Statistical aspects of chemical analysis

Following a brief statement of certain fundamental principles, methods of sampling are dicussed which enable the informaiton sought by the analyst to be obtained as economically as possible. The need for proper randomisation both in sampling and in performing analyses is stressed and a short account is given of the use of 'quality control' charts in analytical work. Attention is drawn to the possibility of estimating the standard error from the range. A method of extracting the maximum information from analytical investigation involving the estimation of a ratio is described. The advantages of the 'factorial' as opposed to the 'classical' type of experimental design are demonstrated and reference is made to the value of carrying out an analysis of variance when examining the experimental data.     

Sample preparation for the analysis of heavy metals in foods

The analysis of foodstuffs for heavy metals continues to be an area of intense activity for analytical chemists. Methods of sample preparation are changing to allow a growing number of samples to be handled and to facilitate 'speciation' studies.     

Meeting reports: International conference on chemometrics in analytical chemistry

In the field of analytical chemistry, chemometrics has been defined as 'the chemical discipline which uses mathematical and statistical methods to achieve the aim of analytical chemistry, namely the obtention, in the optimal way, of relevant information about material systems'. There has been a tremendous growth of interest in the role of chemometrics in analytical chemistry in recent years and this has been reflected in the number of symposia devoted to the subject. Two meetings, held in Europe in September 1982, covered different aspects of chemometrics and some of the more significant points discussed are summarized in the reports below.     

Using an 'electronic spreadsheet' for Plackett-Burman calculations

The trend in analytical chemistry toward statistically designed experiments is reinforced by the trend toward using personal computers. The tedious calculations required to determine which factors significantly affect the performance or yield of an experiment are easily done with one of the 'electronic spreadsheet' programs now available on personal computers.     

Electrophoric release tags: Ultrasensitive molecular labels providing multiplicity

Electrophoric release tags are a new class of analytical reagents which function as molecular labels. These tags can be more sensitive than radioisotopes and their potential for multiplicity allows release-tagged reagents to be used as 'teams' in chemical analysis. Monoclonal antibodies, nucleic acid probes, receptor ligands and enzyme substrates may all benefit from this approach.     

An investigation of the applicability of 2,2'-dianthrimide in spectrophotometry: The determination of selenium(IV)

2,2'-Dianthrimide was studied as an analytical reagent and compared with the properties of 1,1'-dianthrimide. While 1,1'-dianthrimide reacts with B, Ge, Se and Te, 2,2'-dianthrimide was found to react only with selenium(IV).A straight line calibration curve is obtained up to 50 μg of selenium under the optimum conditions but the value of 2,2'-dianthrimide as a reagent for selenium(IV) is reduced by the high absorption of the reagent itself.     

Obsolescence in university instrumentation labs: A concern for industry?

Given industrial research and development's (R&D's) reliance on both highly-trained analytical staff and advanced instrumentation, how does it view the problem of increasing instrument obsolescence in universities? And what is it doing to help?     

Relationship between the general laws of vapor-liquid equilibria and the analytical curve of emission spectrometry

The relationship between the vapor-liquid equilibrium and the analytical curve of emission spectrometry is discussed on the basis of Hirata's equation, i.e., $\text{y}{}_1\text{y}{}_2$ = α($\text{x}{}_1\text{x}{}_2$)^β, where y is the mole fraction in the vapor phase, x in the liquid phase, α and β are constants for binary systems in a certain concentration range, and the indices $\text{1}$ and $\text{2}$ refer to the two components. Evaporation produced by different atomization-excitation systems can be characterized by apparent evaporation constants, α' and β', the values of which fall between the true values, α and β, of the normal distillation, and unity. Two powder techniques were selected representing the limiting cases: injection spark excitation (α' ≈ α, β' ≈ β) and controlled arc excitation (α' ≈ 1, β' ≈ 1). Using these excitation methods, the analytical curves of the impurities in industrial alumina and electrocorundum were studied using cup-electrode techniques with arc excitation. As a result, one of Hirata's rules could be selected for a given pair of elements. An unambiguous correlation between the properties of the analytical curves and Hirata's rules could be established.     

Public relations analyst

Professional scientific societies are becoming increasingly aware of the public image of their members' activities. The Analytical Division of the Royal Society of Chemistry, through the activities of its Honorary Publicity Secretary, is making a conscious effort to inform young people about the activities of analytical chemists and to interest them in the profession of analytical chemistry.     

Characterization (certification) of three wheat flours and a wheat gluten reference material (NIST RM 8436, 8437, 8438 and 8418) for essential and toxic major, minor and trace element constituents

Summary Three wheat flours, Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437), Soft Winter Wheat Flour (NIST RM 8438) and Wheat Gluten (NIST RM 8418) Reference Materials were characterized for essential and toxic major, minor and trace elemental composition by analysts in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods yielded 16–27 best estimate and 3–8 informational concentration values for each of these materials. These reference materials are intended for analytical quality control of element determinations in flour and flour products as well as other agricultural/food materials with related matrices.Contribution No. 92–145 from Centre for Land and Biological Resources Research     

On the thin cell method in time domain spectroscopy

A simple physical picture is given of Fellner-Feldegg's thin cell method in time domain spectroscopy. From this picture an accurate analytical relation is derived for the total reflection coefficient.     

New expressions for the overlap integral of two linear harmonic oscillator wavefunctions

Three new compact analytical expressions for the overlap integral of the wavefunctions of two distorted and displaced linear harmonic oscillators have been otained: unlike Ansbacher's formula, the do not lead to divergence when there is no distortion.     

Differential pulse voltammetric oxidation of polyriboxanthylic acid at the pyrolytic graphite electrode and a method for detection and determination of traces of xanthine and xanthosine-5'- monophosphate in polyxanthylic acid

Poly(X) (polyriboxanthylic acid) gives up to two differential pulse voltammetric oxidation peaks (peaks I and II) at the PGE. Xanthine, which appears to be a trace contaminant of commercial poly(X) samples, exhibits a differential pulse voltammetric oxidation peak at more negative potentials than the peaks of poly(X). Xanthosine-5'-monophosphate also gives up to two differential pulse voltammetric oxidation peaks at the PGE. An analytical method has been developed to determine trace amounts of xanthine and xanthosine-5'-monophosphate in poly(X) samples based on differential pulse voltammetry.     

Estimation of C2−C5 hydrocarbons in air by pre-concentration on silica gel at dry ice temperature

Summary A short stainless steel column packed with silica gel is cooled to –78°C and atmospheric hydrocarbons are preconcentrated from 3 I of air on it. Desorption to the analytical column is by heating for 10 min to 200°C. Analysis is by GC on OPN-Poracil C at 27°C. The sorption efficiencies were nearly 100% for most of the light hydrocarbons.     

Voltamperometry of Aromatic Nitro Compounds Using a Multisensor System of Electrodes Modified with Poly(Arylene Phthalide Ketones)

Electrodes modified with poly(arylene phthalide ketones) were developed for the voltammetric determination of isomers of aromatic nitro compounds. A polynomial algorithm for processing analytical signals from a sensor array was tested in the analysis of ternary mixtures. It is shown that the sensor array offers promise for analyzing multicomponent mixtures in the case when analytical signals overlap.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 576–581.Original Russian Text Copyright © 2005 by Sidel’nikov, Maistrenko, Kudasheva, Kuz’mina, Sapel’nikova, Gileva.Presented at the VI All-Russia Conference (with international participation) on Electrochemical Methods of Analysis (EMA-2004, Ufa, May 23–27, 2004).     

A polarographic study of some N-oxygenated products of N-ethyl-β-methoxy-β-(3'-trifluoromethylphenyl)-ethylamine (sk and f 40652a)

The polarographic behaviour of N-hydroxy-β-methoxy-β-(3'-trifluoromethylpbenyl)-ethylamine, N-ethyl-N-hydroxy-β-methoxy-β-(3'-trifluoromethylphenyl)ethylamine and (3-methoxy-β-(3'-trifluoromethylphenyl)acetaldoxime has been studied over the pH range 0—14. The hydroxylamines gave rise to anodic and cathodic behaviour whereas the oxime gave only a cathodic wave. The mechanism of the oxidation and reduction processes was investigated by d.c. polarography and preparative micro-coulometry. The optimum pH values for analytical purposes were 7, 8 and 4 for the two hydroxylamines and the oxime, respectively. The polarographic behaviour of a mixture of the three compounds was studied and the determination of traces of such compounds by differential pulse polarography is discussed.     

Analytical expressions for temperature programmed reduction patterns using solid-state kinetics

Using solid-state kinetics, analytical mathematical expressions are derived which describe the pattern generated during a temperature-programmed reduction (TPR) experiment conducted under differential conditions. From these expressions the influence of the heating rate on the TPR peak maximum can be established; it is shown that this influence can, in principle, be approximated by Kissinger's equation, independent of the reduction mechanism selected.     

Stark mixing by ion-Rydberg atom (molecule) collisions

Classical molecular dynamics simulations are performed to cover Stark mixing transitions (nℓ→nℓ^′) in Rydberg atoms by collision with slow ions. Accuracy is tested by comparison with the exact analytical classical probabilities previously obtained when the ion–atom potential is taken as the long-range ion–dipole interaction. The results are provided not only for the ion–dipole interaction but also for the full electrostatic interaction. It is shown, by comparison, that the ion–dipole potential alone provides reliable probabilities. The method is highly accurate and is very amenable to ready inclusion of other processes competing with Stark mixing.     

Thermostated radio-frequency excited electrodeless discharge lamps as primary sources in AFS

The performance of Cd and Zn thermostated electrodeless discharge lamps (EDL's) excited at 150 MHz radio-frequency through the inductively-coupled mode in a coil, have been studied with respect to the effect of lamp temperature, amount of material and RF power upon the source radiant output, atomic absorption, atomic fluorescence signals, spectral line width and line profile height of Cd 479.99 nm, Cd 228.8 nm, Zn 481.05 nm and Zn 213.9 nm. Although the lamps show similar behaviour to their microwave excited counterparts, they nevertheless offer several advantages that could renew the interest in EDL's as primary excitation sources in analytical spectroscopy.     

An analytical approximation for the number of states along the reaction coordinate

A variant of a new empirical method, enables one to express a collinear triatomic potential energy surface as a family of Morse curves along “natural” bond order coordinates orthogonal to the reaction coordinate. The procedure depends on a single adjustable parameter which is related to the barrier's height. Because an analytical expression for the number of vibrational states of a Morse oscillator is available, one has an analytical approximation for the number of states along the reaction coordinate. The extrema in the number of states are utilized in various versions of classical microcanonical variational transition state theory (among which is a new version, which is in better agreement with dynamical results), to estimate the probability of a collinear reactions, as a function of the total energy. The analytical expressions are also used to analyze the origins of the maximum and minima in the number of states.