Atomic absorption spectrometry metals

Figure 15-12 is a schematic illustration of a technique known as acid volatile sulfides/ simultaneously extracted metals analysis (AVS/SEM). Briefly, a strong acid is added to a sediment sample to release the sediment-associated sulfides, acid volatile sulfides, which are analyzed by a cold-acid purge-and-trap technique (e.g., Allen et ai, 1993). The assumption shown in Fig. 15-12 is that the sulfides are present in the sediments in the form of either FeS or MeS (a metal sulfide). In a parallel analysis, metals simultaneously released with the sulfides (the simultaneously extracted metals) are also quantified, for example, by graphite furnace atomic absorption spectrometry. Metals released during the acid attack are considered to be associated with the phases operationally defined as "exchangeable," "carbonate," "Fe and Mn oxides," "FeS," and "MeS."... 

At the heart of the ion chromatography system is an analytical column containing an ion exchange resin on which various anions (and/or cations) are separated before being detected and quantified by various detection techniques, such as spectrophotometry, atomic absorption spectrometry (metals) or conductivity (anions). 

Trace metals in sea water are preconcentrated either by coprecipitating with Ee(OH)3 and recovering by dissolving the precipitate or by ion exchange. The concentrations of several trace metals are determined by standard additions using graphite furnace atomic absorption spectrometry. 

The organic reagents are used extensively for determinations series of elements by different methods of analysis. We carry out the systematical investigation of organic derivatives of hydrazine as a reagent for determinations ion of metals by photometric and extractive-photometric methods or analysis, as well as methods of atomic absorption spectrometry. Series procedure determinations ion of metals in technical and environmental objects have been developed. 

DETERMINATION OF HEAVY METALS IN ATMOSPHERIC PARTICLES (PM 10 PM 2.5) BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY... 

Alkaline earth metals and transition metals Elame atomic absorption spectrometry ... 

The element specificity of atomic absorption spectrometry has also been used in conjunction with gas chromatography to separate and determine organo-metallic compounds of similar chemical composition, e.g. alkyl leads in petroleum here lead is determined by AAS for each compound as it passes from the gas chromatograph.75... 

Electrothermal Atomic Absorption Spectrometry of Trace Metals in Biological Fluids... 

Micro-pipetting instruments such as the "Eppendorf or "Oxford pipettors with disposable plastic cone tips are customarily employed to dispense the liquid samples into electrothermal atomizers. Sampling problems which are associated with the use of these pipettors are among the troublesome aspects of electrothermal atomic absorption spectrometry (67,75). The plastic cone-tips are frequently contaminated with metals, and they should invariably be cleaned before use by soaking in dilute "ultra pure nitric acid, followed by multiple rinses with demineralized water which has been distilled in a quartz still. 

Aqueous standard solutions are a source of certain difficulties In electrothermal atomic absorption spectrometry of trace metals In biological fluids The viscosities and surface tensions of aqueous standard solutions are substantially less than the viscosities and surface tensions of serum, blood and other proteln-contalnlng fluids These factors Introduce volumetric disparities In pipetting of standard solutions and body fluids, and also cause differences In penetration of these liquids Into porous graphite tubes or rods Preliminary treatment of porous graphite with xylene may help to minimize the differences of liquid penetration (53,67) A more satisfactory solution of this problem Is preparation of standards In aqueous solutions of metal-free dextran (50-60 g/llter), as first proposed by Pekarek et al ( ) for the standardization of serum chromium analyses This practice has been used successfully by the present author for standardization of analyses of serum nickel The standard solutions which are prepared In aqueous dextran resemble serum In regard to viscosity and surface tension Introduction of dextran-contalnlng standard solutions Is an Important contribution to electrothermal atomic absorption analysis of trace metals In body fluids. 

N1 and Zn from a graphite rod were significantly lower than from a tantalum filament, suggesting that these free metal atoms can be liberated by chemical reduction of their respective oxides, rather than by direct thermal dissociation. Findlay et al (19) emphasized the hazards of preatomlzatlon losses of trace met s In electrothermal atomic absorption spectrometry, when the ashing temperature Is permitted to exceed the minimum temperature for vaporization of the analyte. 

In Table I are listed comprehensive citations of published methods for analyses of trace metals In body fluids and other clinical specimens by means of electrothermal atomic absorption spectrometry. Readers are cautioned that many of the early methods that are cited In Table I have become outmoded, owing to Improvements In Instrumentation for electrothermal atomic absorption spectrometry. All of the published methods need to be critically evaluated In the prospective analyst s laboratory before they can be confidently employed for diagnostic measurements of trace metals In body fluids. Despite these caveats, the author believes that Table I should be helpful as a guide to the growing literature on clinical and biological applications of electrothermal atomic absorption spectrometry. 

Cruz, R. B. and Loon, J. C. van "A Critical Study of the Application of Graphite-Furnace Non-Flame Atomic Absorption Spectrometry to the Determination of Trace Base Metals In Complex Heavy-Matrix Sample Solutions". Anal. Chlm. Acta (1974), 72, 231-243. 

Schramel, P. "Determination of Eight Metals In the International Biological Standard by Flameless Atomic Absorption Spectrometry". Anal. Chlm. Acta (1973), 67 69-77. 

Sunderman, F. W., Jr. "Atomic Absorption Spectrometry of Trace Metals In Clinical Pathology". Hum. Pathol. (1973),... 

Metal ions are most commonly measured using atomic absorption spectrometry. In this technique... 

Eaton AD, Clesceri LS, Greenberg AE. 1995b. Method 3111, Metals by Flame Atomic Absorption Spectrometry, Standard Methods for the Examination of Water and Wastewater, American Public Health Association, Washington, DC. 

First step of the approach is the chemical characterization of leachate using well-established analytical techniques (Fig. 2) GC-MS for polar organic compounds (POCs), HRGC-MS for PCDD/Fs, PCBs and PAHs [18], atomic absorption spectrometry for heavy metals and ion chromatography for ammonia. 

Measurement techniques that can be employed for the determination of trace metals include atomic absorption spectrometry, anodic stripping voltammetry, differential pulse cathodic stripping voltammetry, inductively coupled plasma atomic emission spectrometry, liquid chromatography of the metal chelates with ultraviolet-visible absorption and, more recently, inductively coupled plasma mass spectrometry. 

Many of the published methods for the determination of metals in seawater are concerned with the determination of a single element. Single-element methods are discussed firstly in Sects. 5.2-5.73. However, much of the published work is concerned not only with the determination of a single element but with the determination of groups of elements (Sect. 5.74). This is particularly so in the case of techniques such as graphite furnace atomic absorption spectrometry, Zeeman background-corrected atomic absorption spectrometry, and inductively coupled plasma spectrometry. This also applies to other techniques, such as voltammetry, polarography, neutron activation analysis, X-ray fluroescence spectroscopy, and isotope dilution techniques. 

In the determination of cadmium in seawater, for both operational reasons and ease of interpretation of the results it is necessary to separate particulate material from the sample immediately after collection. The dissolved trace metal remaining will usually exist in a variety of states of complexation and possibly also of oxidation. These may respond differently in the method, except where direct analysis is possible with a technique using high-energy excitation, such that there is no discrimination between different states of the metal. The only technique of this type with sufficiently low detection limits is carbon furnace atomic absorption spectrometry, which is subject to interference effects from the large and varying content of dissolved salts. 

Batley and Farrah [ 120] and Gardner and Yates [118] used ozone to decompose organic matter in samples and thus break down metal complexes prior to atomic absorption spectrometry. By this treatment, metal complexes of humic acid and EDTA were broken down in less than 2 min. These observations led Gardner and Yates [ 118 ] to propose the following method for the determination of cadmium in seawater. 

Adsorptive cathodic stripping voltammetry has an advantage over graphite furnace atomic absorption spectrometry in that the metal preconcentration is performed in situ, hence reducing analysis time and risk of contamination. Additional advantages are low cost of instrumentation and maintenance, and the possibility to use adapted instrumentation for online and shipboard monitoring. 

In contrast, the coupling of electrochemical and spectroscopic techniques, e.g., electrodeposition of a metal followed by detection by atomic absorption spectrometry, has received limited attention. Wire filaments, graphite rods, pyrolytic graphite tubes, and hanging drop mercury electrodes have been tested [383-394] for electrochemical preconcentration of the analyte to be determined by atomic absorption spectroscopy. However, these ex situ preconcentration methods are often characterised by unavoidable irreproducibility, contaminations arising from handling of the support, and detection limits unsuitable for lead detection at sub-ppb levels. 

A typical measurement was performed as follows. The feeder was lowered into the crucible and the sample solution (seawater) was allowed to flow under an inert atmosphere with the suction on. A constant current was applied for a predetermined time. When the pre-electrolysis was over, the flow was changed from the sample to the ammonium acetate washing solution, while the deposited metals were maintained under cathodic protection. Ammonium acetate was selected for its low decomposition temperature, and a 0.2 ml 1 1 concentration was used to ensure sufficient conductivity. At this point the feeder tip was raised to the highest position and the usual steps for an electrothermal atomic absorption spectrometry measurement were followed drying for 30 s at 900 C, ashing for 30 s at 700 °C, and atomization for 8 s at 1700 °C, with measurement at 283.3 nm. The baseline increases smoothly with time as a consequence of an upward lift of the crucible caused by thermal expansion of the material. 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

Armannsson [659] has described a procedure involving dithizone extraction and flame atomic absorption spectrometry for the determination of cadmium, zinc, lead, copper, nickel, cobalt, and silver in seawater. In this procedure 500 ml of seawater taken in a plastic container is exposed to a 1000 W mercury arc lamp for 5-15 h to break down metal organic complexes. The solution is adjusted to pH 8, and 10 ml of 0.2% dithizone in chloroform added. The 10 ml of chloroform is run off and after adjustment to pH 9.5 the aqueous phase is extracted with a further 10 ml of dithizone. The combined extracts are washed with 50 ml of dilute ammonia. To the organic phases is added 50 ml of 0.2 M-hydrochloric acid. The phases are separated and the aqueous portion washed with 5 ml of chloroform. The aqueous portion is evaporated to dryness and the residue dissolved in 5 ml of 2 M hydrochloric acid (solution A). Perchloric acid (3 ml) is added to the organic portion, evaporated to dryness, and a further 2 ml of 60% perchloric acid added to ensure that all organic matter has been... 

Fang et al. [661] have described a flow injection system with online ion exchange preconcentration on dual columns for the determination of trace amounts of heavy metal at pg/1 and sub-pg/1 levels by flame atomic absorption spectrometry (Fig. 5.17). The degree of preconcentration ranges from a factor of 50 to 105 for different elements, at a sampling frequency of 60 samples per hour. The detection limits for copper, zinc, lead, and cadmium are 0.07, 0.03, 0.5, and 0.05 pg/1, respectively. Relative standard deviations are 1.2-3.2% at pg/1 levels. The behaviour of the various chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of seawater. 

Rodionova and Ivanov [667] used chelate extraction in the determination of copper, bismuth, lead, cadmium, and zinc in seawater. The metal complexes of diethyl and dithiophosphates are extracted in carbon tetrachloride prior to determination by atomic absorption spectrometry. 

Orren [663] used atomic absorption spectrometry to determine these elements in seawater in both their soluble and insoluble forms. The alkali metals are determined directly, but the other elements are first concentrated by solvent extraction. The particulate matter content is derived by dissolving the membranes used to filter the sample and determine the metals in the resulting solution. For organic standards of known metal content, the efficiency of the technique was almost 100%. 

Graphite Furnace Atomic Absorption Spectrometry Heavy Metals... 

Cadmium, copper, and silver have been determined by an ammonium pyrrolidine dithiocarbamate chelation, followed by a methyl isobutyl ketone extraction of the metal chelate from the aqueous phase [677], and finally followed by graphite furnace atomic absorption spectrometry. The detection limits of this technique for 1% absorption were 0.03 pmol/1 (copper), 2 nmol/1 (cadmium), and 2 nmol/1 (silver). 

Bruland et al. [122] have shown that seawater samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and flameless graphite furnace electrothermal atomisation is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection Emits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in seawater at their natural ng/1 concentration levels is therefore possible. Samples analysed by this procedure and by concentration on Chelex 100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from seawater by Chelex 100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement. 

---