Simultaneous chiral separation of leucovorin and its major metabolite 5-methyl-tetrahydrofolate by capillary electrophoresis using cyclodextrins as chiral selectors: Estimation of the formation constant and mobility of the solute-cyclodextrin complexes

Summary Capillary electrophoresis with an electrolyte containing cyclodextrin was investigated for the simultaneous separation of the diastereoisomers of 6R,S-leucovorin and its active metabolite 6R,S-5-methyl-tetrahydrofolate. , and -cyclodextrin separated the diastereoisomers of 5-methyl-tetrahydrofolate, while only -cyclodextrin was found to be effective for the chiral separation of leucovorin. The effect of -cyclodextrin concentration was investigated, and subsequently a curve-fitting analysis for the quantitative estimation of the binding constants was attempted. The binding constants were found to be very small, in the range 2–4 M^–1. Although the interaction between -cyclodextrin and the tetrahydrofolates is weak, the high efficiency of capillary electrophoresis and the use of high concentrations of -cyclodextrin allow baseline chiral separation of the diastereoisomers of leucovorin and 5-methyl-tetrahydrofolate. Changes in temperature exert differing effects on the separations of leucovorin and 5-methyl-tetrahydrofolate; higher temperatures improved the separation of leucovorin diastereoisomers but reduced the resolution of 5-methyl-tetrahydrofolate diastereoisomers. The effects of urea and buffer salt concentrations and of buffer pH were also investigated. Capillary electrophoresis with -cyclodextrin was used to analyse plasma samples spiked with clinically-relevant levels of leucovorin and 5-methyl-tetrahydrofolate. Resolution of these compounds in ultrafiltered plasma was demonstrated, but detection sensitivity was not adequate for the routine use of this method for the determination of leucovorin and 5-methyl-tetrahydrofolate in plasma. In addition, a simple technique to reverse the elution order of ionic stereoisomers was demonstrated. By adding a cationic surfactant into the buffer and reversing the separation potential, the elution order of the diastereoisomers of leucovorin and 5-methyl-tetrahydrofolate was reversed.     

Separation and detection of traces of copper,iron and manganese in cotton materials by TLC

Summary A TLC method for the fast detection of copper, iron and managanese ions in cotton materials is described. The optimal solvent system is 812 (v/v), acetone: HCl:H₂O and the locating reagent is rubeanic acid followed by exposure to ammonia vapour. It was found that in cotton materials, metal ions can be detected at a lower limit of 20 g per gram of material.     

Detection and determination of benzophenone present in diphenylhydantoin sodium formulations and drug substance

Summary The detection of benzophenone in sodium diphenylhydantoin formulations and drug substance is carried out by thin-layer chromatography on silica gel 60 F using toluene/methanol/ethyl acetate/acetic acid/chloroform (802015105) or ethyl acetate/methanol/ammonium hydroxide (85105) as solvent and UV-light for visualizing. The determination is performed by measuring the absorption at 248 nm. The method is recommended for production monitoring.

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Nachweis und Bestimmung von Benzophenon in Natriumdiphenylhydantoin-Formulierungen und -Reinsubstanz

Zusammenfassung Der Nachweis erfolgt dünnschicht-chromatographisch auf Silicagel 60 F mit Toluol/Methanol/Äthylacetat/Essigsäure/Chloroform (802015105) oder Äthylacetat/Methanol/Ammoniak (85105) als Lösungsmittel und durch Sichtbarmachung mit UV-Licht. Die Bestimmung wird durch Absorptionsmessung bei 248 nm vorgenommen. Das Verfahren wird zur Produktionskontrolle empfohlen.

     

Simultaneous determination of preservatives,sweeteners and antioxidants in foods by paired-ion liquid chromatography

Summary A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na and acesulfame-K), preservatives (sodium dehydroacetate, sorbic acid, salicyclic acid, benzoic acid, succinic acid, methyl-para-hydroxybenzoic acid, ethylpara-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, isopropyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 mM aqueous -hydroxy-isobutyric acid solution (pH 4.5) (2.2 3.4 or 2.4 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a C₁₈ column with a flow rate at 1.0 mL/min and detection at 233 nm were used. This method was found to be very reproducible with detection limits ranged from 0.15 to 3.00 g. The retention factor (k) of each additive could be affected by concentrations of hexadecyltrimethylammonium bromide and -hydroxyisobutyric acid, and pH and ratio of mobile phase. The presence of additives in some food samples was determined.     

Trennung der 8-Hydroxychinolate von V, Mo, W, Co und Cr durch HPLC

Zusammenfassung 8-Hydroxychinolin-Chelate von V, Mo, W, Co, Cr können mit der Hochdruckflüssigkeits-Chromatographie getrennt werden [polare stationäre Phase: Si 60; Eluentien: Tetrahydrofuran/Chloroform (64) bzw. Dioxan/Chloroform (64)]. Die Nachweisgrenzen sind: < 1 ng für V, Mo und Cr; 0,5 ng für Co; 1,5 ng für W.

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Separation of the 8-hydroxyquinolinates of V, Mo, W, Co and Cr by HPLC

Summary The oxinates of V, Mo, W, Co and Cr can be separated by HPLG employing Si 60 as stationary phase and either tetrahydrofuran/chloroform (64) or dioxan/chloroform (64) as eluents. Limits of detection are: < 1 ng for V, Mo and Cr; 0.5 ng for Co; 1.5 ng for W.

Ich danke der Deutschen Forschungsgemeinschaft für die Bereitstellung von Geräten und Sachbeihilfen.Mein besonderer Dank gilt Frl. Pohlmann für die Durchführung zahlreicher Meßreihen.     

Determination of praseodymium in lanthanum compounds by neutron activation and ion exchange separation

Summary A procedure was developed to determine small amounts of praseodymium in lanthanum compounds by neutron activation analysis. After irradiation of the sample in a reactor praseodymium is separated from lanthanum by anion exchange and Pr-142 is measured by a gamma-ray spectrometer. From the high decontamination factor of 110⁸ a detection limit of 5ppb praseodymium in lanthanum may be calculated. Because of the strong activation of lanthanum, the handling of samples with activities of about 1 Ci La-140 would be required. For the analyses carried out here with respect of sample weights, neutron flux and irradiation time a detection limit of 2.4ppm was obtained.

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Bestimmung von Praseodym in Lanthanverbindungen durch Neutronenaktivierung und Ionenaustausch

Zusammenfassung Zur Bestimmung von geringen Mengen Praseodym in Lanthanverbindungen wurde ein auf Neutronenaktivierungsanalyse basierendes Verfahren entwickelt. Nach Bestrahlung der Probe im Reaktor wird Praseodym mit einem Anionenaustauscher von Lanthan getrennt und Pr-142 mit einem Gamma-Spektrometer gemessen. Der mit der Trennung erreichte Reinigungsfaktor von 110⁸ würde eine Nachweisgrenze von etwa 5ppb Praseodym in Lanthan erlauben. Wegen der starken Aktivierung des Lanthans würde das aber den Umgang mit Proben von ca. 1 Ci La-140 erfordern. Mit den hier gewählten Probenmengen, Neutronenflüssen und Bestrahlungszeiten wurde eine Nachweisgrenze von 2,4ppm erreicht.

Presented at the Ulmer Symposium Analytische Chemie — Elementanalyse mit chromatographischen Methoden, Sept. 19–21, 1979, D-7900 Ulm     

Determination of azidothymidine and its degradation product thymine in pharmaceutical dosage forms by HPLC and HPTLC densitometry

Summary HPTLC densitometry and HPLC are considered for the determination of azidothymidine and its degradation product thymine in pharmaceutical dosage forms. In HPTLC the substances were separated on silica gel with fluorescence indicator in methanol-chloroform (1090) and methanol-chloroform (1585) systems. Absorbance measurement (detection of reflectance) of the separated substances was carried outin situ at 268 nm using four-level calibration (external standard, linear regression function) in the concentration range of 25–100 ng thymine/spot and using single-level calibration (external standard) at the concentration of 100 ng azidothymidine/spot. HPLC was carried out using RP-18 stationary phase and methanol+aqueous 0.03 mol/l KH₂PO₄ (18+82, v/v) as the mobile phase. The temperature was 50°C and the detection wavelength 266 nm. The detection limit of thymidine was 0.05%. The concentration range for azidothymidine was 0.5–1.5 mg/ml and for thymine 1–40 g/ml (for an injection volume of 10 l). The results were evaluated by linear regression analysis.     

Cation thin-layer chromatography in mixed organic solvents containing s-butylamine: Separation of Zn(II) from Cd(II) and Cu(II)

Summary A TLC method has been developed for the separation of Zn(II) from Cd(II) and Cu(II) on silica gel alyers with mixed organic solvents containing s-butylamine. The separation of Zn(II) from Cd(II) in the presence of certain anions and at various pH values of sample solution was examined. A mixture containign s-butylamine, acetone and formic acid in 262 was found to be the best solvent.     

Organic fuelled flames in selective ionization detectors for chromatography

Summary The selectivities of two flame-based ionization detectors identified as a Remote FID (RFID) and a Flame Thermionic Ionization Detector (FTID) have been improved by introducing methane as a fuel for the flame. Both the RFID and FTID feature a detector struture in which the ionization polarizer and collector are located several centimeters downstream of an oxygen-rich flame, rather than immediately adjacent to the flame as in a flame ionization detector. The RFID detects long-lived negative ions produced in the flame by the combustion of lead, tin, phosphorus, or silicon compounds. The FTID re-ionizes and detects neutral electronegative products generated by combustion of nitrogen, halogen, or phosphorus compounds. An organic-fuelled RFID can detect 1 pg Pb (Sn, P)/sec with a selectivity of the order of 10⁶ versus hydrocarbons. An organic fuelled FTID is applicable to detection of compounds at nanogram and higher levels. FTID selectivity for PCB compounds in a transformer oil matrix is of the order of 10⁵1. The improved selectivity achieved by using an organic-fuelled flame is also applicable to the detection of phospholipid and other non-volatile N, P, or Cl compounds using an FID/FTID detector accessory for a TLC/FID analyser.     

Determination of clotiazepam by HPLC with spectrophotometric and amperometric detection

Summary Spectrophotometric and amperometric detectors were compared for the determination of clotiazepam by HPLC. Methanol-water (6040) containing 0.01 mol/l ammonium acetate and methanol-water (7030) containing 0.01 mol/l acetate buffer pH 4 were used as mobile phase in the spectrophotometric and amperometric detection, respectively. The minimum detectability for the spectrophotometric detection was 20 ng injected and the method was applied for the determination of clotiazepam in serum, whereas for the amperometric detection a limit of detection of 2.5 g injected was obtained, using this technique for clotizepam determination in tablets.

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Bestimmung von Clotiazepam durch HPLC mit spektralphotometrischer und amperometrischer Detektion

     

Determination of vitamin D3 in cod-liver oil (Lebertran) by high-pressure liquid chromatography

Summary An HPLC separation of vitamin D₃ in cod-liver oil (Lebertran) on a Partisil-10-pxs (Whatman) column with a mobile phase of chloroform-n-hexaneglacial acetic acid (70301) and detection at 268 nm is described. The vitamin D₃ peak in the sample solution was positively identified by measuring absorbance ratios at different wavelengths and recording a peak spectrum with a LC 55-S digital scanner between 250–350 nm. Analytical results of analysis of 11 samples are compared with those obtained by a chemical method. The coefficient of variation of the HPLC method was found to be ± 2.4%.

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Bestimmung von Vitamin D₃ in Lebertran durch Hochdruck-Flüssigkeits-Chromatographie

Zusammenfassung Ein Verfahren zur HPLC-Bestimmung von Vitamin D₃ in Lebertran mit Hilfe einer Partisil-10 pxs-Säule (Whatman) mit der mobilen Phase Chloroform-n-Hexan-Eisessig (70301) und UV-Detektion bei 268 nm wird beschrieben. Die Identität des Vitamin D₃-Peaks wurde zusätzlich durch eine Peakanalyse bei verschiedenen Wellenlängen sowie durch Aufnahme des Peakspektrums zwischen 250–350 nm mit einem LC-55-S Digital-Scanner sichergestellt. Die Ergebnisse von 11 Lebertranproben wurden den mit einer chemischen Methode erzielten Werten gegenübergestellt. Der Variationskoeffizient der HPLC-Methode beträgt ± 2,4%.

The author thanks Mrs. Petra Grötsch for the very efficient assistance in the experimental work. He is further indebted to Mr. R. Jöster, Perkin-Elmer Corporation, Offenbach (GFR), for recording the peak spectra with a digital scanner.     

Ion-pair extraction and fluorimetric determination of ultratraces of strontium with cryptand 2.2.2 and eosin

A highly sensitive and selective fluorimetric determination of strontium is proposed, based on solvent extraction of the ion-pair formed between the cationic complex of Sr²⁺ with cryptand 2.2.2 and eosinate as counter ion. A linear working range from 0.7 ng/ml (limit of detection) to 500 ng/ml of strontium and a relative standard deviation of 3.5% at the 100 ng/ml level are obtained. The metal: ligand: counter ion molecular ratio in the extracted mononuclear ion-pair is 1 1 1. The equilibrium constants involved in the extraction process were calculated.     

Arylation of aliphatic alcohols with tri-p-tolylbismuth and tri-p-tolylbismuth diacetate in the presence of a copper salt

Tri-p-tolylbismuth diacetate in the presence of a catalytic amount of a copper(II) salt (10.02, mol/mol) and tri-p-tolylbismuth in the presence of copper diacetate (1 2) replace the hydrogen atom of the hydroxyl groups of methanol and butanol with a tolyl group at 80 °C in up to 90 % yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 156–158, January, 1995.     

Synthesis of nitrogen- and iron-containing carbon dots,and their application to colorimetric and fluorometric determination of dopamine

Nitrogen- and iron-containing carbon dots (N,Fe-CDs) are synthesized by hydrothermal treatment of branched polyethylenimine (BPEI) and hemin at 180 °C. The N,Fe-CDs are mainly doped with nitrogen and trace amounts of iron(III). The N,Fe-CDs also display intrinsic fluorescence with excitation/emission maxima at 365/452 nm and a quantum yield of 27 %. The nanodots are shown to act as peroxidase mimics by catalyzing the oxidation of tetramethylbenzidine (TMB) by hydrogen peroxide to form a blue product whose quantity can be determined by photometry at 652 nm. This was exploited to design colorimetric and fluorometric assays for dopamine (DA). The colorimetric assay is based on the oxidation of DA by H₂O₂ in presence of the N,Fe-CDs and TMB. It has an instrumental detection limit of 40 nM (at an S/N ratio of 3), and a visual detection limit of 0.4 μM. The fluorometric assay is based on an inner filter effect that is caused by the formation of oxidized TMB which overlaps (and absorbs) the emission of the N,Fe-CDs located at 452 nm. The fluorometric detection limit is as low as 20 nM (at an S/N ratio of 3).

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Graphical abstract Carbon dots containing nitrogen and iron (N,Fe-CDs) were synthesized by hydrothermal treatment of branched polyethylenimine and hemin. The N,Fe-CDs display excellent fluorescent properties, peroxidase-like activity and potential application in colorimetric and fluorometric detection of dopamine.

     

Method for determining airborne diisocyanates

A method has been developed for quantitatively determining 3 typical diisocyanates, viz. 2,4-toluylene diisocyanate (2,4-TDI), hexamethylene diisocyanate (HDI) and 4,4-diphenyl-methane diisocyanate (MDI). The technique relies on chemisorption onto a suitable carrier material contained in an absorption tube coated with 1-(2-pyridyl)piperazine (2-PP). Stable urea derivatives with high molar absorptivity are formed, desorbed from the carrier material, separated by means of highpressure liquid chromatography and identified. The limits of detection for a sample volume of 20 1 of air are 0.9g m^–3 for 2,4-TDI and HDI, and 0.6g m^–3 for MDI. The derivatives are stable at 4°C for longer than 30 days. The influence of atmospheric humidity and the interference of dibutylamine on the detection reaction were investigated for 2,4-TDI and HDI. The whole procedure is easy to perform, highly sensitive and very reproducible and is suitable for monitoring concentrations of 2,4-TDI, HDI and MDI.Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

CGC/AED and CGC/ECD/NPD comparison for the determination of acaricides in honey after hexane/acetone extraction

Summary The performance of a gas chromatographic system coupled to an atomic emission detector (GC/AED) is tested by comparison with a two-dimensional gas chromatographic system equipped with capillary columns of different polarity and simultaneous electron capture and nitrogen-phosphorus detection (ECD/NPD), for the determination of the acaricides chlordimeform, bromopropylate, amitraz and coumaphos on spiked honey samples. The acaricides were extracted with ann-hexane/acetone mixture (8020, v/v) with a further clean-up step on an octadecylsilane cartridge. The 193 nm carbon emission line is the best choice in terms of sensitivity whereas the ECD/NPD system gives better selectivity.     

Determination of the curcuminoid pigments in turmeric (Curcuma domestica Val) by reversed-phase high-performance liquid chromatography

Summary A rapid, simple and reproducible reversed-phase high-performance liquid chromatographic method was developed for the quantitative determination of curcumin, demethoxycurcumin and bis-demethoxycurcumin in ethanolic extracts of turmeric. The pigments were separated on a styrene-divinylbenzene copolymer column (Hamilton PRP-1), using an acetonitrile-water (5545, v/v) mobile phase. The pigments were monitored with a diode-array detector at 425 nm. The limit of detection was 10.2 ng curcumin, 11.1 ng demethoxycurcumin and 6.2 ng bis-demethoxycurcumin. Comparison of HPLC and spectrophotometric results for the determination of the total curcuminoid content for a number of turmeric samples, reveal that the spectrophotometric method invariably yielded higher results, indicating an overestimation of curcuminoids.     

Separation and quantitation of nicergoline and related substances by high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry

Summary This study demonstrated the utility of high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry (HPLC/API-MS) in the investigation of 10-methoxy-1,6-dimethylergoline-8-methanol 5-bromonicotinic acid ester (Nicergoline) and its related substances. The analysis was performed by using an ODS column with ammonium acetate and methanol mixture as the mobile phase. Nicergoline and its related compounds could be characterized by HPLC/API-MS in terms of their molecular weight. The use of multiple ion detection techniques for the quantitation of these compounds was also investigated. The detection limits of nicergoline and its related substances were 5 to 10 ng each at a signal-to-noise ratio of 4. The method was also applied to the study of the decomposition products of nicergoline in simulated gastric and intestinal fluids.