Tocochromanols composition in kernels recovered from different apricot varieties: RP-HPLC/FLD and RP-UPLC-ESI/MSn study

Composition of tocochromanols in kernels recovered from 16 different apricot varieties (Prunus armeniaca L.) was studied. Three tocopherol (T) homologues, namely α, γ and δ, were quantified in all tested samples by an RP-HPLC/FLD method. The γ-T was the main tocopherol homologue identified in apricot kernels and constituted approximately 93% of total detected tocopherols. The RP-UPLC-ESI/MSⁿ method detected trace amounts of two tocotrienol homologues α and γ in the apricot kernels. The concentration of individual tocopherol homologues in kernels of different apricots varieties, expressed in mg/100 g dwb, was in the following range: 1.38–4.41 (α-T), 42.48–73.27 (γ-T) and 0.77–2.09 (δ-T). Moreover, the ratio between individual tocopherol homologues α:γ:δ was nearly constant in all varieties and amounted to approximately 2:39:1.     

The Development of the In Situ Modification of 1st Generation Analytical Scale Silica Monoliths

Analytical scale silica monoliths are commercially limited to three column selectivities (bare silica, C8 and C18). An in situ modification is reported in detail to overcome this barrier and allow for any functionality of choice to be bonded to the silica surface of the monolithic stationary phase support. The modification method was conducted on a commercial bare silica column to bond the C18 moiety to the silica surface through a silylation reaction. The C18 type of stationary phase was chosen, as this is the most commonly bonded functionality for the majority of stationary phases used for high-performance liquid chromatography (HPLC) separations. The C18-modified monolith’s performance was compared to a commercial C18 monolithic and a particle packed column of the same analytical scale column dimensions (100 × 4.6 mm). The modified C18 monolith proved to be of high quality with an efficiency of 73,267 N m^?1, fast analysis times (operated at flow rates up to 3 mL min^?1 using a conventional 400 bar HPLC system) and improved resolution of a set of polar and non-polar substituted aromatics in comparison to a commercial C18 monolith.     

Nachweis und Bestimmung von Aluminium

Ohne Zusammenfassung     

Phenyl-type and C1 stationary phases for environmentally friendlier chromatography

C1 and phenyl-type stationary phases were assessed in terms of their environmental impact on separations using as test solutes polycyclic aromatic hydrocarbons. Methanol (MeOH) and acetonitrile (ACN) mobile-phase gradients were employed. These stationary phases were examined to determine if different physical and chemical properties possessed by these surfaces decreased the organic solvent consumption, and yet maintained peak capacity. The cumulative energy demand (CED) was used to gauge the environmental impact of the separations. The separation of the polycyclic aromatic hydrocarbon test mixture using current methodologies (i.e. a C18/ACN combination) had a CED of 1.13 MJ-eq, and a peak capacity of 27 peaks (resolving 7 of 12 peak pairs with R_s>1). In comparison, a butyl phenyl stationary phase with a methanol mobile phase had a peak capacity of 26, but with a CED of 0.670 MJ-eq. Monolithic columns containing C18 and C1 phases were also tested. A monolithic C18 column with MeOH had the lowest CED at 0.675 MJ-eq, a peak capacity of 28 peaks and good resolving power (resolving ten peak pairs with R_s>1), suggesting that this is a viable option with respect to reducing environmental impact for these types of analyses.     

Cyano bonded silica monolith—Development of an in situ modification method for analytical scale columns

This study investigates the synthesis and chromatographic behaviour of an analytical size cyanopropyl “cyano” bonded silica monolith. Surface modification was undertaken by treating a neat silica monolith with chloro(3-cyanopropyl)dimethyl silane in dry heptane over a two day period. The resulting monolith showed stability over the duration of the testing program that involved flushing the column with more than 2000 column volumes of mobile phase. Efficiency measurements before and after sylation verified that the integrity of the silica monolith itself was not affected by the modification process, the highest number of theoretical plates (N/m) using anisole was 81,650. A brief selectivity test was then undertaken to assess methylene selectivity and phenyl selectivity. Elemental analysis was used to determine the homogeneity of the carbon load throughout the monolithic bed, and was compared to two commercial C18 and one ‘self’ modified C18 silica monoliths. The development of the in situ modification is also discussed.     

A 14 Parameter Study of UHPLC’s for Method Development Transfer and Troubleshooting

Five ultra-high pressure liquid chromatography (UHPLC) instruments were compared to one another by examining the overall system performance and key functions of the system parts including: pump, auto-sampler, thermo-stated column compartment, and the detector. The five UHPLC systems used in this study were: ThermoFisher Vanquish, Agilent 1290 Infinity I, Agilent 1290 Infinity II, Waters Acquity I-Class, and Shimadzu Nexera X2. The identities of the systems were blinded in the results and discussion section to use this study for scientific purposes only rather than for competition and marketing. The following tests were performed to evaluate and compare the five UHPLC systems: injector linearity and precision, sample carryover, sample (autosampler) temperature accuracy, column temperature accuracy and precision, pressure ripple, pump mixing accuracy, flow rate accuracy, detector drift and noise, detector linearity, wavelength accuracy, extra-column volume, and dwell volume determination. This study presents an approach on how to test the performance of UHPLC systems along with potential problems that analysts may face when using the UHPLC systems, examples of such issues are: retention time irreproducibility, low sensitivity, method transfer failure, etc.     

Determination of submicrogram-per-liter concentrations of caffeine in surface water and groundwater samples by solid-phase extraction and liquid chromatography

A method for determining submicrogram-per-liter concentrations of caffeine in surface water and groundwater samples has been developed. Caffeine is extracted from a 1 L water sample with a 0.5 g graphitized carbon-based solid-phase cartridge, eluted with methylene chloride-methanol (80 + 20, v/v), and analyzed by liquid chromatography with photodiode-array detection. The single-operator method detection limit for organic-free water samples was 0.02 microgram/L. Mean recoveries and relative standard deviations were 93 +/- 13% for organic-free water samples fortified at 0.04 microgram/L and 84 +/- 4% for laboratory reagent spikes fortified at 0.5 microgram/L. Environmental concentrations of caffeine ranged from 0.003 to 1.44 micrograms/L in surface water samples and from 0.01 to 0.08 microgram/L in groundwater samples.     

Reactions of Podophyllotoxin with DDQ

Introduction 2, 3-Dichloro-5, 6-dicyanobenzoquinone (DDQ) can react with lignans of the mono- arylidene-butyrolactone1, aryltetralin2, dibenzylbutane3 and aryltetralin-butyrolactone4,5 series. We have studied the reactions of this reagent with podophyllotoxin 1, which is a well-known natural product on account of its long history of use in folk medicine and the biological activity of its many derivatives6. In particular, derivatives of 4-demethyl epipodophyllotoxin are used in cancer chemo…     

π-Selective stationary phases: (I) Influence of the spacer chain length of phenyl type phases on the aromatic and methylene selectivity of aromatic compounds in reversed phase high performance liquid chromatography

Phenyl type stationary phases of increasing spacer chain length (phenyl, methyl phenyl, ethyl phenyl, propyl phenyl and butyl phenyl, with 0–4 carbon atoms in the spacer chain, respectively) were synthesised and packed in house to determine the impact that the spacer chain length has on the retention process. Two trends in the aromatic selectivity, q_aromatic, were observed, depending on whether the number of carbon atoms in the spacer chain is even or odd. Linear log k′ vs ? plots were obtained for each stationary phase and the S coefficient was determined from the gradient of these plots. For the phenyl type phases, the S vs n_c plots of the retention factors of linear polycyclic aromatic hydrocarbons vs the number of rings exhibit a distinct discontinuity that between 3 and 4 rings, which increases with increasing spacer chain length for even phases but decreases for odd phases. Accordingly, we suggest that the retention factors depend differently on the number of carbon atoms in the spacer chain depending on whether this number is even or odd and that this effect is caused by different orientations of the aromatic ring relative to the silica surface.