Automatic microanalyzers: VII. Automatic analyzer for rapid microdetermination of sulfur

A commercially available analyzer for determination of sulfur (0.5–100%) in organic and some inorganic compounds is described. It involves combustion of the sample at high temperature (1050 °C) to form SO₂ and SO₃ in a vertical reactor. SO₃ is reduced to SO₂ and nitrogen oxides to N₂ on copper at 850–900 °C. At this temperature the chemical reactions of SO₂ and copper are minimized so that SO₂ is obtained quantitatively in this range.Use of a vertical reactor and an autosampler makes an easy and complete automation of the sulfur determination possible. With this automation, great improvements are noticed in accuracy and precision over manual methods. The average time for a single determination is about 8 min.     

Automatic microanalyzers: III. Automatic analyzer for rapid microdetermination of nitrogen

A commercially available analyzer for the microanalytic determination of nitrogen in organic and some inorganic compounds was described. The technique is based on the same principle as Walisch CHN analyzer; it involves flash combustion of the sample in helium with a 3% oxygen content and the use of reduced copper for the reduction of any nitrogen oxides to molecular nitrogen and the removal of excess oxygen.The nitrogen concentration in the helium-nitrogen mixture is determined as a function of time by means of a thermal conductivity detector; the output signal of the latter is integrated and printed automatically.The use of an automatic sample feeder and a vertical reactor makes possible a complete automation of the technique without requiring the operator's attention. The original automatic sample feeder used is very simple and cheap; its magazine is accessible at any time; the operator can introduce a new sample without disturbing the analyzer work. The sample weight ranges from 0.5 to 2.5 mg and a determination lasts between 5 and 6 min.The analyzer makes possible the determination of nitrogen contents in the range of 0.5 to 100% and with further improvements, to be described in a later paper, the former limit will be lowered to about 200 ppm.     

Automatic microanalyzers: IV. Automatic analyzer for rapid microdetermination of chlorine or bromine in organic compounds

An automatic microdetermination of chlorine or bromine in organic compounds is described. The sample is weighed out in an aluminum microbeaker which is dropped into a vertical combustion tube, previously described, the quartz combustion chamber of which is heated up to 1050 °C. A flash combustion in oxygen takes place and the gaseous combustion products are absorbed in a cell with a circulating absorption solution of acetic acid and hydrazine hydrate as a reducing reagent in water.Both halogens give halogenide ions in the absorption solution where they are titrated coulometrically by electrolytic silver ions with an amperometric titration end point. The precision of the results is the same as that obtained with common microanalytical techniques.     

Automatic microanalyzers: I. Automatic introduction device

An automatic introduction device AID which can be used to introduce automatically a sample container made of quartz, silver, aluminum or other material into a pyrolysis or combustion tube is described.This system which consists of two parts, the sample inlet device, made of Pyrex glass, and the collecting tube, made of quartz, is very simple and cheap.Gravity feed is used to introduce the sample containers into the AID; the used containers heap up on the bottom of the collecting tube which has to be changed only when it is full so that it is no longer necessary to withdraw each used container after every single determination.The change of the collecting tube which lasts about 0.25 leaves the microanalyzer in working condition.The AID enabled us to develop several apparatus such as oxygen, carbon-hydrogen and nitrogen microanalyzers with a complete automatic control; they will be described in other papers.     

Automatic microanalyzers: VI. Use of a vertical process system

In order to automate the techniques in microanalysis a new series of analyzers utilizing a vertical processing has been developed. Three automatic microanalyzers, i.e., an oxygen, a carbon-hydrogen, and a nitrogen analyzer, are described. For each of them the same type of vertical reactor is used and therefore this design represents an important standardization of this kind of analyzers.Two possibilities for sample introduction are offered. The so-called “automatic introduction device” allows the automatic introduction of the sample into the analyzer; nevertheless it requires the presence of an operator. A fully automated sample introduction is obtained by using the “automatic sample feeder.” This new device can store up to 50 weighed samples and therefore the analyzer runs continuously. These analyzers can carry out an oxygen determination in 7 minutes, a carbon-hydrogen determination in 11 minutes, and a nitrogen determination in 6 minutes. The analyzers can run several hundred determinations continuously.The results reported show a greater reproducibility than that of the results obtained using the classical analyzers, and at least equal accuracy. In addition, the new analyzers have a larger capability; e.g., the oxygen analyzer can determine the oxygen content in organic compounds containing phosphorus and the carbon-hydrogen analyzer allows the determination of the carbon to hydrogen ratio without weighing.     

Automation in organic analysis II. Simultaneous microdetermination of oxygen and nitrogen

A simple, rapid, and accurate method of simultaneous determination of oxygen and nitrogen in organic compounds, containing (in addition to C, H, and O) Cl, Br, and I, is described. The principle of the method consists in the pyrolytic decomposition of the analyzed compound in a current of hydrogen at 1000–1100 °C and the conducting of the hydropyrolytic product through layers of nickel and platinized carbon (50% Pt) heated at 1050 °C. On this filling the nitrogen-containing products are transformed to elementary nitrogen, the oxygen-containing products are transformed to carbon monoxide, the halogens to hydrohalogenides, and methane is decomposed. After removing hydrohalogenides by soda asbestos, carbon monoxide and nitrogen are separated on a chromatographic column filled with Porapak Q, and determined with a catharometer. The whole analysis, including the weighing of the sample, requires 25 min. Sulfur interferes with the determination.     

A rapid method for the microdetermination of sulfide using N-bromosuccinimide

Summary A new, rapid, convenient and accurate method for the determination of sulfide has been developed. N-Bromosuccinimide has been used for the displacement of iodine from potassium iodide which in turn reacts with sulfide and oxidises it to sulfur. N-Bromosuccinimide can be used as a primary standard and kept for several days if refrigerated and protected from light. Sulfide in the range of 0.6 to 13 mg can be determined with an average relative standard deviation of 1.02%.

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Zusammenfassung Ein neues Verfahren zur Sulfidbestimmung wurde entwickelt. N-Bromsuccinimid(I) dient zur Freisetzung von Jod aus KJ. Sulfid wird so zu elementarem Schwefel oxydiert. I kann als Standardlösung einige Tage im Dunklen gekühlt aufbewahrt werden. 0,6 bis 13 mg Sulfid können so mit einer relativen Standardabweichung von 1,02% bestimmt werden.

     

Radiochemical microdetermination of catecholamines. II. Oxidation with labelled potassium dichromate

Summary A radiochemical method of determination of microquantities of catecholamines by means of oxidation with labelled potassium dichromate is described. A sensitivity of better than one picomole is obtained and with addition of copper ions the determination is rapid and the precision better than 10%.

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Zusammenfassung Eine radiochemische Methode zur Bestimmung von Mikromengen Catecholamin durch Oxydation mit markiertem Kaliumbichromat wurde beschrieben. Die Empfindlichkeit übertrifft ein Picomol. Bei Zusatz von Kupferionen verläuft die Bestimmung rasch. Die Genauigkeit ist besser als 10%.

     

Studies on halogen derivatives of phenylazochromotropic acid: II. Spectrophotometric microdetermination of thorium

A new rapid and accurate method for the spectrophotometric microdetermination of thorium using o, p-dichloro-, p-bromo-, and p-iodophenylazochromotropic acids is given. The optimum conditions favoring the formation of the complexes are extensively investigated. The molecular structure was found to be 1:1 and 1:2 Beer's law is obeyed up to 16.24, 18.56, and 11.60 ppm of Th using the three reagents, respectively.     

A simple and rapid fluorimetric method for the microdetermination of isonicotinic acid hydrazide

A simple, rapid and sensitive fluorimetric method has been developed for the microdetermination of isonicotinic acid hydrazide, based on its formation of a hydrazone with 2-hydroxy-1-naphthaldehyde in acidic medium, in the presence of excess of scandium ions, and the consequent formation of a strongly fluorescent complex (lambda(ex) 430 nm, lambda(em) 510 nm) between the hydrazone and scandium in weakly acidic medium. Kinetic and equilibrium procedures for isonicotinic acid hydrazide determination are proposed. A calibration graph linear up to 5.00 mug/ml is obtained by both procedures, with a mean relative error of about 2.0%. The detection limit for the kinetic procedure is 0.4 ng/ml and for the equilibrium procedure about 0.2 ng/ml.     

Simple and specific microdetermination of organoiodine via oxygen flask combustion

A rapid, simple, and reliable procedure for specific microdetermination of organoiodine is described. This procedure consists of oxygen flask combustion followed by an argentimetric titration with an iodide ion-selective electrode as indicator. Some advantages of this procedure over mercurimetric titration currently used in an AOAC method are detailed.     

可移动式微量氧分析仪检定装置研制

研制一种新型可移动式微量氧分析仪检定装置。该装置由标准气体、零点气、脱氧纯化器、减压阀、调节阀、4通阀、5通阀、不锈钢管路、流量控制系统、移动平台等组成。该装置气密性好,15 min内可将装置内氧气浓度由20.9%降至不大于0.1μmol/mol,对于0~10μmol/mol的微量氧分析仪检定结果的扩展不确定度为Urel=1.7%FS(k=2)。该装置满足气体标准物质的连续切换和在线检定的需要,检定时间短,结果准确可靠,可为在线式和非在线式微量氧分析仪的量值溯源提供有效保障。     

Noncatalytic high temperature extraction-nonaqueous titrimetric microdetermination of oxygen in organic compounds

Summary Oxygen in various organic compounds was directly converted to carbon monoxide by decomposing a sample in a graphite crucible at higher than 1800° C. The decomposition products containing the monoxide were purified with soda-asbestos and heated copper wire using argon as a carrier gas. Then the monoxide was oxidized with heated copper(II) oxide. Carbon dioxide produced was absorbed with dimethylformamide containing 2-aminoethanol, and was titrated with a standard solution of tetra-n-butylammonium hydroxide in benzene plus some methanol using thymolphthalein as an indicator.Various types of oxygen in many organic compounds were converted to carbon monoxide stoichiometrically by the above decomposition process. Down to 2g of oxygen was determined with 0.3g error (standard deviation) without any calibrations. Interferences of nitrogen, sulphur and halogene (including fluorine) were removed thoroughly. The method was also applicable to an organoiron compound.

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Unkatalysierte Hochtemperatur-Extraktion und Titration in nicht wäßriger Phase zur Mikrobestimmung von Sauerstoff in organischen Verbindungen

Zusammenfassung Der Sauerstoff verschiedener organischer Verbindungen läßt sich unmittelbar in Kohlenmonoxid umsetzen, indem man die Probe in einem Graphittiegel höher als 1800° C erhitzt. Die Zersetzungsprodukte mit dem Monoxid werden mit Natronasbest und erhitztem Kupferdraht gereinigt, wobei man Argon als Trägergas verwendet. Dann wird das Monoxid über Kupfer(II)oxid oxydiert. Das Kohlendioxid wird in einer Lösung von 2-Aminoethanol in Dimethylformamid absorbiert und mit einer Standardlösung von Tetra-n-butylammoniumhydroxid in Benzol und etwas Methanol titriert, wobei Thymolphthalein als Indikator dient. — Verschiedenartig gebundener Sauerstoff in vielerlei organischen Verbindungen läßt sich durch das angegebene Zersetzungsverfahren stöchiometrisch in Kohlenmonoxid umsetzen. Bis auf 2g Sauerstoff wurden mit einer Standardabweichung von 0,3g ohne vorhergehende Eichung bestimmt. Störungen durch Stickstoff, Schwefel und Halogene (einschließlich Fluor) lassen sich vollständig vermeiden. Das Verfahren eignet sich auch für organische Eisenverbindungen.

     

Polarographic microdetermination of halogens in organic compounds after oxygen flask combustion

A method for the microdetermination of organic compounds containing halogens, by a polarographic finish, is reported. After the combustion of the organic sample in the oxygen flask, the products are absorbed in a suitable absorbent and chemically treated to produce Cl(-), Br(-), BrO(3)(-) or IO(3)(-) ions in solution before the polarography. The method is applicable to partially, highly, and fully halogenated aromatic and aliphatic compounds, whether solid or liquid. The results are generally within the acceptable limits of error.     

Polarographic microdetermination of sulphur in organic compounds after oxygen flask combustion

Summary Three polarographic micro-methods are described for the determination of sulphur in organic compounds after oxygen-flask combustion. The products are converted into sulphuric acid by oxidation with hydrogen peroxide, the excess of which is expelled through boiling. The methods are based upon allowing the sulphuric acid to react with an excess of barium iodate or bromate, then recording polarographically the cathodic reduction wave of the iodate or bromate ion. The bromate methods are superior to the iodate method being simpler and more rapid, and the results are correct to within ca. ±0.5%.

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Zusammenfassung Drei polarographische Mikromethoden zur Bestimmung von Schwefel in organischen Verbindungen nach deren Verbrennung im Sauerstoffkolben wurden beschrieben. Die Verbrennungsprodukte werden durch Oxydation mit Wasserstoffperoxid in Schwefelsäure umgesetzt. Der Überschuß des Oxydationsmittels wird durch Kochen zerstört. Die Schwefelsäure läßt man mit überschüssigem Bariumjodat oder -bromat reagieren und mißt dann polarographisch die kathodische Reduktionswelle des Jodats oder Bromats. Die Bromatmethode ist der Jodatmethode überlegen, da sie einfacher und rascher zu Resultaten führt, die innerhalb ±0,5% korrekt sind.

     

Potentiometric microdetermination of cadmium in organic compounds after oxygen flask combustion

The sample is burnt in an oxygen flask and the combustion products are absorbed in lM HNO₃. After removal of interfering gases by boiling, the solution is transferred to the titration cell and neutralized with NaOH in the presence of methyl red; Cd(II) is finally titrated potentiometrically in a buffered 50% ethanolic medium with 0.01M sodium diethyldithiocarbamate in 50% ethanol. A silver/sulphide ion-selective electrode and a double junction reference electrode containing a 10% KNO₃ solution in 26% ethanol in the outer compartment are used in combination with a Titroprocessor to detect the end point. The results obtained are very accurate and reproducible: the maximum error does not exceed 0.09%, the recovery of cadmium is in the range 99.67 to 99.95% and the rel. standard deviation is 0.05%. The potentiometric titration with diethyldithiocarbamate, which is useful to determine small Cd(II) amounts down to 30g (2g ml^–1), as well as the oxygen flask combustion of organic cadmium compounds are discussed.     

Membrane oxygen enrichment : II. Economic assessment

The classic membrane gas-separation process that virtually everyone doing membrane research has considered, and many have worked on, is oxygen enrichment of air. There seems to be an almost emotional appeal for membrane oxygen enrichment, perhaps because air is free and the market for oxygen is huge. This paper is an attempt to add some facts to the appeal. The state-of-the-art of membrane oxygen enrichment is analyzed, and the authors' opinions of where the leverage for improvement is, and is not, are presented.     

Improved technique of direct oxygen microdetermination by static flash combustion pyrolysis

Summary The direct oxygen determination by static flash combustion pyrolysis in an empty quartz tube has been improved in two respects. The working temperature of 1120° C given originally is lowered to 900° C by the use of platinized carbon. The 15-minutes period considered necessary for the pyrolysis of the sample and for the conversion of oxygen into carbon monoxide is shortened by half. The method has been successfully applied for the determination of oxygen in sulphur-containing compounds by addition of a liquid-nitrogen trap to the apparatus.

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Zusammenfassung Die direkte Mikrobestimmung des Sauerstoffes nach der statischen Schnellverbrennungspyrolyse im leeren Quarzrohr wurde in zweierlei Hinsicht verbessert. Eine Erniedrigung der Arbeitstemperatur von 1120° C auf 900° C wurde durch die Anwendung von platiniertem Gasruß ermöglicht. Außerdem wurde die als notwendig angegebene Zeit von 15 Minuten für die Pyrolyse der Probe und die Überführung des Sauerstoffes in Kohlenmonoxid auf die Hälfte verkürzt.Die Methode wurde auch erfolgreich auf die Bestimmung des Sauerstoffes in schwefelhaltigen Substanzen angewendet, nachdem die Apparatur mit einer Kühlfalle ausgestattet war.