Trace determination of antimony by hydride generation atomic absorption spectrometry with analyte preconcentration/atomization in a dielectric barrier discharge atomizer

Rapid detection of ultratrace urinary arsenic by direct sampling microplasma vaporization based on silicon nitride

At present, immediate monitoring urinary arsenic is still a challenge for treating arsenic poisoning patients. Thus, a fast, reliable and accurate analytical approach is indispensable to monitor ultratrace arsenic in urine sample for health warning. In this work, a silicon nitride (SN) rod was first integrally utilized as a sample carrier for ≤50 μL urinary aliquot, an electric heater for removing water and ashing sample as well as a high voltage electrode for dielectric barrier discharge vaporization (DBDV). The direct analytical method of arsenic in urine without sample digestion was thus developed using atomic fluorescence spectrometer (AFS) as a model detector. After 4 V electrically heating the SN rod for 60 s, urine sample was dehydrated and ashed outside; then, DBD was exerted under 0.8 A with 0.8 L/min H₂ + Ar (1:9, v:v) for 20 s to vaporize arsenic analyte from the SN rod. After optimization, 0.014 μg/L arsenic detection limit (LOD) was reached with favorable analytical precision (RSD <5%) and accuracy (91-110% recoveries) for real sample analysis. As a result, the whole analysis process only consumes <3 min to exclude complicated sample preparation; furthermore, the designed DBDV system only occupies 25 W and <2 kg, which renders a miniature sampling component to hyphenate with a miniature detector to detect arsenic. Thus, this direct sampling DBDV method extremely fulfills the fast, sensitive and precise detection of ultratrace arsenic in urine sample.

Array Point Discharge as Enhanced Tandem Excitation Source for Miniaturized Optical Emission Spectrometer

A new compact tandem excitation source was designed and constructed by using an array point discharge (ArrPD) microplasma for a miniaturized optical emission spectrometer through coupling a hydride generation (HG) unit as a sample introduction device. Three pairs of point discharges were arranged in sequence in a narrow discharge chamber to construct the ArrPD microplasma, for improved excitation capability owing to the serial excitation. Besides, the discharge plasma region was greatly enlarged, therefore, more gaseous analytes could be intercepted to enter into the microplasma for sufficient excitation, for improved excitation efficiency and OES signal. To better understand the effectiveness of the proposed ArrPD source, a new instrument for simultaneous detection of atomic emission and absorption spectral responses was also proposed, designed, and constructed to reveal the excitation and enhancement process in the discharge chamber. Under the optimized conditions, the limits of detection (LODs) of As, Ge, Hg, Pb, Sb, Se, and Sn were 0.7, 0.4, 0.05, 0.7, 0.3, 2, and 0.08 μg L^-1, respectively, and the relative standard deviations (RSDs) were all less than 4%. Compared with a commonly used single point discharge microplasma source, the analytical sensitivities of these seven elements were improved by 3-6-fold. Certified Reference Materials (CRMs) were successfully analyzed with this miniaturized spectrometer, which features low power, compactness, portability, and high detectability, and is thereby a great prospect in the field of elemental analytical chemistry.

Electrothermal Desolvation-Enhanced Dielectric Barrier Discharge Plasma-Induced Vapor Generation for Sensitive Determination of Antimony by Atomic Fluorescence Spectrometry

A novel simple electrothermal desolvation-enhanced dielectric barrier discharge plasma-induced vapor generation (ETD-DBD-PIVG) method has been developed for sensitive Sb determination by atomic fluorescence spectrometry (AFS). In our proposed ETD-DBD-PIVG, 20 μL sample solution was dried first; then, the resulting solution residue was directly converted into molecular volatile species efficiently through the interactions with hydrogen-doped DBD plasma; and finally, it was transported to AFS for detection. It was found that the desolvation process could greatly enhance Sb vapor generation, and the Sb fluorescence signal intensity is almost independent of its speciation, where comparable sensitivity is achieved for Sb(III) and Sb(V), enabling efficient total Sb detection without pre-reduction. Influencing parameters were evaluated in detail, including heating time, discharge gap, solution pH, and flow rates of argon and hydrogen, as well as coexisting ion interference. Under optimized conditions, the limit of detection was calculated as 0.86 μg L^-1 (17.2 pg) for Sb. The accuracy of the proposed method was validated by the analysis of certified reference materials of simulated natural water samples and several river water samples. Compared with conventional hydride generation, the new ETD-DBD-PIVG offers an alternative green vapor generation technique with several advantages: (1) it eliminates the use of a sample flow system (e.g., no use of any syringe or peristaltic pump); instead, 20 μL of a sample is directly pipetted onto the glass plate for analysis; (2) it greatly simplifies the sample pretreatment steps as no pre-reduction process is needed; (3) it is sensitive and suitable for volume-limited sample analysis: efficient Sb vapor generation without chemical reducing reagents in ETD-DBD-PIVG enables Sb detection with an absolute limit at the picogram level. All the results demonstrate that the proposed method provides a simple, green, and sensitive method for Sb determination and it can also be extended to other elements such as Cd and As.

Atomization of As and Se volatile species in a dielectric barrier discharge atomizer after hydride generation: Fate of analyte studied by selected ion flow tube mass spectrometry

Atomization of hydrides and their methylated analogues in a dielectric barrier discharge (DBD) plasma atomizer was investigated. Selected ion flow tube mass spectrometry (SIFT-MS) was chosen as a detector being capable of selective detection of non-atomized original volatile species allowing thus direct quantification of atomization efficiency. Selenium hydride (SeH₂) and three volatile arsenic species, namely arsenic hydride (AsH₃), monomethylarsane (CH₃AsH₂) and dimethylarsane ((CH₃)₂AsH), were selected as model analytes. The mechanistic study performed contributes to understanding of the atomization processes in atomic absorption spectrometry (AAS). The presented results are compatible with a complete atomization of arsenic hydride as well as its methylated analogues and with atomization efficiency of SeH₂ below 80%. Using AsH₃ as a model analyte and a combination of AAS and SIFT-MS detectors has revealed that the hydride is not atomized, but decomposed in the DBD atomizer in absence of hydrogen fraction in the carrier gas. Apart from investigation of analyte atomization, the SIFT-MS detector is capable of quantitative determination of water vapor content being either transported to, or produced in the atomizer. This information is crucial especially in the case of the low-power/temperature DBD atomizer since its performance is sensitive to the amount of water vapor introduced into the plasma.

A simple graphene modified electrode for the determination of antimony(III) in edible plants and beverage

Antimony(III) is a rare electroactive specie present on Earth, whose concentration is not typically determined. The presence of high concentrations of antimony is responsible for a variety of diseases, which makes it desirable to find convenient and reliable methods for its determination. We have developed a convenient glassy carbon modified electrode with electroreduced graphene oxide GC/rGO for the first time determination of Sb(III) in commercial lettuce, celery, and beverages. The surface of the electrode was characterized by scanning electron microscopy (SEM) and cyclic voltammetry, indicating a heterogeneous and rough surface with a real area of 0.28 cm², which is ~2.5 times the area of GC. The optimal chemical and electrochemical parameters used were: sodium acetate buffer (pH = 4.3), an accumulation potential of -1.0 V and an accumulation time of 150 s. The analytical validation was developed evaluating the linear range (10-60 µg L^-1), limit of detection (2.5 µg L^-1), accuracy, repetibility and reproducibility with satisfactory results (relative standard deviation (RSD) values lower than 10%). All the analyzes performed in real samples by stripping voltammetry were compared with GF-AAS, showing statistically similar values, demonstrating that GC/rGO could be effectively applied in the analysis of food samples.

Effect of additives on cadmium chemical vapor generation and reliable quantification of generation efficiency

Chemical vapor generation (CVG) of cadmium was optimized based on response from atomic absorption spectrometry (AAS) with a heated quartz tube atomizer (QTA). Effect of several modifiers on analytical performance was studied. These additives were: inorganic salts of Cr³⁺, Ti⁴⁺ and Co²⁺ and their on-line synthesized complexes with KCN and thiourea, respectively. The use of these additives resulted in sensitivity enhancement, better repeatability and correspondingly in improvement of overall CVG efficiency. The latter was quantified by two independent approaches: a) by means of ^115mCd radioactive indicator, b) from comparison of sensitivities obtained with conventional solution nebulization and with CVG, both coupled simultaneously to inductively coupled plasma mass spectrometry. Both approaches provided comparable results. The highest efficiency, between 60 and 70%, was reached in the presence of Cr³⁺/KCN and Ti⁴⁺/KCN while 19% was achieved in Co²⁺/ascorbic acid/thiourea environment. Highly irreproducible results with low CVG efficiency ranging from 2.5 to 15% were reached in the absence of any additives. The generated cadmium species were identified to be mostly free atoms regardless of the additives presence or their absence. Cr³⁺/KCN environment was selected as the most robust for CVG of Cd reaching sensitivity of 6.6 s ng^-1 Cd and limit of detection of 60 pg mL^-1 Cd (9 pg Cd absolute) with detection by QTA-AAS.

Fast and High Sensitive Analysis of Lead in Human Blood by Direct Sampling Hydride Generation Coupled with in situ Dielectric Barrier Discharge Trap

A direct sampling hydride generation (HG) system based on modified gas liquid separator (GLS) coupled with in situ dielectric barrier discharge (DBD) is first rendered to detect lead in blood samples. Herein, a triple-layer coaxial quartz tube was employed as DBD trap (DBDT) to replace the original atomizer of atomic fluorescence spectrometry (AFS) to satisfy the in situ preconcentration. After 40-fold dilution, foams generated from protein in a blood sample can be eliminated via the double-GLS set; and lead in a blood sample were generated as plumbane under 3.5% HNO₃ (v:v) and 30 g/L NaOH with 8 g/L KBH₄, 10 g/L H₃BO₃, and 5 g/L K₃[Fe(CN)₆]. Then, lead analyte was trapped on the DBD quartz surface by 9 kV discharging at 50 mL/min air; and subsequently released by 12 kV discharging at 110 mL/min H₂. The absolute detection limit (LOD) for Pb was 8 pg (injection volume = 2 mL), and the linearity (R² > 0.997) range was 0.05 - 50 μg/L. The results were in good agreement with that of blood certified reference materials (CRM), and spiked recoveries for real blood samples were 95 - 104% within a relative standard deviation of 5% (RSD). Via gas phase enrichment, the established method improved analytical sensitivity (peak height) by 8 times. The entire analysis time including blood sample preparation can be kept to within 10 min. The combination of modified GLS and DBDT can facilitate the quickness, accuracy, and sensitivity, revealing a promising future for monitoring lead in blood to protect humans, especially children's health.

In situ preconcentration of lead by dielectric barrier discharge and its application to high sensitivity surface water analysis

A novel dielectric barrier discharge (DBD) reactor was utilized to in situ enrich and atomize lead in gas phase. The structure of DBD reactor was optimized to broaden the acidity window of plumbane generation from 1% to 3.5%, bringing better analytical stability and practicability deriving from hydride generation process. For the first time DBD proved effective in lead preconcentration and broadening the acidity window of plumbane generation. Pb can be trapped quantitatively (~100%) on the quartz surface of DBD tube under O₂-containing atmosphere and released (~100%) under H₂-containing atmosphere. The absolute detection limit (LOD) for Pb was 4.1 pg (injection volume = 1.2 mL), and the linear (R² > 0.999) range was 0.05-100 μg/L. The results were in good agreement with those of certified reference materials (CRMs), and spiked recoveries for surface water samples were 99-104% with 2-8% RSD. By gas phase analyte enrichment, the proposed method reduced absolute LOD by 10 times. It was deduced that plumbane was changed to lead oxide species trapped on the quartz tube surface and then released, and transported in form of atoms to the detection zone.

A portable and field optical emission spectrometry coupled with microplasma trap for high sensitivity analysis of arsenic and antimony simultaneously

In this work, a portable and reliable optical emission spectrometric (OES) instrument based on solid acid hydride generation (HG) and subsequent in situ dielectric barrier discharge (DBD) preconcentration was first developed for simultaneous and field analysis of ultratrace As and Sb in environmental water. In situ DBD fulfilled both gas phase enrichment (GPE) and excitation; effective enrichment made it possible to use a low-cost charge coupled device (CCD) as detector. To simplify field protocol, solid tablet made from sulfamic acid was first used to replace hydrochloric acid for co-generation of As and Sb hydrides. Moisture interference was eliminated by carrier gas sweeping without any desiccant. After calculating peak volume for emission data handling, detection limits (LODs) were 0.5 μg L^-1 for As and 0.2 μg L^-1 for Sb, respectively, with <3% relative standard deviations (RSDs) at 10 μg L^-1; linear dynamic ranges (R²>0.995) were 2-200 μg L^-1 for As and 1-200 μg L^-1 for Sb, respectively. The results agreed with certified values of CRMs and recoveries were 87-97% vs. inductively coupled plasma mass spectrometry. The running costs can be controlled within one dollar per use. This HG-in situ DBD trap-OES scheme, with demonstrated advantages in sensitivity, low-cost, power (<60 W), size (0.6 m × 0.5 m × 0.3 m), weight (15 kg), gas consumption (300 measurements per 4 L tank), and multi-element capability, was implemented in a miniature spectrometer for field analysis.

Deducing rotational quantum-state distributions from overlapping molecular spectra

A novel method for fast and robust calculation of Boltzmann plots from molecular spectra is presented. Its use is demonstrated on the OH(A-X) spectrum near 310 nm. A limitation of the method is identified: for overlapping spectra of the OH(A-X) and N₂(C-B, Δv = 1) band sequence, the calculation may often fail due to insufficient number of measured points. This is solved by introducing experimentally determined bounds for the N₂(C) rotational distribution. Three cases are presented: (i) with undisturbed OH(A-X) emission, (ii) with strong emission of N₂(C-B) in the said spectral range, and (iii) with weak but not negligible nitrogen emission. In case (ii), the data in the spectral range 306-320 nm are sufficient for the analysis. In case (iii), information from another spectral range with undisturbed N₂(C-B) emission is necessary. These illustrate all relevant cases often encountered in laboratory plasmas. The calculated Boltzmann plots are not further analyzed in this article but can be used for development and validation of kinetic models with rotational resolution. The implementation of the reported method using the massiveOES software package written in the Python language is available in the supplementary material.

Behavior of selenium hydride in heated quartz tube and dielectric barrier discharge atomizers

Atomization of SeH₂ in an externally heated multiple microflame quartz tube atomizer (MMQTA) as well as planar dielectric barrier discharge (DBD) atomizer was investigated using a variety of probes. Deposits of Se on inner surfaces of the atomizers were quantified and their distribution visualized by autoradiography with ⁷⁵Se radiotracer. The gas phase fraction of Se transported beyond the confines of the atomizers was also determined. In the MMQTA, a 15% mass fraction of Se was deposited in a narrow zone at both colder ends of the optical arm (100-400 °C). By contrast, a 25-40% mass fraction of Se was deposited homogeneously along the entire length of the optical arm of the DBD, depending on detection technique employed. The fraction of Se transported outside the MMQTA approached 90%, whereas it was 50-70% in the DBD. The presence of H₂ was essential for atomization of selenium hydride in both atomizers. The gaseous effluent arising from the hydride generator as well as the atomizers was investigated by direct analysis in real time (DART) coupled to an Orbitrap-mass spectrometer, enabling identification of major gas phase species of Se.