Versatile flow injection manifold for analytical calibration

A flow injection calibration system, originally designed and tested in our laboratory, is presented here as a versatile analytical tool serving for calibration purposes. It is characterized by a simple construction, easy operation and the possibility of offering rich measurement information with the use of a single standard solution. It is shown that depending on instrumental conditions and the composition of the calibration solutions the manifold is able to realize various calibration procedures according to interpolative, extrapolative and integration modes. As an experimental example, the determination of calcium in the cabbage sample by flame atomic absorption spectrometry has been calibrated by means of dilution method (DM) in the integration mode.     

Flow injection calibration techniques

Summary The role of calibration in the overall analytical procedure is discussed and the potential role of flow injection techniques are assessed. The factors affecting the dispersion obtained in a flow injection system are described and examples given of how control of the various factors can be exploited to produce manifolds for calibration purposes. Most of these examples concern atomic spectrometry methods for which there is considerable interest at present in developing extended range calibrations and flow injection versions of the standard additions method. Several examples of the latter are given.

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Anwendung der Fließinjektions-Technik für Eichmethoden

     

Use of membrane micropumps for introducing the sample solution in flame atomic absorption spectrometry

The advantages of using membrane micropumps to introduce sample or standard solutions in flame atomic absorption spectrometry are discussed, using two entirely computer-controlled manifolds which allow a wide range of dispersion coefficients to be obtained. Coupling micropumps to the manifold facilitates calibration graphs to be obtained using a single standard solution. Other advantages include a handy on-line dilution stage for excessively concentrated samples as well as the possibility of obtaining pulsed absorbance-time profiles that once submitted to the Fourier transformation, provide amplitude-frequency plots representing an innovative, not yet fully exploited vision of atomic absorption analytical data.     

间接原子吸收光谱法测定药物制剂中的西米替丁

本文提出了流动注射原子吸收光谱法间接测定西米替丁的新方法。基于西米替丁与Ag（I）反应可以生成白色的沉淀，经流动注射在线过滤稀释，以原子吸收光谱法测定反应剩余银离子的量来间接测定西米替丁的量。在优化条件下西米替丁浓度在2～80mg／L范围内与吸光度呈良好的线性关系，回收率为97．0％～104．3％。方法用于片剂西米替丁的测定，结果满意。     

On-line filtration system for determining total chromium and chromium in the soluble fraction of industrial effluents by flow injection flame atomic absorption spectrometry

Two manifolds were assessed for the purpose of determining both the total chromium content and that present as a soluble form in industrial effluents by flow injection flame atomic absorption spectrometry (FI-FAAS). To determine the chromium content in the soluble fraction the samples were used without additional treatment, a 0.45 microm filter being included in the FI system. To determine the total chromium content, the samples were acidified with nitric acid 20% (v/v) and heated for 30 s in a microwave oven (temperatures of about 70 degrees C were reached). The problem posed by the very different concentration range in which total and soluble chromium are present was overcome by using programmed flow rate methodology and by only partially emptying the sample loop. A personal computer controlled both the rotation speed of a peristaltic pump and the volume of sample injected into the system, thus obtaining the dispersion degree required. Using the manifold proposed, the chromium content in the soluble fraction can be determined in the 0.5-20 microg mL(-1) range using a 10 microg mL(-1) single standard for calibration. To determine the total chromium content, a calibration line in the 20-200 microg mL(-1) range was obtained using a single 50 microg mL(-1) chromium standard solution. The reliability of the semi-automatic devices was verified by comparing the results obtained with those found by treating the samples and using both FAAS in a conventional way and a spectrophotometric method using diphenylcarbazide at the 95% confidence level (ANOVA test). The proposed procedures showed a RSD lower than +/-3%.     

Direct determination of calcium, magnesium, sodium and potassium in water by flow injection flame atomic spectroscopy, using a dilution chamber

Summary A simple procedure to carry out the direct analysis of calcium, magnesium, sodium and potassium in water by flow injection analysis (FIA) using flame atomic absorption spectroscopy (AAS) or flame photometry (FP) has been developed, using a well stirred dilution chamber to extend the calibration range, and both a double injector and the merging zone technique to add a lanthanum solution to samples and standards. The results obtained in the analysis of real samples agree with those found by a batch flame atomic procedure. The use of the dilution chamber makes it possible to carry out the calibration using the dilution profile of a single concentrate standard for each element, and an empirical dilution equation, which could be employed for all the elements is determined in each work session.

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Direkte Bestimmung von Calcium, Magnesium, Natrium und Kalium in Wasser durch Fließinjektions-Flammen-Atomspektroskopie unter Verwendung einer Verdünnungskammer

     

Sequential injections in flow system as an alternative to gradient exploitation

In flow injection analysis, several plugs can be injected simultaneously into the same carrier system, in order to achieve overlapped zones. The potentialities of such sequential injections are studied in model systems with spectrophotometric detection; the procedure is shown to give better precision than the use of concentration gradients. The method is used with atomic absorption spectrometry to allow the determination of a wide range of manganese contents in rocks, and to facilitate the use of standard additions for the determination of copper in ethanol.     

Determination of bismuth in metallurgical materials using a quartz tube atomizer with tungsten coil and flow injection-hydride-generation atomic absorption spectrometry

A method for the determination of bismuth in metallurgical materials using hydride generation coupled with a merging zones flow system and atomic absorption spectrometry using a quartz tube atomizer with tungsten coil is proposed. The parameters related to the bismuthine generation, the flow injection system and the use of a tungsten coil were studied and the optimized system shows a wide calibration range and good stability over time, without losses in sensitivity. The analytical curve is linear from 10 to 750 μg l⁻¹ of Bi with R0.999. A detection limit of 1.9 ng Bi and an analytical frequency of 60 determinations per hour were obtained. Five metallurgical reference materials were analyzed with the proposed method after their acid dissolution. The results obtained were in good agreement with certified or recommended values, and the relative standard deviations were lower than 5%.     

Determination of palladium by flame atomic absorption spectrometry combined on-line with flow injection preconcentration using a micro-column packed with activated carbon fibre

The versatility of flow injection as a procedure for enhancing the performance of atomic spectrometry is demonstrated by the on-line separation and preconcentration of analyte ions of interest for methods employing atomic spectrometric measurements. In this paper, a sensitive method for the determination of palladium by flame atomic absorption spectrometry associated on-line with the flow injection technique has been developed. A flow system comprising a micro-column packed with activated carbon fibre was used for the concentration of palladium. In order to further enhance the performance of the analysis a new manifold with an additional column has been designed to increase the sensitivity by doubling the analytical signals. The method is sensitive and easily operating with a sampling rate of 15-20/h. The detection limit of this method is 0.3 ng/ml in standard solution and the precision is 3.9% relative standard deviation at 50 ng/ml. Recoveries of palladium in spiked solutions are 103-107%.     

A sequential injection cold-vapor atomic absorption method for the determination of total mercury

A sequential injection (SI) method for the determination of mercury via cold vapor atomic absorption spectrophotometry is presented. The method differs from flow injection (FI) cold vapor methods for the determination of mercury because of the simplicity of the system required for the method: one pump, one valve, a gas-liquid separator, and an atomic absorption spectrophotometer equipped with a quartz cell. Under optimal conditions, the method has the following figures of merit: a linear calibration range of 1.0 to 20 microg L(-1); a detection limit of 0.46 microg L(-1); and a precision of 0.90% RSD (8 microg L(-1)). The procedure allows for a sampling rate of one injection per 80 s (excluding sample pretreatment). Results from the determination of mercury in water and fish specimens are also presented. The figures of merit of the method are compared to two other SI methods for the determination of mercury.     

Immobilization of reagents by polymeric materials. Determination of metamizol

A method for immobilization of inorganic reagents, based on the dispersion of the reagent into an unsaturated polyester solution is applied to immobilization of lead dioxide. The obtained solid is of application in a flow-injection manifold for indirect atomic absorption determination of metamizol in pharmaceutical formulations. The procedure gives a linear calibration graph up to 6 ppm of metamizol with a relative standard deviation of 1.6% (3.0 mg/l) and a sample throughput of 72 hr(-1).     

Study of Analytical Methods for Iron Determination in Complex Organic Liquids by Atomic Absorption Spectrometry

Abstract

In the determination of iron in complex organic liquids by atomic absorption spectrometry (A. A. S.), methods of sample preparation, such as dilution with an organic solvent and sample pretreatment to destroy organic material, are investigated. Moreover, methods of analysis using calibration curve and standard additions are presented. The possible cause of error associated with iron determination in organic samples by flame (F-A. A. S.) and graphite furnace (GF-A. A. S.) atomic absorption spectrometry are discussed.

From all of these studies, the use of graphite furnace atomic absorption spectrometry after sample dilution with methyl isobutyl ketone, and the use of the method of standard additions are advised for iron determination.     

Atomic absorption spectrometry for the automatic indirect determination of ascorbic acid based on-the reduction of manganese dioxide.

A new and simple flow injection method followed by atomic absorption spectrometry has been developed for the indirect determination of ascorbic acid. The proposed method is based on oxidation of ascorbic acid to dehydroascorbic acid using a solid-phase manganese dioxide (30% m/m suspended on silica gel beads) reactor. The flow of the sample through the column reduces the MnO2 to Mn(II) in an acidic carrier stream of 6.3 mM HNO3 (pH 2.2) with flow rate of 4.0 ml/min at room temperature; Mn(II) is measured by atomic absorption spectrometry. The absorbance of Mn(II) is proportional to the concentration of ascorbic acid in the sample. The calibration curve was linear up to 30 mg/L, with a detection limit of 0.2 mg/L for a 220 microL injected sample volume. The developed procedure was found to be suitable for the determination of AsA in pharmaceuticals and foods with a relative standard deviation better than 1.09% and a sampling rate of about 95 h(-1). The results exhibit no interference from the presence of large amounts of organic compounds. The reliability of the method was established by parallel determination against the 2,6-dichlorophenol-indophenol methods.     

A sequential injection cold-vapor atomic absorption method for the determination of total mercury

A sequential injection (SI) method for the determination of mercury via cold vapor atomic absorption spectrophotometry is presented. The method differs from flow injection (FI) cold vapor methods for the determination of mercury because of the simplicity of the system required for the method: one pump, one valve, a gas-liquid separator, and an atomic absorption spectrophotometer equipped with a quartz cell. Under optimal conditions, the method has the following figures of merit: a linear ¶calibration range of 1.0 to 20 μg L^–1; a detection limit of 0.46 μg L^–1; and a precision of 0.90% RSD (8 μg L^–1). The procedure allows for a sampling rate of one injection per 80 s (excluding sample pretreatment). Results from the determination of mercury in water and fish specimens are also presented. The figures of merit of the method are compared to two other SI methods for the determination of mercury.     

Extending the dynamic range of flame atomic absorption spectrometry: a comparison of procedures for the determination of several elements in milk and mineral waters using on-line dilution

Three approaches based on continuous flow methodology are assessed for the purpose of extending the dynamic range of flame atomic absorption spectrometry. The determination of several elements in infant liquid and powdered milk and water samples is used to check the performances of the manifolds. Two of the systems are fully computer-controlled and permit a calibration graph to be obtained by using a single standard solution. The results confirm that continuous flow methodology is a reliable alternative to the time-consuming common dilution procedures based on glassware. Since the systems are versatile and permit a wide range of degrees of dilution to be obtained, they can be easily adapted for the automated or semi-automated analysis of other liquid samples which are too concentrated to be aspirated directly into the atomic absorption spectrometer.     

Extending the dynamic range of flame atomic absorption spectrometry: a comparison of procedures for the determination of several elements in milk and mineral waters using on-line dilution

Three approaches based on continuous flow methodology are assessed for the purpose of extending the dynamic range of flame atomic absorption spectrometry. The determination of several elements in infant liquid and powdered milk and water samples is used to check the performances of the manifolds. Two of the systems are fully computer-controlled and permit a calibration graph to be obtained by using a single standard solution. The results confirm that continuous flow methodology is a reliable alternative to the time-consuming common dilution procedures based on glassware. Since the systems are versatile and permit a wide range of degrees of dilution to be obtained, they can be easily adapted for the automated or semi-automated analysis of other liquid samples which are too concentrated to be aspirated directly into the atomic absorption spectrometer.     

Calibration by the gradient ratio-standard addition method in flow injection flame atomic absorption spectrometry

A calibration method has been developed which is realised in the flow injection analysis (FIA) by the gradient technique. According to this method two transient peaks, one for a sample and the other for a sample with standard addition, are recorded and compared point by point in the entire defined time range. The analytical result is estimated on the basis of information gained about the local analyte concentrations in the sample zone. The method allows the results to be reliable when both the non-linear calibration dependence and the interference effect occur. As an example, calcium in synthetic samples containing silicon, phosphate, aluminium, vanadium and titanium, and also in iron ore sample, were determined by flame atomic absorption spectrometry (FAAS). It has been proved, that the method can be effective in overcoming even extremely strong interferences, providing analytical results with average accuracy equal to ca. 5% and with precision 2–3 times inferior to that obtained by conventional FI calibration.     

Flow injection—atomic absorption spectrometry with organic solvents

A flow injection technique with an organic solvent carrier stream is recommended for the determination of trace elements by atomic absorption spectrometry. Carrier streams of methyl isobutyl ketone and especially n-butyl acetate are effective in enhancing sensitivity. The proposed method permits about 300 determinations per hour with a relative standard deviation of less than 5%.     

On-line ion-exchange preconcentration and determination of traces of platinum by electrothermal atomic absorption spectrometry

A method to determine trace amounts of platinum in different samples based on electrothermal atomic absorption spectrometry is described. The preconcentration step is performed on a chelating resin microcolumn [1,5-bis(2-pyridyl)-3-sulfophenyl methylene thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex 1x8-200)] placed in the autosampler arm. The combination of a peristaltic pump for sample loading and the atomic absorption spectrometer pumps for elution through a selection valve simplifies the hardware. The peristaltic pump and the selection valve are easily controlled electronically with two switches placed in the autosampler, which are activated when the autosampler arm is down. Thus, the process is fully automated without any modification of the software of the atomic absorption spectrometer. Under the optimum conditions with a 60-s preconcentration time, a sample flow rate of 2.4 mL min(-1), and an injection volume of eluent of 40 microL, a linear calibration graph was obtained in the range 0-100 ng mL(-1). The enrichment factor was 14. The detection limit under these conditions is 1 ng mL(-1), and the relative standard deviation (RSD) is 1.6% for 10 ng mL(-1) of Pt. The method has been applied to the determination of platinum in catalyst, vegetation, soil, and natural water samples. The results showed good agreement with the certified value and the recoveries of Pt added to samples were 98-105%.     

Direct determination of iron in urine and serum using graphite furnace atomic absorption spectrometry

A simple, rapid and low-cost method for the routine determination of iron in urine and serum using graphite furnace atomic absorption spectrometry is described which may provide an alternative to the more widespread automated spectrophotometric methods. The urine and serum samples were simply diluted with water prior to analysis. Matrix modification was found to be redundant. The standard additions technique or the use of matrix matched standards (addition calibration) was found to be unnecessary and, therefore, the calibration was performed using aqueous standards. For serum analysis the degree of dilution could be reduced by using the less sensitive 302.0-nm resonance line, yielding more precise determinations, and for urine analysis, interferences were eliminated by means of a L'vov platform. The interferences that exist in the presence of nitric acid are also discussed. Finally, the presence of background absorption was investigated by means of Zeeman effect atomic absorption.