Atomic absorption spectroscopy precision

The possibility of preconcentration of selenium (IV) by coprecipitation with iron (III) hydroxide and lanthanum (III) hydroxide with subsequent determination by flame atomic absorption spectroscopy has been investigated also. The effect of nature and concentration of collector and interfering ions on precision accuracy and reproducibility of analytical signal A has been studied. Application of FefOH) as copreconcentrant leads to small relative error (less than 5%). S, is 0.1-0.2 for 5-100 p.g Se in the sample. Concentration factor is 6. The effect of concentration of hydrochloric acid on precision and accuracy of AAS determination of Se has been studied. The best results were obtained with HCl (1 1). 

Analysis of Corexit 9527. Corexit 9527 in natural waters can be analyzed. The method is based on the formation of a Z>w(ethylenediamine) copper(II) complex, extraction of the complex into methylisobutylketone, and atomic absorption spectroscopy [1564]. The method is suitable for a concentration range of 2 to 100 mg/liter, with a precision as low as 5% relative to standard deviation for samples in the middle- to high range. Only a small sample volume (10 ml) is required. The sensitivity may be substantially increased for trace analysis by increasing the sample volume. 

Agemian and Chau [55] have described an automated method for the determination of total dissolved mercury in fresh and saline waters by ultraviolet digestion and cold vapour atomic absorption spectroscopy. A flow-through ultraviolet digester is used to carry out photo-oxidation in the automated cold vapour atomic absorption spectrometric system. This removes the chloride interference. Work was carried out to check the ability of the technique to degrade seven particular organomercury compounds. The precision of the method at levels of 0.07 pg/1, 0.28 pg/1, and 0.55 pg/1 Hg was 6.0%, 3.8%, and 1.00%, respectively. The detection limit of the system is 0.02 pg/1. 

A different pattern of dissolution was seen with a Zn-Sn alloy containing 26% zinc. In this case the stable dissolution situation established after ca. 90 min showed a ratio of EC to CMT measurements of 1 4. As seen in Fig. 3, this remained fairly constant, though the corrosion potential increased by more than 50 mV. Only selective zinc dissolution took place, and analysis by atomic absorption spectroscopy of the amount of dissolved zinc agreed within 10% with the value according to the titration. This pattern is still difficult to understand. The ratio of ca. 1 4 between EC and CMT measurements could be interpreted in terms of formation of the low-valent zinc species ZnJ, which seems unlikely, or in terms of dissolution of divalent zinc ions accompanied by loss of chunks consisting of precisely three zinc atoms, each time a zinc ion is dissolved. The latter alternative seems to require a more discrete mechanism of dissolution than... 

Since the mid-1960s, a variety of analytical chemistry techniques have been used to characterize obsidian sources and artifacts for provenance research (4, 32-36). The most common of these methods include optical emission spectroscopy (OES), atomic absorption spectroscopy (AAS), particle-induced X-ray emission spectroscopy (PIXE), inductively coupled plasma-mass spectrometry (ICP-MS), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray fluorescence spectroscopy (XRF), and neutron activation analysis (NAA). When selecting a method of analysis for obsidian, one must consider accuracy, precision, cost, promptness of results, existence of comparative data, and availability. Most of the above-mentioned techniques are capable of determining a number of elements, but some of the methods are more labor-intensive, more destructive, and less precise than others. The two methods with the longest and most successful histoty of success for obsidian provenance research are XRF and NAA. 

Howlett and Taylor (1978) used an atomic absorption spectroscopy fitted with a micro-cup assembly (MCAAS) for determining silver levels in human whole blood. The MCAAS technique affords a rapid, precise, and relatively simple method for the measurement of silver in blood. Furthermore, this technique requires no sample preparation prior to analysis except pipetting and drying. A detection limit level of 0.27 pg/100 ml of blood sample was measured. Flowlett and Taylor (1978) noted that repeated measurement of silver in blood using a single nickel cup showed a gradual decrease in sensitivity. 

Salem et al. [48] reported simple and accurate methods for the quantitative determination of flufenamic, mefenamic and tranexamic acids utilizing precipitation reactions with cobalt, cadmium and manganese. The acidic drugs were precipitated from their neutral alcoholic solutions with cobalt sulfate, cadmium nitrate or manganese chloride standard solutions followed by direct determination of the ions in the precipitate or indirect determination of the ions in the filtrate by atomic absorption spectroscopy (AAS). The optimum conditions for precipitation were carefully studied. The molar ratio of the reactants was ascertained. Statistical analysis of the results compared to the results of the official methods revealed equal precision and accuracy. The suggested procedures were applied for determining flufenamic, mefenamic and... 

The standard addition method is commonly used in quantitative analysis with ion-sensitive electrodes and in atomic absorption spectroscopy. In TLC this method was used by Klaus 92). Linear calibration with R(m=o)=o must also apply for this method. However, there is no advantage compared with the external standard method even worse there is a loss in precision by error propagation. The attainable precision is not satisfactory and only in the order of 3-5 %, compared to 0.3-0.5 % using the internal standard method 93). 

Norheim G, Haugen A. 1986. Precise determination of selenium in tissue using automated wet digestion and an automated hydride generator - Atomic absorption spectroscopy system. Acta Pharmacol Toxicol 59 (Suppl 7) 606-609. 

Among the various types of atomic spectroscopy, only two, flame emission spectroscopy and atomic absorption spectroscopy, are widely used and accepted for quantitative pharmaceutical analysis. By far the majority of literature regarding pharmaceutical atomic spectroscopy is concerned with these two methods. However, the older method of arc emission spectroscopy is still a valuable tool for the qualitative detection of trace-metal impurities. The two most recently developed methods, furnace atomic absorption spectroscopy and inductively coupled plasma (ICP) emission spectroscopy, promise to become prominent in pharmaceutical analysis. The former is the most sensitive technique available to the analyst, while the latter offers simultaneous, multielemental analysis with the high sensitivity and precision of flame atomic absorption. 

The elements Na, K, Li, Mg, Ca, Al, and Zn are among the most common elements subjected to pharmaceutical analysis and coincidentally are also among the elements most readily determinable by flame emission. Although it is not as versatile as other methods, flame emission spectroscopy exhibits sensitivity greater than or approximately equal to that of flame absorption spectroscopy for the above elements (Table 2). Where precision of the analysis is critical, however, the analyst should consider the alternative of atomic absorption spectroscopy. 

Sodium and potassium levels are difficult to analyze by titrimetric or colorimetric techniques but are among the elements most easily determined by atomic spectroscopy (2,38) (Table 2). Their analysis is important for the control of infusion and dialysis solutions, which must be carefully monitored to maintain proper electrolyte balance. Flame emission spectroscopy is the simplest and least expensive technique for this purpose, although the precision of the measurement may be improved by employing atomic absorption spectroscopy. Both methods are approved by the U.S. (39), British (40), and European (41) Pharmacopeias and are commonly utilized. Sensitivity is of no concern, due to the high concentrations in these solutions furthermore, dilution of the sample is often necessary in order to reduce the metal concentrations to the range where linear instmmental response can be achieved. Fortunately, the analysis may be carried but without additional sample preparation because other components, such as dextrose, do not interfere. 

Zinc is present in a number of pharmaceuticals, the most important of which is life-sustaining insulin. Many topical preparations contain zinc as the oxide, sulfate, or stearate as an astringent or antipruritic. Some foot powders contain the antifungicidal zinc undecenoate, and zinc pyrithione is used in antidandruff shampoos. After dissolving them in acid, the topical products can be easily analyzed by either atomic emission or atomic absorption spectroscopy (49), since they contain a relatively high concentration of zinc. However, atomic absorption is approximately four orders of magnitude more sensitive than atomic emission for the determination of zinc (Table 2) and offers superior precision for the analysis of injectable insulin (50), where zinc concentrations can be as low as 4 ppm (39). 

Each experiment was accortqjanied the determination of Pd in solution after hot filtration of the solid catalyst at the end of the reaction. Because simple Atomic Absorption Spectroscopy (AAS) was found to not be precise enough for the palladium analysis in this concentration range (detection limit too high.) ICP-OES and/or ICP-MS (Inductively Coupled Plasma - Optical Emission Spectroscopy or Inductively Coupled Plasma - Mass Spectrometry) were applied. To first approximation, the Pd leaching could not be correlated with the properties of the twelve different Pd/C catalysts described above ((1) Correlation of catalyst structure and activity.) There is, however, a strong correlation with the reaction parameters as described below. 

In applications of voltammetry to biological samples, it is often the sample rather than the sensitive voltammetric analyzer that is the limiting factor. Getting the sample into a form that can take full advantage of the instrument capability may be the hardest part of the analysis. For this reason, the sample is usually treated prior to analysis. Such treatment releases the trace metals bound to sample components, and minimizes fouling of electrode (by adsorption of certain sample components) or background currents (from other electroactive constituents). The precision and bias of the data obtained by voltammetric analysis of biological samples will be more dependent on how well the sample is decomposed than with many other analytical techniques (e.g., atomic absorption spectroscopy which relies on atomization of the metal from the solution). 

As in atomic absorption spectroscopy, one or more standards should be introduced periodically to correct for the effects of iiislrumeni drift. The improvement in precision that results from this procedure is illustrated by the data in Tabic 10-2. Note also the iniprtwcd precision when higher concenlraiioiis of analyte arc measured. ... 

Several elements (Zn, Pb, Cuy Ni, Ca, Mg, Fe, and Mn) are determined routinely in water samples using atomic absorption spectroscopy. Sodium and potassium are determined by flame emission. The preparation of the samples the analytical methody the detection limits and the analytical precisions are presented. The analytical precision is calculated on the basis of a sizable amount of statistical data and exemplifies the effect on the analytical determination of such factors as the hollow cathode sourcey the ffamey and the detection system. The changes in precision and limit of detection with recent developments in sources and burners are discussed. A precision of 3 to 5% standard deviation is attainable with the Hetco total consumption and the Perkin-Elmer laminar flow burners. 

Even with the diflBculties cited above, the combination of flame emission and atomic absorption spectroscopy has become in a very short time one of our better methods for the analysis of waters for cations for the following reasons limited sample preparations necessary, high sensitivity, good analytical precision, low cost, and simphcity of equipment. 

The application of stripping voltammetry includes the measurements of metal ions and organic compounds in a variety of chemical, environmental, metallurgical, geological, biological, biochemical, pharmaceutical, and clinical materials [2, 121-123]. They are used in routine trace metal analysis of waters [124] and can serve as reliable, sensitive, and precise methods for the verification of results obtained by atomic absorption spectroscopy, or some chromatographic techniques [125]. 

In the atomic spectroscopy experiment in Figure 20-1, a liquid sample is aspirated (sucked) through a plastic tube into a flame that is hot enough to break molecules apart into atoms. The concentration of an element in the flame is measured by absorption or emission of radiation. For atomic absorption spectroscopy, radiation of the correct frequency is passed through the flame (Figure 20-2) and the intensity of transmitted radiation is measured. For atomic emission spectroscopy, no lamp is required. Radiation is emitted by hot atoms whose electrons have been promoted to excited states in the flame. For both experiments in Figure 20-2, a monochromator selects the wavelength that will reach the detector. Analyte concentrations at the parts per million level are measured with a precision of 2%. To analyze major constituents, a sample must be diluted to reduce concentrations to the ppm level. Box 20-1 describes an application of atomic emission for space exploration. 

Analytical laboratory testing is the most precise way to measure the amount of lead in a particular sample of paint. To test paint, a small piece of paint must be removed, placed in a container, labeled, and brought to a laboratory where it is tested using a scientific method such as atomic absorption spectroscopy (AAS) or inductively coupled plasma (ICP) spectroscopy. The latter is the more accurate method, as AAS tends to underestimate the concentration of lead at higher levels. The spot where the chip was removed must be repaired afterwards to prevent further chipping and dust generation. 

A very elegant analytical technique for the lead alkyls is that of Ballinger and Whittemore. They combined pressure programming with use of an atomic absorption spectrophotometer as a specific detector to produce a rapid, precise, and sensitive analytical technique. A 10 foot column packed with 20% 1,2,3,-tris-(cyanoethoxy)-propane on 60/80 mesh Chromosorb P coated with 1% potassium hydroxide was operated at 85°C. Flow rates were programmed from 10—00 ml/min., (Figure 159). Analysis of the five lead alkyls was completed in less than one and a half minutes. The amount of lead was determined by the absorption of the lead 2833 S. emission line. The method could detect as little as 20 nanograms of lead as lead alkyl. The application of atomic absorption spectroscopy to the determination of lead alkyls separated chromatography has also been discussed by... 

Analytical methods of atomic spectroscopy have been used in forestry and wood product research since their earliest development. Nowadays, almost all of the spectroscopic techniques available are employed in the analysis of metals and trace elements in diverse samples of industrial and environmental origin. The techniques that find most regular application include flame atomic absorption spectroscopy (F-AAS), graphite furnace atomic absorption spectroscopy (GF-AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and, occasionally, also direct current plasma atomic emission spectroscopy (DCP-AES). In many applications F-AAS is a sufficiently sensitive and precise technique however, in the analysis of some environmental samples for trace elements (forest soils, plant material and water) where concentrations may be very low (of the order of 100 ng mL" ) the greater sensitivity of GF-AAS and ICP/DCP-AES is required. In considering the applications of atomic spectroscopy to forestry and... 

When the problem has been defined and needed background information has been studied, it is time to consider which analytical methods will provide the data you need to solve the problem. In selecting techniques, you can refer back to the other chapters in this book. For example, if you want to measure the three heavy metals (Co, Fe, and Ni) that were suspect in the Bulging Drum Problem, you might immediately think of atomic absorption or inductively coupled plasma atomic emission spectroscopies and reread Chapter 8 of this book. How would you choose between them Which would be more accurate More precise Does your lab have both instruments Are they both in working order What if you have neither of them What sample preparation would be needed ... 

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