Krzysztof Greda

The improvement of the analytical performance of direct current atmospheric pressure glow discharge generated in contact with the small-sized liquid cathode after the addition of non-ionic surfactants to electrolyte solutions

A low power direct current atmospheric glow discharge sustained in the open to air atmosphere in contact with a small-sized flowing liquid cathode was used as an excitation source in optical emission spectrometry. The composition of electrolyte solutions served as the liquid cathode was modified by the addition of non-ionic surfactants, namely Triton x-45, Triton x-100, Triton x-405 and Triton x-705. The effect of the concentration of each surfactant was thoroughly studied on the emission characteristic of molecular bands identified in spectra, atomic emission lines of 16 metals studied and the background level. It was found that the presence of both heavy surfactants results in a significant increase in the net intensity of analytical lines of metals and a notable reduction of the intensity of bands of diatomic molecules and the background. In conditions considered to be a compromise for all metals, selected figures of merit for this excitation source combined with the optical emission spectrometry detection were determined. Limits of detection for all metals were within the range of 0.0003-0.05 mg L(-1), the precision was better than 6%, while calibration curves were linear over 2 orders of the magnitude of the concentration or more, e.g., for K, Li, Mg, Na and Rb. The discharge system with the liquid cathode modified by the addition of the surfactant found its application in the determination of Ca, Cu, Fe, K, Mg, Mn, Na and Zn in selected environmental samples, i.e., waters, soils and spruce needles, with the quite good precision and the accuracy comparable to that for measurements with flame atomic absorption spectrometry (FAAS) and flame atomic emission spectrometry (FAES).

Atmospheric Pressure Glow Discharges Generated in Contact with Flowing Liquid Cathode: Production of Active Species and Application in Wastewater Purification Processes

Miniaturized atmospheric pressure glow discharges (APGDs) were generated in contact with small sized flowing liquid cathode systems. As anodes a solid pin electrode or a miniature flow Ar microjet were applied. Both discharge systems were operated in the open to air atmosphere. Hydrogen peroxide (H2O2) as well as ammonium (NH4+), nitrate (NO3−), and nitrite (NO2−) ions were quantified in solutions treated by studied discharge systems. Additionally, an increase in the acidification of these solutions was noted in each case. Emission spectra of the near cathode zone of both systems were measured in order to elucidate mechanisms that lead to the formation of active species in gas and liquid phases of the discharge. Additionally, the concentration of active species in the liquid phase (H2O2, NH4+, NO3− and NO2−) was monitored as a function of the solution uptake rate and the flow rate of Ar. The suitability of investigated discharge systems in the water treatment was tested on artificial wastewaters containing an organic dye (methyl red), hardly removable by classical methods non-ionic surfactants (light Triton x-45 and heavy Triton x-405) and very toxic Cr(VI) ions. Preliminary results presented here indicate that both investigated flow-through APGD systems may successfully be applied for the efficient and fast on-line continuous flow chemical degradation of toxic and hazardous organic and inorganic species in wastewater solutions.

Effect of the addition of non-ionic surfactants on the emission characteristic of direct current atmospheric pressure glow discharge generated in contact with a flowing liquid cathode /

A direct current atmospheric pressure glow discharge generated in contact with a flowing liquid cathode was used to study the effect of the concentration of two non-ionic surfactants, i.e., Triton x-45 and Triton x-405 added to electrolyte solutions, on the emission characteristic of the excitation source by using optical emission spectrometry. The emission intensity of different molecular and atomic species as well as the background level were measured. Selected spectroscopic parameters, i.e., rotational temperatures of OH and N2 molecules, excitation temperatures of Co and H atoms, the electron number density and the intensity ratio for Mg II to Mg I lines, were also determined. The net intensity of atomic emission lines of several metals (Cs, Cu, Hg, Mg, Mn and Pb) was found to be enhanced by more than 4 times in the presence of the heavier surfactant in solution at the concentration corresponding to 5 times its critical micelle concentration. Coincidently, the intensity of the background in the vicinity of these lines and its fluctuation were also significantly decreased. Possible changes in sputtering, collisional-recombination and excitation processes that may occur in the near-cathode zone of the discharge are discussed and the phenomenon explained.

Flowing Liquid Anode Atmospheric Pressure Glow Discharge as an Excitation Source for Optical Emission Spectrometry with the Improved Detectability of Ag, Cd, Hg, Pb, Tl, and Zn

A novel atmospheric pressure glow discharge generated in contact with a flowing liquid anode (FLA-APGD) was developed as the efficient excitation source for the optical emission spectrometry (OES) detection. Differences in the appearance and the electrical characteristic of the FLA-APGD and a conventional system operated with a flowing liquid cathode (FLC-APGD) were studied in detail and discussed. Under the optimal operating conditions for the FLA-APGD, the emission from the analytes (Ag, Cd, Hg, Pb, Tl, and Zn) was from 20 to 120 times higher as compared to the FLC-APGD. Limits of detections (LODs) established with a novel FLA-APGD system were on average 20 times better than those obtained for the FLC-APGD. A further improvement of the LODs was achieved by reducing the background shift interferences and, as a result, the LODs for Ag, Cd, Hg, Pb, Tl, and Zn were 0.004, 0.040, 0.70, 1.7, 0.035, and 0.45 μg L(-1), respectively. The precision of the FLA-APGD-OES method was evaluated to be within 2-5% (as the relative standard deviation of the repeated measurements). The method found its application in the determination of the content of Ag, Cd, Hg, Pb, Tl, and Zn in a certified reference material (CRM) of Lobster hepatopancreas (TORT-2), four brass samples as well as mineral water and tea leaves samples spiked with the analytes. In the case of brass samples, a reference method, i.e., inductively coupled plasma optical emission spectrometry (ICP-OES) was used. A good agreement between the results obtained with FLA-APGD-OES and the certified values for the CRM TORT-2 as well as the reference values obtained with ICP-OES for the brass samples was revealed, indicating the good accuracy of the proposed method. The recoveries obtained for the spiked samples of mineral water and tea leaves were within the range of 97.5-102%.

Direct elemental analysis of honeys by atmospheric pressure glow discharge generated in contact with a flowing liquid cathode

Miniaturized atmospheric pressure glow discharge sustained in a compact discharge cell in contact with a flowing liquid cathode was used for the elemental analysis of honeys by optical emission spectrometry. A simplified sample preparation procedure was proposed and samples of honeys were only dissolved in water and acidified with HCl to a concentration of 0.10 mol L−1. The resulting 1.0% m/v in the case of K and Na and 5.0% m/v in the case of Ca, Cu, Fe, Li, Mg, Mn, Rb and Zn solutions of honeys were directly introduced into the discharge cell acting as the liquid cathode of the discharge. To eliminate matrix effects coming from fructose and glucose, a non-ionic surfactant (Triton X-405) was added to the solutions and this resulted in improved signals of studied elements. For calibration, simple (for K and Na) and matrix-matching (for other elements) standard solutions were used. The method was proved to give reliable results and applied in the analysis of 16 commercial white- to amber-colored honeys with limits of detection at levels of 1.0 (Ca), 0.7 (Cu), 2.5 (Fe), 0.5 (K), 0.02 (Li), 0.2 (Mg), 1.8 (Mn), 0.04 (Na), 0.1 (Rb) and 0.2 (Zn) μg g−1.

Comparison of the performance of direct current atmospheric pressure glow microdischarges operated between a small sized flowing liquid cathode and miniature argon or helium flow microjets

Low power direct current atmospheric glow microdischarges were sustained between miniature Ar or He flow nozzle microjets and a small-sized flowing liquid cathode as new excitation microsources for optical emission spectrometry. The morphology of emission spectra of both microdischarges was compared and the effect of the flow rate of both gases on their performance and the emission characteristic related to molecular bands and atomic lines of selected metals (Ca, Cd, Cu, Fe, K, Li, Mg, Mn, Na and Zn) were studied using optical emission spectrometry. It was established that in the microdischarge with the miniature He flow microjet there were more convenient conditions for the quenching of the band emission originating from OH, N2, NH and NO molecules as compared to those with the Ar microjet. The background level and its fluctuation in the vicinity of analytical lines of metals were lower, while their signal to noise ratios were higher. Under compromised conditions, selected figures of merit for the better microdischarge with the He microjet were evaluated. The detection limits assessed for Ca, K, Li, Mg and Na were within the range of 0.001 to 0.077 mg L−1. These metals were determined in six samples of tap water. The accuracy of this analysis, expressed as the relative error with reference to values determined with flame atomic absorption spectrometry (Ca, Mg) and flame atomic emission spectrometry (K, Li, Na), ranged from −2.1 to +10.1%. In addition, recoveries of metals added to the analyzed tap water samples varied from 90.6 to 106.9%. The precision of the analysis was within 0.2–4.6%.

On the coupling of hydride generation with atmospheric pressure glow discharge in contact with the flowing liquid cathode for the determination of arsenic, antimony and selenium with optical emission spectrometry

The miniaturized atmospheric pressure glow discharge (APGD) sustained between a liquid flowing cathode and a He nozzle jet anode was combined with hydride generation (HG) to improve the performance of the determination of As, Sb and Se with optical emission spectrometry (OES). As(III), Sb(III) and Se(IV) species were converted into volatile hydrides in the reaction with NaBH4 and right after that they were delivered to the near-anode region of APGD through the nozzle. The transport efficiency of As, Sb and Se to the discharge was several times higher, while intensities of atomic emission lines of As, Sb and Se were improved 3 orders of magnitude (as compared to intensities acquired for the near-cathode region in a APGD system with a typical introduction of analytes through sputtering of the flowing liquid cathode). The effect of the concentration of NaBH4 and HCl in a sample solution, the discharge current, the flow rate of He carrier/jet-supporting and He shielding gases on the emission yield coming from As, Sb, Se, He and H atomic lines and OH and N2 band heads as well as the electron number density was thoroughly studied. Under compromised conditions, limits of detection (3σ criterion) of As, Sb and Se were respectively 4.2, 1.2 and 3.1 µg L(-1). Usefulness of the method was confirmed by the analysis of Sniadecki and Marchlewski highly mineralized spring waters (Kudowa Zdroj, Poland) on the content of As, Sb and Se. Recoveries of elements added to these spring waters were within 90.3-103.7% proving good accuracy of the HG-APGD-OES method.

Coupling of cold vapor generation with an atmospheric pressure glow microdischarge sustained between a miniature flow helium jet and a flowing liquid cathode for the determination of mercury by optical emission spectrometry

A direct current atmospheric pressure glow microdischarge (dc-μAPGD), generated between a miniature flow He jet nozzle anode and a small-sized flowing liquid cathode, was combined with a continuous flow cold vapor generation (CVG) system to improve the sensitivity of the determination of Hg by optical emission spectrometry (OES). In this arrangement, Hg(II) ions were converted to cold vapor in the reaction with NaBH4 and subsequently delivered in a stream of He carrier/jet-supporting gas to the microdischarge through the nozzle anode. Additional He shielding gas was used to prevent discharge zones from the access of ambient air. A vertical distribution of emission from the Hg I 253.7 nm line between both electrodes was acquired, and the highest response for Hg was established in the near-anode region of the microdischarge. Several operating parameters that affect the CVG reaction and discharge were optimized. Under compromised conditions, the intensity of the Hg I line was improved over 4000 times compared to that obtained in a μAPGD-OES system without the CVG system. The efficiency of CVG of Hg and its transport to the microdischarge was evaluated to be 98 ± 1%. For comparison, in the μAPGD system without CVG, the efficiency of sputtering was merely lower by about 20%, i.e., 77 ± 4%. A likely explanation of the enhancement of Hg response observed for CVG-μAPGD was discussed. The detection limit (DL) of Hg assessed for CVG-μAPGD-OES was 0.14 μg L−1 (3σ criterion). To assess the accuracy of the new method, Hg was quantified in a certified reference material (CRM) of human hair (NCS ZC 81002). Excellent agreement between certified and measured concentrations of Hg was obtained. In addition, recoveries of Hg added to samples of different waters were evaluated. They were in the range of 96–103% proving the good accuracy of CVG-μAPGD-OES. The repeatability of the signal over the linearity concentration range of 5–500 μg L−1 of Hg was within 2.1–4.1% (as relative standard deviation, RSD).

Production of gold nanoparticles using atmospheric pressure glow microdischarge generated in contact with a flowing liquid cathode - a design of experiments study

Direct current atmospheric pressure glow microdischarge (dc-μAPGD) generated between a miniature flow Ar plasma microjet and a small-sized flowing liquid cathode (FLC) was characterized with respect to the effects of the selected operating factors on the particle size of the synthesized Au nanoparticles (AuNPs). The factors that were investigated were the discharge current, the flow rate of the solution of the FLC, and the flow rate of the Ar plasma microjet-supporting gas. The effects of the individual factors and their inter-factor dependencies on the size and size distribution of the synthesized AuNPs were evaluated by changing the operating conditions according to the Box–Behnken design (BBD) plan and monitoring the wavelength of the maximum (λmax) of the localized surface plasmon resonance (LSPR) absorption band. The response surface methodology (RSM) was used to fit the experimental data with an appropriate regression model and optimize the plasma-reactor system to produce spherical AuNPs having the lowest particle size and size dispersion. It was established that a high discharge current and a low flow rate of the solution of the FLC facilitated the production of spherical, uniform and the smallest in size AuNPs. The correctness of the model was validated by producing the AuNPs in optimal and non-optimal conditions and the analysis of the resultant nanofluids by UV-Vis absorption spectrophotometry, dynamic light scattering (DLS), and scanning electron microscopy (SEM).

Size-controlled synthesis of gold nanoparticles by a novel atmospheric pressure glow discharge system with a metallic pin electrode and a flowing liquid electrode

A direct current atmospheric pressure glow discharge (APGD) operated between a pin-type solid metallic electrode and the surface of a flowing solution (the liquid electrode), positively or negatively charged and serving as the flowing liquid anode (FLA) or cathode (FLC), was used for synthesizing gold nanoparticles (AuNPs). To the best of our knowledge, the synthesis of AuNPs in such a system, with no noble gas required to support the APGD, has never been reported. The effect of the selected operating parameters on the performance of the AuNPs synthesis in the plasma-reaction system with the FLA or FLC was examined. The design of the experiments (DOE) was conducted using the response surface regression (RSR) approach. The response of both systems was the wavelength of the maximum (λmax) of the localized surface plasmon resonance (LSPR) absorption band of the AuNPs. On the basis of the established full quadratic regression models, the optimal operating parameters for both plasma-reaction systems (with the FLA or the FLC) were selected, which allowed for the smallest in size spherical AuNPs to be obtained. Both regression models were validated, the AuNPs produced in both plasma-reaction systems under the optimal operating parameters were characterized by UV-Vis absorption spectrophotometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).