A comparison of three activation analysis methods for iodine determination in foodstuffs

Activation analysis methods based on the nuclear reactions ¹²⁷ I(n, ) ¹²⁸ I, ¹²⁷ I(n,2n)¹²⁶I and ¹²⁷ I( ,n)¹²⁶ I were tested in terms ofdetection limits, accuracy and precision, and applicability for iodine determinationat various levels in foodstuffs. Both nondestructive and radiochemical modeswere employed using one of the two separation procedures developed (alkaline-oxidativefusion and iodine separation either by extraction of elemental iodine in chloroformor AgI precipitation). The lowest iodine detection limit of 1 ng . g ^—1 was achieved by employing the first nuclear reaction followedby separation of elemental iodine. Accuracy and precision of the proceduresdeveloped at largely different iodine levels were proved by analyses of biologicalreference materials having composition similar to that of various food items.     

Gas analytical methods of thermal analysis in comparison

The undisputed advantages of simultaneous detection and analysis of released gases are today frequently utilized in thermoanalytical experiments. Some aspects of the function principles, the coupling systems and the applicability of different gas detectors are discussed. Both, sufficient qualitative and quantitative informations can be expected from the use of mass spectrometry. The coupling techniques between a quadrupole mass filter and a simultaneous high temperature TG-DTA equipment is described as to some theoretical points of view and verified by test results on complex compounds. It has shown, that for universally usable apparatus gas inlet systems with pressure reducing two-stage orifice arrangements as well as direct sample evaporation in high vacuum should be mutually realized.     

A comparison of three methods for cholinesterase analysis

Three methods of cholinesterase analysis in blood are compared: the ΔpH (modified Michel method), pH Stat, and radiometric methods. The ΔpH method was determined to be the best choice for routine laboratory screeening for organophosphate exposure. The methods all agree within experimental variation. The radiometric method uses a thin-layer chromatography (TLC) separation of acetate (¹⁴C) activity from acetylcholine (¹⁴C) activity with direct β counting or scintillation counting to determine the concentration of acetate activity. The methods were compared on freeze-dried human blood and on experimentally carbamate-inhibited mouse blood. The radiometric analysis may be performed using as little as 5 μl of blood. The radiometric method may enhance the ability to detect sublethal exposure to cholinesterase inhibitors. It should be of particular use where sampling size is of greatest importance.     

A comparison of spectrophotometric and chemiluminescence methods for the determination of blood glucose by flow injection analysis

A flow-injection manifold for the determination of plasma glucose (0–25 mM), incorporating a dialysis unit and a wall-coated enzyme reactor, is described. Spectrophotometric and chemiluminescence methods of detection are compared in terms of precision, accuracy, sample throughput, cost and reliability, and the results obtained from both methods are compared with those obtained from an electrochemical star analyser.     

A comparison of methods for the determination of platinum in ores

Fire-assay and wet-extraction methods of determining platinum in ores have been evaluated. The fire-assay procedure using lead as a collector was used in combination with flame and flameless atomic-absorption, emission spectroscopy and X-ray fluorescence. In this last method flattened silver beads were analysed directly, whereas for the other methods the beads were dissolved in aqua regia and the solutions made up with concentrated hydrochloric acid before analysis. The wet procedures involved treatment of the ores with acids and subsequent analysis by flame atomic-absorption or by spectrophotometry after treatment with tin(II) chloride. Chromatographic, ion-exchange and solvent-extraction procedures were used to isolate platinum from base metals, the other platinum metals and gold. Results for each ore by fire assay-flame atomic-absorption, fire assay-emission spectroscopy, and wet extraction combined with spectrophotometry, showed no difference at the 99% confidence level. X-Ray fluorescence and flameless atomic-absorption results tended to be high and low respectively. The most precise method was wet extraction followed by spectrophotometric determination. Emission spectroscopy and X-ray fluorescence generally yielded the poorest precision. Wet-extraction methods were time-consuming and since no advantage was gained in accuracy over the fire-assay methods, a combined fire assay-flame atomic-absorption system was the preferred method of analysis.     

A comparison of the thermal behaviour of α-AIF3 and aluminium fluoride hydrates

The thermal decompositions of-AlF₃ · 3H₂O, AlF₃ · 3.5H₂O, AlF₃ · 1.5H₂O,-AlF₃ and hydroxyfluorides of aluminium were investigated. The literature data were complemented with X-ray results. The first stages of decomposition are described. The AlF₃ hydrates and hydroxyfluorides were used as model systems in order to interpret the thermal behaviour of -AlF₃ in more detail.

---

Zusammenfassung Die thermische Zersetzung von-AlF₃ · 3H₂O, AlF₃ · 3,5H₂O, AlF₃ · 1,5H₂O,-AlF₃ und Hydroxyfluoriden des Aluminiums wurden untersucht und die in der Literatur beschriebenen Ergebnisse durch Röntgenuntersuchungen ergänzt. Die ersten Phasen der Zersetzung werden beschrieben. Die AlF₃-Hydrate und Hydroxyfluoride des Aluminiums können als Modellsystem genutzt werden, um das thermische Verhalten von -AlF₃ detailliert zu beschreiben.

---

-AlF₃ · ₂, AlF₃ · 3,5₂, AlF₃ · 1,5₂,-AlF₃ . . . - lF₃.

     

Sensitive spectrophotometric determination of aluminium using thermal lens spectrometry

The determination of Al³⁺ in solution using a continuous-wave mode mismatched thermal lens spectrometer is reported and two spectrophotometric procedures are compared. The reagent investigated were bromopyrogallol red—tetradecyltrimethylammonium bromide (BPR—TDTA) and chrome azurol S—cetylpyridinium chloride (CAS—CPC). The CAS—CPC system gave a superior detection limit (0.17 μg 1^?1) to the BPR—TDTA system (1.15 mg 1^?1) owing to the higher reagent blanks and concomitant laser noise in the latter system.     

Spectrochemical determination of impurities in telluric acid

An emission spectrographic method is described for determination of 20 elements present as impurities in telluric acid. Samples are excited in a 12-A. d.c. arc with the use of NaCl-KCl as a spectrographic buffer and germanium as internal standard. The limit of determination lies between 10(-5) and 10(-2)%. The precision of the method calculated as relative standard deviation is 10-25%.     

Spectrochemical determination of germanium in tar ashes

A technique for the emission spectrographic determination of germanium in tar ashes is described. Internal standardization was employed, Ge 2651.178 Å and Fe 2645.427 Å being the analysis pair. The effects of varying matrix were diminished by making up the Fe contents of the samples to a convenient limit, and by the addition of calcium carbonate. The technique, applicable to materials of reasonably different matrices, gives a precision of the order of 8–9%, expressed as standard deviation.     

A comparison of the several methods for determination of specific IgE antibodies

The accuracy of measurement using kits in the clinical laboratories is important for the patient diagnosis and treatment. In the present paper, the AL-18, AlaSTAT, CAP, FAST and RAST methods were investigated and were compared among kits the results obtained with serum sample, for determination of specific IgE antibodies. Significant differences among kits were observed from the results of those methods. One of the reasons, why the data discrepancy exists, is that each kit uses a different reference and a different inclusion method of allergen. For the evaluation of data discrepancy among those kits, it might be important that the clinical history of symptoms and in vivo tests against the different allergens compared with results of in vivo tests.     

Spectrochemical determination of tungsten and boron in mineral matrix

The spectrochemical behavior of nonvolatile tungsten and boron was tested by adding different buffers and using 12 A ac arc excitation. The oxidization and sulfidization processes were found to be most effective for facilitating the volatilization. The optimal admixture was the copper oxide buffer for both the detection limit and the precision of the method. The reference values of the background or a palladium line blackening were used.     

Critical comparison of methods for mercury determination in fish

One of the major analytical problem in the analysis of fish tissues for total mercury is the dissolution of the sample. This paper compares two different methods of wet digestion (microwave and closed pressurized vessel), followed by FIAAS as final determination and a Zeeman-solid-sample-AAS determination method without previous mineralization.Six fish samples were selected for this study. The top, the central and the bottom portions of the fish were analyzed separately. The mercury contents in the bottom portions determined by Zeeman-solid-sample-AAS were significantly higher than those obtained by the other two systems. A good correlation was observed among the results of the different techniques.     

Model for successive determination of aluminium and fluoride by combination of fluorimetric and potentiometric methods

Summary The paper represents a non-conventional approach to the successive determination of aluminium and fluoride in the same sample. It is based on the mathematical correction of a complex analytical signal for aluminium in the presence of fluoride (obtained by the fluorescence method). Additionally, a potentiometric determination of the fluoride content is necessary to complete the analysis. A mathematical model to describe the dependence between the complex analytical signal and the concentrations of aluminium and fluoride for a wide range of concentrations of both species is obtained. The approach seems to be useful for continuous monitoring of samples containing both aluminium and fluoride such as tooth paste, cryolite, industrial waste waters etc.

---

Ein Modell für die aufeinanderfolgende Bestimmung von Aluminium und Fluorid durch Kombination von Fluorimetrie und Potentiometrie

Zusammenfassung Die Arbeit beschreibt eine nichtkonventionelle Methode für die Bestimmung von Aluminium und Fluorid in einer Probe. Sie beruht auf der mathematischen Korrektur eines komplexen analytischen Signal für Aluminium in Anwesenheit von Fluorid (durch Fluorescenzverfahren) und nachfolgende Bestimmung von Fluorid durch Potentiometrie. Ein mathematisches Modell, das den Zusammenhang zwischen dem komplexen Signal und den Konzentrationen von Aluminium und Fluorid für einen breiten Konzentrationsbereich beider Ionen beschreibt, wird dargestellt. Die Methode kann für die kontinuierliche Analyse von Proben, die Aluminium und Fluorid gleichzeitig enthalten (z. B. Zahnpasta, Kryolith, Abwasser usw.) eingesetzt werden.

---

---

On leave from Fac. of Chemistry, Chair of Analyt. Chemistry, Univ. of Sofia, 1126 Sofia, A. Ivanov 1, Bulgaria     

Quantitative determination of cristobalite by thermal methods

Cristobalite was quantitatively determined by quartz samples fired between 1350 and 1490°C by thermal methods and specific gravity measurements. The amount of cristobalite was calculated from the thermal expansion coefficient, the area of the differential thermal expansion together with specific heat measurements and specific gravity determinations. The calculated values from the expansion coefficient and specific gravity are misleaing due to the presence of tridymite and glass in the samples. The results of differential thermal expansion compare well with those of specific heat measurements. Therefore, this method could be taken as a very precise measure for the quantitative determination of cristobalite. Also, the temperature of the peak indicates whether ordered or disordered cristobalite is present.     

Spectrochemical analysis of curium and americium samples

Spectrochemical procedures have been developed to determine impurities in americium and curium samples. The simultaneous separation of many impurity elements from the base material (americium and curium) is carried out with extraction and extraction-chromatographic methods using di(2-ethyl hexyl phosphoric acid (D2EHPA).

It is shown that part of the elements (alkalis, alkaline earths, silicon, tungsten, tantalum and other elements) are separated with extraction or sorption of americium and curium; the other part (rare earths, titanium, zirconium, niobium, molybdenum) with the Talspeak process.

Two fractions in the extraction chromatography and three fractions in the extraction separation of americium and curium, containing impurities, are analyzed separately by a.c. or d.c. arc spectrography. To increase the sensitivity of the spectrographic analysis and accelerate the burn-up of impurities from the crater of the carbon electrode bismuth fluoride and sodium chloride were used as chemically active substances. The extraction of impurities from weighed quantities of americium and curium samples of 5–10 mg permits the lower limit of determined impurity concentrations to be extended to 1 × 10⁻⁴–5 × 10⁻³% m/m.