Graphite-furnace atomization of phosphorus

The slopes of the ln (absorbance) vs. T^?1 dependences for platform/graphite furnace atomization of phosphorus in the presence of Ni²⁺ or La³⁺ modifiers are measured, and found to be similar to the theoretical slope calculated for isothermal atomization. It is concluded that in both cases the atomization mechanism is the same and is expressed by P_2(gas) ? 2P_(gas); P_(gas) ? P^*_(gas). The atomic absorption signal for phosphorus appears and reaches its maximum later when the atomization is carried out from the platform in the presence of modifiers. Hence atomization takes place under nearly isothermal conditions and is much more efficient, thus providing the best conditions for the determination of phosphorus. Treatment of a deteriorated graphite surface with ZrOCl₂ solution repairs any defects and improves the sensitivity of phosphorus determination.     

On binary self-dual codes of lengths 60, 62, 64 and 66 having an automorphism of order 9

A method for constructing binary self-dual codes having an automorphism of order p ² for an odd prime p is presented in (S. Bouyuklieva et al. IEEE. Trans. Inform. Theory, 51, 3678–3686, 2005). Using this method, we investigate the optimal self-dual codes of lengths 60 ≤ n ≤ 66 having an automorphism of order 9 with six 9-cycles, t cycles of length 3 and f fixed points. We classify all self-dual [60,30,12] and [62,31,12] codes possessing such an automorphism, and we construct many doubly-even [64,32,12] and singly-even [66,33,12] codes. Some of the constructed codes of lengths 62 and 66 are with weight enumerators for which the existence of codes was not known until now.      

Polarographic and potentiometric determination of the stability constants of lead, cadmium and zinc complexes with dithiocarbaminoacetic acid

The stability constants of lead, cadmium and zinc dithio-carbaminoacetic acid (TCA) complexes have been determined. Lead and cadmium TCA complexes were studied by means of a polarographic method. A competitive polarographic method was used for the study of zinc TCA complexes. Zinc and cadmium TCA complexes were also studied potentiometrically with an amalgam electrode. The stability constants found were: lead, log beta(2) = 13.2; cadmium, log beta(1) = 5.4 (pot.), log beta(2) = 9.3 (pot.), log beta(3) = 13.7 (pot.), 13.6 (pol.); zinc, logbeta(1) = 3.4(pot.), <3.8(pol.), logbeta(2) = 6.6 (pot.), 6.4(pol.), logbeta(3) = 8.9 (pot.), 9.3 (pol.).     

Selective extraction of zinc dithizonate in the presence of dithiocarbaminoacetic acid as masking agent Quantitative treatment of an extraction equilibrium

Dithiocarbaminoacetic acid (TCA) is proposed as an effective masking agent in the dithizone extraction determination of zinc in the presence of lead, cadmium and cobalt(II). The extraction equilibrium is treated quantitatively by means of two approaches: the "conditional distribution coefficient" and the computer program HAL-TAFALL. Both methods give similar results and enable the most suitable conditions for the separation and determination of zinc in the presence of the other ions to be determined. A successful attempt is made to predict the maximum permissible quantity of interfering elements. The experimental check, performed under various conditions, is in satisfactory agreement with the theory.     

Preconcentration of trace elements on a support impregnated with sodium diethyldithiocarbamate prior to their determination by inductively coupled plasma-atomic emission spectrometry

A procedure is developed for determination of As, Co, Se, Cr, Pb, Zn, Cu, Mn, Cd, Sb, and Sn in water by ICP-AES analysis of alcohol eluates after pre-concentration of the samples. The pre-concentration is performed on a sodium diethyldithiocarbamate supported soft polyurethane foam. The sorbed elements are subsequently eluted with 1-propanol and the alcohol eluates are analysed by ICP-AES. A eight-fold concentration is achieved. An increased sensitivity in the analysis of propanol-water (30:70, v/v) solution is established as compared with aqueous solutions. The strongest effect is observed for As, Se, Pb, Cr, Sn, and Cd-increasing is more than twice. For other elements the matrix influence is by a factor of 1.45 (Cu), 1.36 (Sb), 2.08 (Zn). The method is applied to the analysis of natural water samples.     

Dithiocarbaminoacetic acid as a masking agent in complexometry

Dithiocarbaminoacetic acid (TCA) forms very stable, water soluble complexes with a number of metal ions and is a suitable masking agent in complexometry. TCA masks from EDTA and complexometric indicators at pH 2-6 the following elements: bismuth(III), indium(III), thallium(III), cadmium(II), lead(II), mercury(II) and copper(II), thus making possible the complexometric determination of other elements in their presence.     

Experimental and computational studies of the structure and vibrational spectra of aminomethyl-dimethyl-phosphine oxide and its 15N labeled isomer

Infrared (4000-100 cm(-1)) spectra of aminomethyl-dimethyl-phosphine oxide and 15N-aminomethyl-dimethyl-phosphine oxide have been measured. Geometric parameters (bond distances and angles), net electronic charges and vibrational spectroscopic data of both compounds calculated at various levels of theory (B3LYP/6-31G* and Moeller-Plesset perturbational theory (MP2)/6-31G*) are reported. The theoretical spectral results are discussed mainly in terms of comparison with infrared (4000-100 cm(-1)) spectral data. Better coincidence was achieved with the frequencies calculated at the MP2/6-31G* level: the standard deviation is 16 cm(-1). The calculated isotopic frequency shifts, induced by the 15N labeling, are in good accordance with the measured ones. Complete vibrational assignment is made with the help of MP2 force field calculations. Data obtained here are used to reassign some of the vibrational frequencies.     

Co-precipitative pre-concentration with sodium diethyldithiocarbamate and ICP-AES determination of Se, Cu, Pb, Zn, Fe, Co, Ni, Mn, Cr and Cd in water

Sodium diethyldithiocarbamate in the presence of a weak oxidizing agent is used as a co-precipitative agent for the pre-concentration of Se, Cu, Pb, Zn, Fe, Co, Ni, Mn, Cr and Cd. A procedure was developed for ICP-AES determination of these elements after pre-concentration in river and waste water (an enrichment factor of 40). The recovery of all the elements tested for was more than 98%. The limits of determination (mg l⁻¹) (10 S.D. blank) are 0.001 (Cu, Co, Cr, Mn), 0.0007 (Zn, Cd), 0.003 (Se), 0.004 (Fe), 0.007 (Ni), and 0.01 (Pb).     

Distribution and determination of Pb, Cd, Bi and Cu in the sea brine system: solution--colloidal particles--biota

The distribution of Pb, Cd, Bi, and Cu in Black Sea brine system (solution--colloidal particles--biota) produced in Burgas and Pomorie salterns is studied. The established distribution of the title elements among the brine components is as follows: Pb--25% in the salt solution, 30%--in colloidal particles, 45%--in biota (Halobacterium salinarium and microalgae Dunaliela salina); Cu--30% in the salt solution, 22%--in colloidal particles, 48%--in biota. Cd and Bi are not detected in biota. They are uniformly distributed (50%: 50%) between the salt solution and colloidal particles. Two procedures for analysis are developed. The first one is designed for determination of the total content of the studied metals in brine. It involves elimination of the biota interference by addition of ethanol, extraction and pre-concentration of the metals with NaDDC into CCl4 followed by FAAS determination. The second procedure intends determination of the elements in the separate components of the brine. It involves separation of the colloidal particles through centrifugation, separation of the studied elements from the resulting solution as dithiocarbamate complexes on a Millipore filter, dissolution of the retained metal species and subsequent FAAS analysis.     

Arsenic speciation in waste waters by extraction chromatography followed by atomic absorption spectrometry

Summary A method is described for the determination of arsenic(III) and arsenic(V) in water samples. The sample (adjusted to pH 2.5 to 3.5 with HCl or NaOH) is passed through a chromatographic column filled with inert support modified with the organotin reagent (C₈H₁₇)₂SnCl₂. Under these conditions arsenate is quantitatively retained, while arsenite is not. Arsenate is eluted from the column with 2 mol/l HCl (1–2 ml). Both effluate [As(III)] and eluate [As(V)] are analyzed by flame or graphite furnace AAS. The method was applied to the analysis of waste waters from a metallurgical plant and potable water from the same region. Recoveries are in the range of 85–115%.