Leo Harju

Determination of stability constants of chelate complexes: Part I. Theory

Abstract A method for the calculation of the stability constants of chelate complexes from pH and pM values is presented. The method, which is based on a consistent use of side-reaction coefficients, is applicable also to systems containing a large number of complexes. The values of the constants are obtained graphically in a simple way, but in many cases corrections are necessary. Methods of correction are described.

Environmental monitoring of trace elements in bark of Scots pine by thick-target PIXE

Bark samples were taken from Scots pines (Pinus sylvestris L.) from a polluted area near a metal plant and from a relatively non-polluted site. Thick-target particle-induced X-ray emission (PIXE) was used for the analyses after different types of prepreparation of the samples. The bark samples were analysed directly by radially scanning from inner to outer bark in order to study the variability of elemental concentrations in different layers. Some clear differences were found in the chemical composition of the inner and outer bark. The lowest detection limits for the analyses of heavy metal ions were obtained by combining dry ashing at 550 °C with the PIXE method. More than 100 times higher concentrations were found for the heavy metal ions Fe, Ni, Cu, Zn, Ga, As and Pb in the bark samples from a polluted area in comparison to samples from a non-polluted area. The work demonstrated that external-beam thick-target PIXE is a sensitive and reliable method for quantitative determination of heavy metals in tree bark samples.

The stability constants of some metal chelates of triethylenetetraminehexaacetic acid (ttha)

Abstract Stability constants for Al(III), Cd(II), Co(II), Cu(II), Fe(III), Hg(II), La(III), Nd(III), Er(III), Mg(II). Mn(II), Ni(II), Pb(II), Th(IV) and Zn(II) complexes of triethylenetetraminehexaacetic acid (TTHA) have been evaluated from data obtained by pH and pM measurements. The pM method based on measurements with the mercury electrode and the redox system Fe(III)/Fe(II) proved to be very useful when binuclear complexes are formed.

Titrations with complexing agents forming mononuclear and binuclear complexes with metals

Abstract The general theory of titrations with complexing agents forming metal complexes in which the metal :ligand ratios are 1:1 and 2:1 is discussed, and rules are given for the calculation of conditional constants. The theory is applied to the titration of manganese and copper with triethylenetetraminehexaacetic acid (TTHA). Curves plotting the conditional stability constants of the 1:1 and 2:1 complexes as functions of pH are given. Values of pM at the two equivalence points for the two metals are presented as functions of pH. The curves offer a simple means of predicting the courses of complexation titrations under varying experimental conditions. Moreover, the curves enable a choice of the optimum experimental conditions including the selection of a suitable indicator and an estimation of the attainable accuracy. When the correctness of the theory and the values of the constants used were tested by carrying out visual and photometric titrations, satisfactory agreement was obtained.

Compleximetric titrations with triethylenetetramine- hexaacetic acid

Abstract The potentialities of TTHA as a reagent for the compleximetric titration of various metals are discussed, and particular attention is paid to the conditions under which 1:1 and 2 :1 complexes are formed. The conditional constants for the formation of 2:1 and 1:1 complexes are calculated and presented graphically as functions of pH for the metals Ag, Al, Ba, Sr and Ca, Cd, Co(II), Cu(II), Fe(lII), Hg(ll), La and two lanthanides (Nd,Er), Mg, Mn, Ni, Pb, Th and Zn. The pM values at the two equivalence points at different pH values are also given. General comments on the constants and their use are presented.

Tuned galvanostatic polarization of solid-state lead-selective electrodes for lowering of the detection limit.

Lowering of the detection limit of solid-state lead-selective electrodes was achieved by using the tuned galvanostatic polarization method. A Nernstian response was obtained down to nanomolar concentrations (low detection limit 10(-9) mol dm(-3)Pb(2+)). Good repeatability of the calibration curves was achieved by using a well established measuring procedure. Relatively high cathodic current densities were applied to the solid-state membrane in order to shorten the measurement time. Successful determination of lead in a synthetic sample (pPb(2+)=7.97±0.08) was achieved by introducing an analytical protocol and favourably compared to inductively coupled plasma mass spectrometry (pPb=7.93). By applying this method, a significant improvement in the detection limit of solid-state lead-selective electrodes was attained.

Study of seasonal variations of trace-element concentrations within tree rings by thick-target PIXE analyses

Abstract Thick-target PIXE has been used for the quantitative determination of trace elements in annual growth rings of different tree species. A scanning device was developed for the remote control of the sample and a video-camera system for the exact monitoring of the spot to be analyzed. The samples were analyzed in steps of 1 mm. The widths of the tree rings studied were in the range 2.5–8.0 mm. Samples of Norway spruce and Scots pine were collected from Harjavalta, a polluted area in southwestern Finland. The elements studied were S, Cl, Br, K, Ca, Mn, Fe, Zn, Cu, Ni, Pb, Rb and Sr. Large variations were observed in elemental concentrations within individual tree rings. The highest concentrations for most elements were obtained for earlywood in the beginning of the growth season and the lowest values for latewood thus reflecting the biological activity. The method was calibrated using international standard reference materials. For most elements the matrix effects were found to be negligible. The detection limits for most metals studied were in the range 1–5 ppm.

A study on lowering the detection limit with solid-state lead-selective electrodes

The detection limit of a Pb(2+) ion-selective electrode with a solid state (PbS/Ag(2)S) membrane was successfully lowered to the nanomolar range. The electrode was applied in direct potentiometric determination of Pb(2+) in aqueous solutions. Hydrodynamics, redox reaction at the solid-state surface as well as time dependency were investigated and found as key factors affecting the low detection limit. By optimizing these parameters improving detection limit by ca. three orders of magnitude was achieved.

Determination of the solubility products of nitrilotriacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid

Abstract A method is described for the determination of solubility products for polyaminopolycarboxylic acids. The neutral protonated species of NTA (nitrilotriacetic acid), EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) were precipitated at low pH values. The amount of precipitate was quantified by gravimetry and complexometric titrations with a standard zinc(II) solution. The following solubility products were obtained: SH3NTA=10−16.36, SH4EDTA=10−24.66 and SH5DTPA=10−30.43. Those values were used for theoretical calculation and optimization of the precipitation processes of NTA, EDTA and DTPA at different pH values in the absence and presence of the metal ions Fe3+ and Mn2+.

Determination of stability constants of chelate complexes: Part II. Applications

Abstract The proposed simplified method for calculating the stability constants of chelate complexes from pH and pM measurements (Part I) is applied to two systems. On the basis of data reported by Osterberg, the stability constants of copper o -phosphorylserylglutamic acid are calculated and good agreement is achieved. In addition, the stability constants of the mononuclear, binuclear and trinuclear silver complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from potentiometric pAg data. These calculations yielded the following values of the cumulative constants: log β AgL =8.7, log β AgHL = 17.6, log β AgH 2 L = 23.8, log β Ag 2 L = 14.0, log β Ag 2 HL = 20.5, log β Ag 2 H 2 L = 25.6, log β Ag 2 L =17.0.