The elimination of the distillation procedure in the Kjeldahl method

Summary The distillation process in the Kjeldahl method can be eliminated by applying the hypochlorite titration ofKolthoff andStenger. Mercury is used as catalyst; other catalysts which were tried interfered in the titration. Digestion and titration can be done in the same vessel on the micro scale, but a suitable vessel remains to be designed for this to be achieved on the semi-micro scale.The method is not applicable when pre-reduction is necessary, for all the reagents tested interfered with the subsequent titration.

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Zusammenfassung Durch Anwendung der Hypochlorittitration nachKolthoff undStenger läßt sich die Destillation bei der Stickstoffbestimmung nachKjeldahl umgehen. Quecksilber dient als Katalysator; andere Katalysatoren stören die Titration. Veraschung und Titration können im selben Gefäß im Mikromaßstab durchgeführt werden, aber bei der Analyse im Semimikromaßstab wird die zu titrierende Lösung besser in ein anderes Gefäß gebracht.Wenn eine vorhergehende Reduktion nötig ist, eignet sich die Methode nicht, da die hierzu nötigen Reagenzien die Titration stören.

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Résumé Il est possible d'éliminer la distillation que comporte la méthode deKjeldahl par application du titrage par l'hypochlorite deKolthoff etStenger. On emploie le mercure comme catalyseur; les autres catalyseurs qui ont été essayés gênent le titrage. Digestion et titrage peuvent être effectués dans le même récipient à l'échelle microanalytique mais il conviendrait de prévoir un récipient spécial pour permettre de réaliser cette condition à l'échelle semi-microanalytique.Cette méthode n'est pas applicable lorsqu'il est nécessaire d'effectuer une réduction préalable car les réactifs qui sont alors employés réagissent ultérieurement lors du titrage.

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We have great pleasure in dedicating this paper to our good friend Professor Dr.R. Strebinger on the occasion of his 70th birthday.

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Our thanks are due to Mr.E. Parry for carrying out check determinations.     

Bacterial biosynthesis of cadmium sulfide nanocrystals

Semiconductor nanocrystals, which have unique optical and electronic properties, have potential for applications in the emerging field of nanoelectronics. To produce nanocrystals cheaply and efficiently, biological methods of synthesis are being explored. We found that E. coli, when incubated with cadmium chloride and sodium sulfide, have the capacity to synthesize intracellular cadmium sulfide (CdS) nanocrystals. The nanocrystals are composed of a wurtzite crystal phase with a size distribution of 2-5 nm. Nanocrystal biosynthesis increased about 20-fold in E. coli cells grown to stationary phase compared to late logarithmic phase. Our results highlight how different genetic and physiological parameters can enhance the formation of nanocrystals within bacterial cells.     

The role of symmetry and optical selection rules in revealing the molecular structure of the lowest Rydberg and ionic states of the 1,4-diazabicyclo[2.2.2]octane-Arn (n = 1,2,3) van der Waals complexes

The 1,4-diazabicyclo[2.2.2]octane-Arn (n = 1,2,3) van der Waals complexes (DABCO-Arn) have been investigated using a combination of (1 + 1') resonance enhanced multiphoton ionization (REMPI) and zero electron kinetic energy (ZEKE) spectroscopy. The additivity of the spectral shifts observed in both REMPI and ZEKE spectra, taken together with analysis of vibrational structure, suggest that in both DABCO-Ar and DABCO-Ar2 the argon atoms bind in equivalent equatorial (face) locations between two adjacent (CH2)2 bridges. However, the cumulative evidence from both REMPI and ZEKE spectra, together with ab initio results, suggests that the DABCO-Ar3 complex does not revert to D3h symmetry, but rather adopts a C2v structure in which all three argon atoms bind to one side of the DABCO framework. The exceptionally low wave-number vibrational structure observed in the REMPI spectra suggest that the van der Waals interaction in the excited state is extremely weak. However, ionization necessarily increases the strength of the interaction by virtue of the introduction of charge-induced dipole forces, as revealed by a consistent increase in vibrational wave numbers of the modes observed in the resultant ZEKE spectra.     

Molecular emission cavity analysis (meca)—a new flame analytical technique: Part III. The determination of boron

Two highly selective methods are described for the determination of boron by molecular emission cavity analysis. In one, boron (>0.1 p.p.m.) is extracted as its 2-ethylhexane-1,3-diol chelate into methyl isobutylketone; 5-80 ng of boron in 5 μl of the extract is determined by injection into the MECA cavity. In the other, boron (2-30 μl) is converted into volatile methyl borate, and carried into the rear of the cavity by a stream of nitrogen. In both methods, the emission intensity at 518 nm, stimulated by a hydrogen-nitrogen-oxygen flame, is measured. Of the other ions tested, none interfered in the volatilization procedure, and only fluoride ( ? 100 mg) interfered in the extraction method. The precision is ±4%.     

Barium oxalate as a selective solid reagent for the absorption of sulphur trioxide

Barium and calcium oxalate monohydrates have been shown to be more suitable absorbents for sulphur trioxide than either anhydrous or hydrated oxalic acid. All four compounds are selective absorbents for the trioxide and do not absorb sulphur dioxide. Similarly all are elective absorbents for sulphuric acid aerosol, although the calcium salt may be decarboxylated under these conditions. Lead oxalate and formate may be suitable for the absorption of SO(3) and H(2)S, and SO(3), H(2)S and SO(2) respectively.     

Slow anion exchange,conformational equilibria,and fluorescent sensing in venus flytrap aminopyridinium-based anion hosts

The synthesis, anion binding, and conformational properties of a series of 3-aminopyridinium-based, tripodal, tricationic hosts for anions are described. Slow anion and conformational exchange on the (1)H NMR time scale at low temperature, coupled with NMR titration, results in a high level of understanding of the anion-binding properties of the compounds, particularly with respect to significant conformational change resulting from induced fit complexation. Peak selectivity for halides, particularly Cl(-), is observed. The approach has been extended to dipodal and tripodal podands based on 3-aminopyridinium "arms" containing photoactive anthracenyl moieties. The 1,3,5-tripodal host shows a remarkable selectivity for acetate over other anions, in contrast to the analogous unsubstituted tris(3-aminopyridinium) analogue, despite the fact that low-temperature (1)H NMR experiments reveal a total of four acetate-binding conformations. Photodimerization of anthracene units results in the formation of potential fluorescent anion sensors.     

Mercurous nitrate as a reductimetric reagent : The determination of hydroxylamine and nitrates

Hydroxylamine can be determined indirectly using standard mercurous nitráte, by treating the test solution with an excess of standard ferric alum, and back titrating the excess.The same procedure cannot be recommended for the determination of hydrazine and hydroquinone. The results with hydrazine were irregular and generally low. With hydroquinone, the brown colour of the oxidation product masked the endpoint.An attempt was made to determine nitrate after reduction with ferrous ammonium sulphate, but the high acidity required is unfavourable for mercurous nitrate titration, and results are only accurate to about 1 per cent.     

The micro-determination of chloride ion using an amplification procedure

Summary A comparative study has been made of the use of silver iodate, mercurous iodate and mercuric iodate for the determination of the chloride ion on the micro scale. The principle of the method is that the sparingly-soluble iodate reacts with the chloride ion to produce an equivalent amount of iodate ion. After filtration of the solution the iodate ion is titrated iodometrically, a six-fold amplification of titre being obtained.All three of the reagents give results of similar accuracy. Mercuric iodate is slightly superior in this respect to the other two reagents, but has the disadvantage that it cannot be used in acidic solutions. The results obtained are very reproducible, but deviate up to two per cent from the theoretical, depending upon the chloride ion concentration in the range 0.7–3.5 mg.

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Zusammenfassung Es wurden vergleichende Untersuchungen über die Verwendung von Silber-, Quecksilber(I)- und Quecksilber(II)-Jodat zur Mikrobestimmung von Chlorionen durchgeführt. Das Prinzip der Methode beruht auf der geringen Löslichkeit dieser Jodate, die mit Chloridionen unter Bildung äquivalenter Mengen freier Jodationen reagieren. Nach Filtration der Lösung werden diese jodometrisch titriert, wobei sich der sechsfache Titer ergibt.Alle drei Reagenzien geben Resultate ähnlicher Genauigkeit. Quecksilber(II)-Jodat ist den beiden anderen Salzen etwas überlegen, hat aber den Nachteil, daß es in saurer Lösung nicht verwendbar ist. Die Ergebnisse sind gut reproduzierbar, liegen aber bei Anwendung von 0,7 bis 3,5 mg Chloridionen bis zu 2% über der Theorie.

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Résumé On a fait une étude comparée pour l'emploi de l'iodate d'argent, de l'iodate mercureux et de l'iodate mercurique pour le dosage de l'ion chlorhydrique à l'échelle micro. Le principe de la méthode est que l'iodate peu soluble réagit sur celui-ci pour produire une quantité équivalente d'ion iodique. Après filtration de la solution, ce dernier est dosé iodométriquement, ce qui amplifie le titre de six fois. Ces trois réactifs donnent des précisions du même ordre. L'iodate mercurique est légèrement supérieur aux deux autres à cet égard mais il présente l'inconvénient de ne pouvoir servir en solution acide. Les résultats obtenus sont très reproductibles mais s'écartent de 2% au maximum de la théorie suivant que la concentration en ion chiorhydrique est comprise dans le domaine 0,7–3,5 mg.

     

Some factors influencing the solubilities of amine sulphates

The relationship between the molecular structures of amines and the solubilities of their sulphates has been examined with the object of finding a better reagent than benzidine for the determination of sulphate. It has been established that the two aromatic rings must have a tendency to be coplanar and collinear, if the sulphate solubility is to be low. With the help of this theory, 4 : 4'-diaminotolane sulphate has been found to be less soluble than bcnzidine sulphate.