Jinmei Wang

Optimization of experimental conditions by orthogonal test design in a laser-induced breakdown experiment to analyze aluminum alloys

The orthogonal test design is used to optimize the parameters of aluminum alloy laser-induced breakdown spectroscopy (LIBS). The signal to background ratio (SBR) of the line of Al I 396.15 nm dependence on the experimental parameters is analyzed. It is shown that the delay time of the ICCD, the gate width of the ICCD and the laser pulse energy have a great influence on the SBR, the parameters which affect the SBR of Al I 396.15 nm are, in order of the laser pulse energy, delay time of the ICCD, gate width. By optimizing the parameters of the experiment, the optimum conditions are determined and high spectral intensity and SBR are obtained under low laser energy. Besides, the sequential test is used to verify the result of the orthogonal test design, and it shows that they are in good agreement with each other. Therefore the orthogonal test design can be used as an optional scheme for the optimization of the LIBS. There are many advantages of the orthogonal test design, such as greatly reducing the workload, simple and rapid analysis, and with accurate results. It is useful to analyze the components of the aluminum alloy or other solid materials qualitatively and quantitatively under the optimum conditions.

Online mercury determination by laser-induced breakdown spectroscopy with the assistance of solution cathode glow discharge

The trace mercury in an aqueous solution was determined by laser-induced breakdown spectroscopy (LIBS) with the assistance of a solution cathode glow discharge (SCGD) system. The aqueous solution was converted to the gas phase using a high voltage DC discharge, and then the generated mercury vapor was cooled by a gas–liquid separator to improve the concentration of the mercury. Finally, a 1064 nm wavelength Nd:YAG laser was used to produce the plasma. In the present experiment, the characteristic spectral line of Hg I 253.65 nm was selected for the analysis, under the optimal conditions of LIBS, to investigate the influences of the acid anion, the discharge current, the sample flow rate and the carrier gas flow rate. The temporal behavior of the electron temperature and electron number density were also investigated; the results show that the electron temperature decreases from about 10 900 K to 8800 K with a delay time from 200 ns to 6 μs and that the electron number density is in the orders of 1017 and 1018 cm−3, and decreases with delay time. The analytical performance of this method was evaluated under optimized conditions, and a calibration curve of Hg was plotted based on the different concentrations measurement results, and the detection limit (LOD) of Hg was calculated to be 0.36 mg L−1. By this experimental configuration, the detection limit and sensitivity of Hg are improved to some extent. This method provides an alternative analytical method for the measurement of trace mercury in water.

Elemental Analysis of Mineral Water by Solution-Cathode Glow Discharge–Atomic Emission Spectrometry

ABSTRACT A solution-cathode glow discharge was used for atomic emission spectrometry. The acidic reagent, discharge current, and flow rate were optimized. The detection limits for sodium, potassium, calcium, and magnesium were 1.51, 4.13, 131, and 54.9 µg L−1, respectively. The relative standard deviation for five replicates was from 0.52 to 3.00%. Sodium, potassium, calcium, and magnesium were determined in mineral water by solution-cathode glow discharge–atomic emission spectrometry. The results demonstrate that the protocol is suitable for the elemental analysis of mineral water.

A pulsed atmospheric-pressure discharge generated in contact with flowing electrolyte solutions for metal element analysis by optical emission spectrometry

A novel atmospheric-pressure plasma source has been developed for the detection of metal ions in aqueous solution by optical emission spectrometry. In contrast to the common solution cathode glow discharge, this source is sustained by using an alternating-current power supply coupled with a high voltage diode. The electrical characteristics and spectral characteristics of this plasma source are discussed. The effects of operating parameters, including the acid anion, electrolyte pH, discharge voltage, discharge frequency, inter-electrode distance, sample flow rate and vertical distributions of spectral signals, are investigated. The spectral intensities and standard deviations (SDs) of background signals of this source are much lower than those of other electrolyte–electrode devices. In addition, metal element emissions have the same optimum spectral emission positions in the plasma. The detection limits of Li, Na, K, Rb, Cs, Sr and Mg are determined to be 0.0054, 0.0011, 0.0029, 0.04, 0.054, 2.5 and 0.26 mg L−1, respectively. The proposed excitation source provides a promising technique for the detection of metal ions in aqueous solution samples.

Self-organized pattern formation of an atmospheric-pressure, ac glow discharge with an electrolyte electrode

An atmospheric-pressure plasma sustained by an ac power supply was generated using electrolyte solution as one of the electrodes. By altering the power supply, ring-like patterns, double-ring patterns and plasma-spot patterns were observed at the electrolyte–electrode surface. Synchronous current–voltage characteristics and time-resolved images were measured. Important factors for the self-organized patterns, including the electrode gap, power, frequency and electrolyte concentration, were explored. The optical spectrum characteristics of the device were investigated. The pH of the solution after discharge was also explored and the results show that the pH of the solution is evidently reduced after the discharge, implying that acidic components are produced in the solution. This study provides an alternative discharge method for producing patterns on a water surface.

Classification of Chinese Herbal Medicine by Laser-Induced Breakdown Spectroscopy with Principal Component Analysis and Artificial Neural Network

ABSTRACT Chinese herbal medicine has attracted increasing attention because of the unique and significant efficacy in various diseases. In this paper, three types of Chinese herbal medicine, the roots of Angelica pubescens, Codonopsis pilosula, and Ligusticum wallichii with different places of origin or parts, are analyzed and identified using laser-induced breakdown spectroscopy (LIBS) combined with principal component analysis (PCA) and artificial neural network (ANN). The study of the roots of A. pubescens was performed. The score matrix is obtained by principal component analysis, and the backpropagation artificial neural network (BP-ANN) model is established to identify the origin of the medicine based on LIBS spectroscopy of the roots of A. pubescens with three places of origin. The results show that the average classification accuracy is 99.89%, which exhibits better prediction of classification than linear discriminant analysis or support vector machine learning methods. To verify the effectiveness of PCA combined with the BP-ANN model, this method is used to identify the origin of C. pilosula. Meanwhile, the root and stem of L. wallichii are analyzed by the same method to distinguish the medicinal materials accurately. The recognition rate of C. pilosula is 95.83%, and that of L. wallichii is 99.85%. The results present that LIBS combined with PCA and BP-ANN is a useful tool for identification of Chinese herbal medicine and is expected to achieve automatic real-time, fast, and powerful measurements.

Determination of Lead and Copper in Ligusticum wallichii by Laser-Induced Breakdown Spectroscopy

ABSTRACT Laser-induced breakdown spectroscopy was used for the analysis of the Chinese traditional medicine, Ligusticum wallichii. The laser energy and delay time were optimized to obtain best spectral quality. The limits of detection for lead and copper were 15.7 and 6.3 µg g−1, respectively. Multiple linear regression models between the laser-induced breakdown spectroscopy intensity and the mass fraction of lead and copper were constructed. Good agreement was observed between the actual concentrations and predicted values obtained by the models. These results demonstrate that the laser-induced breakdown spectroscopy coupled with multiple linear regression is suitable for the determination of heavy metals in Chinese traditional medicine.

Time-resolved emission spectroscopy and plasma characteristics of a pulsed electrolyte cathode atmospheric pressure discharge system

Herein, a pulsed electrolyte cathode atmospheric pressure discharge (pulsed-ECAD) system was developed as a radiation source for the atomic emission spectroscope (AES) for metal element determination in aqueous solutions. The time-resolved emission spectra of the pulsed-ECAD were obtained at various frequencies, and their evolution behaviours during the modulation period were found to exhibit a strong dependence on the modulation frequency. The temporal behaviors of the metal element spectral intensities of K, Na, Li, Rb, Sr, and Mg as well as the atomic and molecular species emissions originating from water and air (OH, Hα, Hβ, N2, and O) were characterized from the plasma. The temporal evolutions of the pulsed-ECAD plasma parameters, including the rotational temperature, electron density, and ionization temperature, were analyzed. The results showed that the rotational temperatures varied between 950 K and 1350 K. The electron density and ionization temperature ranges of Mg were from 4.3 × 1014 to 2.2 × 1015 cm−1 and from 5200 K to 5500 K, respectively.

Analytical Characterization of a Solution Cathode Glow Discharge with an Interference Filter Wheel for Spectral Discrimination

ABSTRACT Solution cathode glow discharge–atomic emission spectrometry (SCGD–AES) has attracted increasing attention in recent years in water and environmental analysis. In this article, the traditional spectrometer was replaced by an interference filter wheel for spectral discrimination using SCGD–AES. The aforementioned interference filters selected the spectral lines of Na, K, Ca, Li, Sr, Rb, and Cs. These spectral signals were transferred to weak currents using a photomultiplier tube and amplified by a picoammeter. The solution flow rate, discharge current and slit width were optimized individually. The analytical performance of SCGD coupled with an interference filter wheel was studied for atomic emission (SCGD–IFW–AES). The results show that the limits of detection for Na, K, Ca, Li, Sr, Rb, and Cs were 0.16, 0.36, 107, 0.53, 330, 1.93, and 13.58 µg/L, respectively. The relative standard deviations of the spectral intensities for the seven elements were 0.58, 0.94, 0.69, 0.70, 0.63, 0.67, and 0.65%, which indicated that the system operated stably. Matrix effect experiments were performed to study the effect of different concentrations of Na on the spectral intensities of K and Ca. Based on these measurements, the concentration of K in physiological saline was determined to be 0.534 mg/L by SCGD–IFW–AES.

Evaluation of Matrix Effects in a Pulsed Electrolyte Cathode Atmospheric Pressure Discharge Source for Atomic Emission

ABSTRACT In sample measurements, matrix effects are unavoidable. The matrix effects are one of the main factors affecting the accuracy of the pulsed electrolyte cathode atmospheric pressure discharge detection system. The stability of sodium, potassium, and magnesium, under optimized parameters is measured; the relative standard deviation of spectral intensity is found to be no more than 2%; and the relative standard deviation of background intensity is less than 2%. The matrix effects on the elements potassium, sodium, and magnesium were studied, and the experiments showed that high concentrations of sodium and potassium interfere with each other. A concentration of 200 mg L−1 K+ affected the sodium signal with an enhancement of more than 120%; and the K+ intensity increased 20% in the presence of a high concentration of 200 mL−1 Na+. In high concentrations of sodium or potassium, the elemental signal for magnesium enhancement was approximately 8%. Sodium, potassium, and magnesium were quantitatively determined using a mixed calibration sample. When sodium, potassium, and magnesium are present at low concentrations in solution, there were no obvious matrix effects. The sodium, potassium, and magnesium in the calibration samples are quantitatively determined. The relative error and precision are less than 3%, and the recoveries are less than 105%. The detection limits for sodium, potassium, and magnesium were found to be 2.1, 3.4, and 92.6 µg L−1, respectively.