1,720,967 research outputs found
HPLC DETERMINATION OF POLYCYCLIC AROMATIC HYDROCARBONS IN OLIVE OILS
No full textIn this paper, HPLC with spectrofluorimetric detection was applied to the determination of polycyclic aromatic hydrocarbons (PAHs) in olive oils. These compounds may sometimes contaminate vegetable oils because of their specific lipophilic characteristics, which are a significant problem for their extraction and purification from lipid matrices. Some improvements to previously published methods are introduced and satisfactory results for repeatability and recovery were obtained. Data on 51 authentic olive oil samples are reported and it was found that there is usually a limited presence of PAHs in extra virgin olive oils; furthermore, the analysis of some blends of refined and virgin oils shows that the distributions of light and heavy PAHs are different with the content of the former being lower in refined samples. As an example of this fact, two samples of lampante oil were followed throughout the refining step
Development and Optimization of an HPLC-PDA Method for the Determination of Major Cannabinoids in Hemp (Cannabis sativa L.) Essential Oil Obtained by Hydrodistillation
Full text linkThe use of hemp (Cannabis sativa L.) essential oil (EO) has shown a significant increase in interest and use during recent years. In this work, a new and simple reversed-phase HPLC with photodiode-array (PDA) detector method has been developed and optimized for the detection and quantification of cannabidiolic acid (CBDA), cannabidiol (CBD), cannabinol (CBN), Δ9-tetrahydrocannabinol (Δ9-THC), and Δ9-tetrahydrocannabinolic acid (THCA). The cannabinoids were extracted from the EO by partition with n-hexane and water, followed by sonication, evaporation to dryness under nitrogen, and reconstitution with methanol:chloroform (9:1, v/v) before HPLC-PDA analysis. The method shows good selectivity and robustness, linearity in the range 0.5–100 mg L−1 with R2 higher than 0.999 for all cannabinoids analyzed, LOD of 0.11–0.16 mg L−1, and LOQ of 0.35–0.48 mg L−1. The recovery was between 78 and 100% and the intra-day and intermediate precision, expressed as relative standard deviation (RSD), was < 4% and 4–10%, respectively
Measurement of Purine Derivatives and Creatinine in urine by HPLC
No full textTwo HPLC methods to measure the purine derivativcs (PD), including allantoin, uric acid, hypoxanthine and xanthine) and creatinine content in urine are described. PD separation and quantification were achieved using two Spherisorb ODS 2 reversed phase columns connected in series (4.6 x 250 mm) and a Spherisorb ODS 2 Waters pre-column and a Perkin Elmer pump with an autosampler. The mobile phase was NH4H2PO4; NH4H2PO4: acetonitrile (80:20), which was used at a flow rate of 0.8 ml/min and the detection wavelength was at 190 nm. The average recoveries of standard compounds added to urine samples were satisfactory (92-106%) and the low detection limits (0.7-3.4 μM) permitted the precise determination of these compounds in urine.
Separation and quantification of crcatinine was achieved using one Spherisorb ODS 2 reversed phase column (4.6 X 250 mm) and one Spherisorb ODS 2 Waters pre-column and a Perkin Elmer pump with an auto sampler. The mobile phase was NH4H2PO4; NH4H2PO4;-acetonitrile (80:20), used at a how rate of 1.00 m1/min and the detection was at 190 nm. The mean recovery (3 measurements) of standard solution added to urine samples was 101%; detection limit was 7.9 μM
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Prediction of Purine Derivatives Creatinine and Total Nitrogen concentration in urine by FT-Near-Infrared-Reflectance-Spectroscopy
No full textThe objective of this study was to provide an alternative method for the determination of purine derivatives (PD, which include allantoin, uric acid, hypoxanthine and xanthine), creatinine and total nitrogen (N) concentration in urine.
About 180 urine samples from cattle, buffaloes and rabbit were collected and analyzed for PD by HPLC, creatinine by spectrophotometry and N by Kjeldahl method. The urine samples were then analyzed by Fourier Transformed Near Infrared Reflectance Spectroscopy (FT-NIR) to find conformity between this technique and HPLC and colorimetric methods.
FT-NIR can predict allantoin, uric acid, hypoxanthine, xanthine, creatinine, total N and sum of N in both allantoin and uric acid with a satisfactory level of accuracy; the determination coefficient (r2) of validation ranged from 0.888% for uric acid to 0.982% for total N. The coefficients of determination for allantoin, creatinine and sum of N in both allantoin and uric acid were 0.92, 0.894 and 0.90%, respectively.
Hypoxanthine and xanthine in urine samples were not detectable by NIRS, probably because of their low concentrations, and therefore they were not considered for instrumental calibration
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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