Quartz Tube Atomizer Research Articles

Diffusion flame, heated quartz tube or dielectric barrier discharge? Comparing the resistance of hydride atomizers towards interferences with detection by atomic absorption spectrometry

The resistance of three types of hydride atomizers towards interferences from other hydride forming elements and mercury was comprehensively investigated. Four hydride forming elements (Pb, Bi, Se and Te) were used as model analytes while seven hydride forming elements and mercury were investigated as potential interferents. The atomizers studied were based on a diffusion flame - DF, an externally heated quartz tube (multi)atomizer - (MM)QTA as well as a dielectric barrier discharge plasma - DBD. The performance of even two designs of DBD atomizers was compared. The first configuration (REF-SIN) was realized by a DBD chamber with glued electrodes coupled to a power supply source with sinusoidal modulation of high voltage. The second configuration of the DBD atomizer (SE-SW) comprised of a DBD chamber with the sputtered electrodes powered by a square-wave modulated high voltage source. The DF atomizer was found to be the most robust towards atomization interferences. However, its sensitivity was 30 to 50 times lower compared to (MM)QTA and DBD based atomizers due to its short optical path. The DBD atomizer in REF-SIN arrangement can compete very well with (MM)QTA atomizer in terms of resistence to interferences as well as sensitivity. The resistence of DBD atomizer in SE-SW configuration towards atomization interferences is slightly worse compared to (MM)QTA and DBD in REF-SIN design.

Sensitive method for total selenium determination in garlic and nuts by UV–photochemical vapor generation coupled to atomic absorption spectrometry using mild conditions

Photochemical vapor generation (PVG) coupled on–line to atomic absorption spectrometry using a flow injection mode was investigated for the determination of total Se in garlic and nut samples. In the presence of low molecular weight organic acid solutions, Se(IV) is converted by UV irradiation to volatile species which are transported to the heated quartz tube atomizer. Formic and acetic acids were tested as photochemical reagents and a mixture of 1.5 % (v/v) formic and 5 % (v/v) acetic acid was the best alternative. Central composite design was employed for parameters optimization. The effect of potential interfering elements such as hydride–forming elements, transition metals and nitric acid was investigated to ascertain possible effects of the matrix on Se(IV) signal. Under optimized conditions a detection limit (LOD) of 33 ng g–1 (3σ) was reached. Samples of garlic and nuts purchased at a local market were analyzed and Se concentrations spanned the range 0.36–248 µg g–1. These results were compared with ICP–MS measurements utilizing an elliptical joint confidence region (EJCR) with bilinear least squares analysis, and good results were obtained.

T-cut slotted quartz tube-atom trap strategy for the on-line preconcentration of thallium in well water samples

In this study, an on-line preconcentration system was developed for the quantitative determination of thallium in well water samples using hydrogen-assisted T-cut slotted quartz tube atom trapping (HA-T-SQT-AT) coupled to flame atomic absorption spectrometry (FAAS). The method is based on trapping the thallium atoms on the inner surface of the T-SQT for a short period using sample aspiration and lean flame conditions. Then, hydrogen gas as a reducing agent was released instantly to free the trapped analyte atoms, resulting in a sharp and narrow signal. The system analytical performance was enhanced by performing comprehensive optimization of several factors. The linear range and LOD/LOQ values of the optimized method were found to be 7.5–––200 ng/mL and 2.6/8.7 ng/mL, respectively. Accuracy/practicability of the presented method were verified using well water samples, and the percent recoveries calculated using the external calibration approach were all above 80%.

Plasma-mediated vapor generation of mercury species in a dielectric barrier discharge: Direct analysis in a single drop by atomic absorption spectrometry

A plasma-mediated vapor generation (PMVG) by a dielectric barrier discharge (DBD) from a single sample drop of inorganic mercury and methylmercury was investigated and optimized employing for the first time atomic absorption spectrometry (AAS) as a detector. A volume discharge DBD reactor was fabricated together with an inexpensive (<250 USD), but highly flexible laboratory made high voltage power supply. Experimental parameters affecting both the PMVG and subsequent AAS detection steps were optimized. Moreover, the efficiency of PMVG of both species was quantified by two independent approaches: conventional chemical vapor generation (CVG) and the amalgamation technique. Under the optimum PMVG settings, the high voltage power supply was operated at 38 kV, 23 W, 40 kHz and 60% duty cycle, while the DBD reactor was supplied by 150 mL min−1 He discharge gas. Sample volume was optimized to 2 μL. The AAS detection was performed using a quartz tube atomizer kept at ambient temperature. Conversion of both mercury species, Hg2+ and MeHg+, to mercury free atoms (Hg0) inside the DBD reactor has been unequivocally proven. The PMVG efficiency investigated by the two independent approaches was quantified to 87% ± 8% for Hg2+ and 91% ± 10% for MeHg+, respectively. Both mercury species yielded similar sensitivity and limit of detection (LOD) in PMVG-AAS, reaching 0.12 s ng−1 Hg and 100 μg L−1 Hg (200 pg absolute), respectively. Although the generation efficiency as well as the sensitivity reached for both mercury species are comparable between the CVG and PMVG approaches, PMVG reaches significantly worse LODs due to the fact the sample volume is 250-times lower compared to CVG.

Next generation of dielectric barrier discharge hydride atomizers for atomic absorption spectrometry: A case study on Pb, Bi, Se and Te

The performance of hydride atomizers based on dielectric barrier discharge (DBD) was evaluated by atomic absorption spectrometry as a detector employing Pb, Bi, Se and Te as model analytes. Two designs of DBD atomizers either with glued or sputtered electrodes were investigated in combination with sinusoidal or square-wave modulated high voltage power supply sources. Moreover, the effect of gas phase dryers on analyte response was studied. Nafion tubes were found as universal dryers capable of efficient water vapor removal with no losses of analyte. Sensitivity was compared among individual DBD configurations being related also to conventional externally heated quartz tube (multi)atomizers (MM)QTA. For Te and Se comparable sensitivities were reached in all configurations of DBD atomizers and MMQTA. On the contrary, QTA provided three times higher sensitivity for Bi and Pb than DBD atomizers. Sensitivity reached among DBD atomizers was the same regardless of their electrode design and high voltage waveform modulation for Se, Te and Bi. Differences in sensitivity were observed for Pb depending on DBD atomizer configuration. Here the best sensitivity was found in DBD with sputtered electrodes coupled to power source with square-wave modulation of high voltage. It was twice higher than that reached in the DBD atomizer with glued electrodes powered by sine-wave voltage. The sensitivity in DBD atomizers correlates negatively with the amount of analyte deposited in the atomizer during atomization. >90% of Bi and Pb introduced into the system is deposited while the deposited fraction of Te and Se, respectively, decreases to 60% and 35%.

Selected Ion Flow Tube Mass Spectrometry as a Tool to Understand Hydride Atomization and the Fate of Free Analyte Atoms in an Externally Heated Quartz Tube Atomizer.

Hydride atomization and the fate of free analyte atoms in an externally heated quartz tube atomizer (QTA) were investigated employing selected ion flow tube mass spectrometry (SIFT-MS). SIFT-MS proved to be ideally suited to study water concentration in gases leaving the atomizer. This made it possible to quantify the oxygen "contaminant" flow rate to QTA as 0.04-0.05 mL min-1. This is valid for typical conditions of hydride generation. Most significantly, studies of temperature influence on water concentration resulted in detailed insight into hydrogen radical-forming reactions between oxygen and hydrogen. Minimum QTA temperatures required to generate hydrogen radicals under a variety of different flow rates and compositions of the QTA atmosphere were found to be in the range between 585 and 800 °C. The ability of SIFT-MS to detect extremely low concentrations of arsane and selane was employed to quantify the fraction of As and Se removed from the QTA in the form of hydride in dependence on QTA temperature under typical conditions of hydride generation. It was found that free As atoms formed by atomization of arsane decay to different species than to arsane. In the case of selane under typical atomization conditions, the efficiency of the decay of free Se atoms to selane was between 50 and 100% in dependence on actual flow rates and compositions of the QTA atmosphere.

Ultra-Trace Determination of Arsenic by Platinum-Coated Tungsten Coil Hydride Generation (HG) Atomic Absorption Spectrometry (AAS)

A simple, rapid, and sensitive method for the determination of ultra-trace arsenic (III) is reported based on in situ trapping and revolatilization on a platinum (Pt) coated tungsten (W) coil atom trap. First, the analyte species in vapor form were transported by a mixture of Ar and H2 and trapped on the Pt-coated W-coil heated at 60 °C. Next, in the releasing step, the trap was resistively heated to 950 °C; the analyte species are revolatilized and transported to the quartz tube atomizer. The NaBH4 concentration, NaOH concentration, HCl concentration, trapping and releasing temperature, trapping time, and hydrogen and argon gas flow rates were optimized. Using these conditions, a limit of detection of 16 ng L−1 was obtained. The precision was evaluated by relative standard deviation corresponding to 4.8% at 1.0 μg L−1 (n = 11). The surface of the W-coil trap was coated with Pt using electrolytic deposition. Scanning electron microscopy-energy dispersive X- ray (SEM-EDX) analyses were performed to control the surface morphology of the trap. The same trap may be used for at least 350 atomization cycles without losing sensitivity. The accuracy of the proposed method was evaluated by analyzing NIST CRM 1640a (Trace Elements in Natural Water), EnviroMAT (Drinking water), and CRM-023 (Sandy Loam 7) certified reference materials. The measurements of the certified reference materials were in good agreement with the certified values at the 95% confidence level. The developed method was applied to the determination of As in drinking water samples from Muğla province.

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.

A sensitive and accurate analytical method for the determination of cadmium in food samples: Molybdenum coated T-shape slotted quartz tube flame atomic absorption spectrophotometry

In this study, a molybdenum coated T-shaped slotted quartz tube atom trap flame atomic absorption spectrophotometry method (Mo coated-T-SQT-AT-FAAS) was developed for the determination of cadmium with on-line preconcentration. Inner surface of T-SQT was coated with molybdenum to enhance the trapping efficiency. Hydrogen gas was used instead of organic solvents to release trapped atoms. Limit of detection and quantification were found to be 0.057 and 0.082 µg/L, respectively. The developed method has a linear working range between 0.10 and 1.0 µg/L with a low %RSD value (<3.7). About 1202 times enhancement in detection power was recorded over the conventional FAAS system. Recovery experiments were used to determine the applicability of the method developed to real samples (linden, milk powder and mint) and significant results (94.4–100.7%) were obtained for the samples spiked at 0.30, 0.50 and 1.0 µg/L. The method was also applied to Tomato Leaves 1573a SRM to check the accuracy.

Atomization of lead hydride in a dielectric barrier discharge atomizer: Optimized for atomic absorption spectrometry and studied by laser-induced fluorescence

Atomization of lead hydride in a plane-parallel volume dielectric barrier discharge (DBD) atomizer coupled to a high voltage power supply source with sinusoidal waveform (28.5 kHz) was optimized with detection by atomic absorption spectrometry. Argon was found as the best discharge gas under a flow rate of 175 mL min−1 while the DBD optimum peak-to-peak high voltage was 25 kV. The performance of the novel DBD atomizer was compared to that of a conventional externally heated quartz tube atomizer (QTA) operating at 900 °C and 100 mL min−1 Ar carrier gas flow rate. Sensitivity and limit of detection (LOD) in QTA reached 0.21 s ng−1 Pb and 0.6 ng mL−1 Pb, respectively, while they reached 0.04 s ng−1 Pb and 2.3 ng mL−1 Pb in DBD. Laser-induced fluorescence (LIF) was employed to investigate the spatial distribution of free Pb atoms as well as to quantify lead hydride atomization efficiency in both atomizers. Free Pb atoms were present only in a central region of DBD atomizer. Atomization efficiency of lead hydride was quantified by LIF to be 23 ± 7%. On the contrary, free Pb atoms were distributed homogeneously along the whole optical arm in the QTA with atomization efficiency reaching 88 ± 18%.

Hydride generation atomic absorption spectrometry with a dielectric barrier discharge atomizer: Method optimization and evaluation of analytical performance for tin

Atomization conditions for tin hydride in the planar dielectric barrier discharge (DBD) plasma atomizer were optimized with detection by atomic absorption spectrometry (AAS). The effects of apparatus arrangement such as the shape of a waveform function of the high voltage power supply source, DBD atomizer design as well as presence of a dryer tube filled with NaOH pellets to prevent residual aerosol and moisture transport into the DBD were investigated in detail. The optimal experimental setup consisted of a square wave high voltage power supply source coupled to a DBD with vapor-deposited electrodes in the presence of NaOH dryer upstream the DBD atomizer. Argon was found as the best discharge gas under a flow rate of 120 mL min−1 while the DBD optimum high voltage supply rate was 7 kV. A sensitivity of 0.05 s ng−1 Sn and a limit of detection of 1.1 ng mL−1 Sn were reached under optimized conditions. Optimization of the whole experimental setup resulted in 7-fold improvement of sensitivity compared to the original arrangement consisting of a sinusoidal source coupled to a DBD atomizer with glued electrodes in absence of the dryer. The analytical performance of the DBD atomizer under optimized conditions was compared to that of a commonly used externally heated quartz tube atomizer.

Simple approaches to on-line and off-line speciation analysis of mercury in flue gases with detection by atomic absorption spectrometry: A pilot study

Two simple approaches to speciation analysis of mercury in flue gases have been developed distinguishing between elemental mercury Hg0 and oxidized form of mercury (often HgCl2) either in off-line or on-line measurement arrangements. Both approaches employ atomic absorption spectrometry (AAS) as a detector. The off-line approach combines a pair of sorbents from which the first one traps oxidized for of mercury (HgCl2) selectively on a raw alumina sorbent while the second one retains Hg0 quantitatively on a gold-coated alumina filling. Trapped amount of Hg in both sorbents is subsequently determined by AAS employing the advanced mercury analyzer AMA-254. Both sorbents can be regenerated for repeated use. Selectivity and capacity of both sorbents was investigated by means of model gases and compared to other materials. The accuracy and precision of this approach have been proven by analysis of a model flue gas mixture. The on-line approach to speciation analysis is based on direct introduction of flue gases into the AAS spectrometer equipped with an externally heated quartz tube atomizer. The temperature of the atomizer's optical arm or temperature of the gas line upstream the atomizer allow speciation analysis since Hg0 as atomic Hg-vapor can be detected at ambient temperature while HgCl2 as a molecular species requires heating of the atomizer or gas line to 900 °C.

Accurate and Sensitive Analytical Strategy for the Determination of Antimony: Hydrogen Assisted T-Shaped Slotted Quartz Tube-Atom Trap-Flame Atomic Absorption Spectrometry.

Antimony is known to have some adverse health effects on human health. Flame atomic absorption spectrometry (FAAS) is a widely used instrumental for the determination of antimony and other metals. However, it lacks the sensitivity to determine these metals at trace levels. This study was aimed at overcoming this setback by using hydrogen assisted T-shaped slotted quartz tube technique to preconcentrate and determine antimony by FAAS. All the system parameters were optimized to enhance the detection power of the system. Under the optimum experimental conditions, the limits of detection and quantification were found to be 0.75 and 2.49µgL-1, respectively with R2 value of 0.9999. Accuracy of the developed method was validated by experimental results agreeing to the certified value of a standard reference material. Recovery studies were also carried out to determine the method's applicability to tap and mineral water samples, and the results obtained were appreciable.

Determination of Bismuth in Bottled and Mineral Water Samples at Trace Levels by T-Shaped Slotted Quartz tube-Atom Trap-Flame Atomic Absorption Spectrometry

An accurate and reliable analytical method for the determination of bismuth at trace levels in bottled and mineral water samples has been developed based on hydrogen assisted T-shape slotted quartz tube-atom trap-flame atomic absorption spectrometry (T-SQT-AT-FAAS). Conventional FAAS is not sufficiently sensitive to measure trace and ultra-trace levels of metals due to the low nebulization efficiency and short residence time of atoms in the light path. To overcome this problem, atom trapping with a T-shaped slotted quartz tube was coupled to the FAAS system. Bismuth atoms were trapped on the surface of T-SQT and released by hydrogen gas, which provided a reducing environment. All of the system parameters such as flame type, hydrogen flow rate, the height of T-SQT from the burner head, and trapping period were optimized to enhance the analytical signal to attain low detection limits. After obtaining the optimum conditions, the limit of detection and limit of quantitation of the developed method were found to be 0.95 and 3.2 µg L−1, respectively. Recovery values were obtained between 90% and 104% that showed good accuracy and applicability of the proposed method to the analysis of bottled and mineral water samples.

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.

Development of a sensitive analytical method for the determination of cadmium using hydrogen assisted T-shape slotted quartz tube-atom trap-flame atomic absorption spectrophotometry

Cadmium is an element that has several industrial applications and exposure to humans causes serious health problems. Hence, determination of this element in environmental samples surrounding humans is very crucial. In this study, a sensitive, accurate and inexpensive analytical method was developed for the determination of cadmium at trace levels. All the system parameters including acetylene flow rate, T-Shape Slotted Quartz Tube (T-SQT) height, sample flow rate, trapping period and hydrogen flow rate were optimized to obtain lower detection limits. Analytical performance of T-Shape Slotted Quartz Tube-Atom Trap-Flame Atomic Absorption Spectrophotometry (T-SQT-AT-FAAS) was determined under the optimum conditions, and the limit of detection (LOD) was calculated as 0.10 μg L−1. The percent recovery of tap water samples spiked at 2.0, 3.0, 7.0 and 20 μg L−1 were found to be between 99.5 and 102.8%. The %RSD values were all below 8.0%, indicating applicability and good accuracy of the method for the water matrix.

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

Atomization conditions for antimony hydride in the plasma atomizer based on a dielectric barrier discharge (DBD) with atomic absorption spectrometric detection were optimized. Argon was found as the best discharge gas under a flow rate of 50 mL min− 1 while the DBD power was optimum at 30 W. Analytical figures of merit including interference study of As, Se and Bi have been subsequently investigated and the results compared to those found in an externally heated quartz tube atomizer (QTA). The limit of detection (LOD) reached in DBD (0.15 ng mL−1 Sb) is comparable to that observed in QTA (0.14 ng mL−1 Sb). Finally, possibility of Sb preconcentration by stibane in situ trapping in a DBD atomizer was studied. For trapping time of 300 s, the preconcentration efficiency and LOD, respectively, were 103 ± 2% and 0.02 ng mL−1.

Determination of cadmium at ultratrace levels by dispersive liquid-liquid microextraction and batch type hydride generation atomic absorption spectrometry

This study describes the development of a dispersive liquid-liquid microextraction method for the extraction of cadmium and its determination by hydride generation atomic absorption spectrometry. The extraction method served as a clean-up of analyte from its matrix and also concentrated it to get lower detection limits. The hydride generation system was optimized to obtain high cadmium hydride generation efficiency and its transport to the quartz tube atomizer for atomization. Under the optimum experimental conditions, the limits of detection and quantification were 4.2ngL−1 and 14.1ngL−1, respectively. Sensitivity was enhanced about 10,000 folds if compared with conventional FAAS system. The calibration showed good linearity over a wide range and the low relative standard deviations indicated high precision for the extraction process and instrumental readings. The accuracy of the method was validated by the agreement of experimented results to the value of a wastewater certified reference material (EU-L-2). Appreciable recovery results were obtained for wastewater spiked at different concentrations.

Determination of nickel in water and soil samples at trace levels using photochemical vapor generation-batch type ultrasonication assisted gas liquid separator-atomic absorption spectrometry

A photochemical vapor generation system with sonication assisted batch type gas-liquid separator was optimized to improve the sensitivity, precision and accuracy of nickel determination by atomic absorbance spectrometry. The inefficient nebulizer sample introduction unit of the flame unit was replaced by a UV assisted vapor generator, and atomization of the generated volatile species was achieved with a quartz tube atomizer. Parameters optimized included organic acid type and concentration, UV irradiation period, sonication period, carrier gas flow rate and atomizer temperature. Recovery studies were performed to determine the method's applicability to real samples, and interference studies were done to ascertain possible effects of the matrix on the analyte. The limits of detection and quantification were found to be 9.5μgL−1 and 31.7μgL−1, respectively. The low relative standard deviation indicated high precision, and experimented results of a certified reference material conformed to the certified value, validating the method's accuracy. Percent recoveries recorded were between 95% and 104% and the interferents tested showed different effects on the absorbance signals of nickel.

Determination of As by UV-photochemical generation of its volatile species with AAS detection

This work was focused on the development of an analytical method for determination of arsenic in liquid (aqueous solutions of arsenite) by UV-photochemical generation of its volatile compounds. The study contains the optimization, method characterisation and also a study of the influence of selected compounds on the signal measured. The method involves a combination of flow injection analysis, UV-photochemical generation of volatile compounds of arsenic in flow injection arrangement and atomic absorption spectrometry using an externally heated quartz tube atomizer. The attained absorbance was very low after the optimization. In the next step, the influence of selected compounds on UV-photochemical generation was investigated with the aim to find a suitable reaction modifier that would improve the sensitivity of arsenic determination. Bi(III) was found as the best reaction modifier not only for causing the increase of the signal of arsenic measured but also for its persisting effect. The activation with concentration of 10 mg dm−3 of Bi(III) increases the absorbance of arsenic approximately eleven times compared to signals without activation. Following method characteristics were achieved under the optimum experimental conditions: the limit of detection of 18 µg dm−3, the repeatability of 4.5 % expressed as % RSD at 200 µg dm−3, and linear dynamic range 60–500 µg dm−3 of arsenic.