Sample preparation for chromatographic separations: an overview

Chromatographic methods dominate the field of organic analysis. However, many samples are too dilute, too complex or incompatible with the chromatographic system to render separation or detection possible without preliminary matrix simplification and/or preconcentration. A broad selection of the most common, recent and emerging isolation, clean-up and concentration techniques used to prepare samples for chromatographic separations are reviewed.     

EDXRF analysis of suspended particulate matter (SPM) from residential and industrial areas in Cairo,Egypt

Due to the remarkable increasing of the mass concentrations of suspended particulate matter (SPM) as an air pollution indicator in Greater Cairo‐Egypt, regular sampling during autumn 2014 and winter 2014/2015 seasons has been performed from industrial and residential areas. It was found that the average mass concentrations of the SPM collected from residential and industrial areas are equal to 531 ± 198 and 912 ± 230 μg/m³, respectively. These quantities are much higher than the maximum allowance level, especially for the industrial area. By utilizing three secondary targets, energy dispersive x‐ray fluorescence working under vacuum environment was used for elemental analysis of 19 elements namely; Na, Al, Si, S, Cl, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, Rb, and Sr. The present optimized selective excitation energy dispersive x‐ray fluorescence analysis has considerably enhanced the analytical range with respect to our previous similar studies, including low Z elements such as Na, Al, S, and Cl and attaining lower detection limits in the range of ng/m³. Remarkable high elemental concentrations were determined for most of the detected elements from the industrial area samples, strongly indicating the influence of the industrial and anthropogenic activities. The average percentages of the mass concentration of the detected inorganic elements account only for 3.2% and 10.5% of the total mass concentration collected from the residential and industrial areas, respectively, thus directly indicating that the content of organic pollutants in SPM is the dominant contribution.     

New look-ahead Lanczos-type algorithms for linear systems

Summary. A breakdown (due to a division by zero) can arise in the algorithms for implementing Lanczos' method because of the non-existence of some formal orthogonal polynomials or because the recurrence relationship used is not appropriate. Such a breakdown can be avoided by jumping over the polynomials involved. This strategy was already used in some algorithms such as the MRZ and its variants. In this paper, we propose new implementations of the recurrence relations of these algorithms which only need the storage of a fixed number of vectors, independent of the length of the jump. These new algorithms are based on Horner's rule and on a different way for computing the coefficients of the recurrence relationships. Moreover, these new algorithms seem to be more stable than the old ones and they provide better numerical results. Numerical examples and comparisons with other algorithms will be given. Received September 2, 1997 / Revised version received July 24, 1998     

Selective separation of silver(I) and mercury(II) ions in natural water samples using alumina modified thiouracil derivatives as new solid phase extractors

A simple and reliable solid-phase extraction (SPE) method has been developed to synthesise two new sorbents: 6-propyl-2-thiouracil and 5,6-diamino-2-thiouracil physically loaded onto alumina surface, phases I and II, respectively. The synthesis of these new phases has been confirmed by IR-spectroscopy. The surface concentrations of the organic moieties were determined to be 0.182 and 0.562 mmol g^?1 for phases I and II, respectively. The evaluation of the selectivity and metal uptake properties incorporated in these two alumina phases were also studied and discussed for 10 different metal ions: Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Pb(II) and Ag(I) under different controlling factors. The data obtained clearly indicated that the new SP-extractors have the highest affinity for retention of Hg(II) ions. Selective separation of Hg(II) from Ag(I) as one of the most interfering ion, in addition to the other eight coexisting metal ions under investigation, was achieved successfully using the new sorbents at pH = 9.0 under static conditions. Therefore, Hg(II) exhibits major retention percentage (100.0%) using phase I or II. However, Ag(I) exhibits minor retention percentage equal to 1.33% using phase I and 0.67% using phase II. On the other hand, the retention percentage of the other eight metal ions ranged (0.0–3.08%) using phase I and (0.0–1.54%) using phase II at the same pH. The new phases were applied for separation and determination of trace amounts of Hg(II) and Ag(I) spiked natural water samples using cold vapour atomic absorption spectroscopy and atomic absorption spectroscopy with no matrix interference. The high recovery values of Hg(II) and Ag(I) obtained using phases I and II were ranged 98.9 ± 0.1–99.2 ± 0.05% along with a good precision (RSD% 0.01–0.502%, N = 3) demonstrate the accuracy and validity of the new sorbents for separation and determination of Hg(II) and Ag(I).     

SYNTHESIS AND REACTIONS OF 2,3-DIHYDRO- 5-ARYL-5H,6H-THIAZOLO[3,2-b]-2,4-DIAZAFLUORENE-3,6-DIONES OF POTENTIAL BIOLOGICAL ACTIVITIES

Abstract

1,2,3,4-Tetrahydro-l-aryl-3,9-dioxo-2,4-diazafluorenes (2) and 1,2,3,4-tetrahydro-1-aryl-9-oxo-3-thi-oxo-2,4-diazafluorenes (3) were newly synthesized. Compounds 3 reacted with chloroacetic acid, α-bromopropanoic acid, or B-bromopropanoic acid in the presence of fused sodium acetate and acetic anhydride to give 2,3-dihydro-5-aryl-5H,6H-thiazolo[3,2-b]2,4-diazafluorene-3,6-diones (4), 2-methyl-2,3-dihydro-5-aryl-5H,6H-thiazolo[3,2-b]2,4-diazafluorene-3,6-diones (5) and 2,3-dihydro-6-aryl-6H,7H-thiazino[3,2-b]2,4-diazafluorene-4,7-diones (6), respectively.

2,3-Dihydro-2-arylmethylene-5-aryl-5H,6H-thiazolo[3,2-b]2,4-diazafluorene-3,6-diones (7) were prepared by the reaction of compounds (3) with chloroacetic acid and aromatic aldehydes in the presence of fused sodium acetate and acetic anhydride or by the reactions of (4) with aromatic aldehydes in the presence of acetic anhydride.

2-(Arylhydroazono)-5-aryl-2,3-dihydro-5H,6H-thiazolo[3,2-b]2,4-diazafluorene-3,6-diones (8) were synthesized by coupling (4) with aryldiazonium salts in the presence of pyridine.     

Spectral Characterization of Novel 3-Phenyl-2-Substituted Quinazoline and Fused Quinazoline Derivatives

3-phenyl-2-thioxo-quinazolin-4(3H)one 1 was utilized for the construction of some novel 2-substituted quinazolin-4(3H)one derivatives through the formation of 2-hydrazinyl quinazolinone, which was used as the key starting material for the synthesis of 2-heteryl quinazolines via the reaction with one carbon donors, β-diketones and β-ketoester. Infrared, ¹H NMR, and mass spectra of the synthesized compounds were discussed. Some of them showed promising anti-inflammatory activity.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Novel poly(vinyl chloride) based thermoplastic elastomers incorporating vinyl-functionalized silicone rubber

ABSTRACT

Novel poly(vinyl chloride) (PVC) based thermoplastic elastomers were developed by blending with different proportions of vinyl-functionalized silicone rubber. Scanning electron microscopy (SEM) confirmed good compatibility between PVC and silicone rubber which allowed enhancement of the stress-strain behavior. On the contrary to neat PVC, exposure to heat or UV radiation was found not to cause any considerable deterioration to the stress-strain behavior. Fourier Transform Infrared (FTIR) revealed a possible chemical interaction between the blend components involving the vinyl groups from the silicone rubber, which is thought to be the reason for maintaining the mechanical properties unaltered. Further investigation with ultraviolet-visible (UV-Vis.) spectroscopy signified absence of intensive dehydrochlorination usually encountered for PVC after exposure to heat or UV radiation, which indicates a potential stabilizing effect for the silicone rubber and build up of a network structure comprising both hard and soft segments.     

Identification of phenyl-N-methylcarbamates and their transformation products in Tunisian surface water by solid-phase extraction liquid chromatography-tandem mass spectrometry

Liquid chromatography-pneumatically assisted electrospray mass spectrometry with both negative and positive ionization has been used for the determination of carbamates pesticides and their transformation products in Tunisian surface water. Eight pesticides and four of their hydrolysis products were covered in this study.Optimization of electrospray inlet conditions is described as well as results from investigations of the linearity of the detector response. Conditions for tandem mass spectrometry (MS-MS) detection of characteristic daughter ions formed by collision induced dissociation (CID) of the parent ion are described. Detection limits using MS in the selected ion monitoring (SIM) mode were generally in the order of 0.5 μg L⁻¹ or below. A principle of analysis is proposed based on triple quadrupole MS as a method for quantitative determination followed by verification of positive findings by CID-MS-MS. Application of the method for detecting carbamates residues in surface water is demonstrated.     

Reactivity of sugar cane bagasse as a natural solid phase extractor for selective removal of Fe(III) and heavy-metal ions from natural water samples

This work introduces the feasibility of using sugar cane bagasse (SCB) – a sugar cane industry waste – as a selective solid phase extractor for Fe(III). The order of metal uptake capacities in μmol g^?1 for the extraction of six tested metal ions from aqueous solution using static technique is Fe(III) > Cu(II) > Pb(II) > Zn(II) > Cd(II) > Co(II). Since SCB exhibits remarkable binding characteristics for Fe(III), special interest was devoted for optimizing its uptake and studying its selectivity properties under static and dynamic conditions. In this respect, batch experiments were carried out at the pH range 1.0–4.0, initial concentration of metal ion (10–100 μmol), weight of phase (25, 50, 75, 100, 125 and 150 mg) and shaking time (10, 30, 45, 60, 90, 120 and 150 min). FT-IR spectra of SCB before and after uptake of Fe(III) were recorded to explore the nature of the functional groups responsible for binding of Fe(III) onto the studied natural biosorbent. The equilibrium data were better fitted with Langmuir model (r² = 0.985) than Freundlich model (r² = 0.934). Moreover, Fe(III) sorption was fast and completed within 60 min. The adsorption kinetics data were best fitted with the pseudo-second-order type. As a view to find a suitable application of SCB based on its unique property as a benign sorbent, it was found that, Fe(III) spiked natural water samples such as doubly distilled water (DDW), drinking tap water (DTW), natural drinking water (NDW), ground water (GW) and Nile River water (NRW) was quantitatively recovered (>95.0%) using batch and column experiments, with no matrix interferences.     

Optimization parameters for adsorption and desorption of Zn(II) and Se(IV) using rice husk ash: kinetics and equilibrium

An attempt at the use of rice husk ash, an agricultural waste, as an adsorbent of Zn(II) and Se(IV) from their aqueous solution is studied. Studies are carried out as a function of contact time, metal ion concentration, adsorbent dose, and pH at 25 °C. Its adsorption capability and adsorption rate are considerably higher and faster for Zn(II) ions than for Se(IV) ions. Zn(II) adsorption was found fast reaching equilibrium within ≃1 h while Se(IV) adsorption was slow reaching equilibrium within ≃100 h. The Bangham equation can be used to express the mechanism for adsorption. The experimental isotherm data were analyzed using Langmiur, Freundlich, and Temkin models. Desorption experiments were carried out using different media with a view to regenerate the spent adsorbent and to recover the adsorbed metal ion.