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.     

Dual standard addition for quantitative NMR analysis

A technique is described for quantitative NMR measurement which involves the use of a pair of internal standards. This procedure overcomes several of the problems encountered with only one standard material. A computer programme is described for statistical treatment of the results.     

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.     

A comparison of the external standard and standard addition methods for the quantitative chromatographic determination of pesticide concentrations in plant samples

Model samples containing known amounts of pesticides in various plant materials were analyzed, and the accuracies of the external standard and standard addition methods were compared based on a criterion such as the relative analyte concentration. It was found that traditionally recommended procedures for the solvent extraction of pesticides from samples of this kind in combination with quantitative analysis by the external standard method determine only 10–70% of the true concentrations of analytes. This is most likely due to analyte adsorption on matrices and/or incomplete extraction. In almost all cases, the use of the standard addition method compensates pesticide losses at the stages of sample preparation and thereby considerably decreases the systematic error of determination. The extrapolation of analyte concentration to the zero amount of the added reference sample was proposed to additionally control the accuracy of results obtained by the standard addition method. Moreover, it was found that solid-phase extraction as the second stage of sample preparation has no considerable advantages over back solvent extraction in terms of the above criterion. This is because the main analyte losses were observed at the first stage of extraction from test samples.     

Neutron-activation analysis by standard addition and solvent extraction

A new approach to activation analysis is described. Chemical yield determinations are avoided by selective extraction of the required element in conjunction with the standard addition technique. The principle and its application to the determination of traces of uranium in aluminium and the standard granite (G-1) are given. The advantages of this method are its simplicity and rapidity.     

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).     

Principal component analysis for the selection of variables in the application of the H-point and generalised H-point standard addition method

The present paper deals with the selection of variables for the H-point and generalised H-point standard additions methods (HPSAM and GHPSAM, respectively). Both methods are applied for the resolution of spectroscopic interfered signals in the UV-vis range. The HPSAM is a suitable method for the resolution of binary and ternary mixtures when the interferent is known. The GHPSAM is applied for the resolution of samples that contain unknown interferents. In this paper, a method based on the study of a principal components analysis (PCA) for the selection of variables for the HPSAM and GHPSAM is proposed. The PCA results show the isolation of the analyte signal from the sample signal, achieved by the application of the HPSAM and GHPSAM. It is showed that by means of the score and loading plots, it is possible to select the most appropriate variables without a priori establishing any condition.     

Photon and proton activation analysis of iron and steel standards using the internal standard method coupled with the standard addition method

The internal standard method coupled with the standard addition method has been applied to photon activation analysis and proton activation analysis of minor elements and trace impurities in various types of iron and steel samples issued by the Iron and Steel Institute of Japan (ISIJ). Samples and standard addition samples were once dissolved to mix homogeneously, an internal standard and elements to be determined and solidified as a silica-gel to make a similar matrix composition and geometry. Cerium and yttrium were used as an internal standard in photon and proton activation, respectively. In photon activation, 20 MeV electron beam was used for bremsstrahlung irradiation to reduce matrix activity and nuclear interference reactions, and the results were compared with those of 30 MeV irradiation. In proton activation, iron was removed by the MIBK extraction method after dissolving samples to reduce the radioactivity of⁵⁶Co from iron via⁵⁶Fe(p,n)⁵⁶Co reaction. The results of proton and photon activation analysis were in good agreement with the standard values of ISIJ.     

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.     

A rapid method for direct quantitative analysis on chromatographic layers

Summary A rapid method is described for direct quantitative determination on the chromatographic layer. The method is based on the measurement of the length of the chromatographic band in the direction of flow.     

A novel baseline-correction method for standard addition based derivative spectra and its application to quantitative analysis of benzo(a)pyrene in vegetable oil samples

In the present work, a baseline-correction method based on peak-to-derivative baseline measurement was proposed for the elimination of complex matrix interference that was mainly caused by unknown components and/or background in the analysis of derivative spectra. This novel method was applicable particularly when the matrix interfering components showed a broad spectral band, which was common in practical analysis. The derivative baseline was established by connecting two crossing points of the spectral curves obtained with a standard addition method (SAM). The applicability and reliability of the proposed method was demonstrated through both theoretical simulation and practical application. Firstly, Gaussian bands were used to simulate 'interfering' and 'analyte' bands to investigate the effect of different parameters of interfering band on the derivative baseline. This simulation analysis verified that the accuracy of the proposed method was remarkably better than other conventional methods such as peak-to-zero, tangent, and peak-to-peak measurements. Then the above proposed baseline-correction method was applied to the determination of benzo(a)pyrene (BaP) in vegetable oil samples by second-derivative synchronous fluorescence spectroscopy. The satisfactory results were obtained by using this new method to analyze a certified reference material (coconut oil, BCR(?)-458) with a relative error of -3.2% from the certified BaP concentration. Potentially, the proposed method can be applied to various types of derivative spectra in different fields such as UV-visible absorption spectroscopy, fluorescence spectroscopy and infrared spectroscopy.     

Matrix effect and correction by standard addition in quantitative liquid chromatographic-mass spectrometric analysis of diarrhetic shellfish poisoning toxins

An evaluation of the feasibility of liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure ionization was made for quantitation of four diarrhetic shellfish poisoning toxins, okadaic acid, dinophysistoxin-1, pectenotoxin-6 and yessotoxin in scallops. When LC-MS was applied to the analysis of scallop extracts, large signal suppressions were observed due to coeluting substances from the column. To compensate for these matrix signal suppressions, the standard addition method was applied. First, the sample was analyzed and then the sample involving the addition of calibration standards is analyzed. Although this method requires two LC-MS runs per analysis, effective correction of quantitative errors was found.     

Multivariate standard addition method solved by net analyte signal calculation and rank annihilation factor analysis

This article describes the use of the net analyte signal (NAS) concept and rank annihilation factor analysis (RAFA) for building two different multivariate standard addition models called “SANAS” and “SARAF.” In the former, by the definition of a new subspace, the NAS vector of the analyte of interest in an unknown sample as well as the NAS vectors of samples spiked with various amounts of the standard solutions are calculated and then their Euclidean norms are plotted against the concentration of added standard. In this way, a simple linear standard addition graph similar to that in univariate calibration is obtained, from which the concentration of the analyte in the unknown sample and the analytical figures of merit are readily calculated. In the SARAF method, the concentration of the analyte in the unknown sample is varied iteratively until the contribution of the analyte in the response data matrix is completely annihilated. The proposed methods were evaluated by analyzing simulated absorbance data as well as by the analysis of two indicators in synthetic matrices as experimental data. The resultant predicted concentrations of unknown samples showed that the SANAS and SARAF methods both produced accurate results with relative errors of prediction lower than 5% in most cases.     

Use of N-acetylpsychosine as internal standard for quantitative high-performance liquid chromatographic analysis of glycosphingolipids.

The use of N-acetylpsychosine as an internal standard for the quantitative high-performance liquid chromatography (HPLC) of p-nitrobenzoyl derivatives of glycosphingolipids is described. It is suitable because the chromogen reacts on equimolar basis with both N-acetylpsychosine and sample glycosphingolipids. The use of N-acetylpsychosine as an internal standard was validated by determining the glycosphingolipid content of a system of metastatic variants selected from a murine fibrosarcoma line (T3 cells). Reproducible results were obtained throughout several quantitative analyses of cellular glycosphingolipids and it was possible to determine the glycosphingolipid content of as few as 5 x 10(6) cells.     

Application of the internal standard method coupled with the standard addition method in photon activation analysis to trace characterization of environmental materials

The internal standard method coupled with the standard addition method has been applied to the analysis of environmental materials, such as urban particulate matter, vehicle exhaust particulates and coal fly ash by photon activation. High-resolution gamma-ray spectrometry makes possible to use multi-internal standard gamma-rays, in order to crosscheck the analytical results obtained from each internal standard. It was ascertained that this method can provide not only accurate analytical results but also the information of homogeneity of samples, correlation of elements in the sample, loss or contamination in the preparation process.     

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.     

H-point standard addition method in the analysis by differential pulse anodic stripping voltammetry Simultaneous determination of lead and tin

The applicability of H-point standard addition method (HPSAM) to the resolving of overlapping differential pulse anodic stripping voltammetric peaks corresponding to the oxidation of lead and tin is verified. The results show that the H-point standard addition method is suitable for the simultaneous determination of lead and tin in aqueous media. The results of applying the H-point standard addition method showed that Sn²⁺ and Pb²⁺ could be determined simultaneously with the concentration ratios of Sn²⁺ to Pb²⁺ varying from 1:5 to 10:1 in the mixed sample. The proposed method has been successfully applied to the simultaneous determination of lead in the presence of tin in some synthetic samples. Moreover, the applicability of the method was demonstrated by the recovery of lead in a canned soft drink sample.     

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.