Electrode Plasma Atomic Emission Spectrometry Research Articles

Fabrication and Characterizations of Axial View Liquid Electrode Plasma Atomic Emission Spectrometry for the Sensitive Determination of Trace Zinc, Cadmium, and Lead.

Axial view liquid electrode plasma-atomic emission spectrometry (axial view LEP-AES) was proposed and fabricated successfully in this work. The emission spectra from Zn, Cd, Pb, Ca, and K were applied for characterization and optimization. Comparing with conventional radial view LEP-AES devices, the newly designed axial view-LEP provided better sensing ability toward trace heavy metals. Moreover, pulsed voltage discharge was found to be advantageous over continuous discharge under the same discharge time for detection. The optimized parameters facilitate the limit of detection to achieve 0.24, 0.051, and 0.85 μg L-1 for Zn, Cd, and Pb, respectively. Furthermore, the axial view LEP-AES possessed excellent reproducibility and good durability. The real sample tests using two different certified reference water samples revealed the great potential of the axial view LEP-AES as a novel practical elemental analysis tool.

Organic Ion-associate Phase Extraction/Back-microextraction for the Preconcentration and Determination of Lithium Using 2,2,6,6-Tetramethyl-3,5-heptanedione by Liquid Electrode Plasma Atomic Emission Spectrometry and GF-AAS in Environmental Water.

We developed an ion-associate phase (IAP)-extraction/acid back-extraction system for the preconcentration and atomic spectrometric determination of lithium trace amounts in water. The chelating reagent for lithium also works as a constituent of the extraction phase. The lithium in a 10 mL sample solution was converted through a chelate complex reaction with 2,2,6,6-tetramethyl-3,5-heptanedione (HDPM). The addition of a benzyldimethyltetradecylammonium ion caused the formation of IAP suspension in the solution. Centrifugation of the solution led to the isolation of a liquid organic phase and the lithium complex was extracted as the upper phase from the centrifuge tube. After the aqueous phase was removed, lithium was back-extracted with a 400 μL nitric acid solution from the IAP. The acid phase was measured using liquid-electrode-plasma atomic-emission-spectrometry (LEP-AES) or graphite-furnace atomic-absorption spectroscopy (GF-AAS). The detection limits were 0.02 mg/L for LEP-AES and 0.02 μg/L for GF-AAS. This system was applied to the determination of environmental water. The HDPM in the organic phase was reusable.

Study on effect of introduced gas bubbles for the low channel damage in direct and alternating current liquid electrode plasma atomic emission spectrometry

Liquid electrode plasma (LEP) is used as an excitation source for compact and sensitive elemental analysis, where the channel damage by plasma causes the severe tradeoff between sensitivity and lifetime. In alternative current (AC)-LEP, significantly less channel damage (1/3000) was reported compared to direct current LEP (DC-LEP). However, the mechanism has not been clear. In this paper, the effects of external gas introduction into AC-LEP and DC-LEP were studied. The results showed that the external gas bubbles facilitated stable and highly sensitive plasma generation with lower power, reducing channel damage and increasing the lifetime of the analysis chip. These effects are significant in Ar introduction and AC-LEP cases. The facts suggest that the lower damage in conventional AC-LEP without gas introduction is attributed to H2/O2 bubbles generated by hydrolysis at electrodes and consequently introduced into the LEP from outside of narrow channel.

Direct Measurement of Silver Anoparticles Suspended in Aqueous Solution by Liquid Electrode Plasma - Atomic Emission Spectrometry

This paper presents a quantitative measurement of silver nanoparticles in aqueous suspension by liquid electrode plasma atomic emission spectrometry (LEP-AES). The dependence of the LEP-AES signal intensity on voltage-pulse height and duration is investigated. The detection limit and coefficient of variation (CV) are also measured. The CV attains a minimum value of 7% for a pulse height of 1080 V and a pulse duration of 7 ms. The detection limit (3σ) of silver nanoparticles by LEP-AES, under these optimal conditions, was calculated from a calibration curve to be 0.23 µg/g.

Atomic emission spectrometry in liquid electrode plasma using an hourglass microchannel

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a new elemental analysis method that uses microplasma. LEP forms in a vapor bubble generated inside a narrow-center microchannel by using high-voltage DC pulse power.

On-chip solid phase extraction–liquid electrode plasma atomic emission spectrometry for detection of trace lead

This paper reports the application of liquid electrode plasma atomic emission spectrometry (LEP AES) integrated with on-chip solid phase extraction (SPE) for determination of lead (Pb). LEP AES is a novel elemental analysis method employing micro-plasma in the sample solution as excitation source. The integration of SPE to LEP chip shows high potential of application with several merits because on-chip SPE enables the effective use of sample. In the work an improved LEP chip integrated with SPE was developed for trace lead detection. Chip design and pulse voltage were proposed to eliminate the ash generation and minimize the channel expansion. Some analytical parameters were optimized. With sample volume of 1 mL calibration curve in the range of 0–100 ng/mL the correlation coefficient of 0.992 and limit of detection (LOD) of 0.64 ng/mL were obtained. With the support of SPE, LOD was improved about 30 times.

Computer-controlled fluid-flow chemical analysis (CC-FCA) and its application to environmental analytical chemistry

Computer-controlled fluid-flow chemical analysis (CC-FCA) was investigated for the determination of trace amounts of toxic pollutants in the environment. For CC-FCA, automated chemical analysis systems were developed by using computer-controllable pumping and valve modules, and polytetrafluorethylene (PTFE) tubing and connectors. The systems demonstrated in this work were a flow injection-type system, a sequential injection-type system, a mini-column pretreatment system (Auto-Pret system), and an Auto-Pret hyphenated with flow injection analysis (FIA) system. Such systems were fully controlled by a computer program; the lab-made programs were written in Visual Basic. The systems can be hyphenated with some detectors, such as a spectrophotometric detector, an electrochemical detector, electrothermal-atomic absorption spectrometry (ET-AAS), a liquid electrode plasma-atomic emission spectrometry (LEP-AES) and inductively coupled plasma (ICP)-AES. Such systems were successfully applied to the determination of trace amounts of toxic pollutants in environmental water samples: they were heavy metal ions (Pb, Cd, Cr, etc.). In this paper, the author aims mainly at investigating the CC-FCA method for the determination of trace amounts of Cr(VI) in environmental water samples by spectrophotometry. The techniques used in this work were FIA, sequential injection analysis (SIA), and Auto-Pret/FIA, which were all computer-controllable. Limits of detection of Cr(VI) by FIA, SIA, and Auto-Pret/FIA were 8 × 10–9 mol/L (0.4 μg/L), 1.1 × 10–8 mol/L (0.6 μg/L), and 1.4 × 10–9 (0.07 μg/L), respectively. The methods were applied to the determination of Cr(VI) in river and drinking waters.

Sensing Technique of Silver Nanoparticles as Labels for Immunoassay Using Liquid Electrode Plasma Atomic Emission Spectrometry

We report the use of liquid electrode plasma-atomic emission spectrometry (LEP-AES) in protein sensing studies employing Ag nanoparticle labeling. LEP-AES requires no plasma gas and no high-power source and is suitable for onsite portable analysis. Human chorionic gonadotropin (hCG) was used as a model target protein, and the immunoreaction in which hCG is sandwiched between two antibodies, one of which is immobilized on the microwell and the second is labeled with Ag nanoparticles, was performed. Sensing occurs at the narrow pass in the center of a quartz chip following oxidative dissolution of the Ag nanoparticles by nitric acid. hCG was analyzed in the range from 10 pg/mL to 1 ng/mL, and the detection limit for hCG was estimated at 1.3 pg/mL (22.8 fM). The proposed detection method has a wide variety of promising applications in metal-nanoparticle-labeled biomolecule detection.

Characteristics of liquid electrode plasma for atomic emission spectrometry

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a recently developed elemental analysis method that uses microplasma. LEP forms in a vapor bubble generated inside a narrow-center microchannel by using high-voltage DC pulse power. We studied the characteristics of LEP and atomic emission of lead (Pb), as an example element, which has not been described in detail. We estimated the plasma parameters and observed the expansion and shrinkage of a vapor bubble with discharge as well as the time course and spatial distribution of the atomic emission of Pb (405.78 nm). The applied voltage was 2.5 kV and the pulse width was less than 3 ms, which produced a current of about 100 mA. We found that the excitation temperature was about 8000 K and the electron density was about 1 × 1015 cm−3. We also found that two quite different emission phases occurred separately during the time course. The first emission phase corresponds to the first expansion and shrinking of the bubble around atmospheric pressure and the second emission phase corresponds to the re-expansion of the bubble and emission at reduced pressure with higher atomic and lower background emissions. Maximum atomic and background emissions were observed at the narrowed center of the microchannel, but there was an additional local maximum atomic emission region at the anode side bubble–liquid interface where the background emission was very low, which would be a better condition for sensitive measurement. The limit of detection determined in our experiment was 4.0 μg L−1 for Pb.

Highly Sensitive Elemental Analysis for Cd and Pb by Liquid Electrode Plasma Atomic Emission Spectrometry with Quartz Glass Chip and Sample Flow

This paper describes the development of a highly sensitive liquid-electrode plasma atomic emission spectrometry (LEP-AES) by combination of quartz glass chip and sample flow system. LEP-AES is an ultracompact elemental analysis method, in which the electroconductive sample solution is put into a microfluidic channel whose center is made narrower (∼100 μm in width). When high voltage pulses (1500 V) are applied at both ends of the channel, the sample evaporates locally at the narrow part and generates plasma. By the emission from the plasma, elemental concentration is analyzed. In this paper, the limits of detection (LODs) were investigated in various conditions of accumulation time, material of the chip, and the sample flow. It was found that the long accumulation using the quartz chip with sample flow was effective to improve LOD. Authors suggested that this was because bubbles remaining after each plasma pulse were removed from the narrow channel by sample flow, resulting in highly reproducible plasma generation, to enable a high accumulation effect. Finally, LODs were calculated from a calibration curve, to be 0.52 μg/L for Cd and 19.0 μg/L for Pb at optimized condition. Sub-ppb level LOD was achieved for Cd.

Excitation Temperature Measurement in Liquid Electrode Plasma

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a novel elemental analysis method where a sample solution is placed in a small cuvette that has a narrow microchannel at the center. High voltage is applied to the solution from both ends of the cuvette channel, and then microplasma is generated in the channel. The microplasma is employed in atomic emission spectrometry as a plasma source. Excitation temperature was deduced using a Boltzmann plot. The temperature was determined to be 6200 K with a plastic chip at an applied voltage of 800 V. To investigate effects of the experimental conditions on excitation temperature, applied voltage, type of acid, and the shape of the cross section of a microchannel at the center of the cuvette were varied. The excitation temperature was not influenced by applied voltage or type of acid, but was affected by the shape of the cross section of the microchannel.

Liquid Electrode Plasma Atomic Emission Spectrometry Combined with Multi-Element Concentration Using Liquid Organic Ion Associate Extraction for Simultaneous Determination of Trace Metals in Water

液体電極プラズマ発光分析法（LEP-AES）は小型化可能な元素分析法であり，ガス供給や大型電源が不要なため，現場分析に適する．本研究では，LEP-AESと微小体積に短時間で高濃縮できる有機イオン会合体抽出法による濃縮を組み合わせ，微量金属（Cu，Mn，Pd，Zn，Cd，Pb）の一括濃縮/同時定量法を開発した．試料水40 mLにキレート試薬を加え，重金属を錯体とし，水相から生成させた有機イオン会合体中に抽出した．この会合体の体積はμLレベルである．これをメタノールに溶解し，硝酸溶液を加え400 μLとした．40 μLを分取してLEP-AESで測定した．濃縮倍率は100倍である．以上の濃縮/定量法より，短時間で高感度な現場元素分析が可能となり，検出限界は数μg L－1～数百μg L－1となった．いくつかの元素は濃縮倍率以上に感度が上昇した．また，廃液の認証標準物質に適用したところ，測定値は認証値の許容範囲内であった．

Determination of Cadmium in Water Samples by Liquid Electrode Plasma Atomic Emission Spectrometry after Solid Phase Extraction Using a Mini Cartridge Packed with Chelate Resin Immobilizing Carboxymethylated Pentaethylenehexamine

Solid phase extraction using a mini cartridge packed with 22 mg of chelate resin immobilizing carboxymethylated pentaethylenehexamine was successfully utilized for separation/preconcentration of cadmium in water samples prior to liquid electrode plasma atomic emission spectrometric (LEP-AES) determination. The combined method with the extraction and LEP-AES was applicable to the determination of cadmium in the certified reference materials (EU-L-1 wastewater and ES-L-1 groundwater); the detection limit was 0.20 microg in 200 mL of sample solution (500-fold preconcentration).

Quantitative Determination of Lead in Soil by Solid-Phase Extraction/Liquid Electrode Plasma Atomic Emission Spectrometry

新しい原子発光分析である液体電極プラズマ法（LEP-AES法）は，中央が絞られた小型容器（横幅数mm）に数十μLの試料を入れ，そこに高電圧を印加する事でマイクロプラズマを発生させる方式である．ICP-AES法と異なり，アルゴンガスや大電力を必要としないため，小型化並びに可搬化が可能となり，本法を応用したハンディ元素分析装置が開発された．本研究では，認証汚染土壌に含有されているPbをハンディ元素分析装置で測定する事を目的として，装置の性能評価を行った．結果は波長405.8 nmにおける検出限界が1.3 mg/L，相対標準偏差（RSD）は10％ 以下，直線性許容範囲は2桁と，ハンディ元素分析装置としては十分な性能であった．汚染土壌は環境省告示第19号に準拠した方法で溶出液を作成し，固相抽出により分離濃縮後，測定を行った．測定結果は80.2 mg/kg（dry）であり，認証値82.7±3.8 mg/kg（dry）の許容範囲内の値であった．