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1.
A Ce(IV)-based reducing capacity (CERAC) assay was developed to measure the total antioxidant capacity (TAC) of foods, in
which Ce(IV) would selectively oxidize antioxidant compounds but not citric acid and reducing sugars which are not classified
as antioxidants. The method is based on the electron-transfer (ET) reaction between Ce(IV) ion and antioxidants in optimized
acidic sulphate medium (i.e., 0.3 M H2SO4 and 0.7 M Na2SO4) and subsequent determination of the produced Ce(III) ions by a fluorometric method. The fluorescent product, Ce(III), exhibited
strong fluorescence at 360 nm with an excitation wavelength of 256 nm, the fluorescence intensity being correlated to antioxidant
power of the original sample. The linear concentration range for most antioxidants was quite wide, e.g., 5.0 × 10−7–1.0 × 10−5 M for quercetin. The developed procedure was successfully applied to the TAC assay of antioxidant compounds such as trolox,
quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, ferulic acid, glutathione, and cysteine.
The proposed method was reproducible, additive in terms of TAC values of constituents of complex mixtures, and the trolox
equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds gave good correlations with those
found by reference methods such as ABTS and CUPRAC. 相似文献
2.
Two stability-indicating spectrofluorimetric methods have been developed for the determination of ezetimibe and olmesartan
medoxomil, drugs affecting the cardiovascular system, and validated in the presence of their degradation products. The first
method, for ezetimibe, is based on an oxidative coupling reaction of ezetimibe with 3-methylbenzothiazolin-2-one hydrazone
hydrochloride in the presence of cerium (IV) ammonium sulfate in an acidic medium. The quenching effect of ezetimibe on the
fluorescence of excess cerous ions is measured at the emission wavelength, λem, of 345 nm with the excitation wavelength, λex, of 296 nm. Factors affecting the reaction were carefully studied and optimized. The second method, for olmesartan medoxomil,
is based on measuring the native fluorescence intensity of olmesartan medoxomil in methanol at λem = 360 nm with λex = 286 nm. Regression plots revealed good linear relationships in the assay limits of 10–120 and 8–112 g/ml for ezetimibe
and olmesartan medoxomil, respectively. The validity of the methods was assessed according to the United States Pharmacopeya
guidelines. Statistical analysis of the results exposed good Student’s t-test and F-ratio values. The introduced methods were
successfully applied to the analysis of ezetimibe and olmesartan medoxomil in drug substances and drug products as well as
in the presence of their degradation products. 相似文献
3.
Karim MM Jeon CW Lee HS Alam SM Lee SH Choi JH Jin SO Das AK 《Journal of fluorescence》2006,16(5):713-721
A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Δλ=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Δλ=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 μg ml−1 (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 μg ml−1 (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40–102% for acetylsalicylic acid and 90–100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97–99% for acetylsalicylic acid and 97–98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 μg ml−1 and 0.0306 μg ml−1 for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 μg ml−1 of acetylsalicylic acid is 2.75% and for 2.2 μg ml−1of caffeine is 1.7%. 相似文献
4.
A batch type chemiluminescence (CL) determination of enoxacin is described. In this work, it was observed that enoxacin could enhance the chemiluminescence (CL) emission Ru(phen)3
2+–Ce(IV) system and this enhancement effect was dependent on the concentration of enoxacin, based on which, CL system was established for the determination of enoxacin. Under the optimum experimental conditions, the linear range and detection limit are 0.6406–64.06 μg/ml and 0.0210 μg/ml, respectively. The R.S.D. is 1.75%. (n=10). The proposed method has been applied to detect the content of enoxacin in pharmaceutical formulation and human serum with satisfactory results. The possible mechanism of the CL reaction was discussed. 相似文献
5.
P. J. Ramesh K. Basavaiah N. Rajendraprasad O. Zenita Devi K. B. Vinay 《Journal of Applied Spectroscopy》2011,78(3):383-391
Two simple spectrophotometric methods have been developed to analyze ofloxacin (OFX) in pharmaceuticals. The methods are based
on the oxidation of OFX by a measured excess of cerium(IV) sulfate in H2SO4 medium. This was followed by the determination of the unreacted oxidant by reacting it with either p-toluidine (p-TD) and measuring the absorbance at 525 nm (method A) or o-dianisidine (o-DA) and measuring the absorbance at 470 nm (method B). In both methods, the amount of cerium(IV) sulfate reacted corresponds
to the amount of OFX. Calibration graphs were linear over the ranges of 0–120 and 0–4 g/ml OFX for methods A and B, respectively.
The calculated molar absorptivity (2.34⋅103 and 5.99⋅104), Sandell sensitivity, and limit of quantification for the methods are reported. The intra-day precision (%RSD) and accuracy
(%RE) were < 8.0 and ≤ 4.0%, respectively, and the inter-day RSD and RE values were within 5 and 4.0%, respectively. The applicability
of the methods was demonstrated by determining OFX in tablets with an accuracy (%RE) of < 3% and precision (%RSD) of ≤2.65%.
The accuracy of the methods was further ascertained by recovery experiments via a standard-addition procedure. 相似文献
6.
G. V. Mayer T. N. Kopylova Yu. M. Andreev V. A. Svetlichnyi E. N. Tel’minov 《Russian Physics Journal》2009,52(6):640-645
The possibility of parametrical conversion of visible radiation of solid-state organic lasers into the middle-IR range of
the spectrum in nonlinear GaSe1–x
S
x
(x = 0‒0.13) crystals is investigated. Generation at the difference frequency (wavelength λ3 = 9.43 μm) of induced oxazine-1 (at λ1 = 740 nm) and rhodamine-800 (λ2 = 803.4 nm) radiation is excited. The conversion efficiency is estimated, and prospects for its further increase are demonstrated. 相似文献
7.
V. R. Bom J. N. Bradbury J. D. Davies A. M. Demin D. L. Demin C. W. E. van Eijk V. V. Filchenkov A. N. Golubkov N. N. Grafov V. G. Grebinnik S. K. Grishechkin K. I. Gritsaj V. G. Klevtsov A. D. Konin A. A. Kukolkin S. V. Medved' V. A. Nazarov V. V. Perevozchikov A. N. Ponomarev V. Ya. Rozhkov A. I. Rudenko S. M. Sadetsky Yu. V. Smirenin N. I. Voropaev A. A. Yukhimchuk S. A. Yukhimchuk V. G. Zinov S. V. Zlatoustovskii 《Hyperfine Interactions》2001,138(1-4):213-223
Experiments on the study of the muon catalyzed fusion (μCF) process in a double D/T mixture of hydrogen isotopes in the temperature
range 300–800 K at densities 0.3–0.5 LHD are performed at the JINR phasotron. The values of the effective μCF parameters (cycling
rate λ
c
, neutron yield Y
n
, muon losses w) are obtained. Tentative dtμ-molecule formation rates on D2 and DT molecules (λ
dtμ−d
and λ
dtμ−t
) are obtained for different mixture temperatures and densities. The results obtained show that λ
dtμ−t
increases with temperature, but its value is smaller than theoretical predictions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Three sensitive and selective new alternatives for fluorometric determination of cerium(III) are described in this study.
Ce(III) is highly fluorescent in sodium pyrophosphate, sodium trimetaphosphate, and sodium tetrametaphosphate solutions. For
these reagents, the maximum excitation/emission wavelengths are 300/350, 297/340, and 299/352 nm, respectively. Maximum fluorescence
intensities are obtained by irradiating Ce(III) dissolved in 0.033 g L−1 sodium pyrophosphate, 41.4 g L−1 sodium trimetaphosphate, and 0.96 g L−1 sodium tetrametaphosphate at room temperature. The fluorescence intensities are linear over the range 0.001–30, 0.001–75,
and 0.001–70 μg ml−1. The detection limits are calculated as 9.5 × 10−3, 1.1/10−3, and 3.8 × 10-3 μg ml−1 Ce(III), respectively. The relative standard deviations for 15/0.05 Μg ml−1 Ce(III) are 1.1/1.2, 1/1.1, and 1.2/1.3%, respectively. Quenching effects of other lanthanides and some inorganic anions
were investigated. The methods have been applied to rare earth mixtures with a good accuracy. 相似文献
9.
A. M. Efimov A. I. Ignat’ev N. V. Nikonorov E. S. Postnikov 《Optics and Spectroscopy》2011,111(3):426-433
We have measured the UV absorption spectra of photothermorefractive glasses of the system Na2O-ZnO-Al2O3-NaF-SiO2 doped by cerium oxide in the range of (2.8–5.0) × 104 cm−1 (360–200 nm). The spectra have been processed by the method of dispersion analysis based on the analytical convolution model
for the complex dielectric function of glasses. We show that the absorption band centered at 3.3 × 104 cm−1 (∼303 nm) that is attributed to the transition 2F
5/2 → 5d in the Ce3+ ion, is an envelope of three spectral components. The broad absorption range (3.5–4.7) × 104 cm−1 (200–270 nm) that is commonly interpreted as a charge transfer band of the Ce(IV) valence state, is an envelope of at least
three spectral components. 相似文献
10.
ABSTRACT Trace amounts of cerium were analyzed by flow injection kinetic spectrophotometry, based on the decolorization reaction between arsenazo III and Ce(IV) in sulfuric acid medium at room temperature. The absorbance difference (ΔA) of decolorization was linear with the concentration of Ce(IV). The flow injection technique was used to precisely control the timing. Under the optimum conditions, the determination of Ce(IV) in the range 0.0–8.0 µg mL?1 with a correlation coefficient (r) of 0.9982, the regression equation was ΔA = 0.0014 + 0.0406c (µg mL?1). The detection limit (3σ) of 0.2 µg mL?1 was achieved at a sampling frequency of 60 h?1. The proposed method was applied to the analyses of Ce in soil successfully. 相似文献
11.
Luminescent quantum dots (QDs)-semiconductor nanocrystals were promising alternative to organic dyes for fluorescence-based
applications. In this paper, we developed procedures to use mercaptoacetic acid (MAA) to modify ZnSe nanoparticles and made
the nanoparticles to be soluble for the quantitative and selective determination of bovine serum albumin (BSA). Maximum fluorescence
intensity was produced at pH 7.0, with excitation and emission wavelengths at 242 and 348 nm, respectively. Under optimal
conditions, the straight line equation: △
F = 0.38 + 0.34 C (μg/ml) was found between the relative fluorescence intensity and the concentration of BSA in the range of
9.6–124.8 μg/ml, and the limit of detection was 2 μg/ml. 相似文献
12.
V. B. Gavrilov A. V. Lychkovskii E. P. Shostak S. V. Konev 《Journal of Applied Spectroscopy》1998,65(3):379-384
A more simple and sensitive assay for the quantitative determination of tyrosine in blood plasma is developed on the basis
of a modification of the method of S. Udenfriend (1962). A volume of 0.2 ml of plasma is used in the analysis; after its deproteinization
with trichloroacetic acid, it is reacted with sodium nitride, nitrous acid, and 1-nitroso-2-naphthol at 65°C, and the content
of the reaction product is measured by the fluorescence at λex/λem=460/570 nm. The consumption of plasma and reagents is reduced by a factor of 5–10 compared to the original method; in addition,
the stage of extraction with an organic solvent is excluded. The linear dependence of the fluorescence signal on the tyrosine
concentration within the range of 2–60 μg/ml, high specificity, accuracy, and reproducibility of the assay are shown. The
importance of tyrosine determination in monitoring of glucocorticoid therapy and protein catabolism is discussed.
Institute of Photobiology, National Academy of Sciences of Belarus, 27, Akademicheskaya St., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 366–371, May–June, 1998. 相似文献
13.
Two simple, sensitive and specific fluorimetric methods have been developed for the determination of some sulphur containing
compounds namely, Acetylcysteine (Ac), Carbocisteine (Cc) and Thioctic acid (Th) using terbium Tb+3 and uranium U+3 ions as fluorescent probes. The proposed methods involve the formation of a ternary complex with Tb+3 in presence of Tris-buffer method (I) and a binary complex with aqueous uranyl acetate solution method (II). The fluorescence
quenching of Tb+3 at 510, 488 and 540 nm (λex 250, 241 and 268 nm) and of uranyl acetate at 512 nm (λex 240 nm) due to the complex formation was quantitatively measured for Ac, Cc and Th, respectively. The reaction conditions
and the fluorescence spectral properties of the complexes have been investigated. Under the described conditions, the proposed
methods were applicable over the concentration range (0.2–2.5 μg ml−1), (1–4 μg ml−1) and (0.5–3.5 μg ml−1) with mean percentage recoveries 99.74±0.36, 99.70±0.52 and 99.43±0.23 for method (I) and (0.5–6 μg ml−1), (0.5–5 μg ml−1), and (1–6 μg ml−1) with mean percentage recoveries 99.38±0.20, 99.82±0.28 and 99.93±0.32 for method (II), for the three cited drugs, respectively.
The proposed methods were successfully applied for the determination of the studied compounds in bulk powders and in pharmaceutical
formulations, as well as in presence of their related substances. The results obtained were found to be in agree statistically
with those obtained by official and reported ones. The two methods were validated according to USP guidelines and also assessed
by applying the standard addition technique. 相似文献
14.
V. F. Tarasenko 《Russian Physics Journal》1999,42(8):670-673
This paper presents the designs and radiation characteristics for lasers operating by self-limited transitions of nitrogen
(λ=337.1 nm) and neon (λ=614.3 nm) and pumped by a pulsed longitudinal discharge, and for atmosphericCO
2 lasers (λ=10.6 μm) pumped by a transverse electron-beam-initiated discharge or by a transverse discharge with uv preionization.
These lasers were put into operation at IHCE in 1969 (the nitrogen and neon lasers), in 1971 (theCO
2 laser pumped by an electron-beam-initiated discharge), and in 1972 (theCO
2 laser pumped by a transverse discharge with uv preionization).
Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Fizika, No. 8, pp. 14–17, August, 1999. 相似文献
15.
Belal TS 《Journal of fluorescence》2008,18(5):771-780
A simple, rapid, selective and sensitive spectrofluorimetric method was described for the analysis of three nitrofuran drugs,
namely, nifuroxazide (NX), nitrofurantoin (NT) and nitrofurazone (NZ). The method involved the alkaline hydrolysis of the
studied drugs by warming with 0.1 M sodium hydroxide solution then dilution with distilled water for NX or 2-propanol for
NT and NZ. The formed fluorophores were measured at 465 nm (λ
Ex 265 nm), 458 nm (λ
Ex 245 nm) and 445 nm (λ
Ex 245 nm) for NX, NT and NZ, respectively. The reaction pathway was discussed and the structures of the fluorescent products
were proposed. The different experimental parameters were studied and optimized. Regression analysis showed good correlation
between fluorescence intensity and concentration over the ranges 0.08–1.00, 0.02–0.24 and 0.004–0.050 μg ml−1 for NX, NT and NZ, respectively. The limits of detection of the method were 8.0, 1.9 and 0.3 ng ml−1 for NX, NT and NZ, respectively. The proposed method was validated in terms of accuracy, precision and specificity, and it
was successfully applied for the assay of the three nitrofurans in their different dosage forms. No interference was observed
from common pharmaceutical adjuvants. The results were favorably compared with those obtained by reference spectrophotometric
methods. 相似文献
16.
Edward A. Desloge 《International Journal of Theoretical Physics》1976,15(5):357-363
On the basis of elementary symmetry arguments it is shown that (1) if in classical mechanics there exists a quantity λ+Σiμiυi+1/2νυ
2 that is conserved, where λ,μ
i, andν are particle parameters, then theμ
i andν are all proportional to a single parameterμ and the quantityAμ+ΣiBiμυi+C(λ+ 1/2Dμυ
2), whereD ≡ν/μ, is conserved for all values ofA, B
i, andC; (2) if in relativistic mechanics there exists a quantity λ+Σiμiυi[1−(υ
2/c
2)]−1/2+νc[1−(υ
2/c
2)]−1/2 that is conserved, then theμ
i andν are all proportional to a single parameterμ and the quantityAλ+ΣiBiμνi[1−(υ
2/c
2)]−1/2+Cμc [1−(υ
2/c
2)]−1/2 is conserved for all values ofA, B
i, andC. 相似文献
17.
L. N. Bogdanova V. R. Bom A. M. Demin D. L. Demin C. W. E. van Eijk S. V. Filchagin V. V. Filchenkov N. N. Grafov S. K. Grishechkin K. I. Gritsaj A. D. Konin A. V. Kuryakin S. V. Medved’ R. K. Musyaev A. I. Rudenko D. P. Tumkin Yu. I. Vinogradov A. A. Yukhimchuk S. A. Yukhimchuk V. G. Zinov S. V. Zlatoustovskii 《Journal of Experimental and Theoretical Physics》2009,108(2):216-225
The muon-catalyzed fusion (μCF) process in tritium was studied by the μCF collaboration on the muon beam of the JINR Phasotron.
The measurements were carried out with a liquid tritium target at the temperature 22 K and density approximately 1.25 of the
liquid hydrogen density (LHD). Parameters of the μCF cycle were determined: the ttμ muonic molecule formation rate λ
ttμ = 2.84(0.32) μs−1, the ttμ fusion reaction rate λ
f
= 15.6(2.0) μs−1, and the probability of muon sticking to helium ω
tt
= 13.9(1.5)%. The results agree with those obtained earlier by other groups, but better accuracy was achieved due to our unique
experimental method.
The article is published in the original. 相似文献
18.
A. Fernández Gutierrez M. Román Ceba A. Muñoz de la Peña S. G. Schulman 《Journal of fluorescence》1996,6(2):97-102
A photometric and fluorimetric study of the acid-base behavior of 2,2-diquinolyl and 2,2,2-terpyridyl was performed. In sulfuric acid medium, the doubly charged 2,2-diquinolynium ion undergoes the first dissociation atH
0=0.20±0.09, as determined by fluorimetry (ex=336 nm, em=424 nm). Photometric titration is less accurate because of the overlapping of the absorption spectra. The second dissociation constant of 2,2-diquinolyl was determined by fluorimetric titration (ex=336 nm, em=420 nm), obtaining a value of 3.67±0.03. The triply charged 2,2,2-terpyridyl molecule was found to undergo the first dissociation atH
0=–7.17±0.04, as determined by fluorimetric titration (ex=316 nm, em=350 nm), in aqueous sulfuric acid medium. Photometric titration (=335 nm) was performed in the presence of 6.5% ethanol because of the low solubility of the compound in water. In this ethanolicwater medium, a value of the dissociation constant atH
0=–7.39±0.03 was calculated. The second dissociation constant was determined to be 2.81±0.12 by photometric titration at 285 nm, and values of 4.03±0.26 and 4.16±0.20 were found for the third dissociation constant by photometric titrations at 320 and 295 nm, in 10% ethanol, in close agreement with previously reported values. The fluorimetric titration profile obtained by exciting at 274 nm and measuring the fluorescence emission at 350 nm, in the zone betweenH
0=–3 and pH=10, is complicated by the several equilibria involved. 相似文献
19.
M. Bryushinin V. Golubev Y. Kumzerov D. Kurdyukov I. Sokolov 《Applied physics. B, Lasers and optics》2009,95(3):489-495
We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous
glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created
by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal
amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 (λ=442 nm, I
0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 (λ=532 nm, I
0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L
D=0.18 μm. 相似文献
20.
Edward A. Desloge 《International Journal of Theoretical Physics》1976,15(5):349-356
On the basis of simple kinematic arguments it is shown that any quantity, depending only on the nature and velocity of a particle,
that is conserved in a collision must, in classical mechanics, be of the form λ+Σiμiυi+1/2vυ
2 or in relativistic mechanics of the form λ+Σiμiυi[1−(υ
2/c
2)]−1/2+νc [1−(υ
2/c
2)]−1/2 where λ,μ
i, andν are particle parameters. 相似文献