Vol 74, No 7 (2019)

We investigated a possibility of determining two metal ions (Cu²⁺ and Co²⁺, Cu²⁺ and Mn²⁺) in a single water sample using an indicator test tube filled with a carboxylic cation exchanger of a macrocellular (KB-2E-10, KB-2E-16) or a macroporous (Tokem-250) structure. Under dynamic conditions, the separation of the chromatographic zones of colored Cu²⁺ and Co²⁺ ions was achieved in the presence of water macro components, that is, Ca²⁺ and Mg²⁺ ions. An analytical reagent, formaldoxime, was used to determine colorless Mn²⁺ ions. The performance characteristics of the developed procedures are determined. The lowest limit of detection for ions was obtained using a KB-2E-16 cation exchanger; it is 0.016 mg/L for Cu²⁺, 0.045 mg/L for Co²⁺, and 0.003 mg/L for Mn²⁺. The proposed procedures were used to analyze real samples for the concentration of Co²⁺ and Cu²⁺ or Mn²⁺ and Cu²⁺ on their simultaneous presence. The accuracy of the results was evaluated by the standard addition method.

This paper investigates the use of the moving average (MA) filter for the quantitative analysis of the near-infrared (NIR) spectra. The performance of the MA filter is mainly dependent on the right choice of the filter length. The paper also introduces a new technique for the determination of the appropriate length of the MA filter. The use of MA filters for the quantitative analysis of the NIR spectra has not been previously evaluated in the field of chemometrics. The effect of using several types of MA filters on the performance of the partial least squares regression (PLS) model has been studied and evaluated. The efficiency of the model was validated using different mixtures composing of glucose, urea and triacetin dissolved in a phosphate buffer solution. The results demonstrate that the use of a small filter length reduces the signal to noise ratio of the spectra, while the use of a larger filter length introduces a distortion and some information gets lost. In this paper, the exponential MA (EWMA) filter has been used specifically for the quantitative analysis of the NIR spectra for the first time. Its performance has been evaluated and compared to other types of MA and Savitzky- Golay filters. The results show that the standard error of prediction decreases from 35.6 mg/dL when 8 PLS factors are used for the PLS model to 22.4 mg/dL when 9 PLS factors are used for the EWMA−PLS model.

Based on cloud point extraction, a HPLC method was developed for the determination of verapamil in urine. Non-ionic surfactant Triton X-100, an environmentally friendly solvent, was used for the micelle-mediated extraction. Some parameters that influence the extraction, such as the concentration of Triton X-100, effect of pH, incubation time, equilibration temperature and centrifugation parameters, were studied and optimised. The method suggested for the HPLC‒tandem mass spectrometry determination of verapamil in urine after cloud point extraction was validated. The calibration curve was linear in the range of 0.2–50 ng/mL. The limits of detection (3σ) and quantification (10σ) were 0.06 and 0.2 ng/mL, respectively. The matrix effect (96.5%), recovery of the extraction procedure (96%) and overall “process efficiency” (92.6%) were also estimated. All data validation is consistent with international acceptance criteria and no significant matrix effect was observed. The results show that the sensitivity, metrological characteristics, ecological safety, simplicity and convenience of the suggested procedure exceed its analogues based on extraction using organic solvents.

The manifestation of the ligand function of \({\text{Zn}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\) and \({\text{Co}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\)selective electrodes based on higher quaternary ammonium salts is explained by the exchange displacement of zinc and cobalt thiocyanates by SCN^– ions from the membrane into the near-electrode layer of the solution. Its action is limited by the dissociation of the quaternary ammonium salt as an associate with \({\text{Zn}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}\) and \({\text{Co}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}.\) ions. The effect of the background concentration of CoCl₂ or ZnCl₂ on the selectivity of \({\text{Zn}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\) and \({\text{Co}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\)selective electrodes based on higher quaternary ammonium salts to SCN^– ions is studied. The introduction of CoCl₂ or ZnCl₂ into the solution binds cobalt or zinc ions released from the membrane into thiocyanate complexes. The high selectivity of the \({\text{Zn}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\) and \({\text{Co}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\)selective electrodes to SCN^– ions is due to the higher extraction ability of the cobalt and zinc complexes with SCN^– ions compared to acid complexes with the competing anions. It is demonstrated that \({\text{Zn}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\) and \({\text{Co}}\left( {{\text{NCS}}} \right)_{4}^{{2 - }}{\text{-}}\)selective electrodes can be used for the determination of SCN^– ions in process solutions in the production of polyacrylonitrile fibers.