HPLC-SEC: a new approach to characterise complex wastewater effluents

This work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produced the best separation for all wastewater effluents tested at any detection. UV-254 absorbance was higher at neutral and basic eluent pH while tryptophan-like fluorescence depended on the sample composition rather than on the eluent pH or ionic strength. Tyrosine-like fluorescence decreased significantly with the increase of eluent ionic strength. Accurate molecular weight measurements could not be done, the separation being influenced by secondary interactions, but could be approximated using separate calibrations with sodium salts of polystyrene-sulfonates and protein standards. The results show that this method is suitable for determining DOM in wastewater at low eluent concentrations (up to 0.03 M), at neutral or slightly basic pH.     

Studies of the structure of Ce3+ centers in SrS phosphors

It is found that the shape of luminescence spectra of SrS−Ce phosphors is independent of both the species and concentration of a cofactor F, Cl, Br, or 1 introduced in the form of ammonium halide at least up to 6.5 at.%. The only exception is F, which, when added as a coactivator with a concentration of 2.4 at.% and above, gives rise to new longwave luminescence bands, part from the luminescence of the Ce³⁺ ion. Analysis has shown that this additional luminescence spectrum is similar to the Ce³⁺ spectrum but is shifted towards the longwave region by about 0.14 eV. The luminescence decay time constant (τ=57 nsec) is very close to Br, I, and small concentrations of F, a model is valid according to which the halogen that substitutes for sulfur and the Ce³⁺ that substitutes for Sr are the closest neighbors not to each other, but to a probable compensator of the charge of Sr vacancies. At high concentrations of fluorine some of the F ions are located at interstitial lattice sites in the immediate neighborhood of Ce³⁺, providing compensation for the charge of Ce³⁺ ions and having a marked effect on them. Tartu University, 18, Ulikooli St., Tartu EE2400, Estonian Republic. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 173–178, March–April, 1997.     

Reactions of 9-substituted guanines with bromomalondialdehyde in aqueous solution predominantly yield glyoxal-derived adducts

Reactions of 9-ethylguanine, 2'-deoxyguanosine and guanosine with bromomalondialdehyde in aqueous buffers over a wide pH-range were studied. The main products were isolated and characterized by (1)H and (13)C NMR and mass spectroscopy. The final products formed under acidic and basic conditions were different, but they shared the common feature of being derived from glyoxal. Among the 1 : 1 adducts, 1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (6) predominated at pH < 6 and N(2)-carboxymethylguanine adduct (10a,b) at pH > 7. In addition to these, an N(2)-(4,5-dihydroxy-1,3-dioxolan-2-yl)methylene adduct (11a,b) and an N(2)-carboxymethyl-1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (12) were obtained at pH 10. The results of kinetic experiments suggest that bromomalondialdehyde is significantly decomposed to formic acid and glycolaldehyde under the conditions required to obtain guanine adducts. Glycolaldehyde is oxidized to glyoxal, which then modifies the guanine base more readily than bromomalondialdehyde. Besides the glyoxal-derived adducts, 1,N(2)-ethenoguanine (5a-c) and N(2),3-ethenoguanine adducts (4a-c) were formed as minor products, and a transient accumulation of two unstable intermediates, tentatively identified as 1,N(2)-(1,2,2,3-tetrahydroxypropano)(8) and 1,N(2)-(2-formyl-1,2,3-trihydroxypropano)(9) adducts, was observed.     

A note on perfect Lee-codes over small alphabets

Lee-codes, correcting e-errors, over an alphabet with q = 2^m letters are considered. It is proved that a code can be perfect only if $\text{q |(}\text{n ? 1}\text{k}\text{)}$, where n is the block length and $\text{k = [}\text{2e}\text{q}\text{]}$.     

Impurity absorption of SrS-Ce3+ phosphors

We investigate the impurity absorption of SrS−Ce phosphors. For this purpose, we measure the spectra of diffuse reflection of powder phosphors. It is established that the introduction of Ce simultaneously with a coactivator gives rise to a strong absorption band at 2.88 eV, and the introduction of a coactivator (NH₄F, NH₄Cl, NH₄Br, NH₄I, LiCl, NaCl or KCl), to an absorption band at about 2.36 eV. We assume that the absorption band at 2.88 eV is caused by that portion of Ce introduced that forms the center of luminescence of Ce³⁺. Tartu University, Estonian, Republic, 18, Yulikooli St., Tartu, EE2400, Estonia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 542–544, July–August, 1997.