Photodiode Array Spectrometer Research Articles

Routine oxygen heterocyclic compounds analysis of fragrances using an eco-friendly liquid chromatography coupled to tandem mass spectrometry method

ABSTRACT Coumarin and furocoumarins characterization in cosmetics plays an important role in protecting consumer health. The analytical technique mostly employed for the analysis of these molecules is certainly liquid chromatography coupled to photodiode array or mass spectrometer detectors. The aim of this article was to investigate on the oxygen heterocyclic compounds content in fifty hydro alcoholic fragrances using a fast, sensitive and eco-friendly liquid chromatography coupled to a triple quadrupole mass spectrometer detector analytical method without any sample pre-treatment. To the best of the author’s knowledge, this is the first research article on the quantification of thirty-six oxygen heterocyclic compounds in hydro alcoholic fragrances in less than 4 min and with the use of water/ethanol as mobile phase. Thanks to the good performance of the analytical method used, this can be proposed among the routine methods for the quality control of cosmetics and finished products.

Methoxylated flavonols from Vellozia dasypus Seub ethyl acetate active myeloperoxidase extract: in vitro and in silico assays

This study aimed to evaluate the effect of a methoxylated fraction from Vellozia dasypus Seub on myeloperoxidase (MPO)-chlorinating activity and subsequent in silico assays for binding profile prediction. Therefore, the ethyl acetate extract of aerial parts from Vellozia dasypus Seub was fractionated on open-column chromatography containing SiO2 and eluted with solvent in crescent polarity to yield a fraction with a mixture of flavonols quercetin 3-O-methyl ether (1) and 6-C-methyl quercetin 3-O-methyl ether (2). Their chemical structures were proposed by HPLC coupled to photodiode array (HPLC-DAD) and mass spectrometer using electrospray ionization multistage analysis (HPLC-MS/MS). The fraction enriched with compounds 1 and 2 inhibited more efficiently the in vitro MPO-chlorinating activity (IC50 = 40 µg/mL) than the ethyl acetate extract (IC50 = 64.0 µg/mL). Molecular docking studies revealed that these compounds interact with MPO active pocket similarly to trifluoromethyl-substituted aromatic hydroxamate, a well-known MPO inhibitor, co-crystallized at the MPO binding site (PDB ID: 4C1M). Molecular dynamics trajectories confirmed that these two molecules interact with the MPO binding site with a similar energetic pattern when compared to the crystallographic ligand. Taken together, these data expand the sources of phenolic natural compounds that may be further investigated against inflammation-related diseases. Communicated by Ramaswamy H. Sarma

Non-destructive measurement of soluble solids content of three melon cultivars using portable visible/near infrared spectroscopy

In this study, a non-destructive method using visible/near infrared (Vis/NIR) spectroscopy was investigated to predict the soluble solids content (SSC) of intact melons (Cucumis melo L.) cv. ‘Manao’, ‘Jinhongbao’, ‘Xizhoumi’. A set of 360 samples (120 melons of each cultivar) was used to develop the calibration model, and two location (stylar-end and equatorial locations) models were investigated independently. The samples' spectra were obtained by a portable Vis/NIR photo-diode array spectrometer operated in reflectance mode. Multiplicative scatter correction (MSC), first derivative and Savizky-Golay (SG) smoothing in turn were applied to the obtained spectra. The region from 750 to 950 nm was selected to develop NIR models combined with the partial least squares (PLS) regression method. The results indicated that the stylar-end of the intact melon was the proper location to evaluate the SSC in the intact melon due to its suitable and exclusive physiological structure. A competitive adaptive reweighted sampling (CARS) algorithm was used to select effective wavelengths. Results showed that the CARS algorithm had great potential for simplifying the variables. Furthermore, another 195 samples were used for external prediction to evaluate the CARS-PLS model's accuracy and stability, which resulted in a high determination coefficient (R2p = 0.83) and a low root mean square error (RMSEP = 0.73 oBrix).

Effect of consuming a grape seed supplement with abundant phenolic compounds on the oxidative status of healthy human volunteers.

BackgroundDiverse enzymatic and non-enzymatic antioxidants provide protection against reactive oxygen species in humans and other organisms. The nonenzymatic antioxidants include low molecular mass molecules such as plant-derived phenols.Aim of studyThis study identified the major phenolic compounds of a grape seed extract by HPLC and analyzed the effect of consumption of biscuits enriched with this extract on the urinary oxidative status of healthy subjects by measurement of urine redox potential.MethodsThe major phenolic compounds were characterized in a red grape seed extract separated by HPLC with detection by a photodiode array (PDA), fluorescence (FL) and quadrupole mass spectrometer (MS). A nutritional study in a healthy volunteers group was done. Each volunteer ate eight traditional biscuits with no red grape seed extract supplementation. The second day each volunteer ate eight traditional biscuits supplemented with 0.6 % (wt/wt) of grape seed extract. An overnight urine sample was obtained for each treatment. The redox potential was measured at 25 °C using a potentiometer in each urine sample.ResultsEpicatechin, catechin, procyanidin dimers B1 to B4, and the procyanidin trimer C2 were the major phenolic components in the extract. Epicatechin gallate and procyanidin dimers B1-3-G and B2-3′-G were the major galloylated flavan-3-ols. The forty-six healthy volunteers each shown a reduction of the urine redox potential after the treatment by traditional biscuits supplemented with the grape seed extract.ConclusionsThis simple dietary intervention significantly reduced (33 %) the urine redox potential, reflecting an overall increase in antioxidant status. Incorporation of plant-derived phenols in the diet may increase anti-oxidative status.

Fast method for capsaicinoids analysis from Capsicum chinense fruits

Chili peppers are widely utilized in the world as savory food additives due the pungency induced by the capsaicinoids. Also, these compounds have functional properties as antimutagenic, antitumoral, antioxidant and analgesic. These characteristics increase the interest in this compound class, hence the capsaicinoid analysis must be reproducible and accurate. This study aimed to develop and validate a fast, efficient and reproducible method to analyze capsaicinoids in Brazilian Capsicum chinense fruits. The extracts were obtained after an optimization step that indicated the condition 100% of methanol and 10min on ultrasound assisted extraction. The analyses were carried out in an ultra high performance liquid chromatographic system with detection by a photo diode array and mass spectrometer. The analytical method developed permits the separation of 8 capsaicinoids in 4min of time analysis expending only 2mL of solvent as mobile phase. The validation parameters evaluated for the method show the effectiveness and satisfactory performance to answer the analytical needs of this research area, presenting low values to relative standard deviation in repeatability and reproducibility and recoveries ranged from 88 to 112% for capsaicin and 89 to 109% for dihydrocapsaicin. In the extracts from different accessions of C. chinense fruits analyzed, the contents of capsaicin and dihydrocapsaicin were in the range of 156–1442μgg−1 and 26–478μgg−1 of fresh fruit, respectively, showing the large application of this method for quantification of the two major capsaicinoids in fast routine analysis and may be used to determine the concentrations of other minor capsaicinoids once appropriate standards are available.

Calibration of a Photodiode Array Spectrometer Against the Copper Point

This paper describes a method to calibrate photodiode array spectrometers in the spectral radiance mode using a fixed-point blackbody as a reference source. Fixed-point blackbodies are characterized by their excellent emissivity, uniformity, and stability, which make them superior to both conventional standard lamps and variable temperature blackbodies. The temperature of these fixed points is accurately determined being traceable to either the International Temperature Scale (ITS-90) or thermodynamically through radiometric standards. The potential advantage of the fixed-point traceability chain is that it can be universally reproduced without recourse to any hierarchical calibrations or standards. The paper presents the calibration system and discusses the limitations of such an approach. The method used obtained an uncertainty of around 1.4 % (\(k = 2\)) associated with radiance responsivity across the spectral region from 550 nm to 1050 nm, which is comparable to what is readily achieved with a lamp-tile or lamp-illuminated spherical source.

A portable fiber optic system for measuring particle absorption using the quantified filter technique (QFT)

The Quantitative Filter Technique (QFT) has been shown to be an effective method for determining absorption coefficients of aquatic particles retained by filters. Although many investigators use the QFT, its routine use has been limited due in‐part to the required use of a high performance spectrophotometer and prescribed protocols for handling, storage, and transport of filters obtained in the field for later laboratory analysis. We describe a portable fiber optic system for conducting QFT measurements designed to overcome these limitations. The system (QFT2) consists of a high intensity light source, filter holder, and a photodiode array spectrometer configured as a single‐beam optical system. A set of 52 samples consisting of natural samples and cultures were analyzed following standard QFT protocols on a conventional spectrophotometer and the QFT2 system. Optical Density (absorbance) rather than absorption spectra were compared to avoid errors introduced by determining the pathlength amplification factor, β. Optical density (OD) spectra normalized at 400 nm measured using the fiber optic system were very similar to spectrophotometer spectra over a wide range of particle loadings. Strong linear relationships of normalized OD values at 443, 520, 550, 650, and 670 nm were observed for total particulate (r2 = 0.996; P < 0.001, n = 52), detrital particulate (r2 = 0.991, P < 0.001, n = 38), and pigmented particles or phytoplankton (r2 = 0.968, P < 0.001, n = 38). The greatest difference between the two systems was observed at ca. 683 nm where the QFT2 underestimates absorption due to pigment fluorescence.

Temperature and nonlinearity corrections for a photodiode array spectrometer used in the field

Temperature and nonlinearity effects are two important factors that limit the use of photodiode array spectrometers. Usually the spectrometer is calibrated at a known temperature against a reference source of a particular spectral radiance, and then it is used at different temperatures to measure sources of different spectral radiances. These factors are expected to be problematic for nontemperature-stabilized instruments used for in-the-field experiments, where the radiant power of the site changes continuously with the sun tilt. This paper describes the effect of ambient temperature on a nontemperature-stabilized linear photodiode array spectrometer over the temperature range from 5 °C to 40 °C. The nonlinearity effects on both signal amplification and different levels of radiant power have also been studied and are presented in this paper.

Temporal Sensitivity of the Wavelength Calibration of a Photodiode Array Spectrometer

Subtle differences in the relationship between wavelength and pixel on photodiode array spectrometers contribute to difficulties in transferring calibrations from one instrument to another and may even introduce errors on a single instrument over time. To quantify the level of drift that might be expected in photodiode instruments, we calibrated the wavelength scale of two Zeiss MMS-1 photodiode spectrometers weekly over a 12-month period. We found no evidence of drift in the wavelength calibration. The wavelength calibration was consistent within 0.03 nm over at least 150 days and better than 0.1 nm over the year. To provide context for the wavelength accuracy, we applied small perturbations to wavelength in two partial least squares (PLS) models. We found that wavelength perturbations introduced a linear increase in bias of about 7%/nm (for example, a 1-nm perturbation shifted fruit dry matter prediction from 14% to 21%) in a kiwifruit dry-matter model and about 3.6 °C/nm in an Intralipid temperature model. By including small wavelength perturbations in the training sets, we were able to reduce this error to less than 1.7%/nm and 0.2 °C/nm in the dry-matter and temperature models, respectively. These results suggest that the wavelength scale of photodiode instruments can be very stable. However, in light of the high sensitivity of the PLS models we examined, we recommend testing and, where possible, mitigating the sensitivity of PLS models to small wavelength shifts.

Rapid seed oil analysis using UPLC for quality control and authentication

AbstractWithout derivatization and halogenated solvent, various seed oil samples were rapidly characterized using a UPLC (Ultra Performance LC) equipped with UV photodiode array and mass spectrometer detectors. The method acquires multiple types of data in a single injection to authenticate seed oil, analyze triacylglycerol composition, and evaluate seed oil oxidation. It can, for example, identify olive oil samples adulterated with <1% of other seed oils. Compared with conventional high‐performance liquid chromatography methods, the UPLC solution shortens analysis time, reduces solvent usage, and provides more information, resulting in cost benefit. The reduction in analysis time and solvent usage align with the principles of green chemistry.

Physical methods for investigating structural colours in biological systems

Many biological systems are known to use structural colour effects to generate aspects of their appearance and visibility. The study of these phenomena has informed an eclectic group of fields ranging, for example, from evolutionary processes in behavioural biology to micro-optical devices in technologically engineered systems. However, biological photonic systems are invariably structurally and often compositionally more elaborate than most synthetically fabricated photonic systems. For this reason, an appropriate gamut of physical methods and investigative techniques must be applied correctly so that the systems' photonic behaviour may be appropriately understood. Here, we survey a broad range of the most commonly implemented, successfully used and recently innovated physical methods. We discuss the costs and benefits of various spectrometric methods and instruments, namely scatterometers, microspectrophotometers, fibre-optic-connected photodiode array spectrometers and integrating spheres. We then discuss the role of the materials' refractive index and several of the more commonly used theoretical approaches. Finally, we describe the recent developments in the research field of photonic crystals and the implications for the further study of structural coloration in animals.

Molecular Composition of the High-Boiling Components of Needle Coke Feedstocks and Mesophase Development

Mesophase development during the carbonization of needle coke feedstocks in delayed coking affects the microstructural anisotropy (or graphitizability) of the resulting coke. Previous work has employed gas chromatography/mass spectrometry (GC/MS) to study the relationships between the molecular composition of the fluid catalytic cracking decant oil (FCC DO) and mesophase development. In this study, the principal emphasis was placed on analyzing the non-GC amenable fraction of DO samples using a combination of analytical techniques, including high pressure liquid chromatography with photodiode array (PDA) and mass spectrometer detectors in tandem (HPLC/PDA and HPLC/MS/MS), and laser desorption mass spectrometry (LD/MS). The experimental data showed that major molecular species in DO samples consist of 3–6 ring multimethyl-substituted polyaromatic hydrocarbons (PAHs), including phenanthrenes, pyrenes, chrysenes, benzopyrenes, perylenes, and benzo[g,h,i]perylenes. Large differences were observed in the molec...

Dynamic fiber optic strain measurements and aliasing suppression with a PDA-based spectrometer

Dynamic fiber optic strain measurements at 3.3 kHz were performed employing a photodiode array spectrometer. The occurrence of aliasing components in the spectral data is investigated, and their dependence on the spectrometer integration time is analyzed. A theoretical model describing the aliasing components is discussed and could be confirmed by the experimental data. It is shown that the aliasing components can be partly suppressed by maximizing the duty cycle of the spectrometer.

A 21st Century HPLC Workflow for Process R&D

A unique high-performance liquid chromatographic (HPLC) workflow specifically designed for the rigors of process development has been developed. A key feature of the workflow is the creation of an HPLC software–hardware platform designed to automatically and systematically screen samples using a matrix of columns and eluents to aggressively search for impurities. The workflow platform was assembled from commercial hardware components and both custom and commercial HPLC software. The platform can be used to challenge existing HPLC methods or to develop new methods. The screening conditions are complementary to each other, and are useful to assess the complexity of a sample and to chromatographically resolve impurities that may coelute using any single method. The workflow has been designed to support several different modes of HPLC, and can be used with absorption detection, photodiode array spectrometers, evaporative light scattering (ELS) devices, and mass spectrometric (MS) detection. The custom software interface contains a data-viewing feature to simplify analysis of results. The platform is designed to be used by process scientists, and the same simple user-interface is used to control analytical HPLC, LC–MS, and preparative HPLC. Three real world examples are provided to illustrate the utility of the platform to rigorously assess the complexity of samples and to develop new and improved HPLC methods. (JALA 2005;10:381–93)

On‐line monitoring of the acrylate conversion in UV photopolymerization by near‐infrared reflection spectroscopy

AbstractNear‐infrared (NIR) reflection spectroscopy was used to determine the conversion in acrylate coatings after UV photopolymerization in order to test it as a method for process control in UV curing. A probe head was developed which is adapted to the specific requirements of UV curing and which is linked to a photodiode array spectrometer by an optical fiber. Reflection spectra from thin acrylate layers which were taken in intervals down to the millisecond range have shown an excellent signal‐to noise ratio. Quantitative conversion data show good correlation with results from independent reference methods (FTIR, HPLC). Following thesebasic investigations, it was demonstrated that NIR reflection spectroscopy can be used for on‐line monitoring of the acrylate conversion in thin coatings. Some examples of such investigations in pilot scale are presented.

Liquid chromatographic separation and determination of aromatic sulfonates in an aquatic environment using a photodiode array and electrospray ionization-mass spectrometer as detectors.

A simple and rapid method involving high-performance liquid chromatographic separation, followed by photodiode array (PDA) and electrospray ionization-mass spectrometric (ESI-MS) detection of aromatic sulfonates in waste-water effluents of industrial units producing optical whitening agents, has been developed. The separation was achieved on a reversed-phase Hypersil C18 column using gradient elution of a mobile phase consisting of 0.05 M ammonium formate-methanol with decreasing concentration of the buffer at room temperature. The minimum detection limits were determined to be in the range of 0.2 - 1.8 x 10(-9) g using PDA and ESI-MS detectors.

Differential Metabolic Profiling by HPLC–PDA–MS of Wild Type and Transgenic Tobacco Plants Constitutively Producing Salicylic Acid

The metabolite profiles of wild type tobacco plants and transgenic tobacco plants, constitutively producing salicylic acid (SA), were compared by means of liquid chromatography with online photo diode array and mass spectrometer detector (LC–PDA–MS). Statistical analysis of the peak area of 15 major peaks showed significant differences in quantities for three compounds, which are present in the extract before acid hydrolysis, containing mainly aglucones. By comparison of the retention time, UV spectra, and molecular weight with reference compounds, two of these peaks were identified as chlorogenic acid and rutin. The extracts obtained after acidic hydrolysis did not show any significant difference.

In-Situ Dissolution Testing Using Different UV Fiber Optic Probes and Instruments

Introduction: Fiber optic technology for dissolution testing has been a topic of interest for many researchers for some years. Josefson, Johansson, and Tortensson 1 published early research in this field in 1988. They explored the feasibility of using UV fiber optics for in-situ dissolution and to overcome sample turbidity interference without filtration. In 1993, Brown and Lin 2 used a single optical fiber and a photo diode array (PDA) UV/vis spectrometer to track dissolution in a single vessel. Their work was extended thereafter to use six optical fibers and a PDA spectrometer for multiple dissolution vessels 3. In 1995, Cho and coworkers developed a sevenchannel fiber optic dissolution system using a spectrometer with two-dimensional chargecoupled devices (CCD), which allowed the simultaneous monitoring of six dissolution vessels and a seventh reference vessel 4,5. Several other studies around the same time further explored the possibility of using fiber optic technology for special dissolution applications. For example, Chen and his group 6,7 employed a fiber optic based chemical sensor for continuous monitoring of in-situ dissolution. Gemperline et al 8 applied a CCD/fiber optic system for determining two-component dissolution profiles of a pharmaceutical product, which used a full-range spectral principal component regression methodology. Aldridge and coworkers 9 automated a single-probe fiber optic system that used a robot arm to move the probe from vessel to vessel for sequential testing. All these breakthrough studies had great impact on subsequent development of commercial instruments and established the platform for modern in-situ fiber optic dissolution testing. Commercial UV fiber optic dissolution instruments became available in 1999. Several manufacturers in the United States introduced their independently developed instruments one after another. These commercial instruments employed either a spectrometer with multi-channel CCDs 10, 11, multiple PDA spectrometers 12,13, or a scanning spectrometer with a mechanical multiplexer 14,15. Commercialization of this technology and its consequent availability to a broad range of users has attracted much attention from the pharmaceutical industry. Recent publications and research works further described the capability of this technology 16-18 and demonstrated that UV fiber optics is a breakthrough for dissolution testing. A regulatory perspective on this technology has also been discussed in a recent article 19.

Determination of the size-distribution of CuBr nanocrystals in a glassy matrix by means of high-temperature UV–visible absorption spectroscopy

The size-distribution of CuBr nanocrystals embedded in a glassy matrix was investigated using high-temperature UV–visible absorption spectroscopy. The investigations were carried out with a photodiode array spectrometer in the temperature range from 25°C to 350°C. The absorbance of the excitonic z 1/2 and z 3 peaks of the CuBr nanocrystals decreases with increasing temperature. This effect is due to a size-dependent melting of the nanocrystals. We developed an analytical method, to calculate the size-distribution of the nanocrystals from the shape of the excitonic absorbance–temperature curve. The growth of a second crystal generation is observable at longer heat treatment times. Small-angle X-ray scattering (SAXS) investigations support these results. We find three crystal generations (one larger than the detection limit of our spectroscopical method). Gaussian functions are used to fit the size-distribution curves of each of these crystal generations. The sum of the distributions exhibits an increasing asymmetry during the ripening process.

A simple instrument for ultraviolet-visible absorption spectrophotometry in high temperature molten salt media

An inexpensive (<US$5000) spectrophotometer of simple design was constructed from commercially available components for absorption spectroscopic studies in molten chloride salts. The spectrometer consists of a replaceable fused silica cell of 9×9 mm square exterior cross-section housed in a temperature-controlled ceramic tubular furnace of 13 mm inner diameter. Light communication to and from the cell occurs via a pair of 1 mm core silica-on-silica optical fibers from diametrically opposite sides. The light source is a pulsed xenon flash lamp and detection is accomplished by a photodiode array spectrometer card housed in a personal computer. The system has been operated up to temperatures of 950 °C. The effective spectral range is 280–650 nm at 900 °C; higher wavelengths can be accessed at lower operating temperatures. A spectral snapshot can be acquired in as little as 1 ms. With 1 s integration time, the intrinsic system noise level is ∼2×10−4 absorbance units. The system is compact and energy efficient. Applications of the system are demonstrated with spectral studies of some metal chloride systems in an equimolar sodium and potassium chloride eutectic.