Compatibility and universality of the retention prediction system for polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography

Summary System-compatibility and universality of the retention prediction concept has been investigated for polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography. The results clearly indicate that the retention prediction approach has a very high potential for optimization of separation conditions in almost all reversed-phase systems, and allows more precise and rapid analysis. This approach may be one of the best optimization techniques, because the system does not require any standard materials.     

Automated flow enzyme-linked immunosorbent assay (ELISA) system for analysis of methyl parathion

Sensitive detection of pesticides is of utmost importance in environment and food analysis. Immunological methods are widely used to detect pesticides in agricultural and environmental samples wherein antibodies are employed against the target molecules. Accurate diagnosis depends on the affinity and specificity of the antibody preparation used, and high affinity antibodies are essential for the detection of very small amounts of pesticides. Enzyme linked immuno sorbent assay (ELISA) coupled with flow injection analysis (FIA) technique provides a very high sensitivity with high throughput of analyses. Automation of this analysis scheme ensures precise detection with high accuracy. The present development aims at providing a user-friendly system for achieving this objective. It employs a 8952 microcontroller for precise flow of reagents, samples, substrate and conjugates used for analysis to be passed through an immobilized antibody column at predetermined time. With the sequence and flow control of buffers used, it also provides the option for reuse of the immobilized antibody column. The system is flexible to accommodate multiple sequences up to a maximum of 99 steps. It is customizable for different flow ELISA applications. It can control up to eight solenoid valves (dc 24 V) and two peristaltic pumps and has one 12 bit analog channel for data acquisition. With the serial interface port, the system provides convenient means for data acquisition into the computer. The system has been successfully tested for immuno analysis of organophosphorous pesticide methyl parathion.     

The use of stabilizers in the UV assay of ascorbic acid

Sodium thiosulphate (0.04%w/v) has been used to stabilize ascorbic acid in aqueous medium. The method has been used to assay ascorbic acid in commercial tablet preparations. It is very accurate, precise and reproducible. It compares favourably with official titrimetric method. The method is simple and can be adopted for the routine assay of ascorbic acid in single component tablet formulations.     

Spectrometric determination of the fineness of gold

The use of the glow discharge source has been tested for the analysis of refined gold by direct reading emission spectrometry. Careful investigations of the discharge parameters and the introduction of the sputtering rate as internal standard led to a very precise and accurate analytical procedure which has been proved by analysing 100 unknown samples of refined gold. The proposed spectrometric analysis is at least as accurate as the conventional fire assay method and is much faster and laboursaving.     

A very precise high-performance liquid chromatographic procedure for the determination of cefmenoxime, a new cephalosporin antibiotic, in plasma

A simple and very precise high-performance liquid chromatographic procedure has been developed for the determination of cefmenoxime, a new broad spectrum cephalosporin antibiotic, in plasma. The workup procedure involves ultrafiltration of samples which have been treated with sodium dodecyl sulfate to displace the drug from its binding sites on plasma proteins. The ultrafiltrates are then directly injected into a high-performance liquid chromatographic system utilizing a reversed-phase analytical column, and an ultraviolet spectrophotometric detector. The mean assay coefficient of variation over a concentration range of 0.5-200 micrograms/ml is slightly greater than 1% when either p-nitrobenzoic or p-anisic acid is used as the internal standard. Recoveries of drug are essentially quantitative at all levels investigated; hence the calibration curves are rectilinear from the limit of quantification (about 0.05 microgram/ml) to at least 200 micrograms/ml.     

Coupled gas chromatography-atomic absorption spectrometry.

The specific, precise detection of volatile metal chelates has been obtained by coupling the effluent from a gas chromatograph directly to the burner head of a commerical atomic absorption spectrometer (AAS). Quantitation of chromium in the nanogram range has been accomplished with a detection limit of 1.0 ng. The chelation-extraction-gas chromatographic separation procedure coupled with the selective detection by AAS gives a relatively interference-free system that has been used to quantitatively analyse for chromium in standard biological materials NBS SRM 1571 Orchard Leaves and SRM 1569 Brewers Yeast. Metal chelates of iron, copper and cobalt have also been detected by this system.     

Low-Level Quantitation of Formaldehyde in Drug Substance by HPLC–UV

Formaldehyde has been highlighted as potential genotoxic impurity (GTI). Trace-level quantification of GTIs in drug substances requires sensitive, precise and accurate analytical methodologies for their estimation in drug substances and control. Analysis and estimation of formaldehyde is very challenging due to its properties namely volatility, high polarity, low molecular weight and over and above the absence of chromophore. This article presents a validated HPLC–UV method which is sensitive to quantification of formaldehyde in active pharmaceutical ingredient. As formaldehyde does not possess chromophore, the developed HPLC method involves derivatization with 2,4-dinitrophenylhydrazine. Using this method, the detection and quantitation limits achieved are 0.5 and 1.5 ppm, respectively. The calibration curve of formaldehyde was linear over the concentration range of 1.5–20 ppm. The method was found to be sensitive, precise and accurate and the proposed method has been successfully applied to estimate formaldehyde content in scale-up batches of bulk drug.

     

Fine structure analysis of the even parity configuration system of Ti I

Even-parity configuration system of Ti I has been considered on the basis of the experimental data available in literature. The fine structure analysis has been performed with the aid of a linked-parameter method of level-fitting calculations in a large multiconfiguration basis. Fine structure parameters have been determined and precise wavefunctions of even energy levels have been evaluated. Appropriate pseudorelativistic Hartree-Fock ab initio calculations of fine structure parameters have been presented for comparison purposes. Configuration interaction effects on even-parity configurations have been discussed.     

On the use of the Edgeworth-Cramér series to obtain diffusion coefficients from taylor dispersion peaks

Three methods of determining the parameters required for the calculation of diffusion coefficients in Taylor dispersion experiments from quasi-Gaussian output signals have been examined, the height-area method, moment calculation by direct integration, and moment calculation from a nonlinear least squares fit to a truncated Edgeworth-Cramér series.The method using moments determined by integration has been found to be unsatisfactory, as it yields diffusion coefficients very heavily dependent on the choice made for the width of the peak base. Those derived from the height-area method can deviate systematically and significantly from those determined from the variance obtained from the least squares series fit where, as is usual, the peak varies from a true Gaussian. The series fit method, within our reproducibility of 1–2%, yields values consistent with accurate and precise literature data, and is recommended for precise work.     

Is the HCCS radical linear in the excited state?

The A (2)Pi-X (2)Pi 415 nm band system of the linear HCCS radical has been known since 1978, but the vibronic structure in this complex spectrum, which has both spin-orbit and Renner-Teller complications, has never been satisfactorily assigned, despite serious experimental and theoretical efforts. In a further attempt to understand the spectrum, we have studied the laser-induced fluorescence spectra of jet-cooled HCCS and DCCS, produced from thiophene precursors using the discharge jet technique. The 0(0) (0) bands of HCCS and DCCS have been rotationally analyzed, providing precise ground and excited state spin-orbit splittings. The energy levels of the v(')=0 (2)Pi(3/2) component of DCCS are found to be perturbed by a very low-lying (2)Sigma vibronic level, indicating that the HCC bending mode Renner-Teller effect is much larger than predicted by ab initio calculations with a linear excited state geometry. With this observation, the vibronic bands in the spectra of both isotopomers have been consistently assigned for the first time. Model calculations show that the large Renner-Teller effect and substantially different HCCS and DCCS excited state zero-point spin-orbit splittings can be explained with the assumption of a quasilinear excited state geometry.     

Spectrophotometric method for the determination of vanadium in uranium rich hydrogeochemical samples using pyridyl azo resorcinol (PAR)

A simple and precise method has been developed for the determination of traces of vanadium(V), using 4-(2 pyridyl azo) resorcinol, in natural water samples, containing very high concentrations of uranium. CDTA-pyrophosphate buffer has been used for masking interferants, including uranium which otherwise interferes above 125 ppb. The reaction of vanadium with PAR in the presence of buffer requires a waiting period of 45 min. The Sandell sensitivity of the method is 0.003 microg/ml, at 545 nm at an optimum pH of 6.5 +/- 0.2. The precision of the method is +/- 15% at the 100 ppb level of vanadium(V). The method has been successfully applied to a number of natural water samples during hydrogeochemical exploration.     

Synthesis and oligodeoxynucleotide binding properties of pyrrolidinyl peptide nucleic acids bearing prolyl-2-aminocyclopentanecarboxylic acid (ACPC) backbones

A series of novel conformationally rigid pyrrolidinyl peptide nucleic acids (PNA) based on d-prolyl-2-aminocyclopentanecarboxylic acid (ACPC) backbones has been synthesized. Investigation of the binding properties of four stereoisomeric PNAs possessing different stereochemistry at the ACPC part with DNA revealed that a precise stereochemistry of the backbone is very important in determining the binding properties. Only the PNA containing (1S,2S)-ACPC can form a very stable 1:1 complex with the complementary DNA in a sequence-specific manner.     

Precise titrimetric determination of uranium in high-purity uranium compounds

A procedure has been developed for the very precise determination of uranium in high-purity uranium compounds. Uranium(VI) is reduced in a strong hydrochloric acid solution with aluminium in the presence of cadmium ions to uranium(III). It is oxidised to uranium(IV) in the presence of excess orthophosphoric acid and then quantitatively oxidised to uranium(VI) with potassium dichromate using a potentiometric end-point detection. The coefficient of variation based on 20 analyses is -/+ 0.003%.     

A new system of gamma-ray spectrometry for activation analysis

A new system of γ-ray spectrometry has been designed and constructed. This system performs a precise, quick and automatic activation analysis using our nuclear reactor (TRIGA-II Research Reactor) as a neutron source. The main components are detector system consisted of a high resolution Ge(Li) detector settled in a shielding cabinet and a well-type NaI(Tl) scintillation counter for anti-Compton measurement, and data acquisition and spectra analysis system performed independently by two mini computer. The system has operated for atmospheric aerosols as an example of activation analysis.     

Surface chemical analysis and chromatographic characterization of polyethylenimine-coated hydroxyapatite with various amount of polyethylenimine

Polyethylenimine (PEI) has been widely used as a coating material to produce stationary phase for ion-exchange chromatography of biomolecules. However, a precise study of the PEI coating fraction has been lacking, despite such quantification being very important for fundamental research as well as identifying further industrial applications.In this study, we produced four types of PEI-coated hydroxyapatite (PEI-HAp) with various fractions of PEI (0.16%, 0.5%, 1.0%, 1.5%) using a spray-drying system to evaluate correlations between coating fractions and the thermochemical or chromatographic behaviors of theses products. The thermal analyses of these matrices showed two exothermic peaks when the PEI coating fraction exceeded 1.0%. The one peak indicated a PEI decomposition peak and the other would indicate bond dissociation of PEI layers formed over the HAp surface as the PEI concentration increased. Furthermore, the chromatographic analysis for the surface chemical characteristics showed the correlation between coating fraction and the retention time of protein or nucleotide. Acidic or phosphorylated proteins were more strongly adsorbed as the PEI coating fraction increased when the initial coating fraction was low, but at fraction exceeding 0.5%, constant retention was observed. The retention time of nucleotides increased in proportion to the fraction of PEI added. The good selectivity of PEI-HAp may be attributable to multifunctional interactions of electrostatic and bare Ca sites on HAp, not just the amino sites of PEI. These precise studies of PEI coating fraction are our original novel contributions, which could be achieved by quantitative consideration using thermal analysis and chromatography.     

An accurate method for intermolecular interaction measurement at low microwave frequencies

An accurate microwave method for very sensitive measurements of intermolecular interactions of non-polar gases is described. It is based on the precise determination of the O factor of a resonant cavity using an indirect method and computer analysis of the experimental points. This method has been successfully applied for the measurement of the collision induced absorption of CO₂ at the low-frequency spectral wing.     

On the existence of H2F+ in dilute hydrofluoric acid solutions

The existence of H₂F⁺, which has been long postulated in dilute aqueous HF solutions, was investigated by fluoride ion-selective electrode potentiometry. Even under conditions conducive to its formation precise measurements yielded only equivocal evidence for its occurrence. It is thought that H₂F⁺ will exist only in very concentrated HF solutions with low water activities.     

Isotope effects in the infrared spectra of OCS-He complexes and clusters

Infrared spectra of the OCS-He van der Waals complex and of OCS-He(N) clusters have been studied in the region of the OCS nu1 fundamental band using a tunable diode laser to probe a pulsed supersonic slit jet. For the complex, the spectrum of the normal isotope, 16O12C32S-4He, has been considerably extended and the 34S- and 13C-substituted forms have been recorded for the first time. The data could be analyzed satisfactorily using a conventional asymmetric rotor Hamiltonian with sextic centrifugal distortion terms. For the clusters, the 34S- and 13C-substituted forms have been observed and assigned for N = 2-7, including some transitions with higher J values than previously reported for the normal isotope, e.g., R5. The observed vibrational shifts, relative to the free OCS molecule, were very similar to those of the normal isotope, and most of the difference could be explained by simple scaling. These results constitute a subtle and precise probe of intermolecular forces and dynamical effects in a system which is of current interest for cluster studies.