Vol 72, No 1 (2017)

A method is proposed for determining formaldehyde by headspace gas chromatography using an o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatizing agent. Formaldehyde in urine was derivatized to o-(pentafluorobenzyl)oxime and extracted by heating an urine sample with PFBHA in a sealed vial. Gas-chromatographic analysis of the headspace was performed in the temperature-programmed mode using an HP-5 capillary column with a flame ionization detector. The limit of detection is 3.5 μg/L. The accuracy of the procedure, equivalent to an extended relative uncertainty, does not exceed 21%. The examination of the procedure using urine samples of the population of the Irkutsk region has shown that the regional reference levels of formaldehyde concentration are in the range 44–83 μg/L.

An equation i = f(c) is proposed for a calibration curve under the conditions of local voltammetry based on the previous study of the anode dissolution of heterogeneous eutectic alloys with anomalous and divorced eutectics.

Adsorbents based on silica sequentially modified by polyhexamethylene guanidine and nitroso-R salt or nitroso-N salt are proposed for the preconcentration and adsorption-photometric determination of iron. It is shown that these adsorbents quantitatively recovered Fe(III) at pH 3.5–4.0 and Fe(II) at pH 4.5–7.0. In the adsorption of Fe(III) and Fe(II), intensely colored green complexes formed on the adsorbent surface. Based on the absence of signals in EPR spectra, it was concluded that iron in the oxidation state +2 was included into surface complexes with nitroso-R salt or nitroso-N salt. When Fe(III) interacted with nitroso-R salt or nitroso-N salt immobilized on the adsorbent surface, it was reduced to Fe(II). Diffuse reflection spectra of the surface complexes of iron(II) were broad bands with maxima at 720 and 710 nm. Procedures of the adsorption-photometric determination of iron in natural waters and snow samples were developed with the limit of detection of 0.05 μg of iron per 0.2 g of the adsorbent.

A new Ag(I)-ion imprinted polymer (IIP) was prepared by formation of 2-(4-hydroxypent-3-en-2-ylideneamine) phenol complex for selective extraction and preconcentration of silver ions. Polymerization was performed with ethylene glycol dimethacrylate as crosslinking monomer and methacrylic acid as functional monomer in the presence of 2,2-azobis(isobutyronitrile) as initiator via bulk polymerization method. The Ag(I)-imprinted polymeric particles were characterized by scanning electron microscopy and infrared spectroscopy. The template silver ion was removed from the polymeric matrix using 2.0 M HNO₃. Optimum pH for maximum sorption was 6.0. Maximum sorbent capacity and enrichment factor for Ag(I) were 12.5 mg/g and 50, respectively. The relative standard deviation and detection limit of the method were evaluated as ±4% and 2.3 ng/L, respectively. The developed IIP has also been tested for preconcentration and recovery of Ag(I) ions from water and hair samples.

Phenoxy-substituted boron subphthalocyanine was synthesized and studied as an ionophore of plasticized polyvinyl chloride membranes of ion-selective electrodes. The electrodes exhibit reversible response to dobutamine, demonstrating the cation function, as well as reversible response to the salicylate anion. The effects of concentration of the ionophore (0.2–5 wt %) and ionic components (sodium tetraphenylborate, TPhBNa, and tributylhexadecylphosphonium bromide, TBGDPBr), including ionic liquids (ILs), such as diphenylbutylethylphosphonium bis(triflyl)imide, diphenylbutylethylphosphonium hexafluorophosphate, and 1,3-dihexadecylimidazolium chloride, as well as plasticizers, such as ortho-nitrophenyloctyl ether and diethyl sebacate, on the electrochemical characteristics of membranes were studied. For the electrode containing 2% of the phenoxy-substituted boron subphthalocyanine in dobutamine and salicylate solutions, the slopes of the electrode function were 36 ± 1 mV/dec and–46 ± 3 mV/dec and the limits of detection (LODs) were 4 × 10^–5 M and 3 × 10^–4 M, respectively. The addition of an ionic liquid containing the diphenylbutylethylphosphonium cation and the bis(triflyl)imide and hexaflurophosphate anions to the membrane composition had no effect on the response of membrane electrodes to both dobutamine and salicylate. The use of phenoxy-substituted boron subphthalocyanine in an amount of 2% and the TPhBNa additive significantly improved sensor characteristics: the slope of the electrode function (S) for the dobutamine-selective electrode was (54 ± 1) mV/dec and LOD was 1 × 10^–5 M. Dobutamine can be determined in the presence of dopamine, adrenalin, and glucose. Electrodes based on 2% phenoxy-substituted boron subphthalocyanine and 0.5% (C₁₆H₃₃)₂ImCl, or TBGDPBr in salicylate solutions demonstrate the slope of the electrode function close to the theoretical one and a low limit of detection: S = (–59 ± 1) mV/dec, LOD = 2 × 10^–5 M and S = (–57 ± 1) mV/dec, LOD = 4 × 10^–5 M, respectively. The anti-Hofmeister selectivity of sensors was observed. The electrode based on phenoxy-substituted boron subphthalocyanine and (C₁₆H₃₃)₂ImCl was used for the assay of acetylsalicylic acid in the drug Cardiomagnyl.

The present study reports the effect of an ionic liquid (IL), 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO₄]), on the Cu2+-catalyzed lucigenin/H₂O₂ chemiluminescence system in the range of pH 6.5‒10. At pH 8.0, the greatest enhancement on light emission is observed, related to a strong interaction between Cu²⁺ and the imidazolium ring at this pH. Furthermore, the formation of IL microdomains in the aqueous solution enhances in solubility of N-methylacridone, an insoluble emitter that can be very effective in lucigenin chemiluminescence (Luci-CL). The mentioned findings encouraged us to suggest a novel and simple method for the determination of glucose with the detection limit of 7 μM at pH 8.0 based on the detection of H₂O₂ liberated in enzymatic reaction between glucose oxidase and glucose by the [Emim][EtSO₄]/Cu²⁺-catalyzed Luci-CL system. Also, the developed method was successfully applied to the determination of glucose in real plasma and urine samples of diabetic patients and validated against colorimetric spectroscopy method.