform, tetraphenylborate, cyanotriphenylborate, picrate, long-chain sulfates and sulfonates, and some soaps. The reverse titration of quaternary ammonium halides vs dodecylsulfate is also feasible. Some titrations are feasible in a partially nonaqueous medium.

The potentiometric titration of surfactants and soaps using ion-selective electrodes

ZusammenfassungMehrere quaternäre Ammoniumhalogenide wurden für die Fällungstitration von anionischen Tensiden und Seifen ausgewertet. Als Titranten wurden benutzt Hexadecyltrimethylammoniumchlorid und -bromid, Hexadecylpyridiniumchlorid und Diisobutylphenoxyethoxyethyl(dimethyl)benzylammoniumchlorid. Hexadecylpyridiniumchlorid ergab die höchste Genauigkeit und die größte potentiometrische Stufe. Die Titrationen wurden mit Hilfe einer handelsüblichen Fluoroboratindicatorelektrode und einer Double-junction-Bezugselektrode durchgeführt. Auch handelsübliche Perchlorat-, Nitrat- und Calciumelektroden können zur Spannungsanzeige verwendet werden. Dadurch ist es nicht notwendig, besonders Flüssigmembranoder andere Elektroden herzustellen, wie sie bisher bei der potentiometrischen Titration von Tensiden und Seifen verwendet wurden. Natriumdodecylsulfat von Elektrophoresereinheit wird für die Standardisierung der quaternären Ammoniumhalogenide empfohlen. Eine umgekehrte Titration von kationischen Tensiden gegen Standard-Natriumdodecylsulfat ist ebenso ausführbar.SummarySeveral quaternary ammonium halides have been evaluated for the precipitation titration of anionic surfactants and soaps. The titrants were hexadecyltrimethylammonium chloride and bromide, hexadecylpyridinium chloride, and diisobutylphenoxyethoxyethyl(dimethyl)benzylammonium chloride. Hexadecylpyridinium chloride yielded the highest precision and largest potentiometric break. Titrations were monitored with a commercically available fluoroborate ion-selective indicator electrode and a double-junction reference electrode. Commercially available perchlorate, nitrate, and calcium electrodes may also be used for emf monitoring. This obviates the need of preparing special liquid membrane or other electrodes mostly used heretofore in the potentiometric titration of surfactants and soaps. Electrophoresis purity reagent sodium dodecylsulfate is recommended for the standardization of the quaternary ammonium halides. The reverse titration, of cationic surfactants vs. standard sodium dodecylsulfate, is similarly feasible.

Potentiometric semimicrodetermination of some anions with 1,2,4,6-tetraphenylpyridinium acetate

SummaryA new titrant, 1,2,4,6-tetraphenylpyridinium acetate, has been evaluated for the potentiometric precipitation titration of semimicro amounts of some large inorganic anions. Emfs were monitored with a perchlorate ion-selective electrode and a double-junction reference electrode. Satisfactory results were obtained for perchlorate, perrhenate, periodate, dichromate, permanganate, hexafluorophosphate, and hexachloroplatinate. Fluoroborate yielded a smaller endpoint break and poor precision. Thiocyanate, iodide, molybdate, tungstate, and tetrachloropalladate yielded partial or complete precipitation, but no analytically useful titration curves. We consider it likely that large anions such as pertechnetate, hexafluoro anions such as hexafluoroarsenate, and some complex metal chlorides such as those of mercury and tin (IV) can be determined in a similar fashion.ZusammenfassungDas neue Titrationsmittel 1,2,4,6-Tetraphenylpyridiniumacetat wurde zur potentiometrischen Fällungstitration von Semimikromengen einiger großer anorganischer Anionen herangezogen. Das Potential wurde mit einer selektiven Perchloratelektrode und einer doppeltverbundenen Bezugselektrode gemessen. Befriedigende Ergebnisse wurden mit Perchlorat, Perrhenat, Perjodat, Dichromat, Permanganat, Hexafluorophosphat und Hexachloroplatinat erhalten. Mit Fluoborat ergab sich ein schwächerer Endpunkt-Knick und geringere Genauigkeit. Thiocyanat, Jodid, Molybdat, Wolframat und Tetrachloropalladat ergaben teilweise oder vollständige Fällung, aber keine analytisch auswertbaren Titrationskurven. Wir nehmen an, daß sich große Anionen wie Pertechnetat, Hexafluoroarsenat u. dgl. sowie komplexe Metallchloride wie die des Quecksilbers und des Zinn(IV) in gleicher Weise bestimmen lassen.

Semimicrodetermination of oxalate with a lead-specific electrode

Summary A procedure for the semimicrodetermination of oxalate is described. Oxalate is titrated potentiometrically with standard lead perchlorate in 40% p -dioxane solution at pH 3.5 to 10.5. A lead-ion specific electrode in conjunction with an expanded-scale pH meter is used to monitor the emf. Anions forming insoluble lead salts interfere. An excess of formate, acetate, propionate, and phthalate does not interfere.

Lower limits of the potentiometric titration of perchlorate using a perchlorate ion-selective electrode

Abstract Three titrants (tetraphenylarsonium chloride, tetraphenylphosphonium chloride, and tetra-n-pentylammonium bromide) were evaluated for the potentiometric determination of perchlorate. The emf levels were monitored with a perchlorate ion-selective indicator electrode and a double-junction reference electrode. The tetraphenylonium salts were equivalent, yielding the same precision and magnitude of potentiometric breaks. Considerably smaller breaks were obtained with tetra-n-pentylammonium bromide, which, therefore, is not recommended as titrant. The lower limits for the potentiometric titration of perchlorate at ambient temperature were extended to ~0.09 mmol per 50 ml (1.7 × 10−3 N) from the previous 0.25 mmol per 50 ml. If Gran plots are used, they can be further extended to ~0.01 mmol per 50 ml (2.1 × 10−4 N).

Microdetermination and pKa measurement of some aliphatic amines using the copper-ion-selective electrode☆

Abstract Aliphatic amines were determined on the microscale by potentiometric titration with standard cupric sulfate solution in aqueous or partially aqueous (methanolic) medium. Electromotive forces were monitored with a copper-ion-selective electrode or a graphite rod impregnated with silver sulfide/cupric sulfide, and a double-junction reference electrode. Monoamines and diamines up to 1,3-diaminopropane reacted on a 2:1 amine:Cu basis. Diamines from 1,4-diaminobutane to at least 1,7-diaminoheptane reacted on an equimolar basis. The dissociation constants of some of the amines were determined. A linear relationship exists between the emf at half complexation and the dissociation constants of the amines tested.

Micro and Semimicro Determination of Thiols with Ion-Selective Electrodes*

SummaryThis paper describes the potentiometric determination of a variety of thiols. Microamounts (0.01 to 0.1 mM) are titrated with 0.01N mercuric perchlorate while semimicroamounts (0.1 to 0.5 mM) are titrated with 0.05N mercuric perchlorate. A bromide selective indicator electrode and a single-junction reference electrode are used with an expanded-scale pH meter to monitor the emf. Other indicator electrodes based on a silver sulfide matrix may also be used. The preferred solvent is acetone while ethanol andp-dioxane have limited applicability. The electrode response is slower in general than for other titrations using ion-selective electrodes, particularly for the more complex thiols and those attached to a heterocyclic ring system.ZusammenfassungDie potentiometrische Bestimmung verschiedener Thiole wurde beschrieben. Mikromengen (0,01 bis 0,1 mMol) werden mit 0,01-n Quecksilberperchlorat titriert, während Mengen zwischen 0,1 und 0,5 mMol mit 0,05-n Lösung titriert werden. Eine bromspezifische Indikatorelektrode und eine „single-junction“-Bezugselektrode kombiniert mit einem pH-Meter mit gedehnter Skala dienten zur Messung der EMK. Auch andere Elektroden mit Silbersulfidmatrix können verwendet werden. Bevorzugtes Lösungsmittel ist Aceton; Äthanol und 1,4-Dioxan sind nur beschränkt verwendbar. Das Elektrodensignal erfolgt im allgemeinen langsamer als bei anderen ionenspezifischen Elektroden, vor allem wenn es sich um komplexe Thiole oder um solche Thiolgruppen handelt, die an heterocyklische Ringsysteme gebunden sind.