1,720,998 research outputs found
Reaction of phenolic ligands with metal ions. Reaction of chromium(III) with chromotropic acid
No full textThe equil. of Cr(III) with chromotropic acid (I) in 0.5M KCl were studied at 25° by spectrophotometric methods. Mononuclear and binuclear species with metal: ligand ratios 1:1, 1:2, and 2:1 were found in acid medium. The spectrophotometric characteristics and the equil. consts. for the various species are reported. The spectrophotometric detn. of Cr(III) by I is not satisfactory because of modification of I by light and by oxidizing agents, low selectivity (many ions interfere), and low sensitivity compared to complexing agents such as Chromazurol S and pyrocatechol violet
Prediction of HPLC retention times in the determination of the triglyceride composition of oils
No full textIn the HPLC anal. of triglycerides, discrepancies occur between the retention times measured exptl. and those calcd. from the relation between the equiv. C no. (ECN), the total no. of C atoms, and the total no. of double bonds. It is hypothesized that the relative retention time (RRT) is a function of an "activity" of the C atoms and the double bonds. Computer workup of the adjusted ECN values of a no. of plant oils gave results that matched the exptl. HPLC data. The relation between ECN and RRT, characteristic of each triglyceride, is: ECN = 18.1081 + 0.14035(100 log(100RRT)
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
The reaction of iron(II) and nickel(II) with pyrazine-2-carboxylic acid
No full textPyrazine-2-carboxylic acid reacts with Ni2+ and Fe2+ forming sol. or solid complexes depending on exptl. conditions. The equil. in aq. soln. (1M ClO4-, 25°) were studied by spectrophotometric methods. For both systems only mononuclear species with metal/ligand ratios 1:1, 1:2, and 1:3 were found. The spectrophotometric characteristics and the equil. consts. of the complexes are reported. The solid compds. were analyzed by diffuse reflectance, IR spectrophotometry, and thermal anal
Reaction of chromium(III) with Methylthymol Blue in aqueous solution
No full textIn aq. solns. with ionic strength 0.1M (NaClO4) contg. Cr(III) and Methylthymol Blue (H6L) at 25°, the equil. consts. (K) corresponding to Cr3+ + H4L2- = CrH3L + H+, 2Cr3+ + H4L2- = Cr2H3L3+ + H+, Cr3+ + H3L3- = CrH3L, and 2Cr3+ + H3L3- = Cr2H3L3+ are log K = 0.81, 5.14, 3.9, and 8.2, resp. The acid dissocn. consts. corresponding to H6L = H5L- + H+, H5L- = H4L2- + H+, H4L2- = H3L3- + H+, H3L3- = H2L4- + H+, H2L4- = HL5- + H+, and HL5- = L6- + H+ are pKa = -1.9, +1.9, +3.1, +7.02, +10.6, +12.5, resp
Supervised pattern recognition applied to the discrimination of the floral origin of italian honey samples
No full textIn this work a supervised chemornetric approach to the discrimination of Italian honey samples from different floral origin is presented. The analytical data of 73 Italian honey samples from six varieties (chestnut, eucalyptus, heather, sulla, honeydew, and wildflower) have been processed by Linear Discriminant Analysis (LDA), using two different variable selection procedures (Fisher F-based and stepwise LDA). Three and two variables, respectively have been necessary to obtain a 100% predictive ability as evaluated by cross-validation. Successively, a class modeling approach has been followed, using UNEQ. The resulting models showed 100% sensitivity and specificity
Spectrophotometric investigation on the reaction of indium(III) with methylthymol blue in aqueous acidic medium
No full textThe equil. between In(III) and methylthymol blue (MTB) were studied spectrophotometrically in 1 M NaClO4 at 25°. Dinuclear and mononuclear species were found in acidic medium with 2:1, 1:1, and 1:2 metal/ligand ratios. The spectrophotometric characteristics and equil. consts. for the various species are reporte
Determination of vitamins content in enriched pasta
No full textItalian pasta sold on the USA and Canada market is enriched with thiamine, riboflavin and niacin, according to the percentages of U.S.R.D.A.
A HPLC method for vitamins content determination in enriched pasta is proposed and a number of procedures of extraction and preliminary work up is tested, in order to fullfill the following requirements: quantitative recovery, not destructivity and removal of interfering substances
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