Liquid Chromatography-Mass Spectrometry Determination of Six 5-Nitroimidazoles in Animal Feedstuff

A liquid chromatography-mass spectrometry method for the determination of the coccidiostats metronidazole, ronidazole, dimetridazole, secnidazole, tinidazole and ipronidazole in feedstuff was developed. The 5-nitroimidazoles were extracted from animal feed with a pH 2 phosphate buffer solution followed by a solid phase extraction procedure based on HLB cartridges. The liquid chromatographic separation of the extracts was performed on a C₁₈ bonded silica column applying a gradient of elution with pH 4.3 ammonium acetate buffer solution and acetonitrile. Quantification for each 5-nitroimidazole was carried out monitoring its molecular ion [M + H]⁺ obtained by positive electrospray ionisation mode. A pool of feedstuffs was used to optimise and validate the method. Linearity, quantification limit, intra-day and inter-day reproducibility and accuracy were estimated using this pool of feedstuffs spiked with the drugs. For the confirmatory assay, several fragment ions from each 5-nitroimidazole were obtained and monitored. The method was applied successfully to determine 5-nitroimidazoles in feedstuff at level of 0.05 mg kg⁻¹.     

Determination of traces of aluminium with chrome azurol S by solid-phase spectrophotometry

A microdetermination method at sub-mug/1. level for aluminium by solid-phase spectrophotometry has been developed. Chrome azurol S was used as chromogenic reagent to form a blue complex which was easily and strongly sorbed and concentrated on a dextran-type anion-exchange resin. The resin-phase absorbances at 615 and 800 nm were measured directly. Aluminium can be determined in the 0.6-4.0 mug/1. range with a RSD of 2.1%. The method is applied to the determination of aluminium in micaschist, natural and tap water samples.     

Determination of Celecoxib, Rofecoxib, Sodium Diclofenac and Niflumic Acid in Human Serum Samples by HPLC with DAD Detection

A reverse-phase high-performance liquid chromatographic method has been developed for the separation and simultaneous determination of two COX-2 inhibitors, celecoxib and rofecoxib, in addition to two well-known non-steroidal anti-inflammatory drugs (NSAIDs), sodium diclofenac and niflumic acid in human serum samples. Good chromatographic separation was achieved using a C18 bonded silica column applying a gradient with acetronitrile and water, from 15 to 60% acetonitrile. The mobile phase contained 0.1% trifluoroacetic acid as an organic modifier. Detection was made using a diode array detector (DAD) and the analytical parameters were established at the wavelength maximum in the UV spectrum of each drug. Linearity was studied up to 100.0 mg L⁻¹. Calibration functions, quantification and detection limits, intra- and inter-day reproducibility and accuracy were estimated for each drug. Solid phase extraction was needed to separate and concentrate the drugs from human serum samples. The method was successfully applied to determine the drugs in human serum samples at levels of 1.0 mg L⁻¹.     

LED–LED portable oxygen gas sensor

A portable instrument for oxygen determination, based on the quenching of phosphorescent octaethylporphyrin by gaseous O₂, has been developed using the fluorimetric paired emitter–detector diode technique (FPEDD). The instrument configuration consists of two light-emitting diodes (LEDs) facing each other, with an interchangeable support containing a phosphorescent membrane in between, in which one of the LEDs is used as the light source (emitter LED) and the other, working in reverse bias mode, as the light detector. The feasibility of using a LED as a luminescence detector is studied. Its small size enables integration of the instrument into a portable measurement system. A systematic study of the system capabilities as a portable instrument was performed to optimize range, sensitivity, short term and long term stability, dynamic behaviour, effect of temperature and humidity, and temporal drift.     

Studies on the thermal decomposition of some metal complexes of 5,5′-methylendisalicylhydroxamic acid

The thermal behaviour of the chelates of 5,5′-methylendisalicylhydroxamic acid with Pb(II), Zn(II), Ni(II), Cd(II), Fe(III), Cr(III), Al(III), Ti(IV), V(V), Mo(VI) and Cu(II) has been studied by thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy and X-ray diffraction.The compounds decompose through three major steps, dehydration, transformation of the anhydrous hydroxamates to intermediate N-hydroxylactams, which decompose to yield metal oxides as the final products.     

Study of the GC-MS determination of the palmitic-stearic acid ratio for the characterisation of drying oil in painting: La Encarnación by Alonso Cano as a case study

The correct identification of drying oils plays an essential role in providing an understanding of the conservation and deterioration of artistic materials in works of art. To this end, this work proposes the use of peak area ratios from fatty acids after ensuring that the linear responses of the detector are tested. A GC-MS method, previously reported in the literature, was revisited to its developed and validated in order to identify and quantify of eight fatty acids that are widely used as markers for drying oils in paintings, namely myristic acid (C(14:0)), palmitic acid (C(16:0)), stearic acid (C(18:0)), oleic acid (C(18:1)), linoleic acid (C(18:2)), suberic acid (2C(8)), azelaic acid, (2C(9)) and sebacic acid (2C(10)). The quaternary ammonium reagent m-(trifluoromethyl)phenyltrimethylammonium hydroxide (TMTFAH) was used for derivatization prior to GC-MS analysis of the oils. MS spectra were obtained for each methyl ester derivative of the fatty acids and the characteristic fragments were identified. The method was validated in terms of calibration functions, detection and quantification limits and reproducibility using the signal recorded in SIR mode, since two of the methyl derivatives were not totally separated in the chromatographic run. The proposed method was successfully applied to identify and characterise the most widely used drying oils (linseed oil, poppy seed oil and walnut oil) in the painting La Encarnación. This 17th century easel painting is located in the main chapel of the cathedral in Granada (Spain) and was painted by the well-known artist of the Spanish Golden Age, Alonso Cano (1601-1667).     

Determination of nitrite in sea-water by ion-exchanger colorimetry

Summary A microdetermination method (at theg/l level for nitrite) has been developed, based on ion-exchanger colorimetry. The nitrite is reacted with sulphanilamide andN-(1-naphthyl)ethylenediamine to form an azo dye which is then sorbed on Dowex 50W-X2. The resin phase absorbance at 550 and 800 nm is measured directly. The relative detection limit is 0.27g/l and the distribution ratio is 2.6×10⁴. The method has been applied to determination of nitrite in 500-ml sea-water samples and compared with a conventional technique.

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Bestimmung von Nitrit in Meerwasser durch Ionenaustausch-Kolorimetrie

Zusammenfassung Eine Mikromethode zur Bestimmung von Mikrogramm Nitrit/Liter mit Hilfe der lonenaustausch-Kolorimetrie wurde ausgearbeitet. Zu diesem Zweck wird Nitrit mit Sulfanilamid und N-(1-Naphthyl)ethylendiamin zu einem Azofarbstoff umgesetzt, der an Dowex 50W-X2 adsorbiert wird. Die Absorbanz der Harzphase wird unmittelbar bei 550 und 800 nm gemessen. Die relative Nachweisgrenze beträgt 0,27g/l, das Verteilungsverhältnis 2,6×10⁴. Das Verfahren wurde zur Bestimmung von Nitrit in 500-ml-Proben Meerwasser verwendet und mit konventionellen Methoden verglichen.

     

Spectrophotometric extractive determination of iodide as tris(2-(phenyliminomethyl)pyridine) Fe(II) iodide

The iodide:tris(2-(phenyliminomethyl)pyridine) Fe(II) extraction system into nitrobenzene has been studied. The same method is proposed for the determination of iodide. The interference of foreign ions is also determined.