•A novel flowing LCGD-AES technique was established.•The electron temperature (Te) and electron number density (Ne) were calculated.•The stability and the optimized analytical conditions were investigated.•The Ca and Zn in gluconates oral solution and blood samples were simultaneously determinate.•The measurement results of the LCGD-AES were consistent with the ICP-AES and the reference values.A novel flowing liquid cathode glow discharge (LCGD) was developed as an excitation source of the atomic emission spectrometry (AES) for the determination of Ca and Zn in digested calcium and zinc gluconates oral solution and blood samples, in which the glow discharge is produced between the electrolyte (as cathode) overflowing from a quartz capillary and the needle-like Pt anode. The electron temperature and electron density of LCGD were calculated at different discharge voltages. The discharge stability and parameters affecting the LCGD were investigated in detail. In addition, the measured results of real samples using LCGD-AES were verified by ICP-AES. The results showed that the optimized analytical conditions are pH = 1 HNO3 as supporting electrolyte, 4.5 mL min–1 solution flow rate. The power consumption of LCGD is 43.5–66.0 W. The R2 and the RSD ranged from 630 to 680 V are 0.9942–0.9995 and 0.49%–2.43%, respectively. The limits of detections (LODs) for Zn and Ca are 0.014–0.033 and 0.011–0.097 mg L–1, respectively, which are in good agreement with the closed-type electrolyte cathode atmospheric glow discharge (ELCAD). The obtained results of Ca and Zn in real samples by LCGD-AES are basically consistent with the ICP-AES and reference value. The results suggested that LCGD-AES can provide an alternative analytical method for the detection of metal elements in biological and medical samples.Download high-res image (144KB)Download full-size image

•A liquid cathode glow discharge-atomic emission spectrometry (LCGD-AES) was constructed.•The effects of discharge voltage, solution flow rate and capillary diameter on emission intensity were investigated.•The Cu and Pb in ores samples were simultaneously determinate by LCGD-AES.•The measurement results of LCGD were well consistent with the reference values of ICP.•The LCGD has higher excitation efficiency, lower energy consumption and better discharge stability.In this study, a liquid cathode glow discharge-atomic emission spectrometry (LCGD-AES) was constructed for simultaneously determination of Cu and Pb in digested ores samples, in which the glow discharge was produced between the needle-like Pt anode and electrolyte overflowing from quartz capillary. The stability of LCGD and the effects of discharge voltage, capillary diameter and flow rate on emission intensity were systematically investigated. The limits of detections (LODs) of Cu and Pb were compared with those measured by closed-type electrolyte cathode discharge-atomic emission spectrometry (ELCAD-AES). In addition, the measured results of LCGD were verified by ICP-AES. The results showed that the optimization analytical conditions were 675 V discharge voltage, 1.0 mm capillary diameter and 5.5 mL min−1 flow rate. The analytical response curves had good linearity in the range of 1–10 mg L−1. The RSD was 2.05% for Cu and 1.27% for Pb. The LODs of Cu and Pb were 0.36 and 0.20 mg L−1, respectively, which are in agreement with the closed-type ELCAD. The obtained results of Cu and Pb in ore samples by LCGD are consistent with the reference materials of ICP. The recovery of samples is ranged from 85.2–105.6%, suggesting that the determinated results have high accuracy. All the results indicated that the LCGD can provide an alternative analytical method for the determination of metal elements in ores samples.

•The liquid cathode glow discharge-atomic emission spectrometry (LCGD-AES) was constructed.•The effects of the supporting electrolyte, discharge voltage and organic additives on emission intensity were investigated.•A multi-metal simultaneously analyzer of water samples was achieved by LCGD-AES.In this work, a liquid cathode glow discharge-atomic emission spectrometry (LCGD-AES) was constructed for simultaneously determination of K, Na, Ca, Mg and Zn in water samples (tap water, mineral water, Yellow River water and waste water), in which the glow discharge plasma was produced between the needle-like Pt anode and electrolyte around a quartz capillary cathode. The effects of the supporting electrolyte, discharge voltage and organic additives on emission intensity were investigated in detail. The limits of detections (LODs) of metals were compared with those measured by the closed-type electrolyte-cathode discharge-atomic emission spectrometry (ELCAD-AES). In addition, the measured results of water samples using LCGD were verified by ICP. The results showed that the optimal operation conditions are pH = 1 HNO3 as supporting electrolyte, addition of 0.15% formic acid and 650 V discharge voltage. The R2 and the RSD are ranged from 0.9887 to 0.9990 and 1.10% to 2.19%, respectively. LODs of K, Na, Ca, Mg and Zn are 0.02, 0.04, 0.19, 0.04 and 0.05 mg L− 1, which are in agreement with the ELCAD-AES, and satisfied the recommended levels of the China standards for drinking water quality. The obtained results of Na, K, Ca, Mg and Zn in water samples by LCGD and ICP have certain difference. This result provides an alternative analytical method for the determination of metal elements in water samples.

•LCGD-AES technique is developed.•Analytical performance of LCGD-AES was evaluated by determination of Cu.•Addition of 0.15% CTAC can improve the emission intensity of Cu.•The LOD of Cu in LCGD was found to be comparable to those of similar ELCAD systems.•LCGD can be a promising technique for on-line analysis of metal ions in aqueous samples.In this study, a novel liquid cathode glow discharge-atomic emission spectrometry was developed for the direct determination of Cu in aqueous solutions, in which the glow discharge plasma was produced in the solution between the needle-like Pt cathode and the electrolyte around it. The effects of discharge voltage, solution pH, and the ionic surfactant cetyltrimethylammonium chloride (CTAC) on emission intensities were investigated. The limit of detection (LOD) of Cu was compared with those measured by closed-type electrolyte cathode discharge-atomic emission spectrometry (ELCAD-AES). The results showed that the optimal operation conditions are voltage of 135 V, a pH of 1, and addition of 0.15% CTAC. CTAC can enhance the emission intensity and lower the LOD of Cu I. The net intensity of atomic emission lines of Cu I at 324.8 nm with 0.15% CTAC improved by 1.5 fold, and the LODs of the Cu at 135 V with 0.15% CTAC and without CTAC are 0.019 and 0.234 mg L− 1, respectively. The analytical capability of Cu in this study is comparable to the closed-type ELCAD-AES, and it satisfied the recommended levels of Cu in the WHO standards for drinking-water quality. This technique can be effectively used for on-line monitoring of metal ions in aqueous samples.

Reusability and selective adsorption toward Pb2+ with the coexistence of Cd2+, Co2+, Cu2+ and Ni2+ ions on chitosan/P(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylic acid) [CS/P(AMPS-co-AA)] hydrogel, a multi-functionalized adsorbent containing –NH2, –OH, –COOH and –SO3H groups was studied. The CS/P(AMPS-co-AA) was prepared in aqueous solution by a simple one-step procedure using glow discharge electrolysis plasma technique. The reusability of adsorbent in HNO3, EDTA-2Na and EDTA-4Na was investigated in detail. The competitive adsorption of the metal ions at the initial stage was compared between their equal mass concentration and equal molar concentration. In addition, the adsorption mechanism of the adsorbent for adsorption of Pb2+ was also analyzed by XPS. The results showed that the optimum pH of adsorption was 4.8, and time of adsorption equilibrium was about 180 min. Adsorption kinetics fitted well in the pseudo second-order model. The equilibrium adsorption capacities of Pb2+, Cd2+, Co2+, Cu2+, and Ni2+ at pH 4.8 were obtained as 673.3, 358.3, 176.7, 235.0 and 171.7 mg g−1, in their given order. The adsorbent displayed an excellent reusability using 0.015 mol L−1 EDTA-4Na solution as the eluent, and the desorption ratio could not correctly reflect the true characteristics of adsorption/desorption process. Moreover, the adsorbent showed good adsorption selectivity for Pb2+. The molar adsorption capacity at the initial stage with equal molar concentration was more reliable than the mass adsorption capacity during the study of selective adsorption. According to the XPS results, the adsorption of Pb2+ ions by the CS/P(AMPS-co-AA) absorbent could be attributed to the coordination between N atom and Pb2+ and ion-exchange between Na+ and Pb2+.

In this work, a novel chitosan/P(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylic amide) (CS/P(AMPS-co-AM)) hydrogel was successfully prepared by a simple one-step method using glow-discharge-electrolysis plasma (GDEP) initiated copolymerization, in which N,N′-methylenebisacrylamide was used as a cross-linking agent. A copolymerization mechanism of AMPS and AM onto CS initiated by GDEP was proposed. The structure, thermal stability and morphology of CS/P(AMPS-co-AM) hydrogel were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), TG/DTG, and scanning electron microscope (SEM). This hydrogel was employed as an absorbent for the removal of methylene blue (MB) and malachite green (MG) from aqueous solutions. The effects of pH, contact time and equilibrium concentration on the dye adsorption were investigated batchwise. FTIR and XRD indicated that AM and AMPS were grafted onto the CS backbone successfully, forming copolymer. TG/DTG suggested that grafted AMPS and AM onto CS could change the thermal stability of the CS. SEM showed a unique three-dimensional porous structure for the CS/P(AMPS-co-AM) hydrogel. The optimum pH for the removal of cationic dyes was 5.8, and time of adsorption equilibrium was achieved in 90 min. The CS/P(AMPS-co-AM) hydrogel exhibited a very high adsorption potential, and its adsorption capacities calculated based on the Langmuir isotherm for MB and MG were 1,538.5 and 917.4 mg g−1, respectively. The dye adsorption data fitted well to the pseudo-second-order model and Langmuir model at 25 °C with pH 5.8.

A palygorskite/poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylamide) (PGS/P(AMPS-co-AM)) superabsorbent hydrogel was prepared in aqueous solution using glow-discharge electrolysis plasma (GDEP) as an initiator and N,N′-methylene-bis-acrylamide as a cross-linker. A possible copolymerization mechanism initiated by GDEP was proposed. The structure, thermal stability, and morphology of PGS/P(AMPS-co-AM) were characterized by FT-IR, XRD, TG-DTG, and SEM. The swelling kinetics, pH-reversibility, and influence of various pH and salt solutions on the swelling were investigated. Adsorption kinetics and adsorption mechanism of hydrogel for dyes were studied in detail. The results indicated that the equilibrium swelling of hydrogel is 652.6 g g−1 in distilled water. The swelling of the hydrogel in salt solutions from highest to lowest is Na+ > Mg2+ > Fe3+. The hydrogel has pH-reversibility responsive to the pH and salts solutions. The adsorption process of dyes follows the pseudo-second-order kinetic model with multi-step diffusion process. In addition, PGS/P(AMPS-co-AM) hydrogel can be regenerated and reused.

Using Pearson’s hard and soft acids and bases (HSAB) principle as the design guideline, a novel chitosan/poly(ethylene glycol)/poly(acrylic acid) (CS/PEG/PAA) hydrogel adsorbent containing hard Lewis base adsorption site (i.e., amino group, hydroxyl group, ether linkage, carboxylate ions) was prepared by glow-discharge electrolysis plasma (GDEP) technique and then applied for the selective adsorption of Pb2+. A copolymerization mechanism initiated by GDEP was proposed. The structure, thermal stability, and morphology of CS/PEG/PAA adsorbent were characterized by FT-IR, thermogravimetry/differential thermogravimetry (TG/DTG), and SEM. The effects of the solution pH and contact time on the single-component adsorption were examined by batch experiments. Competitive adsorptions of Pb2+ and Cd2+ were carried out under equal mass concentration and equal molar concentration. In addition, regeneration and reusability of adsorbent were also investigated in detail. The results showed that the maximum adsorption capacities for Pb2+ and Cd2+ are 431.7 and 265.0 mg g−1, respectively. The kinetic behaviors of the adsorption and the fourth desorption for single component and the competitive adsorption for Pb2+ follow the pseudo-second-order model with pH = 4.8. The CS/PEG/PAA adsorbent has good adsorption selectivity for Pb2+ with the coexistence of Cd2+. The adsorbent displays excellent regeneration and reusability in the EDTA-4Na solution.

Highly swelling P(2-acrylamido-2-methyl-1-propanesulfonic acid- co-acrylic acid) (P(AMPS-co-AAc)) superabsorbent hydrogel was synthesized in aqueous solution by a simple one-step using glow-discharge electrolysis plasma technique, in which N,N’-methylenebisacrylamide was used as a crosslinking agent. The structure, thermal stability and morphology of P(AMPS-co-AAc) superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. A mechanism for synthesis of P(AMPS-co-AAc) superabsorbent hydrogel was proposed. The reaction parameters affecting the equilibrium swelling (i.e., discharge voltage, discharge time, macroscopic temperature of the liquid phase, mass ratio of AMPS to AAc, and content of crosslinker) were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The hydrogel formed which absorbed about 1,685 g H2O/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl2, and CaCl2) on the equilibrium swelling. In addition, swelling kinetics in distilled water and on–off switching behavior were preliminarily investigated. The results showed that superabsorbent hydrogel was responsive to the pH and salts.