Erbium determination in preforms of optical fibres by inductively coupled plasma-atomic emission spectrometry.

Erbium which is used in the composition of heavy metal fluoride optical fibres was determined in preforms of these materials by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The new analytical procedure developed comprises: solid sample dissolution, via an alkaline fusion with sodium carbonate, and acid leaching with dilute hydrochloric acid, and measurements of emission intensities of 337.276 nm. This method has a detection limit of 31 ng/ml and a reproducibility of 0.90% r.s.d.

Observations on the determination of osmium by inductively-coupled plasma atomic emission spectroscopy.

Osmium tetroxide gives rise to very characteristic atomic emission properties. In acidic samples it gives much higher sensitivity than that given by the lower oxidation states (IV, III, II). However, in alkaline medium (pH 10.5) its atomic emission sharply decreases, and the sensitivity is the same as that for the other oxidation states. It has been shown that there is a direct relation between these characteristics of OsO(4) solutions and pH. With increasing pH the intensity of its atomic emission decreases, the electrode potential of its solutions drops sharply and the molecular absorption of radiation at 193 nm undergoes a hyperchromic and bathochromic shift. The volatility of OsO(4) has also been studied, and found to be minimum at around pH 9.5. This favours its determination at this pH.

Volatilization of methyl borate in iron matrix. Determination of boron in steel by ICP atomic emission spectrometry.

A rapid and reliable method for the determination of boron by ICP-AES in steels is described. The procedure is based on a discontinuous generation of methyl borate, in concentrated sulphuric acid and phosphoric acid medium, after injecting 45 microl of methanol in 20 microl of sample. The gaseous methyl borate and excess methanol are fed into the ICP torch via the intermediate tube by a flow of 430 ml/min Ar carrier gas, without disturbing the discharge. This work simplifies drastically the existing methodology of boron analysis in steels. Acid-soluble boron has been determined, but acid-insoluble boron can also be determined. The determination is carried out without iron interferences, with a reproducibility of 1.90% r.s.d. for a concentration of 20 microg/ml, and an absolute detection limit of 20 ng of total boron, working with a solution volume of 20 microl.

Sulphate determination after its reduction to hydrogen sulphide and volatile separation by molecular absorption spectrometry.

A rapid spectrophotometric method for sulphate determination in a discontinuous mode is described. The method is based on sulphate reduction to hydrogen sulphide followed by its volatilization and absorption in an alkaline solution. The reduction is obtained when a sulphate sample is heated to 287 degrees C for 15 min, with a mixture of Fe(o)/KI and phosphoric acid. The resulting gas is swept by nitrogen flow into a 0.1 M sodium hydroxide solution and the absorbance of the sulphide ions is measured directly at 230 nm. The proposed method enabled us to determine 50-700 mug of total sulphate with a relative standard deviation of the order of 5%. The method has been applied for the determination of sulphates in liquid (mineral waters) and solid (gypsiferous soils) samples.

Silicon determination by inductively coupled plasma atomic emission spectrometry after generation of volatile silicon tetrafluoride.

A method for the determination of silicon by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The procedure is based on a discontinuous generation of volatile silicon tetrafluoride in concentrated sulphuric acid medium after injecting 125 mul of 0.1%, w/v sodium fluoride solution into 100 mul of the sample. The gaseous silicon tetrafluoride is fed directly into the ICP torch by a flow of 250 ml min(-1) Ar carrier gas. The calibration curve was linear up to at least 100 mug ml(-1) of Si(IV) and the absolute detection limit was 9.8 ng working with a solution volume of 100 mul. The relative standard deviation for six measurements of 10 mug ml(-1) of Si(IV) was 2.32%. The method was applied to the determination of silicon in water and iron ores.

Antimony(V) volatilization with bromide and determination by inductively coupled plasma atomic emission spectrometry.

Antimony(V) is volatilized by reaction with potassium bromide in concentrated sulfuric acid media. After volatilization, the gases can be transported to an inductively coupled plasma spectrometer for atomic emission of antimony and its analytical determination. The influent factors, concentrated sulfuric acid volume, concentration and volume of the potassium bromide aqueous solution and carrier gas flow were investigated and optimized using different alternatives. A detection limit of 48ngml(-1) of Sb was achieved under the optimized conditions with a precision of 7.6% and the calibration graph was linear from 0.10 to 10.0mugml(-1) for a sample injection of 130mul. The study of interferences from common cations and anions revealed a good tolerance for most ions, although there was a significant improvement in Sb(V) volatility when As(III) was present. Furthermore, the As(III) sensitization was only produced with Sb(V) species, while the volatility of the Sb(III) bromide species was unaltered. The method was applied to the determination of Sb in real river waters. The results were checked using alternative atomic spectroscopy methods.

Classification of ancient Roman glazed ceramics using the neural network of Self-Organizing Maps.

Artificial neural networks with unsupervised learning strategy known as Self-Organizing Maps were applied to classify ancient Roman glazed ceramics. Their clay ceramic bodies were analyzed by Inductively Coupled Plasma-Atomic Emission Spectroscopy and the chemical composition obtained was processed by this neural algorithm. The results obtained provide two types of information: firstly, classification of ceramic samples with identification of several groups and secondly, differentiation between the elemental chemical information. It was found that there are certain chemical elements which can be considered as principal and which can serve to differentiate between ceramics, whereas other elements give redundant information and do not contribute to sample differentiation. Seven chemical elements were considered principal and provide the necessary information. Two types of element were identified: 1- a group formed by common elements, such as: Ca, Fe, Mg, Mn and 2- another formed by optional elements: K or Na and Ba or Sr and Al or Ti.

Chemical vapor generation for sample introduction into inductively coupled plasma atomic emission spectroscopy: vaporization of antimony(III) with bromide.

A new method for antimony determination in soils is proposed. It is based on the chemical vapor generation of Sb(III) with bromide, after a reaction in sulfuric acid media and transport of the gaseous phase into an inductively coupled plasma for atomic emission spectrometry. The experimental variables influencing the method were delimited by experimental design and the most important were finally optimized by the modified Simplex method. In optimized conditions the method involves the reaction of 579 microl concentrated sulfuric acid with 120 microl 5% w/v KBr and 250 microl antimony solution. Measurement of antimony emission intensity at 217.581 nm provides a method with an absolute detection limit of 3.5 ng and a precision (RSD) of 5.8% for the injection of five replicates of 175 ng Sb(III) (250 microl of 0.7 microg ml(-1) solution). The interference of common anions and cations on the antimony signal was evaluated. A 21% Sb(III) volatilization efficiency was calculated from the mean of six experiments at optimum conditions. The accuracy of the methodology was checked by the analysis of one standard reference soil after acid decomposition heating in a microwave oven.