Multisyringe flow injection analysis system for automation of standard addition calibration method

In the present work, the multi-channel features of multisyringe flow injection analysis (MSFIA) were exploited for the first time to implement calibration based on standard addition method (SAM). For this, standard solutions containing different concentrations of target analyte were placed in each syringe of the multisyringe and connected to a flow network where in-line mixing of sample and standard through a merging zone approach was established prior to detection of analyte. Using this strategy, artifacts reported before in SAM using flow injection analysis were avoided as the concentration of the analyte in the resulting mixture was related to the dilution of sample and added standard within the system, and the concentration of all matrix components was kept constant during all measurements. The feasibility of the proposed MSFIA system was assessed through application to potentiometric determination of chloride ion in electroplating bath and milk samples. Results obtained for samples (n = 15) were not statistically different from those provided by titrimetric procedures, with an excellent throughput (20–31 samples h^{− 1}), comprising four-level addition of chloride ion.     

Eliminating absorbing interference using the H-point standard addition method: case of Griess assay in the presence of interferent heme enzymes such as NOS

Standard calibration methods used to determine trace analytes usually yield significant deviations from the actual analyte value in the presence of interferents in the assay media. These deviations become of particular concern when the concentration of the analyte is low, and when the results are used to draw mechanistic or kinetic conclusions, for instance in enzyme structure-function studies. In these circumstances, the H-point standard addition method (HPSAM) provides superior precision and accuracy. This method is developed here for the case of the spectrophotometric Griess assay used to determine nitrite in various enzymology investigations, such as nitrite determination in studies of nitrite reductases (NiR), or when determining nitrite as a breakdown product of nitric oxide synthesized by NOS enzymes. The results obtained by HPSAM are contrasted with those of the traditional calibration method.Electronic Supplementary Material Supplementary material is available for this article at     

Comparison of the absolute calibration method with the method of standard addition for the determination of halothane in blood by gas chromatographic headspace analysis

As long-term exposure to exhaled halothane can be a cause of hepatitis and/or damage to the liver, the determination of halothane in blood is important in clinical practice. Gas chromatographic headspace analysis appears to be the most successful method. In the present study, two methods of quantitative evaluation of the analysis were compared by statistical treatment and direct comparison. The absolute calibration method was found to be unsuitable since it yields entirely unreliable results. This is due to different contents of lipoid and other components in the blood of the normal population, and this influences the vapour phase concentration of halothane and results in different values for the slopes of calibration curves for different blood samples. The standard addition method gives reliable results.     

Simple algorithms for nonlinear calibration by the classical and standard additions methods

In univariate calibration by both the classical method and the standard additions method, calibration data are fitted to a response function y=f(x), from which the amount of an unknown x(0) is estimated by solving an equation of form y(0)=f(x(0)). Most such calibrations are limited to linear response functions f, for which the uncertainty in x(0) can be estimated from well-known expressions. The present work describes and illustrates one-step algorithms, in which x(0) is treated as an adjustable parameter in a nonlinear fit of the calibration data, with its standard error thus obtained numerically as a direct outcome of the fit. The computations are easily implemented with a number of data analysis programs and are illustrated here for a representative one, KaleidaGraph. The methods handle heteroscedastic data as easily as homoscedastic and nonlinear functions as easily as linear, permitting the analyst to experiment with different response functions in the quest for an optimum calibration. The estimates of sigma (x0) are obtained from the variance-covariance matrix V for the fit, so for weighted fitting with commercial programs, it is important to know which V--a priori or a posteriori--is being used.     

Evaluation of volume and matrix effects for the generalized standard addition method

A volume-dependent problem in use of the generalized standard addition method (GSAM) is evaluated. It is shown both mathematically and experimentally how to correct the deficiency. The revised GSAM was applied with direct current plasma spectroscopy in the presence of a salt and an acetone matrix effect.     

Application of H-Point standard addition method and multivariate calibration methods to the simultaneous kinetic-potentiometric determination of permanganate and dichromate

Simultaneous kinetic-potentiometric determination of binary mixture of permanganate (MnO₄ ^?) and dichromate (Cr₂O₇ ^2?) by H-point standard addition method (HPSAM), partial least squares (PLS) and principal component regression (PCR) is described. In this work, the difference between the rate of the oxidation reaction of Fe(II) to Fe(III) in the presence of MnO₄ ^? and Cr₂O₇ ^2? formed the basis of the method. The rate of the consumed fluoride ion for making the complex was detected by a fluoride ion selective electrode (FISE). The results show that the simultaneous determination of MnO₄ ^? and Cr₂O₇ ^2? could be conducted in their concentration ranges of 0.5?C10.0 and 0.1?C20.0 ??g ml^?1, respectively. The total relative standard error (RSE) for applying the PLS and PCR methods to 9 synthetic samples was 5.30 and 3.17, respectively in the concentration range of MnO₄ ^?, and 3.30 and 2.04, respectively, in the concentration range of Cr₂O₇ ^2?. In order for the selectivity of the method to be assessed, we evaluated the effects of certain foreign ions upon the reaction rate. The proposed methods (HPSAM, PLS and PCR) were evaluated using a set of synthetic sample mixtures and then applied to the simultaneous determination of MnO₄ ^? and Cr₂O₇ ^2? in different water samples.     

Non-linear transformations of factors in the generalized standard addition method

Summary Experimental designs and non-linearly transformed factors (concentrations of analytes) have been applied in the Generalized Standard Addition Method (GSAM). The relationship betweenN measured analytical signals,R ⁽¹⁾,...,R su(n), and concentrations of standard additions, c1,..., cn, ofn analytes has been approximated by the following polynomial models:The regression coefficientsB in models (1) are calculated from thesimple formulae^{1, 3, 4}.Functionsf _i ^(l) (e.g. linear, parabolic, exponential, hyperbolic or logarithmic) are selected on the basis of the experimentally determined relationshipsR ^(l) (l=1, ...,N) vs.c _i (i=1, ...,n). An example concerns the flame emission photometric determination of Na and Ca. 2² factorial and uncomplete second-degree modelsR ^(l) have been applied expressed by linear and hyperbolic functionsf _i ^(l). The results of determination of Na by GSAM reveal significant improvement of accuracy as compared with the conventional single-component standard addition method.

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Nicht-lineare Transformation von Faktoren bei der verallgemeinerten Standardadditio nsmethode

Zusammenfassung Statistische Versuchsplanung und nicht-linear transformierte Faktoren (Konzentrationen der zu bestimmenden Substanzen) wurden für die verallgemeinerte Standardadditionsmethode eingesetzt. Die Bezeichnung zwischen N gemessenen analytischen Signalen,R ⁽¹⁾,...,R ^(N) und den Konzentrationen der Standardadditionszugaben C_i,..., C ^N , vonn zu bestimmenden Substanzen wurde durch Polynome des folgenden Typs approximiert: (wobei ). Die Funktionenf _i ^(l) (z. B. lineare, parabolische, exponentielle, hyperbolische oder logarithmische) werden auf Basis experimentell bestimmter Abhängigkeiten festgelegtR ^(l) (l=1,...,N) gegen C _i (l=1,...,N). Als Beispiel wird die Flammenemissionsbestimmung von Na und Ca herangezogen. Dabei wurden ein 2² faktorieller Versuchsplan und ein unvollständiges Polynom der Ordnung 2R ^(l) mit linearen und hyperbolischen Funktionenf _i ^(l) angesetzt. Die Resultate der Na-Be-stimmung zeigen durch die Verwendung der verallgemeinerten Standard-addition signifikante Verbesserungen der Resultate gegenüber der Einkomponenten-Standardaddition.

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The author thanks Doc. dr. hab. A. Parczewski for his helpful discussion and editorial comments during the preparation of this paper.     

Use of the standard addition method in quantitative chromatographic analysis

Using the standard addition method as an example, several versions of it recommended for the determination of volatile components in complex hydrophobic matrices additionally containing compounds with sorption properties were considered. It was demonstrated that, along with the extrapolation of results to the zero standard addition, the most efficient techniques are the artificial transformation of similar samples into heterophase systems, when the analytes are distributed between both phases and the interfering components are predominantly localized in only one of the phases.     

Revaluation of the internal standard method coupled with the standard addition method applied to soil samples by means of photon activation

In order to achieve the highly accurate and precise multielement determination in environmental materials, the usefulness of the comparative standard provided by the processing method proposed previously for soil samples has been re-examined using calcareous loam soil, light sandy soil and river sediment as unknown samples. As a result, it was also demonstrated that concentrations of 15 trace elements in each sample can be determined effectively and reasonably.     

Kinetic spectrophotometric determination of Fe(II) in the presence of Fe(III) by H-point standard addition method in mixed micellar medium

The H-point standard addition method was applied to kinetic data for simultaneous determination of Fe(II) and Fe(III) or selective determination of Fe(II) in the presence of Fe(III). The method is based on the difference in the rate of complex formation between iron in two different oxidation states and methylthymol blue (MTB) at pH 3.5 in mixed cetyltrimethylammonium bromide (CTAB) and Triton X-100 micellar medium. Fe(II) can be determined in the range 0.25-2.5 microg ml(-1) with satisfactory accuracy and precision in the presence of excess Fe(III) and other metal ions that rapidly form complexes with MTB under working condition. The proposed method was successfully applied to the simultaneous determination of Fe(II) and Fe(III) or selective determination of Fe(II) in the presence of Fe(III) in spiked real environmental and synthetic samples with complex composition.     

Comparison of quantification strategies for one-point standard addition calibration: The homoscedastic case

Two quantification strategies for one-point standard addition calibration have been compared mathematically. One strategy involved the extrapolation of measurement points to their intercept with the x-axis to determine the analyte content in the unknown sample, and the other strategy is based upon direct calculation of the analyte content in the unknown sample using the instrumental responses obtained during measurement. The cases of both conventional standard addition calibration (C-SAC) and sequential standard addition calibration (S-SAC) have been considered. The homoscedastic situation has been considered, where the absolute precision of the instrumental response is constant. It has been determined that the precision ratio of the two strategies is dependent on surprisingly simple parameters: such as the sample to standard mass ratio (for C-SAC) and the analyte content ratio (for S-SAC).     

A modified standard addition method in X-ray fluorescence spectrometry

A modified standard addition method for single element determination by X-ray fluorescence spectrometry has been studied. The attenuation properties of the standard added samples are kept constant by adding decreasing amounts of an attenuation modifier along with increasing amounts of a standard. In this way the standard addition curve will be a straight line in cases where the ordinary standard addition curve is non-linear, and linear regression can be used to evaluate the concentration of the analyte. Standard additions of oxides of a number of elements, with and without modifier, have been made to cellulose powder or a mixture of aluminium oxide and polyethylene as matrices in order to test the method. The method has been applied to the determination of zinc in fly-ash from a steel work and of iron in cement. The fly-ash contained about 5% of zinc and the cement samples between 2 and 5% of Fe(2)O(3). The results were compared with those obtained by ICP-AES after decomposition of samples in lithium tetraborate or lithium metaborate and dissolution of the melt in 10%(v/v) nitric acid. The results agreed within 2%, relative, for fly-ash and within 3-6%, relative, for cement samples.     

Instrumental photon activation analysis of soil samples using the internal standard method coupled with the standard addition method

Multielement determinations in the certified reference materials of soils (IAEA soil-5 and 7) have been studied fundamentally by instrumental photon activation analysis using the internal standard method coupled with the standard addition method. For the soil-5 sample, in the first place, the qualities of the comparative standards prepared by two processing methods were compared with each other. As a result, it was demonstrated that a highly accurate and precise multielement determination can be achieved easily by minor improvement in the processing method of the comparative standard to ensure homogeneity. The utility of this processing method for soil samples was proved further through a similar analysis in another soil sample (IAEA soil-7).     

Improvement in LC-MS calibration by addition of fragment signals

Liquid chromatography-mass spectrometry has become a powerful analytical tool, with high selectivity and sensitivity. Usually in this technique, the calibration function is estimated from the molecular peak signal. This report describes the improvement in sensitivity when the signals from several fragments in addition to the molecular peak are used to establish the calibration function. The influence of the dwell time has also been analysed as an important instrumental parameter that influences the signal range, and consequently, the sensitivity. The calibration function obtained by adding fragment signals was used to estimate the instrumental detection limit using three different procedures, comparing and discussing the results obtained.     

Enhanced spectrofluorimetric determination of aflatoxin B1 in wheat by second-order standard addition method

Determination of aflatoxin B1 (AFB1) in wheat has been accomplished by enhanced spectrofluorimetry in combination with second-order standard addition method (EF-SOSAM). The adopted strategy combined the use of parallel factor analysis (PARAFAC) for extraction of the pure analyte signal and the standard addition method, for a determination in the presence of matrix effect caused by wheat matrix. The method is based on the enhanced fluorescence of AFB1 by beta-cyclodextrin in 10% (w/w) methanol-water solution. After sample treatment and without any extended cleanup steps and derivatization process, four standard additions were performed for each sample. A specific PARAFAC model was built from three-way arrays formed by excitation-emission spectra and 5 measurements (sample plus 4 additions). The scores related to AFB1 were used for a linear regression in the standard addition method. Two naturally contaminated wheat and spiked wheat samples containing AFB1 in the range 0-18 microg kg(-1) were analyzed by EF-SOSAM and compared with HPLC results. EF-SOSAM analysis of spiked wheat samples gave a good correlation with spiked values (R(2)>0.990). The limit of detection of method was 0.9 microg kg(-1) for the determination of AFB1 in wheat samples.     

Stripping voltammetry using sequential standard addition calibration with the analytes themselves acting as internal standards

A novel two-step standard addition calibration procedure for stripping voltammetry, whereby the analytes under investigation act as internal standards for each other, is described. In this way, the benefits of an internal standard for improving precision are obtained, without the requirement to add internal standard solutions. Only the standard solutions used to perform quantification are required. The proposed methodology has been tested against the traditional standard addition method with no internal standardisation, for the measurement of Zn, Cd, Pb and Cu in synthetic and real ambient air sample digests. The new procedure is shown to improve substantially precision and accuracy compared to traditional standard addition without internal standardisation.     

Instrumental photon activation analysis of coal fly ashes using the internal standard method coupled with the standard addition method

Multielement determinations of coal fly ashes (NIST SRM-1633a and BCR CRM-38) have been carried out by instrumental photon activation analysis using 30 MeV bremsstrahlung and the internal standard method coupled with the standard addition method. In these determinations, some major and minor constituent elements in the samples were properly used as effective internal standards. As a result, it was demonstrated that concentrations of 18 elements were determined accurately and precisely. Furthermore, a similar multielement determination has also been examined using 20 MeV bremsstrahlung. In this case, it was proved that better results can be achieved, because all interfering reactions were eliminated completely.