Catalytic microdetermination of mercury

An automatic spectrophotometric reaction-rate method is described for the microdetermination of mercury. The method is based on the catalytic effect of mercury on the reaction of ferrocyanide with nitrosobenzene. The time required for production of a small fixed amount of the violet product as given by a preselected change in the output voltage of a photoconductive circuit, is measured automatically and related directly to the mercury concentration. The possibility of masking interfering ions with EDTA was examined. Amounts of mercury in the range 0.25–2.5 /smg, were determined with relative errors of 1–2% in measurement times of only 15–120 sec. Results obtained with mercurial compounds, treated with bromine water, were within 1–2% of the theoretical values and results obtained with pharmaceutical preparations were within the range assigned to those preparations.     

Catalytic microdetermination of chromium(VI)

An automatic spectrophotometric kinetic method for the microdetermination of chromium(VI) is described, based on catalysis of the hydrogen peroxide-iodide reaction. The time required for the reaction to produce a small fixed amount of tri-iodide is measured automatically, and is proportional to the chromium(VI) concentration. Maximum tolerable amounts of various interfering ions were investigated. From 0.6 to 3.0 mug of chromium(VI) can be determined with relative errors of 1-2%, with measuring times of 10-50 sec.     

Solid-phase spectrophotometric microdetermination of iron with ascorbic acid and ferrozine

 A very sensitive and selective method for the determination of trace amounts of iron has been developed, based on the reduction of Fe(III) to Fe(II) by ascorbic acid, followed by chromogenic chelation of Fe(II) with ferrozine. The complex Fe(II)-ferrozine is easily sorbed on a dextran-type anion-exchange gel packed in a 1 mm cell, and the absorbance of the gel is measured directly at 569 and 800 nm. The extended linear range of the determination is 0.5–10 ng ml^-1 of iron (apparent molar absorptivity=4.4×10⁷ l mol^-1 cm^-1) and the precision (RSD) 1.3% for a concentration of 5 ng ml^-1 of iron (n=10). The detection limit for a sample volume of 1000 ml, using 0.040 g of anion-exchanger, corresponds to 0.12 ng ml^-1. The method has been successfully applied to the determination of iron in natural and waste waters, wine, soil extract and previously digested vegetal tissues, drugs and human hair. Received: 20 November 1995/Revised: 23 January 1996/Accepted: 26 January 1996     

Spectrophotometric microdetermination of zinc in the presence of copper and iron

A simple, rapid, and sensitive procedure for the spectrophotometric microdetermination of zinc in the presence of iron and copper is proposed. Zinc is determined with DPPH (2, 2′-dipyridyl-2-pyridylhydrazone). The determination is carried out in aqueous solution. Iron and copper are reduced by ascorbic acid and masked with cyanide. The zinc-DPPH complex is formed at pH = 12 ± 0.2 and measured at 442 nm no more than 15 min after the addition of DPPH. Beer's law is obeyed at the concentration range of about 0.12 to 1.32 ppm of zinc.     

Spectrophotometric microdetermination of hydroxytriazenes

A method is reported for the determination of hydroxytriazenes, based on development of a pink colour by the reaction of hydroxytriazenes with alpha-naphthylamine. The method is general and can be used for the determination of any hydroxytriazenes.     

Potentiometric microdetermination of oxiranes

Summary A potentiometric microtitration for the determination of high molecular weight oxiranes is presented. It is based on the reaction of oxiranes with quaternary ammonium bromide and titration with 0.01N perchloric acid. The preferred solvent is acetic acid although small amounts of toluene or chloroform may be used. Epoxy equivalents as high as 370,000 have been determined.

---

Potentiometrische Mikrobestimmung von Äthylenoxiden

Zusammenfassung Eine potentiometrische Mikrotitrationsmethode zur Bestimmung hochmolekularer Äthylenoxide wurde vorgeschlagen. Sie beruht auf deren Reaktion mit quaternärem Ammoniumbromid und Titration mit 0,01N Perchlorsäure. Vorzugsweise dient Essigsäure als Lösungsmittel, doch kann man auch kleine Mengen Toluol oder Chloroform verwenden. Epoxyäquivalente bis zu 370 000 wurden bestimmt.

---

---

Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore Laboratory under contract number W-7405-ENG-48.     

Coulometric microdetermination of water

An electroanalytical method for the determination of small amounts of water by controlled potential coulometry has been devised. Excess of iodine is produced coulometrically in a Karl Fischer reagent, the sample is added, and after complete reaction the remainder of the iodine is reduced. The number of coulombs consumed in the cell reaction is determined by integration of the current by means of an electronic integrator. Karl Fischer reagents of various compositions were checked to find the most satisfactory conditions and a special electrolysis cell for water determination was constructed entirely in glass and Teflon. Samples containing 0.1-2 mg of water were added and determined with an accuracy of +/- 0.15 %. The analysis times were 3-12 min.     

Titrimetric microdetermination of lanthanum

Summary A method for titrimetric determination of lanthanum is proposed by oxidising lanthanum rhodizonate with ceric sulphate directly. A violet coloured complex is precipitated when the solution containing sodium rhodizonate and lanthanum nitrate is boiled. By analysis it appears that with one lanthanum three rhodizonates are attached. It is observed that Na⁺, K⁺, and Zr⁴⁺ do not interfere but Ag⁺, Cs⁺, Tl⁺, Be²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Mg²⁺, Hg²⁺, Cu²⁺, Sn²⁺, Pd²⁺, Bi³⁺, Au³⁺, Sb³⁺, Al³⁺, Rh³⁺, Ru³⁺, Ir³⁺, Th⁴⁺, Te⁴⁺, Pt⁴⁺, Se⁶⁺, Cr⁶⁺, W⁶⁺, and U⁶⁺ do.

---

Zusammenfassung Zur maßanalytischen Bestimmung von Lanthan wird die unmittelbare Oxydation von Lanthanrhodizonat mit Cer(IV)-sulfat vorgeschlagen. Beim Kochen einer Lösung von Natriumrhodizonat und Lanthannitrat fällt ein violett gefärbter Komplex aus. Aus der Analyse ergibt sich das Verhältnis La: Rhodizonat =13. Na⁺, K⁺ und Zr⁴⁺ stören nicht im Gegensatz zu Ag⁺, Cs⁺, Tl⁺, Be²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Mg²⁺, Hg²⁺, Cu²⁺, Sn²⁺, Pd²⁺, Bi³⁺, Au³⁺, Sb³⁺, Al³⁺, Rh³⁺, Ru³⁺, Ir³⁺, Th⁴⁺, Te⁴⁺, Pt⁴⁺, Se⁶⁺, Cr⁶⁺, W⁶⁺, und U⁶⁺.

     

Catalytic properties of iron oxides impregnated with copper acetate

Textural and catalytic properties of iron oxides impregnated with copper acetate were investigated. In order to get satisfactory performance in the high temperature shift reaction, 4 impregnation hours are necessary.     

Catalytic performance of iron carbide for carbon monoxide hydrogenation

Novel iron carbide and potassium-promoted iron carbide catalysts were prepared and investigated for CO hydrogenation. The iron carbide showed high activity for CO hydrogenation under high pressures; with the addition of potassium, activity and selectivity to C5+ hydrocarbons were greatly enhanced, and the selectivity to methane was suppressed.     

Indirect photokinetic microdetermination of fluoride

A catalytic-kinetic method for the determination of nanogram amounts of fluoride based on its inhibiting action on the catalyst in the iron(III)-catalyzed photooxidation of thionine is described. The rate measurements are accomplished very simply by measuring the decreasing of absorbance after illumination for a fixed time.     

Investigation of some asymmetric triazines as reagents for the spectrophotometric microdetermination of the iron oxidation state in silicates

The preparation and analytical evaluation of two asym-triazines, 3-(1-isoquinolyl)-5,6-diphenyl-1,2,4-triazine (IQDT) and 3,3′-bis(5,6-diphenyl-1,2,4-triazine (BDT), and their sulphonated derivatives (IQDT-TAS and TSBT-TAS) are described. The sulphonated ferroin chromogens formed intensely coloured tris-chelates with iron(II) in molar acid solutions and chelates were also formed with copper(I) ions. The TSBT-TAS reagent showed an exceptionally high acid tolerance in its ability to chelate iron(II) in concentrated acids. Once formed, the chelates of all four compounds possessed a high degree of stability. The IQDT and IGDT-TAS reagents formed maximal colour at pH 3–8 whereas TSBT-TAS was indifferent to pH changes in the acidic range; the molar absorptivities were 38 340 l mol^?1 cm^?1 at 375 nm and 27 360 at 596 nm for IQDT-TAS, and 23 500 l mol^?1 cm^?1 at 450 nm and 28 240 at 550 nm for TSBT-TAS. Only EDTA, cyanide and comparable amounts of copper(I) and cobalt(II) interfered. The TSBT-TAS reagents and to a lesser extent IQDT-TAS were useful for the spectrophotometric microdetermination of FeO in silicates. Aerial oxidation was prevented by the immediate chelation of iron(II) released from the silicate matrix with a decomposition acid mixture containing TSBT-TAS. More resistant minerals were decomposed in teflon bombs by prolonged heating. Good precision and accuracy were obtained for the analysis of 1–5-mg samples where the average relative standard deviation was 1.73%.     

Bromometric microdetermination of organic sulfides

Summary The possibility of the micro-estimation of organic sulfides by oxidation with a solution of potassium bromate-bromide using indigo-carmine as indicator is shown.     

The nonaqueous microdetermination of nitroguanidine

Summary Nitroguanidine can be determined as a base by nonaqueous titration in acetic anhydride. The titrant is perchloric acid in glacial acetic acid. Endpoints are determined potentiometrically by a glass (or platinum)/modified calomel electrode system. Nitramines such as HMX and RDX do not interfere.

---

Zusammenfassung Nitroguanidin läßt sich als Base in Essigsäureanhydridlösung mit Perchlorsäure, gelöst in Eisessig, titrieren. Der Endpunkt wird potentiometrisch mit Hilfe einer Glas-(oder Platin-) Elektrode gegen eine modifizierte Kalomelelektrode gemessen. Nitramine wie HMX und RDX stören nicht.

---

---

Work performed under the auspices of the U. S. Department of Energy under contract No. W-7405-Eng-48.     

Rapid general microdetermination of fluorine

Summary A rapid micromethod for the determination of fluorine in a wide variety of materials has been developed. The method is based on the liberation of the fluorine (as HF) from the sample by means of pyrohydrolysis with steam at 1120° C, The amount of fluoride in the condensate is subsequently measured with an ion-selective electrode using a simple standard addition technique, which automatically compensates for variations in ionic strength, acidity, etc. Metals that may form stable complexes with fluoride are masked by the addition of a complexing agent to the condensate.Materials analysed included refractory compounds such as the fluorides of the alkaline earth metals, organic and organo-metallic compounds, alumina-base catalysts, anthropological samples, coal, etc. Limit of detection is of the order of 1 g F; standard deviation is about 1% relative. Time required for one determination is 15–20 min.

---

Rasche, allgemeine Mikrobestimmung von Fluor

Zusammenfassung Es wurde eine schnelle Mikromethode zur Bestimmung von Fluor in grundverschiedenen Materialen entwickelt. Fluor (als HF) wird aus der Probe mittels Pyrohydrolyse bei 1120° C freigesetzt. Die Menge des Fluorids im Kondensat wird mit einer ionen-selektiven Elektrode gemessen. Dazu wird eine einfache Standardadditionsmethode angewendet, welche automatisch für die Variation von Ionenstärke und Acidität usw. kompensiert. Zugabe eines Komplexierungsmittels zum Kondensat maskiert Spuren Metall, die stabile Fluorkomplexe bilden könnten.Die nachfolgenden Substanzen wurden analysiert: organische und Organometallverbindungen, Katalysatoren, anthropologische Proben, Kohle, usw. Auch schwer zersetzliche Substanzen, z.B. Erdalkalifluoride, gaben gute Ergebnisse. Die Detektionsgrenze beträgt etwa 1 g F, die relative Standardabweichung 1%, die Analysendauer 15–20 min.

The essential information, contained in this paper, was given as a poster presentation at the International Symposium on Microchemical Techniques, Davos, Switzerland, May 1977     

Direct titrimetric microdetermination of uranium

Summary Direct titrimetric method for the estimation of uranium(VI) in the range of 0.7 to 76 mg is performed by decomposing and oxidising the complex, {U(VI)O₂ · U(V)O₂ · Fe(CN)₆}, with ceric sulphate. The mixed valency state in the above mentioned complex has been confirmed by magnetic measurements, the isolated complex being paramagnetic. Na⁺, K⁺, Cs⁺, Ca²⁺, Sr²⁺, Mg²⁺, Be²⁺, Pd²⁺, La³⁺, Ir³⁺, Ru³⁺, and Te⁴⁺ do not interfere but Ag⁺, Tl⁺, Cu²⁺, Ba²⁺, CO²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Hg²⁺, Sn²⁺, Bi³⁺, Au³⁺, Rh³⁺, Sb³⁺, In³⁺, Ti³⁺, Th⁴⁺, Zr⁴⁺, Pt⁴⁺, V⁵⁺, Se⁶⁺, MO⁶⁺, and Os⁸⁺ do.

---

Zusammenfassung Die Bestimmung von Uran(VI) in der Größenordnung von 0,7 bis 76 mg erfolgt durch Zersetzung und Oxydation des Komplexes U(VI)O₂ · U(V)O₂ · · Fe(CN)₆ mit Cer(IV) sulfat. Die zweierlei Wertigkeitsstufen in diesem paramagnetischen Komplex wurden durch magnetische Messungen bestätigt. Na⁺, K⁺, Cs⁺, Ca²⁺, Sr²⁺, Mg²⁺, Be²⁺, Pd²⁺, La³⁺, Ir³⁺, Ru³⁺, and Te⁴⁺ stören nicht; hingegen stören Ag⁺, Tl⁺, Cu²⁺,Ba ²⁺, CO²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Hg²⁺, Sn²⁺, Bi³⁺, Au³⁺, Rh³⁺, Sb³⁺, In³⁺, Ti³⁺, Th⁴⁺, Zr⁴⁺, Pt⁴⁺, V⁵⁺, Se⁶⁺, MO⁶⁺, and Os⁸⁺.

     

Catalytic C-H bond amination from high-spin iron imido complexes

Dipyrromethene ligand scaffolds were synthesized bearing large aryl (2,4,6-Ph(3)C(6)H(2), abbreviated Ar) or alkyl ((t)Bu, adamantyl) flanking groups to afford three new disubstituted ligands ((R)L, 1,9-R(2)-5-mesityldipyrromethene, R=aryl, alkyl). While high-spin (S=2), four-coordinate iron complexes of the type ((R)L)FeCl(solv) were obtained with the alkyl-substituted ligand varieties (for R=(t)Bu, Ad and solv=THF, OEt(2)), use of the sterically encumbered aryl-substituted ligand precluded binding of solvent and cleanly afforded a high-spin (S=2), three-coordinate complex of the type ((Ar)L)FeCl. Reaction of ((Ad)L)FeCl(OEt(2)) with alkyl azides resulted in the catalytic amination of C-H bonds or olefin aziridination at room temperature. Using a 5% catalyst loading, 12 turnovers were obtained for the amination of toluene as a substrate, while greater than 85% of alkyl azide was converted to the corresponding aziridine employing styrene as a substrate. A primary kinetic isotope effect of 12.8(5) was obtained for the reaction of ((Ad)L)FeCl(OEt(2)) with adamantyl azide in an equimolar toluene/toluene-d(8) mixture, consistent with the amination proceeding through a hydrogen atom abstraction, radical rebound type mechanism. Reaction of p-(t)BuC(6)H(4)N(3) with ((Ar)L)FeCl permitted isolation of a high-spin (S=2) iron complex featuring a terminal imido ligand, ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))), as determined by (1)H NMR, X-ray crystallography, and (57)Fe Mo?ssbauer spectroscopy. The measured Fe-N(imide) bond distance (1.768(2) ?) is the longest reported for Fe(imido) complexes in any geometry or spin state, and the disruption of the bond metrics within the imido aryl substituent suggests delocalization of a radical throughout the aryl ring. Zero-field (57)Fe Mo?ssbauer parameters obtained for ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))) suggest a Fe(III) formulation and are nearly identical with those observed for a structurally similar, high-spin Fe(III) complex bearing the same dipyrromethene framework. Theoretical analyses of ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))) suggest a formulation for this reactive species to be a high-spin Fe(III) center antiferromagnetically coupled to an imido-based radical (J = -673 cm(-1)). The terminal imido complex was effective for delivering the nitrene moiety to both C-H bond substrates (42% yield) as well as styrene (76% yield). Furthermore, a primary kinetic isotope effect of 24(3) was obtained for the reaction of ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))) with an equimolar toluene/toluene-d(8) mixture, consistent with the values obtained in the catalytic reaction. This commonality suggests the isolated high-spin Fe(III) imido radical is a viable intermediate in the catalytic reaction pathway. Given the breadth of iron imido complexes spanning several oxidation states (Fe(II)-Fe(V)) and several spin states (S=0→(3)/(2)), we propose the unusual electronic structure of the described high-spin iron imido complexes contributes to the observed catalytic reactivity.