Interference-free coulometric titration of water in lithium bis(oxalato)borate using Karl Fischer reagents based on N-methylformamide

A non-alcoholic coulometric reagent based on N-methylformamide (NMF) was shown to eliminate the severe interference effect caused by the alcohol component of the conventional Karl Fischer (KF) reagent on the battery electrolyte lithium bis(oxalato)borate (LiBOB). For sample amounts up to 240 μg of water, the stoichiometry of the KF reaction deviated only slightly from the ideal 1:1 ratio for the best reagent composition. Both solid and dissolved (in acetonitrile, tetrahydrofuran (THF), and ethylene carbonate/ethyl methyl carbonate) LiBOB were titrated successfully using a Metrohm 756 KF Coulometer with a diaphragm cell. The detection limit was estimated to be 0.5-1 μg of water using 100 ml of reagent in this system.     

Physico-Chemical Properties of the Most Suitable Spray Reagent for Fluorescence Enhancement in Thin-Layer Chromatography

Abstract

In a fluorescence-enhancing method by spraying with a viscous organic solvent in thin-layer chromatography(TLC), the relationship between fluorescence enhancement and the properties of spray reagents was investigated, using 5-dimethylamino-1-naphthalene-sulfondimethylamide(DNS-DMA) as a fluorescent compound. A stuitable reagent should have two properties of giving high fluorescence intensity to a fluorescent compound and good transmigration from an adsorbent to the reagent medium, i.e., having the large product of relative fluorescence quantum number(RFQN) in the reagent solution and Rf value of the fluorescnet compound in TLC using the reagent as a developing solvent.

A mixture of Triton X-100 and chlofoform(2:8) showed the largest product for DNS-DMA, so that the mixture was expected to be the most suitable reagent, and DNS-amine fluorescences on a plate were enhanced about 100-fold practically. Standard curves for DNS-amines were linear in the range of 1 to 20 pmole per spot. The Triton X-100 mixture also was useful to other DNS-derivatives such as DNS-amino acids and DNS-peptides.

This selection of a suitable spray reagent was also discussed on other fluorescent compounds.     

Extraction and complexation of Cu(II) with undecanoic acid <Emphasis Type="Italic">N,N</Emphasis>-diethylhydrazide

A new reagent, undecanoic acid N,N-diethylhydrazide, was synthesized, and its pK _a1 was determined. The reagent recovers Cu(II) to 99–100% from solutions whose acidity ranges from pH 6 to 1 M NH₃. Copper(II) is extracted in the form of a neutral complex of the composition Cu(II):reagent = 1:2. The reagent is incorporated in the complex in the deprotonated form. An equation for the extraction of Cu(II) from ammonia solutions was suggested. The extraction isotherm was constructred. Ammonium salts, when present in solution, considerably decrease the degree of copper extraction. The reagent is less efficient extractant of copper than N,N-diethylbenzhydrazide.     

Spectrophotometry Determination of Molybdenum with N-Cyanoacylacetaldehyde Hydrazone

N-cyanoacylacetaldehyde hydrazone (CAAH), which is a laboratory synthetic reagent, is proposed as a new reagent for spectrophotometry determination of microamounts of molybdenum at λ_max 790 nm. The reagent forms 1:1 blue coloured complex with molybdenum (VI) in phosphoric acid solution. The stable blue colour is obtained finally after changing from yellow to green. The colour development depends on temperature, time and concentration of phosphoric acid. This reagent is applied for the determination of molybdenum in steel alloys and the results are satisfactory.     

Determination of nickel(II) as the nickel dimethylglyoxime complex using colorimetric solid phase extraction

Colorimetric solid phase extraction (C-SPE) is an analytical technique in which analytes in water samples are extracted onto a solid adsorbent matrix impregnated with a colorimetric reagent and then quantified directly on the adsorbent surface using diffuse reflectance spectroscopy. This paper presents a further development in C-SPE. In this case, the reagent employed to detect the analyte is not impregnated on the extraction medium. Instead, the reagent is weakly immobilized on a solid support (i.e., filter paper) and released into the sample as it flows through the support. The reagent complexes the analyte in solution, forming a highly colored precipitate that is collected on the surface of an extraction membrane. The concentration of analyte is determined using the Kubelka-Munk function calculated from the diffuse reflectance spectrum of the precipitate on the membrane surface. This precipitation-spectrophotometric platform is extensively evaluated by determining nickel(II) using dimethylglyoxime (DMG) as the precipitating reagent. The ability to optimize reaction conditions with immobilized reagents by in-line buffering is also demonstrated. Specifically, borax buffer was utilized to adjust the pH of nickel(II) samples prepared in deionized water. This combination of immobilized buffer and reagent allows C-SPE to operate in a solid-phase mode in which all the reagents requisite for optimal analyte determination are immobilized on solid supports. Using this method, nickel(II) was determined in a single processing step over the concentration range 0.50-5.0 ppm in ∼40 s with 1.0 ml sample volumes.     

Effect of anionic ion-pairing reagent hydrophobicity on selectivity of peptide separations by reversed-phase liquid chromatography

Despite the continuing dominance of trifluoroacetic acid (TFA) as the anionic ion-pairing reagent of choice for peptide separations by reversed-phase high-performance liquid chromatography (RP-HPLC), we believe that a step-by-step approach to re-examining the relative efficacy of TFA compared to other ion-pairing reagents is worthwhile, particularly for the design of separation protocols for complex peptide mixtures, e.g., in proteomics applications. Thus, we applied RP-HPLC in the presence of different concentrations of anionic ion-pairing reagents - phosphoric acid, TFA, pentafluoropropionic acid (PFPA) and heptafluorobutyric acid (HFBA)--to a mixture of three groups of four 10-residue peptides, these groups containing peptides of +1, +3 or +5 net charge. Overall separation of the 12-peptide mixture improved with increasing reagent hydrophobicity (phosphate- < TFA- < PFPA- < HFBA-) and/or concentration of the anion, with reagent hydrophobicity having a considerably more pronounced effect than reagent concentration. HFBA, in particular, achieved an excellent separation at a concentration of just 10 mM, whereby the peptides were separated by charged groups (+1 < +3 < +5) and hydrophobicity within these groups. There was an essentially equal effect of reagent hydrophobicity and concentration on each positive charge of the peptides, a useful observation for prediction of the effect of varying counterion concentration hydrophobicity and/or concentration during optimization of peptide purification protocols. Peak widths were greater for the more highly charged peptides, although these could be decreased significantly by raising the acid concentration; concomitantly, peptide resolution increased with increasing concentration of ion-pairing reagent.     

Direct Monofluoromethylthiolation with S‐(Fluoromethyl) Benzenesulfonothioate

An electrophilic shelf‐stable monofluoromethylthiolating reagent S ‐(fluoromethyl) benezenesulfonothioate ( 1 ) was developed. In the presence of a copper catalyst, reagent 1 coupled with a variety of aryl boronic acids to give the corresponding monofluoromethylthiolated arenes in high yields. In addition, addition of reagent 1 to alkyl alkenes in the presence of a silver catalyst gave alkyl monofluoromethylthioethers in high yields.     

Shift reagent 1H NMR study of methoxycoumarins

The complete assignment of the proton chemical shifts of coumarin ( 1 ), all monomethoxy derivatives and the six possible dimethoxyl substituted compounds at the aromatic ring was achieved at 60 MHz in a quantitative study utilizing Pr(fod)₃ as the shift reagent. It was found that in addition to the complexation at the lactone carbonyl a second interaction of the lanthanide shift reagent occurs when two methoxyl groups are found in an ortho distribution. The results are discussed in comparison to data published for flavones in the presence of Pr(fod)₃ shift reagent.     

CE Determination of 2-(9-Carbazole)ethyl Chloroformate-Labeled Oligopeptides

A pre-column derivatization method for sensitive determination of oligopeptides, using the tagging reagent 2-(9-carbazole)ethyl chloroformate (CEOC-Cl) followed by capillary electrophoresis (CE) with diode-array detection, has been developed. Maximum yield close to 100% were observed when a three to fourfold molar excess of reagent was used at pH 9.0–10.0. Excess reagent was extracted with n-hexane–ethyl acetate 9:1–10:1 (v/v); this enabled direct analysis using CE with no significant disturbance from the major fluorescent reagent degradation by-products. The effects on the results of buffer pH and of SDS and organic modifier concentrations were examined. Good baseline resolution in the separation of five CEOC-peptides was achieved with a 48.5-cm total length (effective length 40 cm) 50-μm inner diameter capillary column.     

A bench-stable reagent for C-4 selective deuteriodifluoromethylation of azines

Deuteriodifluoromethyl (CF₂D) is a challenging and important functional group due to difficult deuterium incorporation and lack of effective precursor reagents. Herein, we report a bench-stable reagent, deuteriodifluoromethyl phosphine (DDFP) from cheap deuterium source for selectivity deuteriodifluoromethylation of azines with a high deuterium incorporation yield. The late-stage modification of complex molecules further confirmed the potential of this reagent for practical applications. We expect that our reagent to find applications in synthesis of isotope-labelled molecules of interests for drug-discovery and related ilucidation of mechanism of action.     

Transition-metal chloride mediated addition reaction of diorganomagnesium to easily enolizable ketones

An alkylation to an easily enolizable ketone, such as β-tetralone, is difficult to perform with Grignard reagent (RMgX) or with diorganomagnesium (R₂Mg), because a deprotonation to form a magnesium enolate occurs predominantly. To avoid the prior enolization, a complex reagent of a transition-metal salt and R₂Mg was examined: A combination of R₂Mg with iron(II) chloride (FeCl₂) or ytterbium(III) chloride (YbCl₃) gave a complex reagent that can realize a nucleophilic reaction to β-tetralone prior to the enolization. A combination of RMgX with these metal salts is inferior to a combination of R₂Mg with them to obtain the nucleophilic complex reagent.     

新荧光试剂双(2-苯并噻唑重氮氨基)-3,3′,5,5′-四甲基联苯的合成及其分析应用

将3,3′,5,5′-四甲基联苯胺和苯并噻唑类试剂结合, 并引入杂环三氮烯结构, 合成了新荧光试剂双(2-苯并噻唑重氮氨基) 3,3′,5,5′-四甲基联苯(BBTDTMB), 其结构经红外光谱、 核磁共振谱和元素分析证实. 研究结果表明, 在碱性介质中, 该试剂在λex/λem=342 nm/420 nm处产生强荧光, 并且Ag(Ⅰ)对其荧光有很好的猝灭作用, 因而建立了BBTDTMB测定Ag(Ⅰ) 的新荧光分析方法. 该方法的线性范围为1.0～240 μg/L, 检测限为 0.5 μg/L, 应用于人发、 茶叶中的Ag(Ⅰ) 的测定, 结果令人满意.     

An investigation of the applicability of 2,2'-dianthrimide in spectrophotometry: The determination of selenium(IV)

2,2'-Dianthrimide was studied as an analytical reagent and compared with the properties of 1,1'-dianthrimide. While 1,1'-dianthrimide reacts with B, Ge, Se and Te, 2,2'-dianthrimide was found to react only with selenium(IV).A straight line calibration curve is obtained up to 50 μg of selenium under the optimum conditions but the value of 2,2'-dianthrimide as a reagent for selenium(IV) is reduced by the high absorption of the reagent itself.     

The use of a new,modified Dittmer–Lester spray reagent for phospholipid determination by the TLC image analysis technique

A new phospholipid‐specific spray reagent is described. A new phospholipid‐specific spray reagent, which is a modification of the Dittmer–Lester reagent, is described in authors' studies. The difference between these two reagents is in the addition of tin (II) chloride to the proposed spray reagent. The use of the described spray reagent together with an image analysis technique allows not only for qualitative, but also for quantitative, determination of major phospholipid classes. Separation of phosphatidylserine (PS), phosphatidylethanolamine (PE) and phosphatidylcholine (PC) was conducted on an HPTLC plate with a mixture of chloroform, methanol and 25% ammonia solution in a volume ratio of 65:25:4 as mobile phase. The calibration curves were linear in the ranges of 5.0–25.0, 1.5–15.0 and 1.0–20.0 µg/spot for PC, PS and PE, respectively. The use of the new spray reagent resulted also in lower limits of detection than the standard molybdenum method for the investigated phospholipids. The proposed method was used to determine the amount of PS in the dietary supplement ‘Session’, and of PS, PE and PC in biological samples, with good results. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of a titanium(IV)–porphyrin complex as a highly sensitive and selective reagent for the determination of hydrogen peroxide: a computational chemistry approach and a critical review

The Ti–TPyP reagent, i.e. an acidic aqueous solution of the oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato] titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for determination of traces of hydrogen peroxide. Using this reagent, determination of hydrogen peroxide was performed by flow-injection analysis with a detection limit of 0.5 pmol per test. The method was actually applied to determination of several constituents of foods, human blood, and urine mediated by appropriate oxidase enzymes. The reaction specificity of the TiO(tpyp) complex for hydrogen peroxide was clarified from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. The results provided a well-grounded argument for determination of hydrogen peroxide using the Ti–TPyP reagent experimentally. This review deals with characterization of the high sensitivity and reaction specificity of the Ti–TPyP reagent for determination of hydrogen peroxide, to prove its reliability in analytical applications. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The synthesis of fluorinated α-pyrans via fluorinated vinylcopper reagents

Fluorinated vinylcopper reagents were prepared in situ via reaction of fluorinated vinylbromides or iodides with cadmium or zinc powder followed by metathesis with Cu(I)Br. Hexafluoro-2-butyne was then added to the solution of the F-vinylcopper reagent which resulted in a stereospecific syn addition of the F-vinylcopper reagent to the alkyne to provide in situ the corresponding dienylcopper reagent. Subsequent acylation of the dienylcopper reagent gave a dienylketone, which spontaneously cyclized to the 2H-pyran. This methodology provides a useful one flask route to fluorinated 2H-pyrans.     

N-p-chlorophenylcinnamohydroxamic acid: A new reagent for the microgram determination of vanadium(V)

A new reagent, N-p-chlorophenylcinnamohydroxamic acid, for the rapid solvent extraction and spectrophotometric determination of microgram quantities of vanadium(V) is reported. Vanadium(V) is extracted from a chloroform solution of the reagent, N-p-chloro-phenylcinnamohydroxamic acid, with 4–8 M HCl. The bluish violet extract has maximum absorbance at 545 nm. The extract obeys Beer's law at 545 nm, and the sensitivity of the reagent is 0.008 μg V/ml. The complex is stable for several days. The effects of acidity, reagent concentrations, and diverse ions are discussed.     

1H and 13C NMR studies of binuclear lanthanide(III):—silver(I) shift or relaxation reagents: Competition between several bonding sites in olefinic,aromatic and heteroaromatic compounds

The relative abilities of weak Lewis bases to complex binuclear lanthanide(III)—silver(I) reagents were checked by inter- or intra- molecular competitions. Preferential complexation at one particular site was shown to be determined mainly by the occurrence of well localized π electrons, by the relief of strain effects or by the lack of steric hindrance. In benzofuran and methoxybenzene derivatives oxygen never interacts directly with the silver reagent and plays a role mainly through electronic effects. Unlike oxygen, sulphur in benzo[b]thiophene is the preferred site of complexation with the silver reagent. On complexation with binuclear shift reagents (lanthanide = Eu, Pr, Yb) the ¹H NMR shifts were shown to result from several mechanisms. Better insight into the precise location of the reagent is obtained in ¹³C NMR by the use of the binuclear relaxation reagent Ag(tfa)-Gd(fod)₃.     

Studies on the extraction of Copper(II) with 4-alkyldithiocarboxylate derivatives of 1-phenyl-3,5-dioxopyrazolidine

The extraction behaviour of copper(II) from acid solutions (pH 0-6) was studied with the new reagent 4-alkyldithiocarboxylate-3,5-dihydroxy-l-phenylpyrazol (HL; alkyl = n-butyl, n-dodecyl). The species extracted was found to be ML(2). The reagent was used to separate copper(II) from iron(III) in an acidic lixiviation solution of a mineral sample composed of enarguite (Cu(3)AsS(4)) and pyrite (FeS(2)). Additionally, the extraction efficiency of this new reagent was compared with the commercially available LIX 984 N extradant of copper (II).     

Palladium(II) Extraction from Hydrochloric Acid Solutions with 4-[(Hexylsulfanyl)methyl]-3,5-Dimethyl-1H-Pyrazole

Palladium(II) extraction from hydrochloric acid solutions with a novel weakly basic complexing reagent, 4-[(hexylsulfanyl)methyl]-3,5-dimethyl-1H-pyrazole, dissolved in chloroform was studied. Palladium(II) was found to be highly efficiently extracted from 0.1–3 mol/L HCl solutions. A coordination mechanism of palladium(II) extraction with a protonated form of the reagent via fast interphase transfer of ion associates was proposed. The composition of the extracted compound, [PdCl₂μ-L]_n (n > 2), was found, and the way of coordination of the reagent to metal ions through N(2) nitrogen atom and thioether sulfur atom was determined. The reagent can be recommended for concentrating palladium(II) and selectively separating it from platinum(IV), copper(II), nickel(II), and iron(III).