A rapid method for determining sulfur in organic compounds

Conclusions A new, rapid method is given for determining sulfur. It is based on high-temperature pyrolysis of the compound.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1646–1648, July, 1968.     

A rapid method for determining the casein content of milk

A method is presented for the rapid determination of the casein content of milk by Direct Injection Enthalpimetry (DIE).A significant heat pulse of precipitation of casein is produced by adjusting the pH of the solution to the pH of the isoelectric point of casein. The method is calibrated against a real sample whose casein content has been determined by a standard method incorporating the time consuming Kjeldahl method, but once calibrated the proposed method can be operated routinely by non-skilled personnel. The method is sensitive and gives results as acceptable as those obtained by standard methods. The method can be applied to most liquid samples without the need for prior preparation. the main advantages of the method are those of time and costs of analysis and the potential of the enthalpimetric method for automation.

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Zusammenfassung Es wird ein Verfahren zur Schnellbestimmung des Kaseingehaltes von Milch mittels Direct Injection Enthalpimetry (DIE) beschrieben.Durch das Einstellen des pH-Wertes der Lösung auf den pH-Wert des isoelektrischen Punktes von Kasein kann infolge des Ausfällens von Kasein ein eindeutiger Wärmeimpuls erzeugt werden. Das Verfahren wurde anhand einer wirklichen Probe geeicht, deren Kaseingehalt mittels dem zeitaufwändigen Kjeldahl-Verfahren bestimmt wurde. Einmal kalibriert kann das neue Verfahren routinehaft auch von Laien durchgeführt werden. Die Empfindlichkeit der Methode ist gut, die erhaltenen Ergebnisse können genauso akzeptiert werden, wie die in Standardverfahren erhaltenen Ergebnisse. Dieses Verfahren kann bei den meisten flüssigen Proben ohne jede vorherige Vorbereitung angewendet werden. Der Hauptvorteil besteht in der Ersparnis von Zeit und Analysenkosten und in der Anwendbarkeit des enthalpiemetrischen Verfahrens zur Automatisierung.

     

A rapid method for determining strontium-90 in urine samples

Rapid bioassay methods for ⁹⁰Sr in urine samples are needed to provide an early estimation of possible internal dose resulting from exposure to radiostrontium in the event of a radiological and nuclear emergency. In this work, a fast column separation method followed by liquid scintillation counting for detection of ⁹⁰Sr in urine was developed. Replicate spike and blank samples were analyzed for performance evaluation of the method. Using this method, a detection limit of ~10 Bq L^?1 for ⁹⁰Sr can be achieved with a sample analysis turn-around time of 4 h for a set of 12 samples. The method is adequate to meet the radiobioassay acceptance criteria and is suitable for quick dose assessment of ⁹⁰Sr exposure following a radiation emergency.     

A combined standardless electrochemical method for determining lead in aqueous solutions

A combined standardless method for determining lead(II) in aqueous solutions is proposed. The method is based on lows stripping voltammetry and controlled-potential coulometry.     

A general method for copper-catalyzed arene cross-dimerization

A general method for a highly regioselective copper-catalyzed cross-coupling of two aromatic compounds using iodine as an oxidant has been developed. The reactions involve an initial iodination of one arene followed by arylation of the most acidic C-H bond of the other coupling component. Cross-coupling of electron-rich arenes, electron-poor arenes, and five- and six-membered heterocycles is possible in many combinations. Typically, a 1/1.5 to 1/3 ratio of coupling components is used, in contrast to existing methodology that often employs a large excess of one of the arenes. Common functionalities such as ester, ketone, aldehyde, ether, nitrile, nitro, and amine are well-tolerated.     

A rapid method for determining recent sunscreen use in field studies

The role of sunscreens in preventing skin cancer and melanoma is the focus of ongoing research. Currently, there is no objective measure which can be used in field studies to determine whether a person has applied sunscreen to their skin, and researchers must use indirect assessments such as questionnaires. We sought to develop a rapid, non-invasive method for identifying sunscreen on the skin for use in epidemiological studies. Our basic method is to swab the skin, elute any residues which have been adsorbed onto the swab by rinsing in ethanol, and submit the eluted washings for spectrophotometric analysis. In a controlled study, we applied 0.1 ml of sunscreen to a 50 cm(2) grid on both forearms of 21 volunteers. Each forearm was allocated one of 10 different sunscreen brands. The skin was swabbed after intervals of 20 min, 1 h, 2 h and 4 h. In a field study conducted among 12 children aged 2-4 years attending a child care centre, sunscreen was applied to the faces of half the children. Swabs were then taken from the face and back of all children without knowledge of sunscreen status. In the controlled study, sunscreen was clearly detectable up to 2 h after application for all brands containing organic sunscreen, and marginally detectable at 4 h. In the field study, this method correctly identified all children with and without sunscreen. We conclude that spectrophotometric analysis of skin swabs can reliably detect the presence of sunscreen on the skin for up to 2 h after application.     

A relaxation method for determining the recombination rate constant in the advanced stage of the acrylonitrile electrochemical polymerization from its

A method for determining the recombination rate constant (k_t) of electrochemically induced acrylonitrile polymerization based on the internal reflection spectrum of the polymerization system is proposed. The changes in the intensity of the absorption band at 2165 cm^?1 due to the acrylonitrile anion-radicals or to their combination with a limited number of molecules of the monomer (specific active microchains) were used for this purpose. The interpretation of the “on” and “off” curves is based on the assumption that the expression of bimolecular recombination describes the termination of the active chains. The method is also suitable for studying the emergence of spectroscopically discernible particles regardless of their method of preparation on the surface of the prism of the unit used for recording internal reflection spectra. The suggested approach differs from the existing ones in that it follows directly the changes in the concentration of the radicals.     

A simple rapid method for determining sucrose concentration in sucrose gradient centrifugation

Summary The red complex formed by hydroxyl groups with ceric ammonium nitrate served as a means for the rapid and direct determination of sucrose in sucrose gradient centrifugation both for analytical and preparative purposes. In the present work rabbit anti bovine serum albumin serum was separated into 7 S and 19 S components concentrating in the 17–20% sucrose and 26–28% sucrose range respectively.

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Zusammenfassung Die von Cerammoniumnitrat mit Hydroxylverbindungen unter Rotfärbung stattfindende Komplexbildung wurde zur raschen direkten Saccharosebestimmung bei der Rohrzucker- Gradientenzentrifugation für analytische und präparative Zwecke herangezogen. Im vorliegenden Fall wurde mit Antirinderserumalbumin sensibilisiertes Kaninchenserum in eine 7 S- und eine 19 S-Komponente getrennt, von denen erstere in 17- bis 20%igem Rohrzucker, letztere in 26- bis 28%igem Rohrzucker angereichert wurde.

     

On the Rodil–Vera method for determining ion activity coefficients

The basic principles of the method that Rodil and Vera described [E. Rodil, J.H. Vera, Fluid Phase Equilib. 205 (2003) 115–132] to calculate the liquid junction potential and to deduce ion activity coefficients from potentiometric data are critically discussed. It is shown that their procedure is based on an inconsistent loop, and the ion activity coefficients it yields are only an artefact of arbitrary assumptions, with no relationship to the real values, which remain unknown. To provide evidence of this fact, an identical procedure is applied to virtual data referring to a simulated potentiometric experiment with a hypothetical electrolyte whose ion activity coefficients are known; the procedure proves to be unable to recover these activity coefficients. The failure is irremediable and affects all activity coefficients of single ions, which have been reported by Vera and co-workers in the numerous papers they have published so far, whose conclusions lack any scientific support.     

A general method for copper-catalyzed arylation of arene C-H bonds

A general method for copper-catalyzed arylation of sp (2) C-H bonds with p K a's below 35 has been developed. The method employs aryl halide as the coupling partner, lithium alkoxide or K 3PO 4 base, and DMF, DMPU, or mixed DMF/xylenes solvent. A variety of electron-rich and electron-poor heterocycles such as azoles, caffeine, thiophenes, benzofuran, pyridine oxides, pyridazine, and pyrimidine can be arylated. Furthermore, electron-poor arenes possessing at least two electron-withdrawing groups on a benzene ring can also be arylated. Two arylcopper-phenanthroline complex intermediates were independently synthesized.     

A rapid method of sample preparation for determining arsenic in water by stripping voltammetry

A procedure was developed for sample preparation for the further determination of arsenic in potable and natural water and process solutions by stripping voltammetry (SV). To minimize the losses and simplify the procedure, arsenic(III) was oxidized by the ozonation or UV irradiation of the solution in the presence of sulfite, chloride, or hydroxide ions, which increased the oxidation efficiency. The time required for 100% oxidation does not exceed 60 s for an arsenic concentration of no more than 1 mg/L. The reduction to arsenic(III) was performed photochemically in the presence of sodium sulfite for 5 min. Further stripping voltammetric determination was performed in the same solution using a gold-plated carbon electrode. The developed procedure is rapid, simple, and easy-to-automate.     

A new method for determining membrane diffusion coefficients from their response to regular forced concentration waves

It is shown that when a membrane separates two permeant solutions, initially at equilibrium, and subsequently one of the solutions is forcibly oscillated, the concentration waves detected on the other side will show reduced amplitude and a change in phase angle. Using mathematical models it is shown that these may be expressed as explicit functions of the permeability and diffusion coefficient of the permeant, respectively. Solutions for cosine and square concentration waves are given. An experimental system was devised to exploit these effects and measure diffusion coefficients directly from the phase shift of the emergent waves. Input waves were generated using alternating sprays (concentrated and dilute) from two artists' air brushes. In preliminary experiments, diffusion coefficients for salt through test membranes were easily obtained to a precision of 5%.