Comparison of high-performance liquid chromatography separation of red wine anthocyanins on a mixed-mode ion-exchange reversed-phase and on a reversed-phase column

Anthocyanins, which confer the characteristic color to red wine, can be used as markers to classify wines according to the grape variety. It is a complex separation that requires very high chromatographic efficiency, especially in the case of aged red wines, due to the formation of pyranoanthocyanins. A coelution between these kinds of compounds can affect the R_ac/coum ratio of aged wines, and might lead to false results when classifying the wine variety. In 2007, the use of a novel mixed-mode ion-exchange reversed-phase column was reported to separate anthocyanins extracted from grapes of Vitis labrusca with different selectivity than C-18 columns. In the present work, the separation of anthocyanins including pyranoanthocyanins in young and aged Cabernet Sauvignon wines and other varieties is evaluated. The most interesting contributions of this research are the different elution order and selectivity obtained for anthocyanins and pyranoanthocyanins (only formed in wine), compared with those observed in C-18 stationary phases. Also interesting is the separation of the polymeric fraction, which elutes as a clearly separated peak at the chromatogram's end. However, a comparison with a high efficiency C-18 column with the same dimensions and particle size demonstrated that the tested mixed-mode column shows broader peaks with a theoretical plate number below 8000, for malvidin-3-glucoside peak, while it can be up to 10 times higher for a high efficiency C-18 column, depending on the column manufacturer. Under the tested conditions, in mixed-mode phase, the analysis time is almost twice that of a C-18 column with the same dimensions and particle size. A mixed-mode phase with increased efficiency should provide an interesting perspective for separation of anthocyanins in wine, due to its improved selectivity, combined with a useful role in a second-dimension separation in preparative anthocyanin chromatography.     

Preparation of iron carbonyl complexes of germanium(II) and tin(II) each with a terminal fluorine atom

The reaction of β-diketiminate substituted germanium(II) and tin(II) fluorides (LGeF (1) and LSnF (2)) (L = CH{(CMe)₂(2,6-iPr₂C₆H₃N)₂}) with diiron nonacarbonyl, Fe₂(CO)₉ at room temperature, leads to the iron carbonyl complexes of germanium(II) LGeFFe(CO)₄ (3) and tin(II) LSnFFe(CO)₄ (4), respectively. Compounds 3 and 4 were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Furthermore, both complexes (3 and 4) were investigated by X-ray structural analysis which shows that both compounds are monomeric in the solid state containing terminal fluorine atoms.     

On the Number of Cylinders Touching a Ball

In this note we prove an upper bound of seven for the maximum number of unit cylinders touching a unit ball in a packing. This improves a previous bound of eight by Heppers and Szab. The value conjectured by Kuperberg in 1990 is six.     

Validated assay for the simultaneous quantification of total vincristine and actinomycin‐D concentrations in human EDTA plasma and of vincristine concentrations in human plasma ultrafiltrate by high‐performance liquid chromatography coupled with tandem mass spectrometry

A sensitive, specific and efficient high‐performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) assay for the simultaneous determination of total vincristine and actinomycin‐D concentrations in human plasma and an assay for the determination of unbound vincristine are presented. Electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and heated electrospray ionization (H‐ESI) were tested as ionization interfaces. For reasons of robustness ESI was chosen followed by tandem mass spectrometry (ESI‐MS/MS). For the plasma assay a 30 µL aliquot was protein precipitated with acetonitrile/methanol (50:50, v/v) containing the internal standard vinorelbine and 10 µL volumes were injected onto the HPLC system. To determine unbound vincristine, ultrafiltrate was produced from plasma using 30 kDa centrifugal filter units. The plasma ultrafiltrate was mixed with methanol (50:50, v/v), internal standard vinorelbine was added and 20 µL aliquots were injected onto the HPLC system. Separation was achieved on a 50 × 2.1 mm i.d. Xbridge C₁₈ column using 1 mM ammonium acetate/acetonitrile (30:70, v/v) adjusted to pH 10.5 with ammonia, run in a gradient with methanol at a flow rate of 0.4 mL/min. HPLC run time was 6 min. The assay quantifies in plasma vincristine from 0.25 to 100 ng/mL and actinomycin‐D from 0.5 to 250 ng/mL using plasma sample volumes of only 30 µL. Vincristine in plasma ultrafiltrate can be quantified from 1 to 100 ng/mL. Validation results demonstrate that vincristine and actinomycin‐D can be accurately and precisely quantified in human plasma and plasma ultrafiltrate with the presented methods. The assays are now in use to support clinical pharmacological studies in children treated with vincristine and actinomycin‐D. Copyright © 2009 John Wiley & Sons, Ltd.     

Photochromic behaviour of ozonated and photoirradiated cellulose studied by fluorescence spectroscopy

Samples of ozonated pure cotton cellulose have been subjected to three extended periods of irradiation with monochromatic light at 350 nm, with intervening dark periods. The changes during the treatments were monitored using fluorescence spectroscopy. Photochromic behaviour, comprising a fairly rapid emission intensity decrease during irradiation and a slower recovery of the emission intensity in the dark at ambient temperature, was observed. Starting from the completion of the first irradiation/dark treatment the intervening dark reaction almost completely restored the situation prevailing before irradiation. The photochromism observed for a reference sample of cellulose not pretreated with ozone and for microcrystalline cellulose was similar but differed both in amplitude and in fluorescence recovery during the dark periods. The ozonated sample was also irradiated with the entire spectrum of a medium pressure Hg lamp. This treatment caused a strong increase in the emission intensity and a red-shift of the emission maximum. The changes caused by ozonation and irradiation were also studied by diffuse reflectance FT-IR and UV-visible reflectance spectroscopy.     

Use of tryptophan peptides for an HPLC racemization test with fluorescence detection

A new HPLC test has been developed for monitoring the racemiza-tion which occurs during the coupling of Z-Ala-Trp-OH with Val-OMe by various methods. It is based on reversed phase HPLC separation of tripeptide diastereomers (LLL – LDL ) and fluorescence rather than UV detection. The extent of racemization has been estimated for different carbodiimides, mixed anhydrides, and additive-releasing reagents.     

UV-curable epoxy systems containing hyperbranched polymers: Kinetics investigation by photo-DSC and real-time FT-IR experiments

The effect of the presence of a hyperbranched OH-functionalized polymer (HBP) on the kinetics of cationic photopolymerization of an epoxy system was investigated employing two complementary techniques, photo-DSC and real-time FT-IR spectroscopy.Lower rates of cross-linking reactions and higher conversion degrees were obtained in photo-DSC experiments with respect to real-time FT-IR spectroscopy. A limited amount (10% wt) of HBP influenced to a certain extent the cure kinetics of the epoxy resin followed by RT-IR; a final conversion of epoxy groups equal to 100% was achieved by increasing the content up to 20% wt The addition of 10% wt of HBP leaves the cure kinetics of the CE resin studied by p-DSC almost unchanged. By increasing the HBP content, a slightly lower reaction rate is observed at lower reaction times. The presence of the HBP produced a continuous decrease of the T_g of the UV-cured epoxy resin but only modest reductions in its thermo-oxidative stability.     

All-optical generation of 40 Gb/s single sideband signals using a fiber Bragg grating

In this work, we demonstrate a reliable all-optical technique for performing optical double sideband (ODSB) to single sideband (OSSB) format conversion of a 40 Gb/s non-return-to-zero signal. It is based on the optimization of a detuned optical filter, which was implemented on a fiber Bragg grating (FBG) with a complex apodization profile. An OSSB signal with negligible distortion was obtained, as the FBG presented a nearly ideal frequency response. Higher tolerance to chromatic dispersion enabled by the OSSB signal in comparison to the ODSB signal was demonstrated on both simulation and experimental results.