Calculations and interpretation of the results of stoichiographic analysis of solid multi-element multi-phase compounds and materials

Methods and approaches to the calculations and interpretation of the results of stoichiographic analysis of solid multi-element multi-phase compounds and materials using the flow mode of the differential dissolution (DD) method are reported. Special features of calculationls as well as the objective reasons for the necessity of obtaining more or less precise results of stoichiographic calculations are discussed. The details of the procedure of stoichiographic calculations, refinement, and interpretation of the results are considered on an example of the DD-analysis of the Co-Ni-Fe-Bi-K-P-Mo-O/SiO₂-catalyst for the selective oxidation and oxidative ammonolysis of hydrocarbons. The specific details and methods used for the estimation of the performance characteristics of the DD analytical procedure are discussed.     

Statistical Model for Organic Chromatographic Trace Analysis of Complex Samples. A Case Study: Plant Extracts

Abstract

The use of pooled plant extracts is described in the estimation of matrix interference in HPLC (UV and EC) determinations of organic compounds in plant extracts. An extract from freeze dried leaves of 134 different plant species was used for this purpose. It was split in different subgroups with solid extraction clean-up procedures. UV, EC and chromatographic data of the subgroups were used in the calculation of minimum concentrations of organic compounds which are still accurately determinable in plant samples with HPLC methods. The UV and/or EC characteristics of the compound must be known. The contribution of the solid phase extraction procedures and of the analytical system to the selectivity of the method can be estimated. Information is also supplied which allows rapid comparison of the selectivity of the UV and EC (single, or dual parallel) detectors for the determination of a specified compound.     

Comparison of different methods for the determination of volatile organic compounds in water samples

The aim of this work was to compare the characteristics of three methods, membrane inlet mass spectrometry (MIMS), purge-and-trap gas chromatography-mass spectrometry (P&T) and static headspace gas chromatography (HSGC), for the determination of volatile organic compounds in water samples as used in routine analysis. The characteristics examined included linear dynamic ranges, detection limits of selected environmentally hazardous volatile organic compounds (e.g. toluene, benzene and trichloroethene) in water, required analysis time and reproducibility of the analytical methods. The MIMS and P&T methods had the lowest detection limits for all the tested compounds, ranging from 0.1 to 5 mug 1(-1). Linear dynamic ranges using the MIMS method were about four orders of magnitude and using the P&T method about two orders of magnitude. Detection limits of the HSGC method were 10-100 times higher than those of the other two methods, but the linear dynamic ranges were larger, even up to six orders of magnitude. The analysis time per sample was shortest for the MIMS method, from 5 to 10 min, and ranged around from 35 to 45 min for the HSGC and P&T methods. The reproducibilities of the methods were of the same order of magnitude, in the range of 1-13%. Agreement between the analytical results obtained for spiked samples and for environmental water samples by the three different methods was very good.     

Electrochemical Sensors,a Bright Future in the Fabrication of Portable Kits in Analytical Systems

Analysis of food, pharmaceutical, and environmental compounds is an inevitable issue to evaluate quality of the compounds used in human life. Quality of drinking water, food products, and pharmaceutical compounds is directly associated with human health. Presence of forbidden additives in food products, toxic compounds in water samples and drugs with low quality lead to important problems for human health. Therefore, attention to analytical strategy for investigation of quality of food, pharmaceutical, and environmental compounds and monitoring presence of forbidden compounds in materials used by humans has increased in recent years. Analytical methods help to identify and quantify both permissible and unauthorized compounds present in the materials used in human daily life. Among analytical methods, electrochemical methods have been shown to have more advantages compared to other analytical methods due to their portability and low cost. Most of big companies have applied this type of analytical methods because of their fast and selective analysis. Due to simple operation and high diversity of electroanalytical sensors, these types of sensors are expected to be the future generation of analytical systems. Therefore, many scientists and researchers have focused on designing and fabrication of electroanalytical sensors with good selectivity and high sensitivity for different types of compounds such as drugs, food, and environmental pollutants. In this paper, we described the mechanism and different examples of DNA, enzymatic and electro‐catalytic methods for electroanalytical determination of drug, food and environmental compounds.     

Estimation of precision and efficiency mass transfer steps for the determination of pesticides in vegetables aiming at the expression of results with reliable uncertainty

A 'bottom-up' approach for the expression of results obtained from analytical methods that include analytical steps with recovery inherently different from 100% [mass transfer steps (MTS): extraction, evaporation, clean-up procedures, digestion, etc.] is presented. The estimation of the combination of all MTS uncertainty involves the comparison of the experimental dispersion of replicated analyses of spiked samples with the estimation of the uncertainty obtained for the combination of all uncertainty sources except MTS ones ('incomplete' estimation). The estimation of MTS uncertainty by difference is performed after evaluating the statistical difference between the 'incomplete' estimation and the experimental dispersion (F-test). When the two estimations are statistically equivalent, the MTS uncertainty is considered to be negligible in relation to the other sources budget. The assumption of constancy of MTS performance within the analytical range is tested through single analyses at several concentration levels and is evaluated by the inclusion of the expected values at the intervals resulting from the combination of the MTS uncertainty estimation performed at one concentration level and the 'incomplete' estimation. The developed methodology can also be useful for method optimisation and validation and for the detection of small trends in results. The determination of pesticides in sweet peppers by GC-NPD was used to explore the above concepts.     

An Empirical Study on the Impact of Bioanalytical Method Variability on Estimation of PK Parameters

The effect of the experimental error of bioanalytical methods on the estimation of pharmacokinetic (PK) parameters was formerly studied with simulation experiments. The results showed that the precision of affects both accuracy and precision of pharmacokinetic parameters. In particular for drugs with small within-individual pharmacokinetic variability the contribution of bioanalytical imprecision of 15% may become unacceptable. The above-mentioned simulation results were confirmed by a recent experiment where plasma curves were analysed in multifold in the same and in different analytical batches, thereby being able to quantify correlations between bioanalytical within-day and between-day variability and PK variability. The results showed that for compounds or formulations with large between-subject or within-subject/between-dosing variability more bioanalytical variability may be acceptable than for drugs with small between-subject variability. Acceptability of analytical precision and accuracy depends on the compound and the study design. Influence of bioanalysis on final outcome is generally insignificant. In general it can be stated that most bioanalytical assays used for regulatory support are very suitable if they are operated within current guideline criteria.     

An appraisal of experimental designs: Application to enantioselective capillary electromigration techniques

Enantioresolution processes are vital tools for investigating the enantioselectivities of chiral compounds. An analyst resolves to optimize enantioresolution conditions once they are determined. Generally, optimization is conducted by a one-factor-at-a-time (OFAT) approach. Although this approach may determine an adequate condition for the method, it does not often allow the estimation of the real optimum condition. Experimental designs are conducive for the optimization of enantioresolution methods via capillary electromigration techniques (CETs). They can efficiently extract information from the behavior of a method and enable the estimation of the real optimum condition. Furthermore, the application of the analytical quality by design (AQbD) approach to the development of CET-based enantioselective methods is a trend. This article (i) offers an overview of the application of experimental designs to the development of enantioselective methods from 2015 to mid-2020, (ii) reveals the experimental designs that are presently employed in CET-based enantioresolutions, and (iii) offers a critical point of view on how the different experimental designs can aid the optimization of enantioresolution processes by considering the method parameters.     

Green analytical methodologies for the discovery of bioactive compounds from marine sources

The application of green analytical chemistry in search of bioactive compounds is of paramount importance, leading to the development of environmentally friendly methodologies for their isolation. This work provides an up-to-date overview of the analytical methodologies based on a green perspective for the discovery of bioactive compounds from marine sources, namely to their extraction and structural characterization. Both the characteristics of marine bioactive compounds and the sustainable evaluation of their bioactivity are also addressed.     

Application of a novel chemometric approach to the determination of aqueous photolysis rates of organic compounds in natural waters

The utility of multivariate optimization methods in the determination of aqueous photolysis rates of organic compounds is examined in this study. A basic pursue was to designate the appropriate experimental design plan that extend the analytical utility of multivariate methods from qualitative data interpretation approaches, as applied thus far, to quantitative estimation methods. A three-level second-order central composite design with parameter concentrations (factor levels) beyond the environmental realistic concentrations was employed for that purpose enabling statistically significant effects to be determined. Method application is demonstrated in the first photodegradation study of two UV absorbing chemicals in natural waters. The results suggest that the proposed approach of enables a good approximation of the real behavior in terms of both qualitative and quantitative data interpretation with minimal loss of information.     

Analytical Methods for Speciation of Organotins in the Environment

The growing awareness over the environmental fate of organotin compounds is reflected in the large number of analytical methods developed for their separation. Organotin compounds have varying degrees of toxicological properties, depending on the nature and number of alkyl groups bonded to the tin atom. Most of the analytical speciation methods applied to actual environmental media have involved prior derivatization to transform organotin compounds into volatile hydrophobic analytes amenable to separation and identification by gas chromatography coupled to a sensitive and selective tin-detector. Evidence exists that members of the same homologous series are related by environmental degradation pathways. Chemical treatment prior to analysis, or high temperatures associated with gas chromatography separation, may alter the relative amounts of organotins in samples and blur the true environment picture. To avoid species redistribution that may occur during derivatization or gas speciation analysis, methods based on liquid chromatography and supercritical fluid chromatography have been investigated. This review documents analytical methods for determination of tin and speciation of organotin compounds, in the hope that it will be of value to those interested in initiating a programme for assessing the impact of such species on the environment.     

Ligand Sensitized Flourometric Determination of Dysprosium(III) Ion Using Terephthalic Acid

Several trivalent lanthanide ions are known to exhibit excellent luminescence characteristics when they are coordinated with appropriate organic ligands. Various analytical methods have been developed to determine lanthanide ions or organic compounds by taking advantage of these luminescence characteristics. The luminescence enhancement of the lanthanide ions by complexation with organic ligands has been explained on the basis of a ligand to metal energy transfer process.     

Quantifying the measurement uncertainty of results from environmental analytical methods

The Eurachem-CITAC Guide Quantifying Uncertainty in Analytical Measurement was put into practice in a public laboratory devoted to environmental analytical measurements. In doing so due regard was given to the provisions of ISO 17025 and an attempt was made to base the entire estimation of measurement uncertainty on available data from the literature or from previously performed validation studies. Most environmental analytical procedures laid down in national or international standards are the result of cooperative efforts and put into effect as part of a compromise between all parties involved, public and private, that also encompasses environmental standards and statutory limits. Central to many procedures is the focus on the measurement of environmental effects rather than on individual chemical species. In this situation it is particularly important to understand the measurement process well enough to produce a realistic uncertainty statement. Environmental analytical methods will be examined as far as necessary, but reference will also be made to analytical methods in general and to physical measurement methods where appropriate. This paper describes ways and means of quantifying uncertainty for frequently practised methods of environmental analysis. It will be shown that operationally defined measurands are no obstacle to the estimation process as described in the Eurachem/CITAC Guide if it is accepted that the dominating component of uncertainty comes from the actual practice of the method as a reproducibility standard deviation.     

Comparison between micellar liquid chromatography and capillary zone electrophoresis for the determination of hydrophobic basic drugs in pharmaceutical preparations

The determination of highly hydrophobic basic compounds by means of conventional reversed-phase liquid chromatographic methods has several drawbacks. Owing to the characteristics of micellar liquid chromatography (MLC) and capillary electrophoresis (CE), these techniques could be advantageous alternatives to reversed-phase chromatographic methods for the determination of these kinds of compounds. The objective of this study was to develop and compare MLC and CE methods for the determination of antipsychotic basic drugs (amitryptiline, haloperidol, perphenazine and thioridazine) in pharmaceutical preparations. The chromatographic determination of the analytes was performed on a Kromasil C(18) analytical column; the mobile phase was 0.04 m cetyltrimethylammonium bromide (CTAB), at pH 3, containing 5% 1-butanol, at a flow rate of 1 mL/min. The CE separation was performed in a fused-silica capillary with a 50 mm tris-(hydroxymethyl)-aminomethane buffer, pH 7, at an applied voltage of 20 kV, using barbital as internal stardard. The proposed methods are suitable for a reliable quantitation of these compounds in the commercial tablets and drops in terms of accuracy and precision and require a very simple pre-treatment of the samples. By comparing the performance characteristics and experimental details of the MLC and CE methods we conclude that CE seems to be slightly better than MLC in the determination of highly hydrophobic compounds in pharmaceuticals in terms of resolution and economy, taking into account that the limits of detection are not a handicap in pharmaceutical samples.     

Speciation of trace metals in environmental samples at the fisheries laboratory,Burnham on crouch

The methods used by the MAFF Directorate of Fisheries Research for analysis of organometallic compounds are described. These analytical techniques are used for determination of trace quantities of the compounds in water, sediment and biota in UK estuaries and coastal waters.     

Quantifying the measurement uncertainty of results from environmental analytical methods

The Eurachem–CITAC Guide Quantifying Uncertainty in Analytical Measurement was put into practice in a public laboratory devoted to environmental analytical measurements. In doing so due regard was given to the provisions of ISO 17025 and an attempt was made to base the entire estimation of measurement uncertainty on available data from the literature or from previously performed validation studies. Most environmental analytical procedures laid down in national or international standards are the result of cooperative efforts and put into effect as part of a compromise between all parties involved, public and private, that also encompasses environmental standards and statutory limits. Central to many procedures is the focus on the measurement of environmental effects rather than on individual chemical species. In this situation it is particularly important to understand the measurement process well enough to produce a realistic uncertainty statement. Environmental analytical methods will be examined as far as necessary, but reference will also be made to analytical methods in general and to physical measurement methods where appropriate. This paper describes ways and means of quantifying uncertainty for frequently practised methods of environmental analysis. It will be shown that operationally defined measurands are no obstacle to the estimation process as described in the Eurachem/CITAC Guide if it is accepted that the dominating component of uncertainty comes from the actual practice of the method as a reproducibility standard deviation.     

Chromatographic analysis of tocol-derived lipid antioxidants

This paper provides a comprehensive overview of existing chromatographic methods for the analysis of tocol-derived lipid antioxidants in various sample matrices. After a brief introductory discussion on biological and nutritional aspects of the vitamin E active compounds, the review focuses on various techniques for the isolation, purification, chromatographic separation, and detection of tocopherols and tocotrienols. Compiled published normal-phase (NP) and reversed-phase (RP) high-performance liquid chromatographic (HPLC) methods demonstrate general trends and analytical variability and versatility of HPLC methodology. The relative merits of the two HPLC methods are assessed. NP and RP elution characteristics are delineated to aid in the identification of antioxidant components. Technical novelty of certain analytical procedures for non-food samples warrants their inclusion in this review in light of the potential applicability in food assays.     

Assessment of uncertainty in pesticide multiresidue analytical methods: main sources and estimation

The estimation of the uncertainty associated to analytical methods is necessary in order to establish the comparability of results. Multiresidue analytical methods lack very often of information about uncertainty of results with likely implications when results are compared with maximum residue levels (MRL) established by regulations. An adequate identification and estimation of each uncertainty source allows to laboratories to establish the accuracy of results and to balance with time-consuming and costs.     

Comprehensive two-dimensional liquid chromatography x gas chromatography: evaluation of the applicability for the analysis of edible oils and fats

Edible fats and oils are complex mixtures containing a wide range of (classes of) compounds. The most important group of compounds are the triglycerides (triacylglycerides, TAGs). Because of the large number of possible fatty acid combinations, an enormous number of TAGs is possible. In the present feasibility study, the applicability of different modes of comprehensive two-dimensional LCXGC for detailed oil and fat analysis is evaluated. Comprehensive LCXGC was found to be an extremely powerful analytical method for the analysis of complex TAG samples. Using the new comprehensive set-ups, TAGs can be separated according to two independent parameters: carbon number vs. number of double bonds, or fatty acid composition vs. number of double bonds. The information content of comprehensive separations by far exceeds that of the current generation of analytical methods. The quantitative results of the separations show a good agreement with data obtained from standard analytical methods. The comprehensive methods studied can also be used for fingerprinting of oil samples, as well as for the analysis of target compounds or compound groups. Highly detailed separations of olive oil samples were obtained. Zooming in on one region of the chromatogram allowed reliable analysis of wax esters without interferences of sterol esters.     

The clas program for classification and evaluation

Multivariate classification methods are needed to assist in extracting information from analytical data. The most appropriate method for each problem must be chosen. The applicability of a method mainly depends on the distributional characteristics of the data population (normality, correlations between variables, separation of classes, nature of variables) and on the characteristics of the data sample available (numbers of objects, variables and classes, missing values, measurement errors). The CLAS program is designed to combine classification methods with evaluation of their performance, for batch data processing. It incorporates two-group linear discriminant analysis (SLDA), independent class modelling with principal components (SIMCA), kernel density estimation (ALLOC), and principal component class modelling with kernel density estimation (CLASSY). Most of these methods are implemented so as to give probabilistic classifications. Multiple linear regression is provided for, and other methods are scheduled. CLAS evaluates the classification method using the training set data (resubstitution), independent test data, and pseudo test data (leave-one-out method). This last method is optimized for faster computation. Criteria for classification performance and reliability of the given probabilities, etc. are determined. The package contains flexible possibilities for data manipulation, variable transformation and missing data handling.     

Comprehensive two-dimensional liquid chromatography×gas chromatography: evaluation of the applicability for the analysis of edible oils and fats

Edible fats and oils are complex mixtures containing a wide range of (classes of) compounds. The most important group of compounds are the triglycerides (triacylglycerides, TAGs). Because of the large number of possible fatty acid combinations, an enormous number of TAGs is possible. In the present feasibility study, the applicability of different modes of comprehensive two-dimensional LC×GC for detailed oil and fat analysis is evaluated. Comprehensive LC×GC was found to be an extremely powerful analytical method for the analysis of complex TAG samples. Using the new comprehensive set-ups, TAGs can be separated according to two independent parameters: carbon number vs. number of double bonds, or fatty acid composition vs. number of double bonds. The information content of comprehensive separations by far exceeds that of the current generation of analytical methods. The quantitative results of the separations show a good agreement with data obtained from standard analytical methods. The comprehensive methods studied can also be used for fingerprinting of oil samples, as well as for the analysis of target compounds or compound groups. Highly detailed separations of olive oil samples were obtained. Zooming in on one region of the chromatogram allowed reliable analysis of wax esters without interferences of sterol esters.