共查询到20条相似文献,搜索用时 31 毫秒
1.
Nai-Xing Wang Lei Wang Wei Jiang Yue-Zhen Ren Zhi-Kun Si Xun-Xing Qiu Gao-Ying Du Ping Qi 《Analytical and bioanalytical chemistry》1998,361(8):821-824
Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium
in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes
with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands
found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second
derivative spectrum, Beer’s Law is obeyed from 5.0 × 10–5∼ 2.5 × 10–4 mol dm–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10–5 mol dm–3 of neodymium, 6.1 × 10–5 mol dm–3 of holmium and 6.0 × 10–5 mol dm–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth
elements with good accuracy and selectivity, is described.
Received: 18 December 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998 相似文献
2.
Nai-Xing Wang Lei Wang Wei Jiang Yue-Zhen Ren Zhi-Kun Si Xun-Xing Qiu Gao-Ying Du Ping Qi 《Fresenius' Journal of Analytical Chemistry》1998,361(8):821-824
Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium
in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes
with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands
found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second
derivative spectrum, Beer’s Law is obeyed from 5.0 × 10–5∼ 2.5 × 10–4 mol dm–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10–5 mol dm–3 of neodymium, 6.1 × 10–5 mol dm–3 of holmium and 6.0 × 10–5 mol dm–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth
elements with good accuracy and selectivity, is described.
Received: 18 December 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998 相似文献
3.
Parikshit Goswami Richard S. Blackburn Jim Taylor Patrick White 《Cellulose (London, England)》2009,16(3):481-489
To understand the effect of alkali pre-treatment on the dyeing of lyocell fabrics, samples are pre-treated with 0.0–7.0 mol dm−3 NaOH using a pad-batch process and then dyed with different types of reactive dyes. Exhaustion, fixation, and visual colour
strength (K/S values) are measured. It is observed that sodium hydroxide pre-treatment significantly improves the colour yield, exhaustion,
and fixation for all dyes used. Highest K/S values are obtained when the fabrics are pre-treated with 2.0–2.5 mol dm−3 NaOH. Cross-sectional analysis shows that below this optimum concentration the core fibres in the yarn are not dyed; at optimum
concentration all fibres in yarn cross-section are homogeneously dyed. Cross-sectional analysis shows that as the pre-treatment
concentration of NaOH increases above 2.5 mol dm−3, the fibres change progressively from a circular to angular cross-section, forming a solid unit. The decrease in K/S above the treatment concentration of 2.5 mol dm−3, though the %E and %F remains almost constant, is attributed to the distribution of dye over a larger surface area of the outer fibres in the yarn
cross section, forcing the K/S at λmax to decrease.
This paper was presented at the 2nd International Cellulose Conference, Tokyo, Japan, 24th October 2007. 相似文献
4.
Samples of precipitations were collected quarterly and analyzed for90Sr and137Cs. The values obtained ranged from 0.001 to 0.004 Bq dm–3, with a maximum of 0.010 Bq dm–3 for90Sr;137Cs values ranged from 0.001 to 0.005 Bq dm–3, with a maximum of 0.070 Bq dm–3. The highest values were observed during the 2nd and 3rd quarters of 1981. 相似文献
5.
Mei-Wo Yii Zal U’yun Wan Mahmood 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):819-833
This study with sampling expeditions of marine sediment, seawater and biota were performed at 30 stations within Malaysian
Exclusive Economic Zone (EEZ). A total of >400 samples were collected to determine the activity concentration of anthropogenic
radionuclides (239+240Pu, 137Cs) and their activity ratio (239+240Pu/137Cs) in sediments, seawater and biota. The purpose of this study was to determine the concentration levels for these radionuclides
and to evaluate any occurrence of radioactive contamination. Sediment cores were obtained using multicorer device, while water
samples via co-precipitation techniques and biota was purchased from local fishermen. The activity concentrations of 239+240Pu in sediment, seawater and biota were ranged 0.21–0.45 Bq/kg dry wt., 2.33–7.95 mBq/m3 and <0.008 Bq/kg fresh wt., respectively. Meanwhile, the values of 137Cs were ranged <1.00–2.71 Bq/kg dry wt. in sediment, 3.40–5.89 Bq/m3 in seawater and <0.05–0.41 Bq/kg fresh wt. in biota, respectively. Activity ratios of 239+240Pu to 137Cs obtained seem to confirm that these artificial radioactivities were mainly due to global nuclear fallout. 相似文献
6.
The effect of ammonium nitrate concentration in the citric acid biosynthesis by Aspergillus niger NC-12 in single-stage continuous cultures with biomass retention was investigated. Experiments were carried out in a BIOMER
laboratory fermenter with 5 dm3 working volume. At the initial stage of each cultivation, the substrate in the bioreactor contained 1.5 g NH4NO3 dm−3. After 120 h onwards, the bioreactor was fed continuously at a constant dilution rate of 0.009 h−1. NH4NO3 concentration in the feed was varied from one culture to another, ranging between 0.5 g dm−3 and 2.5 g dm−3. Promising results were obtained when NH4NO3 concentration of 1.5 g dm−3 was used. The observed concentration of citric acid (c
P) and yield of citric acid with respect to the introduced sucrose (Y
P/S) were 117.88 g dm−3 and 78.59 %, respectively. The efficiency coefficient of citric acid biosynthesis (K
ef) was very high, amounting to 83.38.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
7.
Simultaneous production of citric acid and erythritol from crude glycerol by Yarrowia lipolytica Wratislavia K1 总被引:2,自引:0,他引:2
This study shows a possible microbial process for utilization of crude glycerol generated by the biodiesel industry for citric
acid and erythritol production. Simultaneous production of citric acid and erythritol under nitrogen-limited conditions with
glycerol as the carbon source was achieved with an acetate negative mutant of Y. lipolytica Wratislavia K1 in fed-batch cultivations. The effect of the initial glycerol concentration (from 30–180 g dm−3) on the citrate and erythritol production was investigated. As a result of the experiments, maximum citric acid production
(110 g dm−3) and a very high amount of erythritol (81 g dm−3) were determined after 168 h of fed-batch cultivation with the initial glycerol concentration of 150 g dm−3 and the total glycerol concentration of 250 g dm−3. In addition, the citric acid to isocitric acid ratio of the products from this strain was 35.5:1.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
8.
The specific adsorption of corrosion inhibitors (inorganic and organic compounds) was studied at a metal oxide (hematite)
in 0.5 mol dm–3 NaClO4 solution by an indirect radiotracer technique. This indirect radiotracer technique is based upon the application of labeled
indicator species, which were sulfate species at a concentration of 2×10–4 mol dm–3. The displacement of sulfate species was found in all the cases studied. The order of the inhibition efficiency of the corrosion
inhibitor molecules is in good agreement with the order of their adsorbabilities.
Electronic Publication 相似文献
9.
Adenosine, adenosine monophosphate, and adenosine triphosphate adsorption from aqueous solutions on the surface of carbon
nanotubes is studied. Adsorption isotherms are plotted and adsorption free energies, as well as areas per molecules of the
adsorbates, are calculated at their concentrations in solutions of 0–10−3 mol/dm3. It is shown that the monomolecular adsorption is characterized by rather loose packing of adsorbate molecules on the nanotube
surface, with the packing density increasing in the presence and upon a rise in the concentration of phosphate groups in adsorbate
molecules. In the range of the polymolecular adsorption, at high adsorbate concentrations in solutions (C > (5–6) × 10−4 mol/dm3), the adsorption decreases in a series adenosine > adenosine monophosphate > adenosine triphosphate, i.e., with an increase
in the solubility of the examined compounds in water. 相似文献
10.
The profile distribution of arsenic(III) and arsenic(V) species in soil and groundwater was investigated in the samples collected
in 2005 from a hand-drilled well, in the Bozanta area, Baia Mare region, Romania. The total content of arsenic in the soil
was in the range of 525–672 mg kg−1 exceeding 21–27 times the action trigger level for sensitive soil. 0.9–11.3 % of the total content was soluble in water,
83.0–92.6 % in 10 mol dm−3 HCl and 2.6–13.3 % was the residual fraction. Arsenic(V) was the dominant arsenic species in the soil in the range of 405–580
mg kg−1. The distribution and mobility of arsenic species was governed by soil pH and contents of Al, Fe, and Mn. The mobility of
arsenic(V) decreased with depth, while that of arsenic(III) was high at the surface and in the proximity of groundwater. The
total concentration of arsenic in groundwater was (43.40 ± 1.70) μg dm−3, which exceeded the maximum contaminant level of 10 μg dm−3.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
11.
Wiesława Ferenc Beata Bocian J. Sarzyński 《Journal of Thermal Analysis and Calorimetry》2006,84(2):377-383
Four new complexes of 2,3,4-trimethoxybenzoic acid
anion with manganese(II), cobalt(II), nickel(II) and copper(II) cations were
synthesized, analysed and characterized by standard chemical and physical
methods. 2,3,4-Trimethoxybenzoates of Mn(II), Co(II), Ni(II) and Cu(II) are
polycrystalline compounds with colours typical for M(II) ions. The carboxylate
group in the anhydrous complexes of Mn(II), Co(II) and Ni(II) is monodentate
and in that of Cu(II) monohydrate is bidentate bridging one. The anhydrous
complexes of Mn(II), Co(II) and Ni(II) heated in air to 1273 K are stable
up to 505–517 K. Next in the range of 505–1205 K they decompose
to the following oxides: Mn3O4,
CoO, NiO. The complex of Cu(II) is stable up to 390 K, and next in the range
of 390–443 K it loses one molecule of water. The final product of its
decomposition is CuO. The solubility in water at 293 K is of the order of
10–3 mol dm–3
for the Mn(II) complex and 10–4 mol dm–3
for Co(II), Ni(II) and Cu(II) complexes. The magnetic moment values of Mn2+,
Co2+, Ni2+ and Cu2+
ions in 2,3,4-trimethoxybenzoates experimentally determined in the range of
77–300 K change from 5.64–6.57 μB (for Mn2+),
4.73–5.17 μB (for Co2+), 3.26–3.35 μB
(for Ni2+) and 0.27–1.42 μB (for Cu2+).
2,3,4-Trimethoxybenzoates of Mn(II), Co(II) and Ni(II) follow the Curie–Weiss
law, whereas that of Cu(II) forms a dimer. 相似文献
12.
Farrokh Gharib Ali Shamel Sahar Mohajeri 《Russian Journal of Inorganic Chemistry》2010,55(10):1651-1656
The dependence on ionic strength of protonation of nitrilotriacetic acid and its complexation with W(VI) is reported in sodium
perchlorate, sodium nitrate and sodium chloride solutions as background salts. The measurements have been performed at 25°C
and various ionic strengths in the range 0.1–1.0 mol dm−3, using a combination of potentiometric and spectrophotometric techniques. The overall analysis of the present and the previous
data dealing with the determination of stability constants at different ionic strengths allowed us to obtain a general equation,
by which a formation constant determined at a fixed ionic strength can be calculated, with a good approximation, at another
ionic strength, if 0.1 ≤ ionic strength ≤ 1.0 mol dm−3 sodium perchlorate, sodium nitrate or sodium chloride. 相似文献
13.
The behaviors of low-concentration aqueous solutions of 10-undecenoic acid and its sodium salt were studied by several techniques.
The acid does not have a critical micelle concentration, but gives an emulsion of very small droplets at (0.8–1) × 10−4 mol dm−3. The emulsion was clearly visible by eye at 0.002 mol dm−3. The sodium salt has a stepwise aggregation process, giving premicellar aggregates at 0.023 ± 0.008 mol dm−3, which grow to form micelles at 0.117 ± 0.007 mol dm−3. The compositions of the solution and the micelles were also studied.
Received: 25 February 1999 Accepted in revised form: 21 June 1999 相似文献
14.
Abstract
The characterization of an optical sensor membrane is described for the determination of tin (II) based on the immobilization of dithizone on a triacetylcellulose membrane. The membrane responds to tin (II) ions by changing color reversibly from green to red in buffer solution at pH 6 and wavelength 611 nm. This optode has a linear range of 0.3–6.33 μg cm−3 (2.52–53.32 μmol dm−3) of Sn2+ ions with a limit of detection of 0.15 μg cm−3 (1.26 μmol dm−3). The response time of the optode was about 8–10 min depending on the concentration of Sn2+ ions. The selectivity of the optode to tin (II) ions at pH 6 was good. The sensor can be readily regenerated by exposure with EDTA solution. The color is fully reversible, and the optical sensor could be fully regenerated. Experimental results showed that the optode could be used as an effective tool in analyzing the tin content in canned foods. 相似文献15.
Jonathan F. Ojo Jide Ige Grace O. Ogunlusi Olanrewaju Owoyomi Esan S. Olaseni 《Transition Metal Chemistry》2006,31(6):782-785
The kinetics of the reactions between Fe(phen)
3
2+
[phen = tris–(1,10) phenanthroline] and
Co(CN)5X3− (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm−3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H+] = 0.01 mol dm−3) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm3 mol−1 s−1. Ion-pair constants K
ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 104, 3.00 × 102 and 4.02 × 104 mol−1 dm−3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K−1 mol−1) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K−1) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E
a
(kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm3 mol−1 s−1) = (7.079 ± 0.035) × 1016, (1.413 ± 0.011) × 1017, and (9.772 ± 0.027) × 1020 for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions. 相似文献
16.
Jonathan F. Ojo Jide Ige Grace O. Ogunlusi Olanrewaju Owoyomi Esan S. Olaseni 《Transition Metal Chemistry》2006,31(3):337-339
The reactions between Fe(Phen)32+[phen = tris-(1,10) phenanthroline] and Co(CN)5X3− (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm−3 (NaCl/HCl). Plots of k2 versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (ZAZB) for the reactions of Fe(Phen)32+ with the chloro-, bromo- and iodo- complexes respectively. ZAZB of ≈ −2 suggests that the charge on these CoIII complexes cannot be −3 but is −1. This suggests the possibility of protonation of these CoIII complexes. Protonation was investigated over the range [H+] = 0.0001 −0.06 mol dm−3 and the protonation constants Ka obtained are 1.22 × 103, 7.31 × 103 and 9.90 × 102 dm6 mol−3 for X = Cl, Br and I, respectively. 相似文献
17.
Yizhak Marcus 《Journal of solution chemistry》2009,38(5):513-516
In concentrated salt solutions the average distances between the ions, d
av=1.1844⋅(∑ν
i
c
i
)−1/3 nm, are commensurate with the sizes of the solvated ions, so that no ‘bulk solvent’ remains. This is illustrated with two
saturated aqueous solutions, where 16.67 mol⋅dm−3 CsF at 75 °C has d
av(Cs–F)=0.368 nm and 14.54 mol⋅dm−3 LiI at 80 °C has d
av(Li–I)=0.385 nm. The minimal distance required for the bare ions (sum of their radii) are 0.303 nm for CsF and 0.289 nm for
LiI. Hence no water molecule, diameter 0.276 nm, can be fitted between the ions to form linear or slightly bent hydrogen bonds.
Some recent work ignoring such constraints, even in 3–6 mol⋅dm−3 solutions, is criticized on this account. 相似文献
18.
Radhey M. Naik Raj K. Tiwari Pradeep K. Singh Shiv Bali S. Yadav Abhas Asthana 《Transition Metal Chemistry》2008,33(5):615-623
It is observed that Ag(I) catalyzes the rate of substitution of phenylhydrazine (PhNHNH2) into hexacyanoferrate(II), producing a cherry red colored complex, [Fe(CN)5PhNHNH2]3−. The reaction was monitored at 488 nm leading to the formation of the complex under the conditions: [Fe(CN)6]4− (5.0 × 10−3 mol dm−3), PhNHNH2 (2.0 × 10−3 mol dm−3), temperature (25 ± 0.1 °C), pH (2.8 ± 0.02), and ionic strength, I (0.02 mol dm−3), (KNO3). Under optimum conditions, absorbance at fixed times (A
t
) is linearly related to Ag(I) in the concentration range 10.79–97.08 ng cm−3, in the presence of several diverse ions. The highest percentage error and relative standard deviations in the entire range
of Ag(I) determination are found to be 2.5% and 0.16, with a detection limit of 8.75 ng cm−3 of silver(I). The experimental accuracies expressed in terms of percentage recoveries are in the range of 97.87–102.50. The
method was successfully applied for the determination of Ag(I) in a few synthetic samples and found to be in good agreement
with those obtained from atomic absorption spectrophotometry (AAS). The validity of the proposed method has also been tested
for Ag(I) determination in spiked drinking water samples. The present catalytic kinetic method (CKM) is highly sensitive,
selective, reproducible, and inexpensive. A review of recently published catalytic spectrophotometric methods for determination
of Ag(I) has also been presented for comparison. 相似文献
19.
The isoelectric point (IEP) of rutile is shifted to higher pH values in the presence of greater than 10−4 mol dm−3 Ba2+, Ca2+ and Mg2+, and when a critical concentration (5 × 10−4 mol dm−3 for Ba2+ and 1 × 10−3 mol dm−3 for Ca2+) is exceeded there is no IEP at all and the ζ potential is always positive. A common intersection point for the ζ-potential
curves of the different concentrations of salt is found, but for the various salts the point is shifted from ζ = 0 mV for
Mg2+ up to ζ = 20 mV for Ba2+. Between the IEP and the charge-reversal point a rheologically unstable region is discovered. The shear stress of rutile
dispersions (2.5 g rutile + 4 g electrolyte solution) at shear rates of 116 s−1 shows the same pH dependence irrespective of the concentration of alkaline-earth metal cations up to 10−2 mol dm−3. The shear stress is less than 1 Pa below pH 3.8 and in the pH range 5–12 it assumes a value between 50 and 80 Pa at 116 s−1 with some scatter; however, no systematic trend with concentration of alkaline-earth metal cations and a rather insignificant
decrease with pH at pristine conditions are observed. The acidic branch of the yield stress (pH) and low shear rate viscosity
(pH) curves is insensitive to the presence of alkaline-earth metal cations, and the same behaviour is found for the ζ potential.
The alkaline-earth metal cations induce an increase in viscosity in the basic region and a shift in the pH of maximum viscosity
to high pH values. It was also discovered that the effect different alkaline-earth metal cations have on the rheological properties
at the same concentration is different from the effect induced by indifferent electrolytes. When the ζ potential increases
the viscosity at high pH is increased in a series which follows the increase in size of the cation.
Received: 9 September 1998 Accepted in revised form: 12 January 1999 相似文献
20.
P. Vesterbacka S. Klemola K. Salahel-Din M. Saman 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(3):441-448
An intercomparison of the methodology (alpha, beta and gamma spectrometry) used for 238U, 235U and 210Pb determination was carried out based on 38 sediment samples. The activity range of the samples varied from 10–700 Bq/kg
for 210Pb, 1–35 Bq/kg for 235U and 10–800 Bq/kg for 238U. Results obtained using the three methods were not statistically different at high activity levels, but agreement between
the results decreased at lower sample activity levels. For 210Pb, the smallest difference was found between alpha and gamma spectrometry. A good correlation between results from alpha
and gamma spectrometry was observed over the whole activity range. In beta spectrometry, the results were slightly higher
than those obtained by alpha or gamma spectrometry due to the impurity of 228Ra. In 238U analysis, good correspondence was observed between 238U determined by gamma and alpha spectrometry, particularly at higher 238U activity concentrations over 100 Bq/kg. In 235U analysis, attention needs to be paid to interference from 226Ra and its reduction. 相似文献