Ljiljana Solujic

Rapid Distillationless "Free Cyanide" Determination by a Flow Injection Ligand Exchange Method

In the first part of this research, extensive species-dependent cyanide recoveries studies were performed using the approved standard methods available for determination of free cyanide. The data obtained show that serious problems are associated with both the CATC (cyanide amenable to chlorination) and WAD (weak and dissociable cyanide) methods. In the second part, a novel flow injection gas-diffusion method for the determination of free cyanide was developed. Complete cyanide recoveries even in the presence of a large excess of the free CN- ion were found for the following species : [Zn(CN) 4 ] 2- , [Cd(CN) 4 ) 2- , [Nl(CN) 4 ) 2- , [CU(CN) 4 ] 3- , [Ag(CN) 2 ] - , [Hg(CN) 4 ] 2- , and Hg(CN) 2 . No recoveries of CN- were obtained from the species that are considered as non free cyanide producing ones, such as [F e (CN) 6 ) 3-/4- , [Co(CN) 6 ) 3- , and [Au(CN) 2 ] - . The method developed is rapid, selective, reproducible, and easy to automate.

[2 + 2] Photocycloadditions of [(η5-C5H5) Ru(DMPP)2L]PF6 complexes

A series of [(η5-C5H5)Ru(DMPP)2L]PF6 complexes, DMPP = 1-phenyl-3,4-dimethylphosphole, L = CH3CN, Ph3P, PhS(O)2CHCH2, (CH3)2NC(O)CHCH2, PhNC, CO and (CH3O)3P, was found to undergo sunlight initiated [2 + 2] photodimerization of the coordinated phospholes only when L is a good π-acceptor ligand. These [2 + 2] dimerizations are accompanied by [4 + 2] dimerizations. The ratio of the [2 + 2] to [4 + 2] cycloaddition products is a function of the steric bulk of L. The nature of the photoexcited state has been probed by electron absorption and emission spectroscopy. The electron absorption spectra show high ɛ bands in the near UV region that are attributed to DMPP π → π* transitions. The emission spectral lifetimes are a function of L and their magnitude at 77 K (about 0.2 to 2.0 μs), together with large Stokes shifts, is indicative of phosphorescence from a triplet excited state. It is postulated that this triplet excited state undergoes cycloaddition by way of a biradical intermediate. The complexes have been characterized by elemental analyses, infrared, electronic, and 1H, 1H31P, 13C1H and 31P1H NMR spectroscopy and cyclic voltammetry. The structure of (η5-C5H5)Ru(DMPP)2[2 + 2](CO)PF6 was confirmed by X-ray crystallography. The complex cation possesses a non-crystallographic mirror plane, the two RuP distances (2.282(1) and 2.281(2) A) are equivalent and the cyclobutane ring has a long (1.607(8) A) and a short (1.550(8) A) CC bond.

Total cyanide determination by a segmented flow injection–on-line UV digestion–amperometric method

Extensive species and concentration dependent cyanide recovery studies were carried out using a novel automated segmented flow injection–on-line UV digestion–amperometric (FI-UV) method for determination of total cyanide in water and wastewater samples. In addition, the response of the method to the presence of potential interferents was tested. The performance of the proposed method was compared with that of the standard method. The data obtained show that the FI-UV method has significant advantages over the EPA/ASTM approved procedures. Total cyanide levels and spike recoveries were determined for nine different industrial effluents. The precision and accuracy of the method, when applied to these effluents, expressed in terms of mean relative standard deviation and average percentage of spike recovery, were 1.5% and 101.0%, respectively. The technique developed eliminates the need for the time consuming, labor intensive distillation called for in the EPA/ASTM approved procedures. The method is rapid, selective and reproducible with a detection limit of 0.2 µg L–1 and a throughput of 30 analyses per hour.

Photocatalytic detoxification of cyanide and metal cyano-species from precious-metal mill effluents

Photochemically-induced detoxification of various cyanide species from a selected precious-metal mills tailings was investigated in detail. The studies were conducted in the presence or absence of a titanium (IV) oxide semiconductor photocatalyst utilizing simulated sunlight as the irradiation source. It was established that the cyanide ion (both free and complexed) was photocatalytically oxidized to nitrate via cyanate and nitrite. In addition iron, copper, zinc, mercury and arsenic were stabilized as precipitates. The results obtained may have ramifications for the possible use of solar energy for the efficient treatment of large quantities of precious-metal mill-tailing wastes that contain various cyano-species.

Formation of thiocyanate during removal of sulfide as lead sulfide prior to cyanide determination

Most standard and other analytical procedures for the determination of cyanide suffer from sulfide interferences. As sulfide and cyanide co-exist in many ‘real world’ samples, this presents a significant problem. The standard procedure for removal of sulfide is its precipitation with a lead salt. However, lower cyanide recoveries are often obtained if this procedure is performed improperly. In this paper, the chemistry of the sulfide interferences in cyanide determination methods is explained and procedures are suggested for alleviating the problem.

Photochemistry of Aqueous Solutions of Dicyanomercury(II) and Potassium Tetracyanomercurate(II)

Photochemically induced reactions of dicyanomercury(II) and potassium tetracyanomercurate(II) in alkaline aqueous solutions were investigated in detail. The studies were conducted in the presence or absence of a titanium(IV) oxide semiconductor photocatalyst utilizing sunlight as the irradiation source. It was established that the cyanide ion liberated from the thermodynamically stable mercury-cyano species can be photocatalytically oxidized via cyanate and nitrite to nitrate. In addition, the process removes over 99 mol% of mercury from the solution. In the absence of the photocatalyst, no photoproducts were detected and mercury remained in solution. The results obtained may have ramifications for the use of solar power for the efficient treatment of large quantities of precious metals mill tailings wastes containing various cyanide species. In addition, in order to follow the fate of cyanide in these experiments, a novel gas-diffusion flow injection analysis system for the determination of cyanide from the thermodynamically stable mercury-cyano complexes was utilized.

Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System

SummarySimultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 200μ1 and 1 ml sample volumes were 120 and 60 h−1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50μg ml−1 and 0.67% for Cr(III) (0.10,μg ml−1) and the corresponding limits of detection were 85 ng ml−1, and 16 ng ml−1, respectively.

Determination of ethylenediaminetetraacetic acid by flame atomic absorption spectrometry with a chelating ion-exchange flow injection conversion system

A flow injection method (FI) has been developed for the determination of ethylenediaminetetraacetic acid (EDTA) by flame atomic absorption spectrometry (FAAS). In the first step a copper(II) regenerant solution was injected on to an on-line column packed with Chelex-100 resin. The excess of copper ion, not retained on the column, was washed by an ammonia solution carrier. In the second step an EDTA sample was injected. The analyte displaced an equivalent amount of copper(II) from the chelating column. Eluted copper was determined by an FAA spectrometric detector positioned downstream. The signal obtained was proportional to the concentration of EDTA present in the injected sample. Using this FI-FAAS conversion method the detection limit was 0.1 µg ml–1. The precision of the technique was better than a relative standard deviation of 1.5% at 0.50 µg ml–1 levels, with a throughput of 45 samples h–1. The effect of sample volume and of ionic and organic ligand interferents on the FI-FAAS signals was studied. Only glycylglycine was found to interfere significantly.

Reaction of formaldehyde with cyano(ethylenediamine)(glycylglycinato)cobalt(III): crystal structures of cyano(ethylenediamine) [N-(4-carbonyl-4-hydroxymethyl-oxazolidine)glycinato]cobalt(III)·3.5H2O and dicyanobis(ethylenediamine) {μ-N-[N-(((methylimino)methyl)carbonyl)-α-methylserinato)glycylglycinato}dicobalt(III) tetrahydrate

Abstract The reaction of [Co(NH2CH2CONCH2CO2)CN(en)] with formaldehyde under basic conditions leads to the formation of four products: cyano(ethylenediamine) [N-(4-carbonyl-4-hydroxymethyl-oxazolidine)glycinato]cobalt(III) ([Co( CH 2 OCH 2 NHC (CH2OH)CONCH2CO2)CN(en)]) (1), dicyanobis(ethylenediamine) {μ-N-(((methylimino)methyl)carbonyl)(α-methylserinato)-glycylglycinato}dicobalt(III) tetrahydrate ([Co(en)CN(CH3NCHCON C(CH 2 OH)CO 2 )-Co(N HCH2CONH2CO2)CN(en)]·4H2O) (2), cyano(ethylenediamine) (N-methylidene-glycylglycinato)cobalt(III) monohydrate ([Co(CH2NCH2CONCH2CO2)CN(en)]·H2O) (3), and cyano(ethylenediamine) (N-hydroxymethylglycylglycinato)cobalt(III) ([Co(HOCH2NHCH2CONCH2CO2)CN(en)]) (4). The products obtained were separated by adsorption chromatography on a cationic exchanger, in the hydrogen form, and characterized by elemental analysis, 1H and 13C NMR spectroscopy. The structures of complexes 1 and 2 were determined by X-ray crystallography. The central features of the investigated reaction are: (a) condensation of formaldehyde takes place with the amino and both of the methylene groups of the coordinated glycylglycine; (b) formation of a binuclear complex in which one of the introduced formaldehyde moieties links two coordinated dipeptidato ligands. A possible mechanism for the reaction is proposed.

π-Facial selectivities in the coordination of an optically pure fused cyclopentadienyl ligand to arene ruthenium moieties. NMR spectral and structural characterization of a single diastereomer of [(PCp)Ru(Me6C6)]PF6

Abstract Optically pure thallium (1R)-(−)-9,9-dimethyltricyclo[6.1.1.02′6]deca-2,5-dienide (TIPCp) reacts with [(n6-arene)RuCl2]2 (arene = C6H6, MeC6H4, p-MeC6H4CHMe2, Me6C6) and NH4PF6 to form two isomers of the complexes [(n5-PCp)Ru(n6-arene)]PF6. The π-facial stereoselectivity for coordination of PCp is a function of the steric bulk of the arene increasing from a 1:1 (C6H6) to a 14:1 (Me6C6) exolendo isomer ratio. New complexes were characterized by elemental analyses, physical properties, differential pulse voltammetry and 1H and 13C{1H} one- and two-dimensional NMR spectroscopy. The structure of [(n5-PCp)Ru(n6-Me6C6)]PF6 was confirmed by X-ray crystallography. This compound crystallized in the acentric space group C2221 in a unit cell with the following dimensions: a = 11.451(4), b = 13.426(5), c = 31.249(3) A, V= 4804(3) A3, Z = 8. Refinement converged to R(F) = 0.056 for 1723 independent observed (I>3σ(I)) reflections. Ruthenium coordinates to the less sterically hindered exo face of the PCp ligand, anti to the gem-dimethyl group, and is closer to the arene (Ru-ring centroid = 1.73 A) than to the PCp ligand (Ru-ring centroid = 1.79 A).