Metal nitrates spectrometry

Table 2.1 Mass spectrometry studies of thermal decomposition of metal nitrates...

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

Elemental composition Gd 59.65%, Cl 41.35%. GdCL aqueous solution is analyzed for Gd metal by AA or ICP spectrometry, and for chloride ion by ion chromatography, chloride ion selective electrode, or titration with silver nitrate using potassium chromate indicator. 

An official method has been published for the determination of nickel in 1M ammonium nitrate extracts of potassium from soil [178]. The level of potassium in the extract is determined by flame photometry. Inductively coupled plasma atomic emission spectrometry (Sect. 2.55) and stable isotope dilution (Sect. 2.55) have been applied to the determination of potassium in multi-metal analyses. 

Although ionization of sodium is negligible and potassium small in an air—propane flame, some ionization is experienced in the recommended hotter air—acetylene flame. Ionization should be suppressed by the incorporation of excess potassium or cesium (for sodium determinations) or excess sodium or cesium (for potassium determinations), at concentrations of 1000/igml-1 or greater, in the form of chlorides or nitrates, in both sample and standard solutions. Cesium is the more effective but more expensive ionization suppressant. Extent of ionization is inversely related to analyte concentration with errors due to incomplete suppression thus being greater at low concentrations. As it is difficult to obtain alkali metal salts free from traces of other alkali metals, possible contamination must be considered, especially at low analyte levels. Use of a branched capillary for introduction of ionization buffer has been advocated for flame spectrometry to... 

It was shown that tryptophan is also nitrated by peroxynitrite in the absence of transition metals to one predominant isomer of nitrotryptophan, as determined from spectral characteristics and liquid chromatography-mass spectrometry analysis. Typical hydroxyl radical scavengers partially inhibited the nitration" . The yields of the nitration of tyrosine and salicylate by peroxynitrite are significantly improved by the Fe(III)-EDTA complex " ". ... 

The application of CFD methods also makes it possible to carry out the analysis of such inorganic substances as anions and metals. As an example let us consider the analysis of trace amounts of nitrates in water. Tan [44] proposed a simple and sensitive method for determining nitrates in aqueous solutions using GC—mass spectrometry (MS) with an ionic detector-multiplier. The method is based on the nitration of 1,3,5-trimethoxy-benzene (TMB) in sulphuric acid. In this medium the nitration follows the hydrolysis of the ether groups of TMB, and nitrobenzene is formed as the final product [44]. The reaction mixture is analysed by GC and detected with a mass spectrometer. Hexamethyl-benzene (HMB) is used as an internal standard. To avoid interference from nitrates and chlorides, sulphamic acid and mercury(ll) sulphate are used. 

The range of off-line instruments available for water analysis Is wide. In fact, any analyser with optical or electrochemical detection can be adapted for this purpose. The use of liquid chromatography for the detection and quantitation of detergents or non-volatile organic compounds, of atomic absorption spectrometry for the analysis for heavy metal traces and of UV spectrophotometry for the determination of phosphates, nitrates and nitrites are representative examples of the potential utilization of conventional analysers for water analysis. 

Chemical analysis provides much more precise data about the sample, particularly the determination of metallic elements, mainly lead, cadmium, iron, calcium, sodium as well a.s anions, chlorides, fluorides, nitrates, carbonates and sulphates. The analyses are performed most frequently by spectrophotometry, atomic absorption spectrometry, or polarography in recent years radionuclide X-ray fluorescence and activation analysis have been used. 

Compared with classical analytical methods such as gas chromatt raphy, HPLC, atomic absorption or mass spectrometry, the detection of pollutants by biosensors is generally less specific. These devices provide valuable information on a class of pollutants rather than a mere information about a specific compound, although the use of mutants that are resistant to specific pollutants can render them more selective. Biosensors provide valuable information about the real biological effects of the pollutants in a sample since phytotoxicity is determined from the measurement of electron transport activity, photocurrent or photosynthetic oxj en evolution. It is important to note that althoi the PSII complex is sensitive to various pollutants (herbicides, heavy metals, sulphites, nitrates, carbonates), its susceptibility to these compounds is highly variable, tanging from nanomolar to milhmolar concentrations. 

A typical DGT device for use in waters consists of a gel impregnated with a chelating resin, covered by a diffusive hydrogel (0.4-0.8 mm thick polyacrylamide) topped with a 100 pm thick, 0.45 pm pore size cellulose nitrate or polysulfone membrane, and contained in a plastic holder with a 2 cm diameter window (Figure 2). For sediment and soil monitoring another sampler that allows sectioning of fine vertical strips is used. Typically, DGT samplers might be deployed for 24-72 h, at the end of which the Chelex gel is removed and placed in a known volume of dilute nitric acid. The elutriate is subsequently analyzed for trace metals by a sensitive technique such as inductively coupled plasma mass spectrometry (ICP-MS). 

Atomic spectrometric techniques such as flame atomic absorption spectrometry (FAAS), electrothermal AAS (ETAAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), and ICP-MS are used for the determination of elements, particularly metals. ICP-MS is the most sensitive, typically with microgram per liter detection limits and multielement capability but it has high start-up and operating costs. UV-visible spectrophotometry is also used for the determination of metal ions and anions such as nitrate and phosphate (usually by selective deriva-tization). It is a low cost and straightforward technique, and portable (handheld) instruments are available for field deployment. Flow injection (FI) provides a highly reproducible means of manipulating solution chemistry in a contamination free environment, and is often used for sample manipulation, e.g., derivatization, dilution, preconcentration and matrix removal, in conjunction with spectrometric detection. Electroanalytical techniques, particularly voltammetry and ion-selective electrodes (ISEs), are... 

In one of the most relevant papers in this field, Dima et al. [13] studied the electrocatalytic behavior of different polycrystalline metals such as Ru, Rh, Ir, Pd, Pt, Cu, Ag and Au for nitrate (100 mM) reduction in 0.5 M H2SO4. On the basis of the peak current density related to nitrate reduction on cyclic voltammograms, the activities of each electrode were compared. It was determined that rhodium is the most active catalyst among the noble metals for the reduction of nitrate, with the activity decreasing in the order Rh, Ru, Ir, Pt, Pd and Cu, Ag, Au for transition metals. The high electrocatalytic performance of Rh for nitrate reduction was also observed by Brylev et al. [19]. By using Differential Electrochemical Mass Spectrometry (DEMS), a reduction mechanism for nitrate reduction has been determined for transition metals (Fig. 2). 

---