A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline

Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R =- H,- CH₃, - OCH₃, - Cl, - CN, - OH and - NO₂), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l^–1 KH₂PO₄ with methanol (4+6) or acetonitrile (7+3), or a mixture of water, methanol, acetonitrile and 80% H₃PO₄ (200+200+200+3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10^–6 mol l^–1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10^–5 mol l^–1) but it can be used for selective detection of 4-NO₂-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH₃-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH₃-NMA and 4-NO₂-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.     

Ion-exchange chromatography using vanadyl and vandate salts as mobile phases with indirect detection

Summary Vanadyl sulfate, VOSO₄, was characterized as the mobile phase for the ion exchange separation of Li⁺, Na⁺, NH ₄ ⁺ , and K⁺ using indirect photometric detection at 254 nm. Detection limits ranged from 0.2 ppm for Li⁺ to 1 ppm for K⁺. Indirect electrochemical detection of these separated cations by reduction of VO (II) to V³⁺ was compared to spectrophotometric detection. The potential of the vanadate species, HVO ₄ ^2– , for the separation of F^–, Cl^–, and SO ₄ ^2– , with indirect photometric detection was also demonstrated.     

Spectrophotometric determination of thiosulfate and tetraphenylborate ions through ligand exchange reaction at solid surface

Summary A Spectrophotometric method is presented for the microanalysis of analytically important thiosulfate and tetraphenylborate anions in an aqueous solution. The method is based on ligand exchange in a dynamic approach incorporating a solid reagent mercuric chloranilate. The common cations Na⁺, K⁺, Al³⁺, Ca²⁺, and Mg²⁺ do not interfere and the anions CH₃COO^–, C₂O₄ ^2–, SO₄ ^–, C₃H₄OH-(COO)₃ ^3– and NO₃ ^– do not cause any adverse effects. The heavy metals Pb²⁺, Cd²⁺, Fe²⁺, Cu²⁺, and Zn²⁺ cause a negative interference while the halogens and SCN^– type of anions give a positive interference. The method is sensitive up to 5 ppm of tetraphenyl-borate anion and 10 ppm of the thiosulfate anion.

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Zusammenfassung Ein spektrophotometrisches Mikroverfahren zur Bestimmung von Thiosulfat und Tetraphenylborat in wäßriger Lösung wurde angegeben. Es beruht auf dem Ligandenaustausch mit Hilfe von Quecksilberchloranilat. Die üblichen Kationen Na, K, Al, Ca und Mg stören nicht; auch die Anionen Acetat, Oxalat, Sulfat, Zitrat und Nitrat haben keinen störenden Einfluß. Die Schwermetalle Pb(II), Cd, Fe(II), Cu(II) und Zn verursachen negative Fehler, die Halogene, Thiocyanat und dgl. haben positive Fehler zur Folge. Die Methode ist empfindlich bis zu 5 ppm Tetraphenylborat und 10 ppm Thiosulfat.

     

Separation of inorganic anions by reversed-phase ion-pair chromatography with direct UV detection

In this paper, a separation method of the inorganic anions including I^–, NO ₂ ^– , NO ₃ ^– , IO ₃ ^– and SCN^– on the reversed-phase ion-pair chromatography with direct UV detection has been developed, and the limits of detection of these inorganic anions were determined. The effects of the organic modifier volume fraction and concentration of the ion-pair reagent on the retention of inorganic anions were discussed.     

Correlation ion chromatography with indirect UV detection

Summary A binary pseudo-random injection of a sample containing low concentrations of common anions into the anion exchange column was used to enhance the signal-to-noise ratio of indirect UV detection of the ions. The detection limits obtained in our experiment (14 ppb, 14 ppb, and 64 ppb for Cl^–, NO ₃ ^– and SO ₄ ^2– respectively) are in good agreement with theoretical predictions. The large amplitude system peaks inherent to single column IC do not generate remarkable ghost peaks, which is indicative of the suitability of the input devices used in our studies.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Mixed-mode liquid chromatography of aliphatic anionic surfactants with a naphthalenetrisulfonate mobile phase

Summary Separation of three classes of anionic surfactants (alkyl sulfates, alkanesulfonates, and alkyl phosphates) are achieved on a mixed-mode reversed phase (RP) phenyl/-anion exchange column using a naphthalenetrisulfonate (NTS)-acetonitrile (ACN) mobile phase via indirect photometric, indirect fluorometric, direct or indirect conductivity detection. Mixtures of C₅–C₁₈ sulfates, C₆–C₁₈ sulfonates, and C₁–C₄ phosphates (mono- and di-ester) can be separated in less than 20, 24, and 20 min respectively. Although hydrophobic effects are more pronounced in mixed-mode chromatography, equivalent-per-equivalent exchange of analysis and eluent ion is still required for sensitive indirect photometric, fluorometric, or conductivity detection. The detection limits of alkyl sulfates and alkanesulfonates are in the range of 3–15 pmoles which are at least an order of magnitude better than suppressed conductivity detection. The determination of surfactants in a variety of real samples is also presented.     

Influence of Anions on Electrochemical Properties of Polypyrrole-Modified Electrodes

The influence of anions ClO₄ ^–, NO₃ ^–, Cl^–, SO₄ ^2–, and DDS^– (dodecyl sulfate) on the cyclic voltammetric response of polypyrrole-modified electrodes is studied. The change in the film composition is examined by electron probe microanalysis. It is established that essential changes in the shape of voltammograms take place during cycling if the anions are not sufficiently freely mobile in the polymer film and insertion of cations from the solution is necessary to guarantee electroneutrality of the system. Some differences between the mobility of Cl^– ions and ClO₄ ^– or NO₃ ^– ions are in good agreement with the results of semi-empirical quantum chemical calculations showing that the interaction of Cl^– and Br^– ions with pyrrole oligomers is stronger than that of NO₃ ^– or ClO₄ ^– ions. Nevertheless, it is established that the peak current determined from voltammograms increases linearly with the increase of the scan rate with very high correlation coefficient. It means that it is possible to describe the behavior of ClO₄ ^–, NO₃ ^– and Cl^– ions in the framework of the model of free ions. The redox behavior of the PPy films doped with anions of low mobility such as SO₄ ^2– and DDS^– depends essentially on the nature of cations in the test solution. It is found that the mobility of cations increases in the row Li⁺ < Na⁺ < K⁺ < Cs⁺. The mobility of DDS^– ions in the PPy in ethanolic solution is significantly higher and their electrochemical properties are quite similar to PPy|Cl or NO₃ ^– film in aqueous solution.     

A study of HPLC separation and spectrophotometric and voltammetric detection of 4′-substituted derivatives of 3-carboxy-4-hydroxy-6-acetylaminoazobenzene

 Optimised conditions have been found for the separation of 3-carboxy-4-hydroxy-6-acetylaminoazo-benzene derivatives substituted in the position 4′ (4′-R-CHAAB, where R=–H, –CH₃, –OCH₃, –Cl, –COCH₃, –NO₂ and –NHCOCH₃) using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of 0.01 mol/L NaH₂PO₄ at pH 4 with methanol (1+1), 0.01 mol/L NaH₂PO₄ at pH 2 with acetonitrile (1+1) or 1% aqueous acetic acid with methanol (4+6). UV photometry is the most universal detection technique and yields limits of detection around 10^-6 mol/L. Direct anodic voltammetry on a glassy carbon fibre array detector yields lower limits of detection for –COCH₃ derivatives and higher limits of detection for –NO₂ and –NHCOCH₃ derivatives. When the analytes are chemically reduced using zinc powder in acetic acid, the voltammetric detection has limits of detection one order of magnitude lower than those obtained UV photometrically. Received: 27 June 1996/Revised: 25 October 1996/Accepted: 3 November 1996     

Dye-coated stationary-phases: A retention model for anions in ion-interaction chromatography

Summary The separation of inorganic anions (NO₃ ⁻, NO₂ ⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻, S₂O₃ ²⁻) by ion-interaction chromatography mediated with a specific dye has been investigated. Chromatography was performed on a LiChrospher RP-18 colum dynamically coated with crystal violet, using acetonitrile-water buffered with phthalate as the mobile phase. The presence of the dye in the eluent enabled indirect spectrophotometric detection of the analytes, which have no significant UV absorption. Retention data were collected for the different anions by varying the composition of the mobile phase according to a full factorial experimental design. A theoretical model for the retention of singly- and doubly-charged analytes, on the basis of the two main processes of ion-exchange and ion-pair formation, has been proposed and validated with the experimental data.     

Determination of inorganic anions in mushrooms by ion chromatography with potentiometric detection

A simple method for determination of common inorganic anions in mushroom samples has been developed by using suppressed ion chromatography with a pH detection unit. The detection unit which was constructed in such a way that practically no additional dispersion occurred consisted of a flow-through quinhydrone pH sensor and a small reference electrode. Chromatographic separation was performed in the order F⁻, Cl⁻, NO₂⁻, Br⁻, PO₄³⁻, ClO₃⁻, NO₃⁻, and SO₄²⁻, at room temperature by using Ion Pac AS 9-HC anion exchange column. Anion extracts from dried mushroom samples at room temperature were homogenized and filtered before injection. Under optimized analytical conditions, the detection limits of the method were between 2 × 10⁻⁶ and 3 × 10⁻⁴ M, depending on the anion studied. The results showed that the concentrations of fluoride and bromide in all mushroom samples were below their limit of detection. Nitrite was found to be the lowest abundant ion, while the most abundant ion was sulfate in all the mushroom samples studied.     

1, 2-Dithiolium salts

4-(p-Tolyl)-1,2-dithiolium hydrogen sulfate (I) is not a specific analytical reagent for the majority of anions, and it is not very selective, only in a few cases attaining pD=5 (MoO₄ ^2–, [Hg(CNS)₄]^2–, and [PtCl₆]^2–). All strongly colored anions give colored salts with I. Among the weakly colored anions, the [Fe(CN)₆]^4– anion is worthy of special note, since it forms a deeply colored salt with I. This anion can be detected with I in the presence of Cl^–, Br^–, I^–, CNS^–, ClO₄ ^–, IO₄ ^–, and ReO₄ ^–, which form fairly readily soluble salts with I. Compound I is also a fairly selective reagent for Pd²⁺ in acid solution (pD=5).For part II, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 595–597, May, 1970.     

Identification and Separation of Some Anions on Plain and Mixed Adsorbent Layers Using Water as Eluent

The analytical potential of water as an eluent in thin layer chromatographic separation of various anions on plain adsorbent layers (silica gel "G" alumina, and cellulose) as well as on beds containing different combinations of silica gel, alumina, or cellulose has been investigated. In addition to some important separation of anions, microgram separation of IO⁻₄ from milligram quantities of IO⁻₃, Bro⁻₃, MoO²⁻₄, and Fe (CN)³⁻₆ has been realized. The effect on pH of the sample in the separation of IO⁻₄ from accompanying ions has also been studied. The limits of detection and dilution limits of anions on alumina thin layers have been determined. NO⁻₂ in artificial seawater has been detected. The effect of CaCl₂, MgCl₂, and NaHCO₃ on some ternary separations of analytical importance has been examined.     

A direct carbon-13 and nitrogen-15 NMR study of europium(III) complexation-nitrate and europium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature nuclear magnetic resonance spectroscopic study of europium(III)-nitrate contact ion-pairing has been completed, and preliminary results for europium(III)-isothiocyanate have been obtained. In water-acetone-Freon mixtures, at –110°C to –120°C, four¹⁵N NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence indicate the formation of Eu(NO₃)²⁺, Eu(NO₃) ₂ ¹⁺ , and two higher complexes, possibly the tetra-, with either the penta-or hexanitrato. This correlates well with similar¹⁵N NMR results obtained for Ce(III), Pr(III), Nd(III), and Sm(III). As a result of a higher dielectric constant, complex formation is significantly less in water-methanol mixtures, wheein only three complexes form with Eu(NO₃) ₂ ¹⁺ dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by³⁵Cl NMR chemical shift and linewidth measurements, as well as¹⁵N NMR. Initial experiments with the Eu³⁺-NCS^– system show four coordinated anion signals, displaced from the bulk anion peak by about –250 ppm and –2,500 ppm in the¹³C and¹⁵N NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)²⁺ through Eu(NCS) ₄ ^1- in these solutions. A consideration of the chemical shifts identified the nitrogen atom as the site of binding in the NCS^–. A discussion of these preliminary results, as well as those for several other metal-ions, will be presented.     

A field-desorption study of thermal stability in potassium pentacyanocobaltates(III)

Field desorption has been applied to research the thermal stability of the compounds K_n[Co(CN)₅X], where X=SO₃ ^2–, CN^–, NO₂ ^–, NO^–, Cl^–, Br^–, I^–, and H₂O. A likely mechanism is proposed for the thermal decomposition. There is a correlation between the tetragonal-distortion parameters and the temperature of onset of destruction for the [Co(CN)₅X]^n– anion.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 111–115, January–February, 1985.     

Cobalt(II) complexes of 1,2-(diimino-4′-antipyrinyl)ethane and 4-N-(4′-antipyrylmethylidene)aminoantipyrine

Cobalt(II) complexes of the Schiff bases 1,2-(diimino-4-antipyrinyl)ethane (GA) and 4-N-(4-antipyrylmethylidene)aminoantipyrine (AA) have been prepared and characterised by elemental analysis, electrical conductance in non-aqueous solvents, i.r. and electronic spectra, as well as by magnetic susceptibility measurements. The complexes have the general formulae [Co(GA)X]X (X = ClO^– ₄ or NO₃ ^–), [Co(GA)X₂] (X = Cl^–, Br^– or I^–), [Co(AA)₂]X₂ (X = ClO₄ ^–, NO₃ ^–, Br^– or I^–) and [Co(AA)Cl₂]. GA acts as a neutral tetradentate ligand, coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate and nitrate complexes of GA one anion is coordinated in a bidentate fashion, whereas in the halide complexes both anions are coordinated to the metal, generating an octahedral geometry around the Co ion. AA acts as a neutral bidentate ligand, coordinating through the carbonyl oxygen derived from the aldehydic moiety and the azomethine nitrogen. Both anions remain ionic in the perchlorate, nitrate, bromide and iodide complexes of AA, whereas both anions are coordinated to the metal ion in the chloride complex, resulting tetrahedral geometry around the Co ion.     

Thermal transformations in systems based on zeolites Y,X, and A containing zinc and sodium nitrates

Thermal transformations in systems formed by interaction of Zn and Na nitrates with Y, X, and A zeolites were studied by TG—DTA technique. Temperature regions of existence of adsorbed water, water of crystallization, and decomposition of NO₃ ^– anion were determined. These intervals depend on the composition, structure, method of preparation, and pre-treatment conditions of zeolite systems. The extent of NO₃ ^– decomposition depends not only on the zinc and sodium content but also on the presence of ammonia involved in NO₃ ^– reduction. The zeolite matrix strongly stabilizes the occluded NO₃ ^– anions. A portion of zinc oxide formed by zinc nitrate decomposition is probably localized inside the zeolite cavities as the [Zn—O—(ZnO) _n —Zn]²⁺ particles. The latter compensate charges of the isolated [AlO₄]^– tetrahedra.     

Determination of anions by non-suppressed ion chromatography using an amine column

Summary The Synchropak AX300 column has been used to separate a wide range of anions. A standard solution containing F^–, Cl^–, NO ₂ ^– , NO ₃ ^– , HPO ₄ ^2– , SO ₄ ^2– ions can be analysed in 8–14 minutes using a phthalate or phthalate/citrate eluent at pH 6–7. Addition of citrate to a phthalate eluent has a pronounced effect on the times of analysis. Detection by direction and indirect UV absorption enables the analysis of a wide range of anions. Application of the technique range from rain water to ash pond liquor analysis.     

In situ Near-Infrared Spectroelectrochemical Investigation of Redox States of Polyaniline during Growth and Doping

In situ near-infrared (NIR) spectroelectrochemical studies during growth and dedoping/redoping of polyaniline (PANI) in the range between 1200 to 3000 nm are carried out in 1 M aqueous solutions of HCl, H₂SO₄, and HClO₄ acids andp-toluene sulfonic acid (PTSA). The results show three characteristic absorption bands around 1440, 1900, and 2500 nm. The band at 2500 nm is characteristic of mobile charge carriers. The PANI prepared in HClO₄ keeps memory of the size of the doping anion (ClO₄ ^–) and can be redoped only with the same or smaller anions (Cl^– and SO₄ ^2– or HSO₄ ^–) while it cannot be redoped to any significant extent by a larger anion (PTSA^–).     

Relative efficiencies of substituted aromatic monocarboxylic acids as eluents in ion chromatographic separation of inorganic and organic anions

The eluent strengths of para, ortho and meta substituted hydroxy-, nitro-, amino- and sulfobenzoic acids in single column ion chromatographic separations of inorganic and organic anions have been evaluated and compared with benzoic acid.o-Sulfobenzoic acid turns out to be a stronger and efficient eluent compared to others for the separation and determination of monovalent (Cl^–, NO ₂ ^– , Br^–, NO ₃ ^– ) and divalent (SO ₄ ^2– , SeO ₄ ^2– , S₂O ₃ ^2– , S₂O ₆ ^2– ) inorganic anions. In addition it also functions as an appropriate mobile phase for the detection and quantification of some substituted benzoate ions in an aqueous medium.     

Peak parking technique for the simultaneous determination of anions and cations

An ion chromatography method is described for the simultaneous determination of anions (Cl^–, NO₃^–, and SO₄^2–) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) using a single pump, a single eluent and a single detector. An anion-exchange column modified with chondroitin sulfate C facilitated the elution of the above three anions using 5 mM tartaric acid as the eluent in isocratic mode, whereas the same eluent facilitated the separation of the above five cations on a commercially-available cation-exchange column. The separation columns were connected in series via two six-port switching valves, so the required cation-exchange or anion-exchange separation could be carried out by selecting the appropriate positions for the switching valves. The separations were completed in 30 min.