Etude du comportement thermique des n-alcanes dans des milieux hydrocarbones complexes par analyse calorimetrique differentielle. II. Determination du taux de n-alcanes contenu dans un gazole. Determination du point de trouble

The study of the thermal behavior of n-alkanes in a hydrocarbon matrix has been carried out by means of a Mettler TA 2000 B heat flow differential scanning calorimeter. A quantitative method to determine the composition in n-alkanes contained in a gas oil is described. It is assumed that the determination of the cloud point by means of DSC measurements can be obtained with a good precision.     

Etude analytique et dosage de micro- et submicro-traces de manganese par polarographie inverse

A method is proposed for the determination of manganese(II) by anodic stripping polarography. A systematic study was made of the various factors affecting the course of pre-electrolysis as well as the anodic stripping. A procedure is given for the determination of i ng of manganese with a precision of ± 12.7%. The selectivity of the method was studied in the presence of 14 cations ; hydrogen ions interfere at pH <5, Co²⁺ interferes at concentrations equal to that of Mn²⁺, and Mo⁷⁺ and V⁵⁺ at concentrations ?50 times that of Mn²⁺. The other ions studied do not interfere at concentrations 100–1000 times higher. An application to pharmaceutical analysis is described.     

Le dosage spectrophotometrique du cobalt dans le fer de tres haute purete

A spectrophotometric study of the cobalt-β-nitroso-α-naphthol complex between 200 and 350 nm showed the existence of a very sensitive absorption maximum at 308 nm. Utilization of this wavelength allows cobalt in the range 10^-6–10^-5 g to be determined with good precision. The proposed method is very suitable for the determination of cobalt in high-purity iron.     

Flie?injektionsanalyse in der Bodenuntersuchung und Pflanzenanalyse

Summary It could be shown that the flow injection technique can be well introduced in labs which need a high sample throughput without any loss of precision. For normal labs with agrochemical tasks it is possible to adapt the proposed flow injection methods for nitrogen and phosphorus. For the determination of ammonia in juices and musts flow injection is better in precision and faster than the conventional methods. The determination of nitrate in plant extracts can be performed without any clean-up of the crude extract by introducing a dialysis cell in the normal flow injection system. For the determination of proline and arginine methods were developed for flow injection. Both are selective with a high precision and crude plant extracts can be injected for determination. Flow diagrams and equipment parameters are described.     

Precision study on capillary electrophoresis methods for metacycline

A CE method for metacycline (MTC) determination was investigated in an inter-laboratory experiment. Many problems were encountered in this study, most of which were related to the transfer of the method to different CE equipment. The reported problems could be classified into different categories: problems related to the precision, to the parameters in the protocol, and to the MTC peak shape. As the peak shape problem was partially responsible for the poor precision, a new CE method was developed in order to obtain a good MTC peak shape on all equipment. The precision of this new method for MTC determination was examined in an intermediate precision study, where the influence of the factors "time" and "equipment" was investigated. Although the new method could be transferred to different instruments, the precision remained poor mainly due to the contributions of the between-replicate and the between-injection variances.     

Study of the determination of acetylcholine after enzymatic hydrolysis by triangle programmed coulometric flow titration

A new method for the determination of acetylcholine is introduced and studied. The method uses enzymatic hydrolysis of acetylcholine carried out in a flow-through analytical reactor column, while for the detection triangle programmed coulometric flow titration is employed. The flow-through coulometric titration system and the preparation of the enzyme reactor are described. The operation conditions for the hydrolysis and for the titration were optimized. The flow-through coulometric titration technique offers a better precision for the determination of acetylcholine in small concentration ranges than methods based on the detection of pH change. Working conditions of the system can be easily adjusted for different sample concentration ranges. The limit of detection for the determination of acetylcholine was found to be 8x10(-5) M. The method described could be advantageously used for indirect determination of acetylcholinesterase inhibitors.     

Determination of nanogram amounts of cesium by a concentration-dependent distribution method

Paper impregnated with Prussian blue sorbs cesium in low concentration to a different extent if varying initial concentrations of cesium are present. This dependence can be employed for the determination of submicrogram amounts of cesium. The selectivity and precision of the method are discussed. The method is applied to the determination of specific activity in “carrier-free” ¹³⁷Cs samples.     

Analyse isotopique de l'azote par spectrometrie optique,pour de faibles teneurs en 15n

For mixtures of ¹⁴N₂ and ¹⁴N¹⁵N low in ¹⁵N (isotopic abundances less than 2%), previous optical spectrometric methods do not produce rapid results of sufficient precision. In this paper, operating conditions are described for the determination of the isotopic content to ±3% near the natural abundance and to ±1% when the sample contains an atom ratio of ¹⁵N: ¹⁴N of 1.5:100. The time required for a determination is ca. 10 min. A spectrometer is modified by the substitution of an exit slit and a photomultiplier in place of a photographic plate. The excitation of the electrodeless discharge tube is made by a high-frequency field. The method has been applied to samples of ammonium salts, fertilisers and plant material. In all cases, the precision of the isotopic measurements was greater than that required for most agricultural studies (5–6%).     

Determination of photopeak energy in instrumental neutron activation analysis

The precision and accuracy of the peak energy allocation in γ-ray spectrometry govern the subsequent computer processing of the data. By applying the main procedures for peak energy determination to a well-defined case, it is possible to define the minimal statistical uncertainties to be expected. The systematic bias of the energies obtained is caused mainly by changes in the total count rate. A correction can be applied based on the pulser peak. From the precision and the accuracy of the peak energy determination, the scanning width for automatic peak indexing follows.     

Determination of the Stoichiometric Composition of High-Temperature Superconductors by ICP-OES for Production Control

 A procedure to dissolve and analyse different types of high-temperature superconducting materials in order to determine their stoichiometric com- position is described. As sample materials Y-Ba-Cu-O and (Pb)Bi-Sr-Ca-Cu-O were analysed. They were dissolved with hydrochloric acid and analysed by simultaneous ICP-OES, which fits best for this analytical task because of its multielement capacity, its high precision of determination and accuracy. Each of the relevant metals (Pb, Bi, Sr, Ca, Y, Ba, Cu) could be determined successfully. The precision of the determination was found to be better than 2% relative standard deviation and usually even below 1%. The sample preparation and determination procedure described allows a high sample throughput, which is essential for production control. Also precursors of the superconducting materials (e.g. nitrate solutions) could be analysed by the procedure described.     

Capability of ICP-MS (pneumatic nebulization and ETV) for Pt-analysis in different matrices at ecologically relevant concentrations

ICP-MS both with conventional nebulization and with ETV (Electro Thermal Vaporization) have been applied for the determination of Pt in different matrices, e.g. occupational samples like urine and dust samples. It can be used also for other matrices like soil, plants, tissues etc. dependent on the concentration ranges and on a suitable decomposition method. The evaluation, based on the different Pt-isotopes and the quality criteria (detection limit, precision, accuracy) is discussed. Very low determination limits in the range of 1 ng/l can be achieved by ICP-MS-ETV using the standard addition method. This method allows to determine Pt in urine without any sample pretreatment.     

Sensitive determination of diquat by a kinetic method using the stopped-flow mixing technique

A simple, sensitive, selective, fast and inexpensive assay for the determination of diquat is proposed. The method is based on the reduction of the herbicide to a strongly fluorescent monocation radical with sodium dithionite. The initial rate of this reaction is directly proportional to the diquat concentration. The stopped-flow mixing technique was used because the kinetic data can be obtained in only 7 s, meaning that the method can be automated. The calibration graph is linear over the range 5-500 ng ml-1 and the precision (RSD) is close to 1.2%. The applicability of the method was demonstrated by determining the herbicide in different kinds of samples.     

Simultaneous determination of oxygen and nitrogen in iron and steel by spark-source mass spectrography

A conventional technique has been developed for the simultaneous determination of oxygen and nitrogen in iron and steel by spark-source mass spectrography in the range of 2-400 ppm with a precision of 20%. The instrumental background can be reduced by cryosorption pumping and sample cooling. The adsorbed oxygen on the surface of the sample is easily eliminated by presparking to exhaust the surface concerned. A difference in matrix effect in oxygen determination was observed between iron and steel.     

Determination of manganese in natural waters by atomic absorption spectrometry with a carbon tube atomizer.

A method is described for the accurate and precise determination of alumina and silica in bauxites with the aid of a ²²⁷Ac-Be isotopic neutron source with a total neutron output of 10⁸ n s^-1. Three ores can be analysed in triplicate within 4 h, including the determination of the natural radioactivity of the ores. Samples are pellets pressed from a mixture of 4.5 g of powdered bauxite and 0.9 g of a wax as pelleting agent. The special flux distributions of the source allow irradiations at very different fast-to-thermal flux ratios without cadmium neutron absorbers. The drying and water re-uptake of bauxite and the natural radioactivity in these ores are discussed. The method was tested with several certified standards. A relative precision of 0.7% for the alumina determination was obtained for triplicate analyses. Vanadium is the only interfering element, the concentration of which should be determined separately or estimated; a correction procedure is given.     

一种新的五日生物需氧量分析方法

利用荧光氧传感器连续监测封装在密闭培养皿中的废水溶氧浓度，提出了一种新的ＢＯＤ５分析方法，建立了两套ＢＯＤ５检测装置。实验结果表明，利用荧光氧传感器检测ＢＯＤ５，提高了测量的准确性和精度，可望成为新的标准化检测方法。     

Application of chemically modified probe-atomic absorption spectrometry (CMPAAS)-I. Determination of Bi in copper alloy and lead by trioctylphosphine oxide-coated tungsten probe-AAS

A trioctylphosphine oxide (TOPO) coated tungsten probe has been prepared and used for the determination of Bi and the mug/g level in copper alloy and lead. Bismuth is preconcentrated on the probe which is placed in a graphite-cup furnace for AA determination of bismuth. The method has good sensitivity and minimises analysis time. Microgram per gram levels of Bi can be determined with good precision and accuracy.     

Estimation of limits of detection and determination in X-ray fluorescence analysis by the dependence of the relative standard deviation on analyte concentration

An experimental dependence of the relative standard deviation on analyte concentration of hyperbolic type, characterizing the precision of quantitative chemical analysis, was used to estimate the limits of detection and determination in the X-ray fluorescence analysis. A method is proposed for the determination of their values using the approximation of the experimental dependence of the relative standard deviation on the analyte concentration by a power function. The choice of the values of the relative standard deviation, being criteria for the estimation of these limits, is substantiated. A concept of the limits of detection and determination of an analytical procedure is formulated, according to which the limit of detection of an analytical procedure is an objective value depending only on the precision of determinations, and the limit of determination of an analytical procedure is a subjective value depending not only on the precision of determinations but also on the requirements to their limiting (admissible) accuracy. The limits of detection and determinations of an analytical procedure found by this approach completely characterize the possibilities of an analytical procedure in determining low concentrations of analytes. The proposed approach can be used for the estimation of the limits of detection and determination of analytical procedures and in other methods of chemical analysis with the hyperbolic dependence of the relative standard deviation on the analyte concentration.     

Preconcentration and flame atomic absorption spectrometry determination of cadmium in mussels by an on-line continuous precipitation-dissolution flow system

A rapid, sensitive, accurate and precise flame atomic absorption method is described for the determination of cadmium in mussels. The method is based on the continuous precipitation of cadmium as an ion pair between tetraiodocadmate and quinine and dissolution of the precipitate with ethanol. The metal can be preconcentrated 32-fold using 15 ml of sample solution by using a time-based technique at a sampling flow rate of 3.0 ml min(-1). The proposed method allows the determination of cadmium in the range 0.25-5.5 mug g(-1). The precision (relative standard deviation) obtained for different amounts of cadmium is in the range 1.5-4.7% at the 0.25-5.0 mug g(-1) level. The method demonstrates high tolerance to interferences, and the data obtained are in agreement with the certified value of a selected reference material. This procedure was applied to the determination of cadmium in mussel samples from estuaries in Galicia (Spain).     

Quantitative analysis by nuclear magnetic resonance using precision coaxial tubing

Quantitative analysis by n.m.r. using precision coaxial tubing is described. A solution of the intensity standard is placed in the central capillary and the sample of interest in the surrounding annulus. By this method the contamination of the sample by the standard compound can be avoided and an accurate determination can be carried out by using solutions of correct concentrations of the intensity standard. Applications to several types of quantitative problems are given. In order to get a higher accuracy and precision the experimental conditions were also studied.     

Capability of ICP-MS (pneumatic nebulization and ETV) for Pt-analysis in different matrices at ecologically relevant concentrations

ICP-MS both with conventional nebulization and with ETV (Electro Thermal Vaporization) have been applied for the determination of Pt in different matrices, e.g. occupational samples like urine and dust samples. It can be used also for other matrices like soil, plants, tissues etc. dependent on the concentration ranges and on a suitable decomposition method. The evaluation, based on the different Pt-isotopes and the quality criteria (detection limit, precision, accuracy) is discussed. Very low determination limits in the range of 1 ng/l can be achieved by ICP-MS-ETV using the standard addition method. This method allows to determine Pt in urine without any sample pretreatment.Dedicated to Professor Dr. Peter Brätter on the occasion of his 60th birthday