1,721,091 research outputs found
Optimized use of a 50 um internal diameter secondary column in a comprehensive two dimensional gas chromatography system
No full textThe focus of the present research is directed toward the
development of a comprehensive two-dimensional gas
chromatography (GC × GC) method, characterized by a
greatly increased separation power, if compared with GC
× GC approaches using classical column combinations.
The analytical objective was achieved by using a 0.05 mm
internal diameter (i.d.) capillary as second dimension, a
split-flow approach reported in previous research (Tranchida,
P. Q.; Casilli, A.; Dugo, P.; Dugo, G.; Mondello,
L. Anal. Chem. 2007, 79, 2266-2275), and a twin-oven
GC × GC instrument. The column combination employed
was an orthogonal one: an apolar 30 m × 0.25 mm i.d.
column was linked, by means of a Y-union, to a flame
ionization detector (FID)-connected high-resolution 1 m
× 0.05 mm i.d. polar one and to a 0.20 m × 0.05 mm
i.d. uncoated capillary segment; the latter was connected
to a manually operated split valve, located on top of the
second GC. As previously shown, the generation of
optimum gas linear velocities in both dimensions can be
attained by splitting gas flows at the outlet of the first
dimension (Tranchida, P. Q.; Casilli, A.; Dugo, P.; Dugo,
G.; Mondello, L. Anal. Chem. 2007, 79, 2266-2275).
An optimized GC × GC method was developed and
exploited for the analysis of a complex petrochemical
sample. The satisfactory results attained were directly
compared with those observed using the same instrumentation,
equipped with what can be defined as a
classical GC × GC split-flow column set: the same primary
column was connected to an FID-linked 1 m × 0.10 mm
i.d. polar one and to a 0.30 m × 0.10 mm i.d. uncoated
capillary. It will be herein illustrated that there is still
room for significant progress in the GC × GC field
Separation of lipids
No full textLipid analysis and profiling is a crucial task in diverse fields including metabolomics, food analysis, pharmaceuticals, cosmetics, surfactants, fuels, and other commercial applications. As a consequence, lipid analysts have always been on the forefront of developments in separation science, greatly spurring the development of new techniques and methods of separation, including liquid chromatography. Consistent with the global trend toward greening of analytical procedures, a considerable effort has been put recently to implement alternative procedures that reduce or eliminate the use or generation of hazardous substances as well as energy consumption. As in any successful analytical methods, an efficient procedure for lipid analysis should be a flawless combination of extraction, separation, detection, and data processing; all these steps will be included in the discussion. Selection of the most suitable technique by lipid analysts ultimately requires a proper knowledge of the physical structure and location of the principal lipids present in a sample; this topic is therefore described in the chapter as well as the subject of lipid nomenclature and classification
Characterization of essential oil of Pummelo (cv. Chandler) by GC-MS, HPLC and physicochemical indices
No full textInhibition of nitric oxide biosynthesis by anthocyanin fraction of blackberry extract.
Full text linkAnthocyanins are natural colorant belonging to the flavonoid family, widely distributed among flowers, fruits, and vegetables. Some flavonoids have been found to possess anticarcinogenic, cytotoxic, cytostatic, antioxidant, and anti-inflammatory properties. Since increased nitric oxide (NO) plays a role in inflammation, we have investigated whether the pharmacological activity of the anthocyanin fraction of a blackberry extract (cyanidin-3-O-glucoside representing about 88% of the total anthocyanin content) was due to the suppression of NO synthesis. The markedly increased production of nitrites by stimulation of J774 cells with lipopolysaccharide (LPS) for 24 h was concentration-dependently inhibited by the anthocyanin fraction (11, 22, 45, and 90 μg/ml) of the extract. Moreover, this inhibition was dependent on a dual mechanism, since the extract attenuated iNOS protein expression and decreased the iNOS activity in lungs from LPS-stimulated rats. Inhibition of iNOS protein expression appeared to be at the transcriptional level, since the extract and similarly cyanidin-3-O-glucoside (10, 20, 40, and 80 μg/ml, amounts corresponding to the concentrations present in the extract) decreased LPS-induced NF-κB activation, through inhibition of IκBα degradation, and reduced ERK-1/2 phosphorylation in a concentration-dependent manner. In conclusion, our study demonstrates that at least some part of the anti-inflammatory activity of blackberry extract is due to the suppression of NO production by cyanidin-3-O-glucoside, which is the main anthocyanin present in the extract. The mechanism of this inhibition seems to be due to an action on the expression/activity of the enzyme. In particular, the protein expression was inhibited through the attenuation of NF-κB and/or MAPK activatio
On the Genuineness of Citrus Essential Oils. Part LIII. Determination of the composition of the oxygen heterocyclic fraction of lemon essential oils (Citrus limon (L.) Burm. F.) by normal phase high performance liquid chromatography
No full textThe oxygen heterocyclic fraction of cold-pressed lemon essential oils has been studied by normal-
phase HPLC. The components of the fraction have been isolated by column chromatography, TLC and semi-
preparative HPLC with recycle. The identi®cation of the isolated components has been carried out by
1H-NMR and mass spectrometry. Three coumarins (5-geranyloxy-7-methoxycoumarin, citropten, 5-isopente-
nyloxy-7-methoxycoumarin) and ten psoralens (bergamottin, 8-geranyloxypsoralen, oxypeucedanin, byakange-
licol, oxypeucedanin hydrate, byakangelicin, imperatorin, phellopterin, isoimperatorin, 5-isopent-20-enyloxy-8-
(20,30-epoxyisopentyloxy)-psoralen) have been isolated and identi®ed. The main components were bergamottin
(160±291 mg/100 g of oil) and 5-geranyloxy-7-methoxycoumarin (180±250 mg/100 g of oil). Moreover,
herniarin, a coumarin characteristic of lime essential oil, has been detected. Herniarin had been reported
previously in essential oils obtained from Citrus limon L. var. Eureka
Combining linear retention index and electron ionization mass spectrometry for a reliable identification in nano liquid chromatography
No full textThe present research is focused on the object to improve identification capability in liquid chromatography (LC), by creating a system as similar as possible to gas chromatography (GC), where the combination/complementarity of Linear Retention Index (LRI) and Electron Ionization Mass Spectrometry (EI-MS) data makes the identification process easy, automatic and reliable. Conversely, in LC the untargeted characterization of real-world samples is still a challenge, due to the not repeatable and poorly informative nature of typical atmospheric pressure ionization mass spectrometry, normally hyphenated to LC. In the last decades the miniaturization of LC instrumentation together with the considerable progresses in MS vacuum pump capability has made the LC-EI-MS hyphenation more feasible. In the present work, a prototypal nanoLC-EI-MS system was used for the determination of typically LC-amenable compunds, such as coumarins, furocoumarins and polymethoxyflavones in citrus essential oils. All the compounds provided high quality EI-MS spectra, evaluated by the comparison with thousands of spectra present in commercial EI-MS libraries. Spectral similarities major than 80% were achieved.
Furthermore, an LRI system, based on the use of an alkyl aryl ketone homologue reference series, was proposed as additional filter to achieve a univocal identification. Then, a novel dual-filter LRI/EI-MS library was built and resulted very helpful in the case of isomeric compounds characterized by identical EI-MS spectrum, but different retention behaviour. The very low inter-day variability attained for each LRI value, together with the satisfactory chromatographic resolution of the developed method, led to a 100% reliability of the identification process based on LRI
Authentication of Bergamot Essential Oil by Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometer (GC-C-IRMS)
No full textThe quality assessment of bergamot essential oils was established employing the gas chromatography-combustion-isotope ratio mass spectrometer (GC-C-IRMS) technique. An authenticity range was obtained investigating the carbon stable isotope ratio of genuine Italian bergamot essential oils (harvest period 2008-2009), in order to compare the GC-C-IRMS data of several industrial, commercial and foreign bergamot essential oil samples. Moreover, with the aim to test the efficiency and the sensibility of IRMS device, self-adulterated in laboratory bergamot oil samples were analyzed. The data were compared with those achieved by conventional enantioselective gas chromatography (Es-GC) and high resolution gas chromatography (GC-FID). Results of this work indicated that GC-C-IRMS was able not only to detect the presence of adulterants in the samples, hut also to discriminate the bergamot oil samples according to their geographic provenance and the nature of the adulterants added
A flow-modulated comprehensive gas chromatography–mass spectrometry method for the analysis of fatty acid profiles in marine and biological samples
No full textThe present investigation is focused on the development of a flow-modulator (FM) comprehensive 2D GC (GC×GC)-quadrupole mass spectrometry (qMS) approach, for the analysis of fatty acids. A recently developed flow modulator interfaced an apolar–polar column set, and was used for the first time with a mass spectrometer. Method development was achieved by using a standard mixture, containing fatty acid methyl esters (FAMEs). The total run time was approx. 40 min, thus relatively rapid. The optimized FM GC×GC–qMS method was applied to marine and biological FAMEs. Validation parameters such as intraday and inter-day repeatability, limits of identification (mass spectral quality was evaluated at various FAME concentrations), and quantification were measured. Peak assignment was performed using pure standard compounds (when available), linear retention indices (LRIs), a dedicated FAME MS database, and specific bidimensional chromatogram positions. The MS database contained one-dimensional LRI information, exploited as a filter during the MS database search procedure. A good agreement was observed
between database LRI values, and those calculated on the twin-column set. The FM GC×GC–qMS method can be considered as a valid counterpart, with respect to cryogenically modulated GC×GC, in the fatty acid field of research
Advances of Modern Gas Chromatography and Hyphenated Techniques for Analysis of Plant Extracts
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