Flame Atomic Emission Spectrometry Research Articles

Nonlinear calibration by the standard addition method

The possibility of using the standard addition method (SAM) for calibration in the case of nonlinear relationship between the analytical signal and the analyte concentration is investigated. Analysis of both the precision and the accuracy of SAM has been theoretically carried out assuming that the measurement data are produced with constant random error and then fitted by parabolic function. Several empirical parameters were considered, including, e.g., the number and size of additions, and the curvature degree. Theoretical examinations have been verified by experimental results of some determinations performed by flame atomic absorption and emission spectrometry. Criteria for the selection of linear and nonlinear approximations were discussed. Consequently, the experimental conditions have been suggested allowing the nonlinear calibration by SAM to be applied in practice.

A Study of Illicit Cocaine Seizure Classification by Pattern Recognition Techniques Applied to Metal Data

Fifteen metallic species, silver (Ag), aluminum (Al), calcium (Ca), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), nickel (Ni), lead (Pb), strontium (Sr) and zinc (Zn), were determined in 46 cocaine samples confiscated by the Spanish police in Galicia (northwest Spain). Classification of these cocaine samples according to their geographic origin (Colombia and Venezuela) was achieved by the application of pattern recognition techniques to the metallic content data. Cocaine samples, around 0.5 g, were directly dissolved in 2 mL of 35.0% (v/v) HNO3, diluted to 10 mL with ultrapure water. The metals were quantified by means of electrothermal atomic absorption spectrometry (Ag, Al, Cd, Cr, Cu, Mn, Ni, Pb and Sr), flame atomic absorption spectrometry (Ca, Fe, Mg and Zn), and flame atomic emission spectrometry (K and Na). Results show that two geographic origins can be established through the presence of trace and major elements.

Protective effects of selenium, vitamin C and vitamin E against oxidative stress of cigarette smoke in rats.

Cataractous lenses have been found to have an altered distribution of the intracellular ionic environment: the concentrations of potassium and magnesium being decreased and the concentrations of sodium and calcium increased. These changes arise as a result of changes to lens membrane characteristics causing an increase in lens membrane permeability. In this study flame atomic absorption spectroscopy (AAS) was used for calcium, magnesium, iron and zinc determination, and flame atomic emission spectroscopy (AES) was used for sodium and potassium contents in normal and cigarette smoke-exposed rat lenses. The methods are sensitive enough to detect quantitatively all six cations in a single rat lenses. In this work, six elements, including Ca2+, K+, Na+, Zn2+, Fe2+ and Mg2+ in experimental rat eye lenses and normal transparent lenses were determined. It was found that the concentrations of Ca2+, Na+, Zn2+, and Fe2+ were increased dramatically while K+ and Mg2+ decreased in smoke-exposed rat lenses when compared to the control rat lenses. There were no significant changes between 'smoked' rats supplied with vitamin C and control groups. A positive correlation was found also in the other two groups of 'cigarette smoked' animals supplemented with selenium plus vitamin E and selenium when compared with 'cigarette smoked' without any supplements. These data provide support for the hypothesis that cigarette smoking increases the risk of cataract formation. We investigated whether vitamin C is the most important antioxidant in the body. The roles of diet with optimum amounts of antioxidant vitamins C and vitamin E and the antioxidant mineral selenium are discussed.

Survey of serum potassium reference measurements.

We compared the quality of reference measurements for serum potassium in four reference laboratories from three different European countries, using a panel of 60 native patients' samples. The reference methods were based on either ion chromatography (one laboratory) or flame atomic emission spectrometry (three laboratories). Performance specifications for serum potassium measurements were defined as a maximum overall coefficient of variation (CV) of 1.5%, a maximum bias of 0.65% and a maximum total error of 3.0%. The overall imprecision for all laboratories was in the range of 0.7 to 1.3%, and was thus below the proposed specification of 1.5%. However, two laboratories reported 12 and 13 quadruplicates with CVs exceeding this limit. The mean bias (expressed as deviation from the overall mean of all laboratories) for all reference laboratories was < 0.65%. In the lower concentration range, however, one laboratory exceeded this limit. No laboratory measured samples with a total error above 3.0%. From these results, it can be concluded that the reference measurements, and, thus, also the reference methodologies, based on ion chromatography and flame atomic emission spectrometry were equivalent, and able to satisfy current analytical specifications for serum potassium measurements.

Development of a Digital Micromirror Spectrometer for Analytical Atomic Spectrometry

A digital micromirror device (DMD) has been incorporated into a novel spectrometer for use in analytical atomic spectrometry. The device can be taken from a commercial computer projector. A protective glass window covering the DMD chip limits the viewable wavelengths to the visible range. The DMD is used to project an image of the light source onto the exit plane of a flat-field spectrograph. A single photomultiplier tube is used for detection. The high switching rate of the micromirrors (15 μs) enables rapid full-spectrum capture, wavelength-modulation, source-modulation, fast narrow-wavelength window scans, and rapid-wavelength "jumping." Calcium, sodium, and potassium have been determined in several standard reference materials (tomato leaves, bovine liver, rice flour, total diet) by flame atomic absorption and emission spectrometry. Absorption sensitivities for each element are near the 0.02 μg/mL level, and detection limits for both absorption and emission are near the 0.01 μg/mL level. Elemental recoveries were within 10% of certified values for most reference materials.

Lithium homeostasis in Xenopus oocytes: Implications for the study of signal transduction

The Xenopus oocyte has been shown to be a useful model for the study of signal transduction pathways. The present study investigated whether or not the oocyte could be used to study the effects of lithium on signal transduction mechanisms by comparing the dynamics of lithium homeostasis in the oocyte and a human immortalized hippocampal cell line using Flame Atomic Emission Spectroscopy (FAES). A biphasic pattern of lithium uptake was observed in the oocyte in the presence of 5 mM extracellular lithium. The late phase of lithium uptake, which started after 30 minutes of incubation time, was sensitive to phloretin, an inhibitor of Na + Li + counter-transport. Differences in lithium efflux kinetics further characterized the two observed phases of accumulation and also suggested that lithium might be distributed in different pools within the oocyte, including one sequestered in organelles or associated with cytosolic proteins. An analogous sequestered pool was not, however, observed in the hippocampal cell line indicating that lithium is distributed differently in these cell types. This suggests that the Xenopus oocyte might not be a suitable model for evaluating the effects of lithium on signal transduction pathways because of the unknown contribution of the sequestered pool on predicting relevant physiological effects.

Using Microwave Sample Decomposition in Undergraduate Analytical Chemistry

A shortcoming of many undergraduate classes in analytical chemistry is that students receive little exposure to sample preparation in chemical analysis. This paper reports the progress made in introducing microwave sample decomposition into several quantitative analysis experiments at Truman State University. Two experiments being performed in our current laboratory rotation include closed vessel microwave decomposition applied to the classical gravimetric determination of nickel and the determination of sodium in snack foods by flame atomic emission spectrometry. A third lab, using open-vessel microwave decomposition for the Kjeldahl nitrogen determination is now ready for student trial. Microwave decomposition reduces the time needed to complete these experiments and significantly increases the student awareness of the importance of sample preparation in quantitative chemical analyses, providing greater breadth and realism in the experiments.

Removal of iron, chromium and sodium impurities from zinc tungstate (ZnWO4)

Removal of Fe, Cr and Na impurities from ZnWO 4 was carried out by the chemical purification of the starting materials for crystal growth. Tungsten trioxide (WO 3 ) and zinc oxide (ZnO) were prepared by novel methods based on homogenous precipitation (using hydrogen peroxide as a complexing agent for sodium tungstate) and liquid-liquid extraction techniques, respectively. The impurity concentrations were determined by graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic emission spectrometry (FAES). The quality improvement of the crystals grown from purified starting materials was demonstrated by ultraviolet-visible (UV-VIS) spectrophotometry.

Techniques for boron determination and their application to the analysis of plant and soil samples

This paper reviews techniques for determining B concentration and isotopic ratio and their application to soil and plant samples. Boron concentration has been determined utilising spectrophotometry, potentiometry, chromatography, flame atomic emission and absorption spectrometry, inductively coupled plasma (ICP) optical emission (OES) and mass spectrometry (MS), and neutron activation analysis using neutron radiography and prompt-γ activation analysis. Isotopic ratios of B have been measured by ICP–MS, thermal ionisation mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS). For isotopic measurements, TIMS and SIMS are more sensitive and provide higher degrees of accuracy and resolution than ICP–MS, however, extensive sample preparation and purification, and time-consuming measurements limit their usefulness for routine analyses.

Validation of candidate reference methods based on ion chromatography for determination of total sodium, potassium, calcium and magnesium in serum through comparison with flame atomic emission and absorption spectrometry

Objectives: We report on the validation of candidate reference methods based on ion chromatography for the determination of total sodium, potassium, calcium, and magnesium in serum. The current study is a continuation of previous investigations in which we were able to show the potential of ion chromatography to serve as a reference method principle. The validation consisted of comparison of the ion chromatographic methods with generally recognized reference methods based on flame atomic emission (for sodium/potassium) and absorption (for calcium/magnesium) spectrometry. Methods: Sample preparation consisted of acidic dilution and pre-purification with reversed phase cartridges. Ion chromatography with suppressed conductivity was performed with polymeric stationary phases chemically modified with carboxylate and sulfonate functional groups for sodium/potassium and calcium/magnesium, respectively. Single-point calibration was used in combination with individual adaptation of serum sampling and diluting to give similar responses in samples and standards. In the study, more than 25 control sera were analyzed in parallel with the ion chromatographic methods and the traditional reference methods. The measurement protocol consisted of quadruplicate analysis of each sample per run, in 3 different runs. In each measurement series, internal quality control with certified reference materials from the National Institute of Standards and Technology and the Bureau Communautaire de Référence was applied. The performance criteria to fulfill were predefined ( i.e., the maximum within-day and overall coefficient of variation, the confidence interval, the daily and overall deviation from the certified value and the maximum total analytical error). Results: The comparison is presented as difference plot ( i.e., deviation of the results obtained with ion chromatography from those obtained with the respective traditional reference methods). The mean deviations were +0.9% for sodium, +1.0% for potassium, ±0.0% for calcium, and +0.1 % for magnesium. With the exception of 2 values each for sodium and potassium, all deviations were within the limit of 2 times the allowed total analytical error. From the data obtained for internal quality control during the different measurement campaigns, we further estimated the long-term precision and accuracy of our methods. The overall coefficient of variation (respectively the bias) amounted to 0.7% (+0.1%) for sodium, 0.9% (−0.3%) for potassium, 1.3% (−0.1 %) for calcium, and 1.0% (±0.0%) for magnesium. Conclusion: From the precision and accuracy reached by our ion chromatographic methods, we conclude that they can be proposed as candidate reference methods for the determination of total sodium, potassium, calcium, and magnesium in serum.

Atomic Absorption and Atomic Emission Spectrometry for the Determination of the Trace Element Content of Selected Fruits Consumed in the United States

Flame atomic absorption spectrometry (AAS) and flame atomic emission spectrometry (AES) were used to determine calcium, copper, iron, magnesium, manganese, potassium, sodium, and zinc in 32 fruits. Samples were wet ashed using nitric acid and hydrogen peroxide and calibration was accomplished using calibration against aqueous standards. Data obtained are reported in mg/100 g and are compared with literature values. Data for less commonly consumed fruits such as tangerines, nectarines, kiwi, star fruit (carambola), mangos, papayas, and plantains are also presented. Fruits are identified which may be considered good sources of the trace elements studied based on the FDA definition that a serving contains 10% of the Daily Value. When possible, differences in elemental content for multiple varieties is studied.

Flow system based on a binary sampling process for automatic dilutions prior to flame atomic spectrometry

A microcomputer-controlled flow system to perform automatic dilutions exploiting a binary sampling process is proposed. Introduction of precise volumes of sample and solvent was achieved by solenoid valves. The possibility to get different volumetric fractions was realized by software, which defined the time delays of the valves and could be used, e.g., for samples with analyte concentrations exceeding the analytical range. A noteworthy feature is that sample and standards processing is not necessarily the same. The analytical performance was exhaustively investigated, in particular the precision of standard measurements generated after application of different dilutions, or repeatability of results of 20 and 40 times diluted real sample solutions. The feasibility of the approach was demonstrated by the on-line automatic dilution of plant digests for determining Ca and K by flame atomic absorption and emission spectrometry. Precision of measurements performed on a solution produced by the automatic 10-fold dilution of a 100 mg l solution was characterized by a R.S.D. < 1%. Accuracy was assessed by analysing vegetal reference materials after diluting 10 or 20 times. Results were in agreement at 95% significance level with the certified values. Comparison of automatic and manual dilutions by using a paired t-test on a set of samples with varying composition presented no statistical difference at the 95% significance level.

International consensus on the standardization of sodium and potassium measurements by ion-selective electrodes in undiluted samples.

The International Federation of Clinical Chemistry (IFCC) and the National Committee for Clinical Laboratory Standards (NCCLS) are about to recommend to adjust sodium and potassium measurements by ion-selective electrodes in undiluted samples to the amount of substance concentration in the sample as determined, e.g., by flame atomic emission spectrometry. The adjustment is only valid in case of normal standardized sera (or plasma), implying "normal" water concentration (normal concentration of proteins, lipids or other macromolecules), "normal" binding of the pertinent electrolytes and "normal" coefficient of activity. If these criteria are not met, results obtained by "adjusted" ISE's will differ from total molar concentration. That is: in individual samples of patients results from ISE's and total molar concentration will differ unpredictably. It forced IFCC to propose new quantities for the measurements by adjusted ISE's: ionized sodium and ionized potassium. The reference interval for ionized sodium and ionized potassium is identical to the pertinent reference interval for molar concentration of total sodium and total potassium, but it is in contrast independent from water concentration and valid, e.g., in hypoproteinaemia as well as in hyperlipaemia or hyperproteinaemia. Accuracy control of ionized sodium and ionized potassium based on reference method values is hampered by abnormal water concentration and inadequate properties of the matrix of many control sera. Alternative approaches how to report measurements by ISE's in undiluted samples, such as activity or free molal concentration are discussed with their pros and cons regarding accuracy control by reference method values. The need for appropriate control materials with a matrix similar to native human sera is stressed.

Short-term variation in the concentration of selected ions within individual tropical rainstorms

Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl−, NO3 − and SO4 2− were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a “first-flush” effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.

Ion chromatography as potential reference methodology for the determination of total sodium and potassium in human serum

The potential of ion chromatography to serve as a new reference method principle for the determination of total sodium and potassium in human serum was investigated. Sample pretreatment consisted of acidic dilution and filtration and detection was based on conductivity. Methods for the separate and simultaneous determination of both analytes were investigated. Further, the influence of calibration (using either a single-point calibration or a standard curve) on method imprecision, inaccuracy and analysis time was examined. The best method performance was achieved by separate analysis using single-point calibration with bracketing analysis scheme. For this variant, the mean total coefficient of variation for sodium and potassium was 1.0% and the mean method bias was −0.2% for sodium and +0.2% for potassium, as determined with three control materials from the National Institute of Standards and Technology. Our results are comparable to those of reference methods based on flame atomic emission spectrometry. Therefore, we consider ion chromatography as a valuable reference methodology for the determination of total sodium and potassium in human serum.

Using instrumental techniques to increase the accuracy of the gravimetric determination of sulfate

A gravimetric method for the determination of sulfate in a sulfate solution standard by the precipitation of barium sulfate is coupled with the instrumental determination of trace sulfate and precipitate contaminants to improve the accuracy and precision of the analysis. Sulfate in a solution of potassium sulfate is separated by a reverse precipitation with barium chloride in very dilute hydrochloric acid. Coulometry, ICP-MS, and flame atomic emission spectrometry (FAES) are used to quantify the level of the contamination in the barium sulfate precipitate and the solubility loss of sulfate in the filtrate, from which correction factors are calculated. Coprecipitating contaminants contribute about 0.3% to the total precipitate mass, while the analyte lost to the filtrate contributes 0.4%. Despite the poorer precision and accuracy of instrumental methods, the over-all precision and accuracy of the sulfate determination is actually improved, since the instrumental methods are used to determine only a very small part of the analyte. The expanded uncertainty (k= 2) of the method is below 0.2% relative to the precipitate mass.

Line Selection and Interference Correction for the Direct Trace Element Analysis of Tungsten Matrix by Inductively Coupled Plasma Atomic Emission Spectrometry.

A method for the direct determination of trace amounts of elements in tungsten matrix by inductively coupled plasma atomic emission spectroscopy is described, with emphasis on line selection and spectral interferences. Microwave assisted sample digestion method was used for the decomposition of metal samples. The spectral interference coefficients were calculated for the 270 spectral lines of 67 elements. These values were used for line selection and to calibrate concentrations of the analytes. The limits of detection of the elements for this method were determined and compared with those obtained by flame atomic absorption spectrometry and direct current carbon arc emission spectroscopy. Analytical reliability of the proposed method was estimated by analyzing spiked solutions. The results indicated that the accuracy of multi-element analysis is satisfactory.

Simultaneous detection and quantitation of sodium, potassium calcium and magnesium in ocular lenses by high- performance capillary electrophoresis with indirect photometric detection

A high-performance capillary electrophoresis (HPCE) method which can be used to quantitatively determine Na +, K +, Ca 2+ and Mg 2+ simultaneously in ocular lenses has been developed. The proteins in the lens aqueous homogenates were precipitated by 10% trichloroacetic acid. The precipitated proteins were removed after a brief centrifugation, and the supernatant containing the cations was washed with ether and directly used for HPCE analysis. A 50 μm × 75 cm fused-silica capillary was used for separation and the detection wavelength was set at 214 nm. A 20-m M imidazole at pH 6.0 containing 0.1% hydroxypropyl methyl cellulose was used as background electrolyte. Sample solution was injected at 15 kV for 10 s, and the electrophoresis was carried out at 15 kV. All the cations can be separated and quantified from the peak areas within 9 min. The values obtained by this method were comparable with commonly used flame atomic absorption and flame atomic emission spectroscopy. It is demonstrated that this HPCE method can be used to quantify all the cation levels simultaneously within a short time even in a small single rat or mice lens.

Lithium determinations evaluated in eight analyzers

We compared five ion-selective electrodes (ISEs; AVL 985S, Baxter Lytening 2Z, Beckman EL-ISE, Ciba-Corning 654 Na/K/Li, and Nova CRT 11) and a colorimetric method (Ektachem) for determination of lithium with flame atomic absorption and atomic emission spectroscopy. We evaluated precision, recovery, interference by drugs (procainamide, N-acetylprocainamide, quinidine, lidocaine, carbamazepine, and valproic acid) and inorganic analytes (Na, K, Ca, Mg, and Br), and performance with sera from patients receiving lithium. Imprecision was < 5% (CV) for all analyzers except Ektachem and Beckman. Analytical recovery was 100% +/- 5% for all analyzers except Ektachem and Baxter. Some drug interference was seen with all analyzers except AVL and Corning. Calcium caused interference with AVL, Corning, and Ektachem analyzers, and sodium and potassium interfered with the Ektachem analyzer. The results with the Baxter, Beckman, and Corning analyzers were closest to those by flame atomic emission (mean differences, 0.01 to 0.02 mmol/L); the AVL and Nova analyzers gave lower results (mean differences, -0.11 to -0.13 mmol/L) and the Ektachem gave higher results (mean difference, 0.08 mmol/L).

Interferences in the determination of lithium by flame atomic emission spectrometry with platinum-loop atomizer

Although flame atomic emission spectrometry (AES) is the most popular method for the determination of Li, the method is subject to interference from alkaline and alkaline earth elements. The effects of CaOH and SrO emission bands are particularly severe. The use of a Pt-loop atomizer was found to eliminate interference from Ca and Sr, as salts of these elements remained as solid residues on the loop material. High contents of F–, Cl–, SO42– and PO43– were found to reduce the Li signal, this was largely due to loss of LiCl in the case of Cl–, in the case of F–, SO42– and PO43–, the reduction in the Li signal was due to lithium oxide formation. The accuracy of the Pt-loop technique was shown to be satisfactory in matrices of high Ca and Sr contents. The detection limit obtained with the Pt-loop was at least one order of magnitude better than that of conventional AES. The technique was applied in the determination of Li in several sample types.