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1.
On the basis of the electronic absorption spectra it was found that 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone exists in acidic solutions in mono- and diprotonated forms. It was established by means of calculations by the Pariser—Parr—Pople (PPP) method that in the neutral and protonated forms the quinone hydrazone tautomer of the phenylazopyrazolone is more stable than the azo tautomer, and it was determined that the protonation center is the N(2) atom of the pyrazolone ring. The diprotonated form is most likely the quinone hydrazone tautomer protonated at the heteroring N(2) atom and the -nitrogen atom of the azo group. In an alkaline medium the phenylazopyrazolone exists in the form of an anion with predominance of the azo form. The effect of substituents ion the diazo component of the phenylazopyrazolone on the long-wave bands of the electronic absorption spectra in various media was explained on the basis of calculation of the distribution of the -electron density during electron transitions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1331–1336, October, 1991.  相似文献   

2.
Five closed-vessel microwave digestion methods were compared for the accurate determination of arsenic and selenium in NIST SRM 1645 River Sediment by flow-injection hydride-generation atomic absorption spectrometric methods. The digestion methods using five different acid mixtures (HNO3/ H2SO4, HNO3/HCl04, HNO3/HCl, HNO3/HCl/HF, HNO3/H2SO4/HClO4) were all found to be reliable for the determination of the analytes. Taking into consideration the safety and suitability for the analysis of other metals, the methods based on the use ofaqua regia are recommended for closed vessel microwave digestion with pressure control. Using the quick digestion program, the presence of up to 10% organic content in soil samples did not adversely affect the closed vessel digestion and did not cause the loss of volatile analytes. After digestion, opening the vessel under an inner pressure of below 345 kPa (50 psi) had no effect on the accuracy of the results. The recommended digestion methods (HNO3/HCl and HNO3/ HCl/HF) for the reliable determination of arsenic and selenium in different sediment samples were demonstrated. The calculated detection limits (3 b ) were less than 0.030 g/g and 0.033 g/g for arsenic and selenium, respectively. All analytical results for arsenic and selenium in SRM 1645 River sediment, NRCC BCSS-1 Marine Sediment and NIES CRM Pond Sediment were within or near the certified and reported ranges, with the exception of selenium in NIES CRM No. 2 Pond Sediment.  相似文献   

3.
An extraction-spectrophotometric method for the determination of trace amounts of iron based on its extraction into chloroform with 2-(2-benzothiazolylazo)-4,6-dimethylphenol (BTADMP) from a pH 6.5 medium has been developed. The extracted 12 FeBTADMP complex species allow the determination of 4–30gmg of iron (=3.92×1041·mol–1·cm–1 at 790 nm). The method is highly selective and has been applied to the determination of iron in polymineral-polyvitamin pharmaceutical products.  相似文献   

4.
In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 g ml–1, for an analytical curve of 18.8 ng ml–1 to 2.40 g ml–1, molar absorptivity of 2.80 × 104 1 mole–1 cm–1 and a detection limit of 5.5 ng ml–1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 g of vanadium(V) do not interfere with determination of 5.00 g of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).  相似文献   

5.
A neutron activation analysis method for the determination of Se(IV) in natural waters is described. It is based on the coprecipitation of the metal dibenzyldithiocarbamate with phenolphthalein. The precipitate is collected on 0.45 m membrane filters and selenium is determined by instrumental neutron activation. A Se(IV) radiotracer (75Se, T=120 d) was used to establish optimum conditions and to evaluate the chemical yield. Samples of sea and canal water were analyzed.  相似文献   

6.
Zusammenfassung Thiolutidinsäure-N,N-dimethylamid (TLSMA) bildet bei pH 14 ein violett gefärbtes Eisen(II)chelat mit hohem molarem Extinktionskoeffizienten. Das Reagens ist sehr empfindlich und hat in saurem Milieu reduzierende Eigenschaften. pH-Abhängigkeit, zeitlicher Verlauf der Komplexbildung und die Zusammensetzung des Chelats wurden untersucht. Ein Verfahren zur spektralphotometrischen Bestimmung von Eisenspuren (0,04–4g/ml) wurde beschrieben.
Thiolutidinic acid-N,N-dimethylamide as sensitive iron reagent
Summary At pH 14, thiolutidinic acid-N,N-dimethylamide yields a violet iron(II)-chelate with a high molar extinction coefficient. The reagent is very sensitive and has reducing properties in acid milieu. Its pH-dependence, the relation of time to the complex formation and the composition of the chelate were investigated. A procedure for the spectrophotometric determination of traces of iron (0.04 to 4g/ml) is decribed.


Herrn Prof. Dr. Erich Ziegler zum 60. Geburtstag gewidmet.  相似文献   

7.
A method for the determination of Fe(III), Co(II) and Cr(III) by flame atomic absorption spectrophotometry (FAAS) after preconcentrating on a column containing S. carlsbergensis immobilized on Amberlite XAD-4 has been developed. The optimum values of pH, amount of adsorbent, elution solution and flow rate of the sample solution were determined for the quantitative recovery of the analytes. The effect of interfering ions on the recovery of the analytes was also investigated. Under the optimum conditions, recoveries of Fe(III), Co(II) and Cr(III) by S. carlsbergensis immobilized on Amberlite XAD-4 were 99±2, 100±2 and 98±2% at 95% confidence level, respectively. The limit of detections for Fe(III), Co(II) and Cr(III) were 2.8, 3.9 and 7.4ngmL–1, respectively. The proposed method was applied to the determination of the analytes in various water samples. The validity of the method was checked with spiked water samples. Fe(III), Co(II) and Cr(III) was determined with a relative error of less than 5%.  相似文献   

8.
The influence of pH on the oxygen-dependent step observed during the iron(III)-catalyzed autoxidation of sulfur(IV)-oxides was studied over the pH range 1.5 pH 4. A maximum decomposition rate of the iron(III)-sulfito complexes is observed around pH 2.3. The pH- time profile for the iron(III)-catalyzed autoxidation of sulfur(IV)- oxides exhibited no dependence on the initial [O2] when the reaction is initiated at pH 6.1, but shows an oxygen dependence when the reaction is initiated at pH 2.5. pH-shift experiments clearly demonstrate the reduced catalytic activity of dimeric and polymeric iron(III) hydroxo species. A decrease in the catalytic activity of the iron(III) solutions with time was observed, which depended on the initial pH. This decrease was ascribed to the formation of dimeric and polymeric iron(III) hydroxo species as a result of slow hydrolysis processes during aging. The employed iron(III) salt had no effect on the decrease in the catalytic activity due to aging.  相似文献   

9.
Conclusions The conditions for the spectrophotometric and atom-absorption determination of selenium-(IV) when based on ferricenium cation were studied. The sensitivity of the atom-absorption determination of selenium when based on ferricenium ion is 0.04 g/ml per 1% of absorption, which is more than 5 times more sensitive than the direct determination of selenium [3].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 921–923, April, 1979.  相似文献   

10.
A novel High Performance Liquid Chromatography (HPLC) method for the separation of selenium species with specific detection by off-line Electrothermal Atomization Atomic Absorption Spectrometry (ETAAS) or on-line focused microwave digestion (MW) Hydride Generation Atomic Absorption Spectrometry (HG-AAS) is described. Vesicular mobile phases of the cationic surfactant didodecyldimethylammonium bromide (DDAB) have been evaluated for the liquid chromatographic separation of inorganic selenium (selenite and selenate) and different selenoaminoacids (selenocystine, selenomethionine and selenoethionine) on a C18 reversed-phase column modified by DDAB molecules. The effects of different parameters (pH, buffer and vesicle concentrations) of the mobile phase on the retention times have been determined. The detection limit for selenium with the proposed off-line HPLC-ETAAS method has been found to be 5 g/L of Se. The detection limit using HPLC-on line focused microwave digestion-HG-AAS has been found to be 1 g/L of Se, with a precision (repeatability) better than ± 5%. The latter proved to be an exceptional on-line real-time chromatographic detector for selenium speciation purposes.  相似文献   

11.
Summary We have previously described a normal-phase HPLC method for the simultaneous determination of , , and tocopherol, thecis andtrans isomers of retinol, and total carotenes in different Italian cheeses and milk. In this paper we describe a reversed-phase HPLC method using solely methanol as the mobile phase for the determination of -tocopherol, -+-tocopherols, total retinols, cholesterol, -sitosterol, campesterol and stigmasterol, and - and -carotene. The method developed has been applied to some new dairy products such as natural Quark, with olive, basil or banana and to processed cheese with tomato and the results have been compared with the corresponding results obtained by the normal-phase method. The conclusion is that more complete evaluation of the tocopherol, retinol, carotene and sterol content of dairy products, especially when vegetables and fruits are present, is necessary and can be obtained using both the normal- and reversed-phase HPLC methodologies.  相似文献   

12.
Effect of substituent in the para position with respect to the diazo group in diazotized orthanilic acid derivatives on the rate and selectivity of azo coupling with 7-acetylamino-4-hydroxynaphthalene-2-sulfonic acid was studied in citrate-phosphate buffers. The selectivity of azo coupling at the 3-position of the azo component almost does not depend on the nature of electron-donor substituent. Electron-acceptor groups considerably reduce the selectivity of formation of the 3-isomer. Previous conclusions, according to which the rate-determining stages are different depending on the site of azo coupling of diazotized orthanilic acid with 7-acetylamino-4-hydroxynaphthalene-2-sulfonic acid, were found to be also valid for some 5-substituted orthanilic acid derivatives. The rate-determining stage in the azo coupling at the 3-position can change upon introduction of strong electron-acceptor substituents capable of interacting with the diazo group. The contribution of the multicenter mechanism of deprotonation of the -complex with participation of water molecules was presumed to increase in going to the diazo components having electron-donor substituents.  相似文献   

13.
A controlled potential coulometric method for the determination of uranium in the presence of iron or plutonium using a platinum working electrode has been developed. The method consists of reduction of uranium in 8M H2SO4 by Ti(III) followed by destruction of excess Ti(III) and selective oxidation of Fe(II) or Pu(III) to Fe(III) or Pu(IV), respectively, by sodium nitrite. The U(IV) is subsequently determined by electrolytic oxidation at Pt electrode using Fe(III) as an intermediate. The method was employed for the determination of uranium in synthetic mixtures of U+Fe and U+Pu containing varying ratios of U/Fe or U/Pu. The precision obtained for uranium results was ±0.25%.  相似文献   

14.
Zusammenfassung Es wird ein papierchromatographischer Nachweis beschrieben, wonach Selenit als blauer und Selenat als orangeroter Fleck entwickelt werden. Die Methode ist besonders zur Erkennung kleiner Mengen Selen(IV) neben viel Selen(VI) geeignet (11000). Die Nachweisgrenze liegt bei 0,2 g SeIV bzw. 2,0 g SeVI. Der Nachweis kann mit entsprechend geringerer Empfindlichkeit auch als Tüpfel- oder Fällungsreaktion ausgeführt werden.Zum Zwecke der quantitativen Bestimmung werden die Selenverbindungen mit Wasser aus dem Chromatogramm extrahiert, nachdem Selenat durch gasförmiges HCl vorher zu Selenit reduziert worden ist. Nach Zugabe von Kaliumjodid wird der Selengehalt der Lösungen photometrisch bestimmt. Die dabei erhaltenen Werte stimmen gut mit den Resultaten der Analyse im Makromaßstab überein. Die beschriebene Methode empfiehlt sich dort, wo Fremdsubstanzen die üblichen Bestimmungsverfahren für Selenit und Selenat nebeneinander stören.
Summary A paper-chromatographic detection is described, by which selenite is developed as a blue and selenate as an orange-red spot. This method is especially suitable for the detection of small amounts of selenium(IV) in the presence of large amounts of selenium(VI) (11000). The detection limit is 0,2 g of SeIV and 2,0 g of SeVI, respectively. The reaction may also be carried out as a spot test or a precipitation with a correspondingly lower sensitivity.For the purpose of determination the selenium compounds are extracted from the paper by water; selenate is reduced to selenite by gaseous HCl before. After addition of KI the selenium content of the solutions is determined by photometric measurements.The values obtained are in good agreement with the results of quantitative analysis in macro scale. The method described is well suitable, if foreign substances interfere with the usual determination of selenite and selenate in the presence of each other.
  相似文献   

15.
Monomers which contain unsaturated linkages and amine groups have been intercalated to form either mono- or bi-layers. The monomertrans-N,N-diethyl-2-butene-1,4-diamine (NNBD) has been intercalated into -tin(IV) hydrogen phosphate. The guest molecule, NNBD, forms a monolayer (d 001 = 1.35 nm) in which the amine groups are paired to protons on opposite faces of the phosphate layers. The resultant compound has the formula Sn(C8H18N2)0.73(HPO4)2·H2O indicating that NNBD does not cover a large proportion of the available protons. 4-vinylpyridine slowly forms an intercalate in which the host molecule forms a bilayer (d 001 = 1.56 nn). However, with 4-vinylpyridine there is surface modification in preference to intercalation.  相似文献   

16.
Summary Spectropbotometric Determination of Trace Amounts of Iron(III) by Extraction of Mixed-Ligand Iron-Tartrate-Purpurin or Iron-NTA-Purpurin Complex A selective method is described for the determination of microgram amounts of iron(III) by means of its reaction at pH 9.0 with purpurin (1,2,4-trihydroxyanthraquinone) and tartrate or NTA and extraction into methyl isobutyl ketone. The molar absorptivity of the 112 iron(III)-auxiliary ligand-purpurin complex is 4.8×104 1·mole–1·cm–1 at 595 nm. Beer's law is obeyed from 0.05 to 0.25 ppm of iron in the aqueous phase. Procedures for determination of iron in tartrate or NTA medium, and fluoride-tartrate-NTA medium are given. The method is suitable for determining iron in Zn metal, W metal, NTA, drinking water, wines, urine and tartrates.  相似文献   

17.
5-Cyano-6-(-dimethylamino)vinyl-1-methyl-4-pyrimidinone was synthesized by the interaction of -cyano--(N-methylamino)crotonamide with N,N-dimethylformamide diethylacetal. Recyclization of the product in alkaline medium leads to 3-cyano-4-methylamino-2-pyridone. Nitration of the latter and transformation of the nitropyridone by boiling in POCl3 gave 2-chloro-3-cyano-4-methylamino-5-nitropyridine. This is a key compound for various transformations including the synthesis of derivatives of dipyrido[1,2-a:3,2-e]pyrimidine, thieno[2,3-b]pyridine, and (2-pyridylamino)polyene derivatives.  相似文献   

18.
Summary Mixed-ligand complexes formed by reaction of Cu(ClO4)2 with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (dppt) as primary ligand and 2,2-bipyridine (bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp), N,N-bis(pyrid-2-ylmethyl)amine (dipica), N,N-bis(benzimidazol-2-ylmethyl)amine (bba), 1,3-bis(2-benzimidazolyl)-2-thiapropane (bbms) and 1,5-bis(benzimidazolyl)-3-thiapentane (bbes) as the secondary ligands have been isolated. They are of the type [Cu(dppt)L](ClO4)2·nH2O, where n = 0 or 2. All complexes exhibit only one ligand field band and their cryogenic solution e.p.r. spectra are axial, with vmax and g values diagnostic of a square-based geometry. The spectral and redox data are consistent with facial coordination of the tridentate ligands. All the complexes exhibit a positive redox potential (versus n.h.e.). The weak -bonding of dppt, caused by the highly electron-withdrawing phenyl rings, the strong -back bonding involving phen and dmp, and interligand repulsions appear to be responsible for the relatively positive CuII/CuI redox potentials.  相似文献   

19.
Summary Ultramicro amounts of selenium in sulphuric acid are determined by a new atomic absorption spectrophotometric method. Selenium(IV) is directly determined ater extraction into toluene with an aromatic o-diamine and addition of nickel(II) prior to atomization; the determination of total selenium (0, IV and VI) needs a treatment of the sample with selected oxidizing and reducing agents.In the studied samples, total selenium (0.003–0.022 g of Se in 1 ml sulphuric acid) is present only in the tetravalent state. The detection limit of the method is 0.003 g of selenium.
Atomabsorptions-spektralphotometrische Bestimmung von Ultramikromengen Selen(IV) und Gesamtselen in Schwefelsäure
Zusammenfassung Selen(IV) kann direkt bestimmt werden nach Toluolextraktion der mit einem aromatischen o-Diamin behandelten Lösung und Zusatz von Nickel(II). Die Bestimmung von Gesamtselen (0, IV, VI) erfordert eine Vorbehandlung mit Perchlor- bzw. Salpetersäure und Wasserstoffperoxid. Die Nachweisgrenze des Verfahrens beträgt 0,003 g Se. In den untersuchten Proben war das Gesamtselen (0,003–0,022 g/ml) nur als Se(IV) vorhanden.
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20.
《Analytical letters》2012,45(17):1913-1925
Abstract

The electrochemical behaviour of the R-nitroso salt in 0.5 M HAc/NaAc at pH 4.7 is studied by cyclic voltammetry. The compound shows a very sharp reduction peak at -0.37 V vs SCE giving the corresponding amine derivative. The height of the peak is shown to be inversely proportional to the iron (II) concentration of the solution. A linear calibration plot is obtained between 0 and 56 ppm of iron (II) using, initially, 4.0 mM solution of the salt. A simple and fast procedure was developed for the analysis of standard samples of ferrous iron.  相似文献   

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