High-performance liquid chromatographic determination of Levetiracetam in human plasma: comparison of different sample clean-up procedures

An accurate and precise high-performance liquid chromatographic method using diode array detection for the determination of the novel antiepileptic, Levetiracetam, has been developed. Three clean-up procedures for the analysis of Levetiracetam in human plasma were implemented and evaluated, namely solid-phase extraction, deproteinization by addition of organic solvents and formation of insoluble salts. Adenosine was used as the internal standard for all three sample pretreatment procedures. Among the several cartridges used for solid-phase extraction, the hydrophilic-lypophilic balance (Oasis) HLB) phase provides the best extraction yield of Levetiracetam, together with high precision. With the two other clean-up procedures involving plasma deproteinization by addition of methanol or zinc sulphate, lower sensitivity and precision of the assays were obtained. However, they are cheaper and faster when compared with the solid-phase extraction procedure.     

Electron–Electron interaction energy in homonuclear diatomic molecules

The derivative of the electron–electron potential energy U_ee with respect to internuclear separation R is studied for light homonuclear diatomic molecules at equilibrium. It is readily related to nuclear–nuclear potential energy U_nn, the force constant K, and the electron–nuclear potential energy U_en. An approximate expression, based on the simplest form of density functional theory, is then used to eliminate dU_en/dR|_Re. The result thus obtained for dU_ee/dR|_Re transcends an earlier proposal of Kryachko by including a term 2/3R_eK, with K the force constant. Numerical tests at SCF–RHF level are presented for nine homonuclear diatomic molecules.     

Etude de la reaction de lactonisation de l'acide ethylenedioxy-1,1 methyl-2 oxo-3 cyclopentane-2- propionique

The lactonisation of ethylene 1,1-dioxy 2-methyl 3-oxo cyclopentane-2 propionic acid has been affected by a new method whose mechanism is discussed. The formation of a β-diketone and other products by isomerisation of the enol lactone has been avoided. The enol lactone is an important intermediate in the total synthesis of steroids and has been prepared with a good yield by the new method.     

A pilot study for the preparation of a new Reference Material based on antarctic krill

The preparation of new Certified Reference Materials (CRMs) of antarctic matrices forms the backbone of an ongoing project in the framework of the Italian National Program for Antarctic Research. The first CRM of this kind (MURST-ISS-A1 Antarctic Marine Sediment) is already available. The second phase focuses on the certification of antarctic krill, a small shrimp extremely abundant in the Southern Ocean. The total mass of krill available for this purpose is approximately 44 kg and results from the combination of three different catches (Ross Sea, Marguerite Bay and Livingston Island, respectively). The quantification of the following elements in the raw mass appears to be affordable by current analytical techniques, values being in the range of (in μg/g) 0.11–0.30 for As, 0.03–0.12 for Cd, 0.06–0.23 for Cr, 6.1–21 for Cu, 5.7–7.6 for Fe, 0.005–0.008 for Hg, 0.7–1.2 for Mn, 0.013– 0.077 for Ni, 0.04–0.57 for Pb and 12–16 for Zn. On the other hand, the average values ascertained in freeze-dried krill are as a rule one order of magnitude higher, i.e., (in μg/g), 3.2 for As, 0.6 for Cd, 1.8 for Cr, 75 for Cu, 61 for Fe, 0.025 for Hg, 4.6 for Mn, 0.7 for Ni, 2.1 for Pb and 81 for Zn. Information on the pretreatment of krill and details on the planned certification campaign are also given. Received: 10 June 1997 / Revised: 24 September 1997 / Accepted: 28 September 1997     

Gamma-radiolysis of quinoline in 2-propanol solution

In the last twenty years the ionizing effects on matter of⁶⁰Co γ-rays have been widely discussed. However, regarding organic compounds, mainly aromatic ones, results are scarce, particularly those obtained in alcoholic solution. γ-Radiation is used mainly in industry and medicine, particularly for sterilization of surgical materials. In this work we studied the chemical and radiolytic stability of products by radiation from quinoline in isopropanol solution. Doses were from 2×10⁴ to 3×10⁵ Gy and the samples concentration was 1∶1 by volume. We have observed significant effects for high radiation doses. Lower doses effected the solvent with the production of long polymeric hydrocarbons. Products formed were characterized by capillary gas chromatography coupled to a mass-selective detector (GC/MSD). We have used a fused silica capillary column 25 m long, 0.2 mm in internal diameter, covered by a 0.33 μm thick film of crosslinked 5% phenyl methyl silicone.     

Determination of melatonin in commercial preparations by micellar electrokinetic chromatography and spectrofluorimetry

Melatonin was determined in pharmaceutical preparations by means of two simple and reliable analytical methods based on micellar electrokinetic chromatography (MEKC) and spectrofluorimetry. The fluorescence emission values were measured at λ=350 nm when exciting at λ=275 nm. The MEKC analysis was achieved using a system consisting of 40 mM SDS in phosphate buffer (20 mM, pH 7.5). The extraction of melatonin from the tablets was achieved by means of a simple one-step dissolution with methanol/water. Both methods were applied for the determination of melatonin in commercial formulations and galenic preparations. The MEKC procedure allows the quantitative determination of melatonin in all pharmaceutical preparations tested. On the contrary, the spectrofluorimetric method is not suitable for tablets which also contain tryptophan; this interference can be eliminated by a suitable liquid-liquid extraction procedure. The results obtained with the two methods are in good agreement and satisfactory in terms of precision and accuracy.     

Reversed-phase capillary electrochromatography for the simultaneous determination of acetylsalicylic acid, paracetamol, and caffeine in analgesic tablets

The separation and simultaneous determination of caffeine, paracetamol, and acetylsalicylic acid in two analgesic tablet formulations was investigated by capillary electrochromatography (CEC). The effect of mobile phase composition on the separation and peak efficiency of the three analytes was studied and evaluated; in particular, the influence of buffer type, buffer pH, and acetonitrile content of the mobile phase was investigated. The analyses were carried out under optimized separation conditions, using a full-packed silica capillary (75 microm ID; 30.0 cm and 21.5 cm total and effective lengths, respectively) with a 5 microm C8 stationary phase. A mixture of 25 mM ammonium formate at pH 3.0 and acetonitrile (30:70 v/v) was used as the mobile phase. UV detection was at 210 nm. Good linearity was found in the range of 50-200, 20-160, and 4-20 microg/mL for acetylsalicylic acid (r2=0.9988), paracetamol (r2=0.9990) and caffeine (r2=0.9990), respectively. Intermediate precision (RSD interday) as low as 0.1-0.8% was found for retention times, while the RSD values for the peak area ratios (Aanalyte/AIS) were in the range of 1.9-2.9%. The optimized CEC method was applied to the analysis of the studied compounds present in commercial tablets.     

Beyond p-Hexaphenylenes: Synthesis of Unsubstituted p-Nonaphenylene by a Precursor Protocol

The synthesis of unsubstituted oligo-para-phenylenes ( OPP ) exceeding para-hexaphenylene—in the literature often referred to as p-sexiphenyl—has long remained elusive due to their insolubility. We report the first preparation of unsubstituted para-nonaphenylenes ( 9PP s) by extending our precursor route to poly-para-phenylenes ( PPP ) to a discrete oligomer. Two geometric isomers of methoxylated syn- and anti-cyclohexadienylenes were synthesized, from which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical, infrared and solid-state ¹³C NMR spectroscopy as well as atomic force microscopy and mass spectrometry, and compared to polymeric analogues. Due to the lack of substitution, para-nonaphenylene, irrespective of the precursor isomer employed, displays pronounced aggregation in the solid state. Intermolecular excitonic coupling leads to formation of H-type aggregates, red-shifting emission of the films to greenish. 9PP allows to study the structure–property relationship of para-phenylene oligomers and polymers, especially since the optical properties of PPP depend on the molecular shape of the precursor.