A comparison of three methods for cholinesterase analysis

Three methods of cholinesterase analysis in blood are compared: the ΔpH (modified Michel method), pH Stat, and radiometric methods. The ΔpH method was determined to be the best choice for routine laboratory screeening for organophosphate exposure. The methods all agree within experimental variation. The radiometric method uses a thin-layer chromatography (TLC) separation of acetate (¹⁴C) activity from acetylcholine (¹⁴C) activity with direct β counting or scintillation counting to determine the concentration of acetate activity. The methods were compared on freeze-dried human blood and on experimentally carbamate-inhibited mouse blood. The radiometric analysis may be performed using as little as 5 μl of blood. The radiometric method may enhance the ability to detect sublethal exposure to cholinesterase inhibitors. It should be of particular use where sampling size is of greatest importance.     

A combined QSAR and partial order ranking approach to risk assessment

QSAR generated data appear as an attractive alternative to experimental data as foreseen in the proposed new chemicals legislation REACH. A preliminary risk assessment for the aquatic environment can be based on few factors, i.e. the octanol-water partition coefficient (Kow), the vapour pressure (VP) and the potential biodegradability of the compound in combination with the predicted no-effect concentration (PNEC) and the actual tonnage in which the substance is produced. Application of partial order ranking, allowing simultaneous inclusion of several parameters leads to a mutual prioritisation of the investigated substances, the prioritisation possibly being further analysed through the concept of linear extensions and average ranks. The ranking uses endpoint values (log Kow and log VP) derived from strictly linear 'noise-deficient' QSAR models as input parameters. Biodegradation estimates were adopted from the BioWin module of the EPI Suite. The population growth impairment of Tetrahymena pyriformis was used as a surrogate for fish lethality.     

A comparison of three activation analysis methods for iodine determination in foodstuffs

Activation analysis methods based on the nuclear reactions ¹²⁷ I(n, ) ¹²⁸ I, ¹²⁷ I(n,2n)¹²⁶I and ¹²⁷ I( ,n)¹²⁶ I were tested in terms ofdetection limits, accuracy and precision, and applicability for iodine determinationat various levels in foodstuffs. Both nondestructive and radiochemical modeswere employed using one of the two separation procedures developed (alkaline-oxidativefusion and iodine separation either by extraction of elemental iodine in chloroformor AgI precipitation). The lowest iodine detection limit of 1 ng . g ^—1 was achieved by employing the first nuclear reaction followedby separation of elemental iodine. Accuracy and precision of the proceduresdeveloped at largely different iodine levels were proved by analyses of biologicalreference materials having composition similar to that of various food items.     

Atomic-absorption methods for analysis of high-purity substances

A review is given of the use of atomic-absorption methods for determining the trace impurities in high-purity metals.     

A comparison of various pyrolysis experiments for the analysis of reference humic substances

The interpretation of the results of pyrolysis studies of humic substances is fraught with difficulties if only a single analytical technique is employed for substructure analyses. In this paper we have carried out investigations into humic substances utilising the additional information from the combination of gas chromatography/infrared spectroscopy and gas chromatography/mass spectrometry detection following Curie-point pyrolysis at five different temperatures. The results were compared to those obtained from conventional flash pyrolysis. The aim was to ensure the validation of the results of the compounds identified by at least one other spectroscopic technique. Some 30 substances have been positively identified by infrared spectroscopy, although their appearance is dependent on pyrolysis method and temperature. Most assignments were validated by mass spectrometry or the substance class confirmed.     

Direct comparison of methods for extracting the rate from first order data with background

Many methods involving a lag or retardation can linearize A exp(?kt) + Z data, allowing k to be obtained from the slope. A classification scheme is found in which the efficiencies are related to the classes of methods. The methods yielding k with the smallest standard deviations (σ_k) are compared quantitatively. The resulting error factors for k and the lags are tabulated for each of the four methods compared, for use by the experimenter. This is done for various ranges, backgrounds, and kinds of random noise. Effects on k and σ_k due to correlation, incorrect weighting, choice of lag, and the distribution of the plotted data are detailed. Effects at high noise levels are discussed for the (usually) best direct method, due to Guggenheim. These include the onset and extent of bias in k and failure of the method to yield any k.     

A comparison of three absorptiometric methods for the determination of copper in biological materials

Absorptiometric methods for traces of copper based on dithizone, 2,9-dimethyl-1,10-phenanthroline (neocuproine) and bis-cyclohexanone-oxalyldihydrazone (BCOD) were compared by carrying out replicate analyses on specimens of liver; the amount of sample taken was varied so as to provide a means of detecting systematic errors. Agreement between the results by the different methods was poor, the neocuproine method giving higher and more variable results than the other two. A systematic error, inconsistent with the sample size, was detected in the BCOD method. The dithizone method showed no systematic error and possessed better precision and sensitivity.     

A comparison of different methods for the calculation of the chemical potentials of polymer systems

In an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length v and one of length v+1 at any density. (Ref.9) In this paper we begin by formally proving that the chemical potential of a whole chain of length v can be obtained by sequentially summing the incremental chemical potentials of all chains whose lengths are smaller than v under the same conditions. We then compare the numerical value of chain chemical potentials computed in this fashion to those obtained by inserting whole chains into the simulation cell following the configurational bias procedure proposed by Smit and Frenkel. (Ref.5) It is found, for the two cases considered here, that the results obtained from the two different calculations agree within simulation uncertainty, thus verifying the validity of the proposed arguments.     

Comparison of three methods for trace analysis of polycyclics

Summary Several analytical techniques for the determination of polycyclic aromatic hydrocarbons in air have been evaluated. Two solvents, benzene and cyclohexane, were compared for their efficacy in the preliminary preparation of the air sample. To identify and measure the polycyclics, the techniques of ultraviolet absorption and fluorescence were used. Air sample extracts were analyzed with and without prior Chromatographic separation. A rapid Chromatographic procedure using benzene as elutant was employed for the first time. The extract aliquot or eluate fraction was chromatographed on fully activated alumina using benzene as the eluting solvent. BaP and BkF are eluted from such a column in 30 minutes or less in a total eluate volume of perhaps 50 ml and the two hydrocarbons are determined by fluorescence emission. Work in progress suggests that benzene may be replaced in this application by the less toxic toluene.By any method used the BkF values found were in good agreement. The agreement between the various BaP values was poor, suggesting not all were of equal validity. The highest, and also least accurate, BaP values seem to be associated with the use of benzene as extractant, or ultraviolet absorption as a measuring technique.

---

Zusammenfassung Verschiedene Analysenverfahren zur Bestimmung polycyklischer aromatischer Kohlenwasserstoffe in Luft wurden ausgearbeitet. Benzol und Cyklohexan wurden hinsichtlich ihrer Wirksamkeit als Lösungsmittel bei der Vorbereitung der Luftproben verglichen. Zur Identifizierung und Messung der polycyklischen Substanzen wurde die UV-Absorption und die Fluoreszenz herangezogen. Die Luftprobenextrakte wurden mit und ohne vorherige chromatographische Auftrennung analysiert. Bin rasches chromatographisches Verfahren mit Benzol als Elutionsmittel wurde erstmals verwendet. Extraktanteil oder Eluatfraktion wurden auf hochaktivem Aluminiumoxid chromatographiert und mit Benzol eluiert. Benzo(a)perylen (BaP) und Benzo(k)fluoranthen (BkF) werden aus einer solchen Säule in 30 Minuten mit etwa 50 ml eluiert und durch Fluoreszenzmessung bestimmt. Es scheint naheliegend, statt Benzol das weniger toxische Toluol zur Elution zu verwenden. Die nach jeder Methode erhaltenen BkF-Werte stimmen gut überein im Gegensatz zu den BaP-Werten. Die höchsten und gleichzeitig wenigst genauen BaP-Werte treten offenbar auf, wenn Benzol als Extraktionsmittel und UV-Absorption zur Messung verwendet werden.

---

---

Presented at the Anachem Conference, Detroit, Mich., U. S. A., October 11, 1966.     

A computer program for ranking analytical methods according to their fitness for purpose

A program for conducting automatic searches for analytical methods, selecting the most suitable ones according to quality requirements, and ranking them based on quality indices calculated from various pre-selected quality parameters is proposed. The program uses an externally updated database (Analytical Abstracts CD-ROMs or other) and customised quality schemes based on accuracy, precision, sensitivity, applicability to real samples, determination range (ratio), throughput and impact factor (from the Citation Index). It can, therefore, be used for a variety of purposes in analytical chemistry.     

Plates for thin-layer chromatography with adsorption-immobilized reagents in chemical test analysis methods

The use of plates for thin-layer chromatography (TLC) with adsorption-immobilized organic reagents in chemical test methods for analysis is considered. Triarylmethane, triazine, eirodine, acridine, and rhodamine dyes are used for immobilization. The degree of retention of the reagents is 52–98%. It is found that the absorption spectra of these reagents on TLC plates exhibit a hypsochromic shift of absorption bands by 8–30 nm in comparison with their absorption spectra in solutions. The retention is higher for the reagents that exhibit a hypsochromic shift of absorption bands on TLC plates. The sorption isotherms of the reagents on TLC plates are obtained and analyzed. Test methods have been developed for the determination of 1–200 mg/L Au(III) and 0.1–5 M acids and alkalies with the use of reagent TLC plates. The relative standard deviation of the results of analysis is no larger than 10%; the time of analysis is 3–7 min.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 291–296.Original Russian Text Copyright © 2005 by Amelin, Tretyakov.     

A comparison of geometric methods with other methods for the characterization of density matrices

Some recently developed geometric methods for characterizing the subset of density matrices within the space of Hermitian matrices are compared with methods commonly used for the approximate characterization of reduced density matrices. The decomposition of a density matrix into components in terms of the reducing basis set is compared with decomposition in terms of representations of U(r).     

Determination of organic substances by kinetic-catalytic methods of analysis

A review on the determination of organic substances by kinetic-catalytic methods of analysis is given.Methods based on homogeneous catalyzed solution reactions as well as those based on heterogeneous catalyzed electrode reactions are discussed.     

Quantification methods of Black Carbon: comparison of Rock-Eval analysis with traditional methods

Black Carbon (BC) quantification methods are reviewed, including new Rock-Eval 6 data on BC reference materials. BC has been reported to have major impacts on climate, human health and environmental quality. Especially for risk assessment of persistent organic pollutants (POPs) it is important to account for risk reduction caused by BC, as suggested for POP safety assessment in the framework of the new European Community Regulation on Registration, Evaluation, Authorization and Restriction of Chemicals (REACH). Four major classes of BC quantification methods are reviewed including application to BC reference materials. Methods include chemical oxidation, thermal oxidation, molecular marker, optical methods and Rock-Eval analyses. Residual carbon from Rock-Eval 6 analysis correlated well with BC data from 'gentle' methods like optical and molecular marker methods, which capture a major part of the BC continuum including labile fractions (e.g. char). In contrast, the temperature at which 50% of the organic matter was oxidized (T(50%)) in an oxidation-only Rock-Eval analysis, correlated well with data from chemothermal oxidation (CTO), which captures only refractory BC fractions (e.g. soot). Rock-Eval analysis can further be used for BC characterization through deconvolution of the dominant peaks of the thermogram and appears to be a powerful tool in BC analysis.     

A comparison of three algorithms for chromatograms alignment

In this paper the performance of three alignment algorithms, correlation optimized warping, parametric time warping and semi-parametric time warping, is compared on real chromatograms. Among these, parametric time warping is the simplest and fastest; generally less than 1s is required to align two chromatograms. It does not require the optimization of input parameters and allows the alignment of peak shifts in only one direction, or non-complex peak shifts in both directions. With correlation optimized warping and semi-parametric time warping complex peak shifts in both directions can be corrected but at the expense of the optimization of two input parameters. Semi-parametric time warping requires the selection of the proper number of B-splines in the warping function and, if necessary, the optimization of the penalty parameter. Often the default values can be used to obtain aligned signals. The optimization of the input parameters for correlation optimized warping (section length, slack) is not easy and time-consuming. Moreover, dependent on the input parameters, the computation time of the correlation optimized warping algorithm can be twice as long as for semi-parametric time warping for which computation times up to 23 s are required. However, the performance of both algorithms is equally good considering the improvement of the precision of the peak retention times and correlation coefficients between the chromatograms, after alignment. For the data aligned in this study, the average retention time precision and the lowest correlation before warping were 14 and 0.17, and were improved to three and 0.83, and six and 0.87 after warping, with correlation optimized warping and semi-parametric time warping, respectively.     

Primary methods of measurement in chemical analysis

 Primary methods of measurement have a central function in metrology. They are an essential component in the realisation of the SI units and therefore are indispensable for establishing traceability of measurements of all kinds of physical quantities to the corresponding SI units. This is also true for chemical analysis. Gravimetry, titrimetry, coulometry, and isotope dilution mass spectrometry (IDMS) are evaluated with regard to their potential to be primary methods according to a general definition of primary methods recently given by the Comité Consultatif pour la Quantité de Matière (CCQM). Optical absorption spectrometry and methods based on colligative properties are also considered. A general scheme for establishing traceability of chemical measurements to the SI units using primary methods is discussed. Received: 17 April 1997 · Accepted: 9 August 1997