On-line Diode-array Detector Research Articles

Historical formulations of lake pigments and dyes derived from lac: A study of compositional variability

“Lac” is a term referring to a pink-red-purple organic colourant derived from an insect and used as a lake pigment or a dye. Although historical sources indicate extensive usage, findings in historical samples remain scarce and are based on the detection of laccaic acids A and B, which are the main colourant molecules in lac.In this work various lake pigment and dye production methods were investigated, with the aim to explore the compositional variability derived from changing fundamental parameters, such as temperature and pH. Exhaustive research focusing on historical recipes was fundamental in order to create a series of 16 mock-up samples. Preliminary investigations were carried out using colorimetry and photo-induced luminescence imaging to evaluate the differences in colour and luminescence behaviour. Visible-induced visible luminescence imaging (VIVL) in the range c. 540–700 nm was particularly efficient at detecting the presence of included shellac in lac lake pigments. High performance liquid chromatography coupled with an online diode array detector followed by electrospray ionisation and quadrupole time-of-flight detection (HPLC-DAD-ESI-Q-ToF) was ultimately applied to assess the chemical composition of the samples and principle component analysis (PCA) was used to establish correlations between the chemical composition and the production methods.The results demonstrated that, regardless of the pigment/dye production method, a transfer of shellac components always occurs from the sticklac raw material into the lake pigment or dye. More specifically, although an increase in temperature and alkaline pH during the extraction promote the inclusion of high molecular weight shellac components, a variety of shellac components are also found when mild conditions, such as room temperature and neutral pH, are used. The results obtained for artificially aged lac-dyed textile samples showed that lac colourants are more prone to degradation than shellac components. The use of mass spectrometric detection for the identification of lac in historical objects is therefore recommended, as this technique is able to detect non-colourant molecules, which may be present in the pigment or dye as a result of the production methods.

Potential role of gold nanoparticles for improved analytical methods: an introduction to characterizations and applications

Nanoparticle-based material is a revolutionary scientific and engineering venture that will invariably impact the existing analytical separation and preconcentration for a variety of analytes. Nanoparticles can be regarded as a hybrid between small molecule and bulk material. A material on the nanoscale produces considerable changes on various properties, making them size- and shape-dependent. Gold nanoparticles (Au NPs), one of the wide variety of core materials available, coupled with tunable surface properties in the form of inorganic or inorganic-organic hybrid have been reported as an excellent platform for a broad range of analytical methods. This review aims to introduce the basic principles, examples, and descriptions of methods for the characterization of Au NPs by using chromatography, electrophoresis, and self-assembly strategies for separation science. Some of the latest important applications of using Au NPs as stationary phases toward open-tubular capillary electrochromatography, gas chromatography, and liquid chromatography as well as roles of run buffer additive to enhance separation and preconcentration in the field of chromatographic, electrophoretic and in chip-based systems are reviewed. Additionally, we review Au NPs-assisted state-of-the-art techniques involving the use of micellar electrokinetic chromatography, an online diode array detector, solid-phase extraction, and mass spectrometry for the preconcentration of some chemical compounds and biomolecules.

Identification of the Position of Mono-O-glucuronide of Flavones and Flavonols by Analyzing Shift in Online UV Spectrum (λmax) Generated from an Online Diode Array Detector

The beneficial pharmacological effects of flavonoids such as chemoprevention against cancer, aging, and heart diseases are severely limited due to their extensive in vivo glucuronidation by UDP-glucuronosyltransferases (UGTs). UGTs showed regiospecificity (i.e., position preference) in the glucuronidation of the flavonoids based on the substrate's chemical structure. In this paper, glucuronide(s) of 36 flavones and flavonols were generated using an in vitro glucuronidation reaction. UPLC/MS/MS was used to confirm the degree (mono- or di-) of glucuronidation in flavonoids with up to four hydroxyl groups. UV spectra of flavonoids and their respective mono-O-glucuronides were generated using UPLC with an online diode array detector. Analysis of the extent of shift in spectra of glucuronides in band I (300-385 nm) and band II (240-280 nm) regions as reflected by changes in lambdamax value was used to identify the position of glucuronidation. The data showed that glucuronidation of the 3- and 4'-hydroxyls resulted in band I lambdamax hypsochromic shifts (or blue shift) of 13-30 and 5-10 nm, respectively. Glucuronidation of the 5-hydroxyl group caused a band II lambdamax hypsochromic shift of 5-10 nm. In contrast, glucuronidation of the 7-hydroxyl group did not cause any lambdamax change in band I or II lambdamax, whereas glucuronidation of the 6-hydroxyl group did not cause predictable changes in lambdamax values. The paper demonstrated for the first time that a rapid and robust analysis method using lambdamax changes in online UV spectra can be used to pinpoint region-specific glucuronidation of flavones and flavonols with hydroxyl groups at the 4'-, 3-, 5-, and/or 7-position(s).

Determination of boron at sub-ppm levels in uranium oxide and aluminum by hyphenated system of complex formation reaction and high-performance liquid chromatography (HPLC)

Boron, at sub-ppm levels, in U 3O 8 powder and aluminum metal, was determined using complex formation and dynamically modified reversed-phase high-performance liquid chromatography (RP-HPLC). Curcumin was used for complexing boron extracted with 2-ethyl-1,3-hexane diol (EHD). Separation of complex from excess reagent and thereafter its determination using the online diode array detector (DAD) was carried out by HPLC. Calibration curve was found to be linear for boron amounts in the sample ranging from 0.02 μg to 0.5 μg. Precision of about 10% was achieved for B determination in samples containing less than 1 ppmw of boron. The values obtained by HPLC were in good agreement with the data available from other analytical techniques. The precision in the data obtained by HPLC was much better compared to that reported by other techniques. The present hyphenated methodology of HPLC and complex formation reaction is interesting because of cost performance, simplicity, versatility and availability when compared to other spectroscopic techniques like ICP-MS and ICP-AES.

Preparation of Cu(II) complexes of oxidized chlorophylls and their determination by thin-layer and high-performance liquid chromatography

Abstract Different allomerization products of pheophytins a and b have been obtained by alkaline treatment in the presence of atmospheric oxygen and isolated by normal phase thin-layer chromatography (NP-TLC) and semi-preparative high-performance liquid chromatography (HPLC). 3 1 ,3 2 -Didehydro-151-hydroxy-15 1 -hydroxy-rhodochlorin-15-acetic acid δ-lactone-15 2 -methyl-17 3 -phytyl ester ( a and b ) and 3 1 ,3 2 -Didehydro-rhodochlorin-15-glyoxylic acid-17 3 -phytyl ester ( a and b ) have been identified as principal products. Identification was based on UV-Vis and mass spectra, retention times and R F values. The molecular mass of allomerized pheophytins was confirmed by positive-ion fast-atom bombardment mass spectrometry and positive/negative ion electrospray mass spectrometry. The corresponding Cu(II) complexes of these compounds were prepared by chelation reaction with CuCl 2 and separated by reversed-phase ion-pair high-performance liquid chromatography (RP-IP-HPLC) using a gradient of water and ion suppressor-methanol-acetone. The Chromatographic characteristics in NP-TLC and RP-IP-HPLC of the Cu(II) complexes are reported. The corresponding UV-Vis spectra obtained with an on-line diode-array detector have been included.

7-HETE, 10-HETE, and 13-HETE Are Major Products of NADPH-Dependent Arachidonic Acid Metabolism in Rat Liver Microsomes: Analysis of Their Stereochemistry, and the Stereochemistry of Their Acid-Catalyzed Rearrangement

A complex profile of metabolites of [ 14C]arachidonic acid are formed in NADPH-dependent reactions in liver microsomes from phenobarbital-treated rats. The products were resolved by HPLC and analyzed initially with an on-line diode array detector set to monitor 205, 220, 235, and 270 nm. In addition to the epoxyeicosatrienoic acids and their diol hydrolysis products, prominent hydroxyeicosatetraenoic acids (HETE) metabolites were identified as omega-hydroxy derivatives and three bis-allylic products, 7-HETE, 10-HETE, and 13-HETE. The formation of 13-HETE was reported by Oliw et al. ( Arch. Biochem. Biophys. 300, 434-439 (1993)). Structures of the new products were established by GC MS, and for 10-HETE, by comparison to authentic synthetic material. Chiral column analysis indicated that 7-HETE and 10-HETE were essentially racemic. The 13-HETE resolved into a 40:60 ratio of 13S:13R. The bis-allylic HETEs readily undergo rearrangement to conjugated diene-containing HETEs in mild acidic conditions (1% acetic acid). Using [ 18O]13-HETE we observed 69% retention of the labeled oxygen in the 11- and 15-HETE arrangement products. Furthermore, steric analysis of products from acid treated 10-HETE and 13-HETE enantiomers revealed partial retention of chirality (80:20 ratio of enantiomers for methyl esters, and 60:40 ratio for free acids) in the course of mild acid-catalyzed rearrangement. This represents a novel reaction of this class of arachidonic acid metabolites of cytochromes P450.

Human epidermis transforms exogenous leukotriene A4 into peptide leukotrienes: possible role in transcellular metabolism.

Leukotriene B4 formation can take place by cell interaction between keratinocytes and neutrophils. Thus, keratinocytes without proven 5-lipoxygenase activity can transform neutrophil-derived leukotriene A4 into leukotriene B4. The purpose of the present study was to investigate whether human epidermis is able to transform leukotriene A4 sequentially into the peptide leukotrienes (LTC4, LTD4 and LTE4). Epidermis isolated using the suction blister technique or keratomed skin specimens were incubated with either neutrophils or exogenously added leukotriene A4. Peptide leukotrienes were determined by integrated optical density after RP-HPLC separation, and the identity of leukotrine C4 was confirmed by (1) the retention time similarity with authentic leukotriene C4; (2) the UV spectrum determined with an on-line diode array detector; and (3) conversion by gamma-glutamyl transpeptidase of the peak coeluting with authentic leukotriene C4 into a new peak coeluting with authentic leukotriene D4. The results of this study showed that while human epidermis cannot form detectable amounts of peptide leukotrienes by itself, it can transform exogenous leukotriene A4 into peptide leukotrienes. Furthermore, coincubation of human epidermis and neutrophils resulted in a marked increase (90%) in peptide leukotriene formation when compared with neutrophils alone, indicating that human epidermis can transform neutrophil-derived leukotriene A4 into peptide leukotrienes. These results indicate that human skin contains leukotriene C4 synthase activity capable of producing significant amounts of leukotriene C4 from leukotriene A4, and that the keratinocytes may play a more active role in peptide leukotriene formation in the skin than previously thought.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of glucuronic acid conjugates of a novel angiotensin receptor antagonist.

Nanogram quantities of glucuronic acid conjugates of GR117289 in rat and dog bile have been analysed by semi-microbore high-performance liquid chromatography (HPLC)/ionspray mass spectrometry with on-line UV diode array detection. The determination of drug metabolites in bile has often proved problematical due to the large number of endogenous components in this biological matrix, in particular the bile acids. Semi-microbore HPLC is useful for concentrating small quantities of material and, in combination with an on-line diode array detector, for distinguishing between drug related and endogenous components. A novel angiotensin II receptor antagonist, GR117289, had proved difficult to analyse by thermospray mass spectrometry because of its thermal lability. The use of the less thermally dependent technique of ionspray mass spectrometry allowed the characterization of nanogram quantities of glucuronic acid metabolites of GR117289 in bile.

Characterization of products formed during the autoxidation of β-carotene

The anticarcinogenic actions of carotenoids such as β-carotene has been frequently ascribed to their antioxidant properties. However, very little is actually known about the nature of the antioxidant reaction or the products that are formed. β-Carotene was exposed to either spontaneous autoxidation conditions or to radical-initiated autoxidation conditions. The products were separated by reverse-phase HPLC, and individual peaks were characterized with an on-line diode array detector. Carbonyl products were isolated and characterized by several procedures, including borohydride reduction to the corresponding alcohols, derivatization with O-ethyl-hydroxylamine to the corresponding O-ethyl-oximes of the carbonyls, and analysis by GC-MS. Under the conditions of the experiments, the formation of a homologous series of carbonyl products was demonstrated, including β-apo-13-carotene, retinal, β-apo-14′-carotenal, β-apo-12′-carotenal, and β-apo-10′-carotenal. Several very hydrophobic compounds were formed, which have not been previously identified. In addition, the products of NaOCl-treatment of β-carotene were analyzed, and shown to be significantly different from the autoxidation products. This type of product analysis should be useful in determining the nature of the oxidants reacting with β-carotene in vivo.