Search

In this study, a foamed nickel trap (NT) was first utilized as a gas-phase enrichment (GPE) material to preconcentrate Cd under ambient temperature and then release it by heating. This is the first time that 100% trapping of Cd could be achieved via on-line GPE following electrothermal vaporization (ETV) introduction. The solid-sampling ETV method coupled with NT was thus developed for the direct detection of Cd in soil samples via atomic fluorescence spectrometry (AFS) as a model detector. Due to the gaseous matrix separation and analyte enrichment caused by the NT, the detection limit (LOD) of Cd reached 0.035 ng g−1 for a 20 mg sample size, and the relative standard deviations (RSDs) were within 4% for Cd standards and 6% for real soil samples, respectively, indicating favorable analytical sensitivity and precision. The measured Cd levels were consistent with the certified values of soil certified reference materials (CRMs) and those obtained by microwave digestion inductively coupled plasma mass spectrometry; furthermore, the recoveries were 95–106% for a series of real soil samples. The analysis time could be controlled within 5 min and allowed elimination of the acid digestion process. As a result, the proposed NT is an effective GPE tool with 100% Cd-trapping efficiency and only ∼100 W power consumption, revealing its promising potential for the miniaturization and portability of direct solid-sampling analyzers in the future. [ABSTRACT FROM AUTHOR]

In this work, a novel field analysis method for analysing Pb in environmental water samples was developed using a portable optical emission spectrometric (OES) instrument coupled with solid acid hydride generation (HG) and a subsequent in situ dielectric barrier discharge (DBD) trap. Due to the DBD trapping and release processes, moisture interference generated from the HG process can be eliminated completely using carrier gas sweeping without the use of any desiccant. In addition, solid citric acid was first utilized to replace the commonly used HCl for HG in the determination of Pb, avoiding the inconvenient transportation problem of liquid acid for the field analysis. Under optimal conditions, a limit of detection (LOD) of 0.12 μg L−1 was achieved for Pb, with a 3% relative standard deviation (RSD) at 20 μg L−1 (n = 11). The proposed method was validated using simulated natural water certified reference materials (CRMs) and real environmental water samples. The obtained results of all CRMs are within their certified values; for real environmental water samples, the recoveries were 94–111% vs. the ICP-MS method. With advantages of small size (0.6 m × 0.5 m × 0.3 m), low manufacturing cost, high sensitivity and low energy consumption (<60 W), the proposed method is especially suitable for the field analysis of Pb in environmental water and has the potential for the simultaneous analysis of more elements. [ABSTRACT FROM AUTHOR]

In this work, an in situ dielectric barrier discharge trap (DBDT) was first utilized to preconcentrate inorganic arsenic (iAs) species coupled with liquid chromatography hydride generation atomic fluorescence spectrometry (LC-HG-AFS), and a novel LC-HG-in situ DBDT-AFS instrument was thereby fabricated. Considering the relatively deficient sensitivity of LC-HG-AFS and retention of As(V) in a strong anion exchange column, As(V) was chosen as a model species for iAs preconcentration. During the extraction of arsenic species in a rice sample using 1% (v/v) HNO3 and 1% (v/v) H2O2, As(III) was oxidized to As(V) being regarded as iAs. After LC separation, according to the retention time, only As(V) was trapped by 11 kV discharging under 110 mL min−1 air mixed with Ar; following sweeping by Ar gas for 190 s, iAs was released with 13 kV at 180 mL min−1 H2-rich Ar to the AFS for measurement. Via preconcentration, the limit of detection (LOD) of iAs reached 0.05 μg L−1 with ∼10 times enhancement in analytical sensitivity; the linearity (r) was > 0.997 ranging from 0.5 μg L−1 to 50 μg L−1 with 1.9% RSD (5 μg L−1, n = 6). The measured iAs in certified reference materials (CRMs) were all within their certified values, and the spike recoveries were in the range of 93–102%. With sensitivity, robustness, low power, small size and easy operation, the combination of LC and DBDT fulfilled the analysis of trace iAs in rice samples. In fact, other arsenic species can also be preconcentrated and detected to enhance the sensitivity by this proposed LC-HG-in situ DBDT technique via precisely synchronizing DBD trap and release with chromatographic retention. To focus on the food safety, iAs was chosen as a model arsenic species to verify the availability of in situ DBDT. Considering the versatility of DBD, in situ DBDT demonstrates a promising application for elemental speciation analysis and LC atomic spectrometry. [ABSTRACT FROM AUTHOR]

In this paper, a fast, cost-effective and sensitive method for the direct determination of Cd in rice was developed based on miniaturized direct current atmospheric pressure glow discharge microplasma (4 mm × 10 mm) atomic emission spectrometry (APGD-AES) coupled with solid sampling electrothermal vaporization with a tungsten coil trap (ETV-TC). During the analysis, milligram (1–15 mg) rice samples firstly went through dehydration and pyrolysis with Cd being vaporized from the residue and trapped on a cold tungsten coil. Then the trapped Cd was released from the tungsten coil by heating and introduced into an APGD plasma for excitation via an Ar/H2 stream. The whole process takes approximately 3 min. The operating parameters of the ETV-TC device and APGD were optimized and possible interference from coexisting ions and organic substances was also evaluated. Under the optimized conditions, the detection limit for Cd (228.8 nm) was calculated to be 2.6 pg, namely 0.26 μg kg−1 using 10 mg of rice sample. The accuracy of the proposed method was validated by the analysis of a rice certified reference material (GBW(E)100360). In addition, it was also successfully applied to the analysis of 7 rice samples and compared with conventional microwave digestion ICP-MS methods. Very good agreement was obtained between the measured and certified values of Cd in the CRMs or values obtained using well-established ICP-MS methods, demonstrating its reliability for the determination of traces of Cd in rice. The proposed method provides a promising, simple and low-cost approach to develop a portable instrument for routine monitoring of Cd contamination in rice samples. [ABSTRACT FROM AUTHOR]

In this study, the slurry sampling hydride generation (SLS-HG) system was first coupled with in situ dielectric barrier discharge atomic fluorescence spectrometry (DBD-AFS) for arsenic analysis in biological samples based on the gas phase enrichment (GPE) principle. After a simple slurry dilution with 5% HCl (v/v) for microbiological and hair samples, the as-prepared slurry was introduced into the SLS-HG unit for arsine generation under 8 g L−1 KBH4 in 1.5 g L−1 KOH. Here, the in situ DBD apparatus, comprising of the three-concentric quartz tubes, was employed to pre-concentrate arsenic to enhance the analytical sensitivity of the HG-AFS, as well as to eliminate interferences due to the dilution effect and matrix separation. This was followed by trapping with 11 kV at 110 mL min−1 of air carrier gas, and 190 s Ar gas sweeping, arsenic was released with 13 kV at 180 mL min−1 H2 to the AFS for measurement. Under optimal conditions, 8 pg or 14 pg detection limits (2 mL sampling) for the microbiological or hair samples were achieved without extra pre-concentration, respectively. The linearity R2 was 0.996 ranging from 0.05 μg L−1 to 300 μg L−1. The spiked recoveries for the real paramecium and micro diatom samples were 93–102%, and the measurements were in accordance with the certified reference material (CRM) values. The proposed SLS-HG-in situ DBD-AFS method is extremely suitable for ultratrace arsenic determination in biological samples to protect human health and environmental safety. [ABSTRACT FROM AUTHOR]

The accurate, stable and fast analysis of mercury species, such as Hg2+, MetHg and EtHg, in complicated aquatic animal matrices is an ongoing challenge. Herein, an efficient analytical method for Hg species was developed using a QuEChERS-like approach (QuEChERS is a sample preparation method for pesticide residue determination based on dispersive solid phase extraction which is quick, easy, cheap, effective, rugged and safe) followed by liquid chromatograph atomic fluorescence spectrometry (LC-AFS). For the first time, a novel concentric tube extraction cell consisting of an outer tube (o-tube), an inner tube (i-tube), a cap for the o-tube and a stopper for the i-tube with a series of PVDF membranes was designed as an integrated tool for extracting and purifying Hg species, where the membrane acts as a “valve” driven by centrifugal force vs. the membrane surface tension force. Here, the newly designed QuEChERS automated sample preparation system was used for shaking and centrifugation of the test samples. Aquatic animal samples were extracted with 10% HCl + 1% thiourea + 0.15% KCl solution in the o-tube by shaking at 800 rpm for 12 min; then, under the force arising from centrifugation at 4000 rpm for 5 min, the analyte solution containing Hg species penetrated the membrane into the i-tube; after shaking at 600 rpm for 3 min and centrifuging at 4000 rpm for 2 min, 0.5 mL chloroform pre-added to the i-tube separated the proteins and lipids from Hg species; finally, the upper layer extract in the i-tube was studied by LC-AFS. Under the optimum conditions, from 5 μg L−1 to 1000 μg L−1, the linear regression coefficient (R2) was ＞0.998; the spiked recoveries of Hg2+, MetHg and EtHg in aquatic animal samples were in the 88% to 104% range, and the method could achieve desirable limits of detection below 3 μg kg−1 (sample mass = 2 g). The relative standard deviations (RSD) were ＜10% for 10 μg kg−1 standards and real samples, including fish, lobster, scallop and carp; this precision was found to be acceptable. The whole sample pre-treatment duration can be controlled within 25 min, namely an average of ∼2 min per sample considering 12-sample throughput of the automated sample preparation system. The proposed QuEChERS-like LC-AFS method is suitable for Hg2+, MetHg and EtHg determination in aquatic animal samples, with advantages of simplicity, quickness, accuracy, high sensitivity and minimum personal error, to protect public health against mercury hazards. [ABSTRACT FROM AUTHOR]

On the basis of the vaporization temperature difference principle between Hg and Cd analytes, a novel solid sampling system coupled with atomic fluorescence spectrometry (AFS) was developed for the sequential determination of trace Hg and Cd in food samples. The solid sampling system mainly comprised a gold coil trap for Hg and a tungsten coil (TC) trap for Cd to eliminate matrix interference, and an on-line Ni–Cr heating coil as the Hg electrothermal vaporizer (ETV) as well as a sample ashing furnace, and a porous carbon tube as the Cd ETV. These units were connected by a modified gas line system integrating air and Ar/H2 (v/v = 9 : 1). The optimal vaporization (500–600 °C), trapping (ambient temperature), and pre-heating conditions of the gold coil (800 °C for 14–16 s) for Hg were all investigated, as well as the sample ashing (the same as Hg vaporization), vaporization (1200 °C for 20 s), and releasing (2000 °C for 1 s) conditions for Cd at 600 mL min−1 of both air and Ar/H2 carrier gases. Under the optimum conditions, the detection limits (LODs) could reach 0.7 pg for Hg and 0.5 pg for Cd with less than 15% relative standard deviations (RSDs), namely 0.07 μg kg−1 and 0.05 μg kg−1 when introducing 10 mg sample mass, respectively. Furthermore, the spiked recoveries were 95.0–115.0% for Hg and 84.0–113.0% for Cd. The Hg and Cd concentrations measured by the proposed solid sampling method were all consistent with the certified reference material (CRM) values and those obtained by microwave digestion inductively coupled plasma mass spectrometry. The solid sampling Hg–Cd analyzer was extremely suitable for the in-field, rapid and accurate monitoring of Hg and Cd in food samples. [ABSTRACT FROM AUTHOR]

A two-stage diameter-varied quartz tube (QT) consisting of a QT electrothermal vapourizer, a quartz tube atom trap (QTAT) and two separate Ni–Cr electrical heating coils was interfaced with atomic fluorescence spectrometry (AFS). This is the first time that an atom trap is employed to trap Pb using electrothermal vapourization (ETV) as a solid sampling approach. The optimum ashing, vapourization, trapping, and releasing procedures and carrier gas were investigated. Under the optimized conditions, Pb in the ashed sample residues was vapourized at 850 °C, followed by analyte separation from the matrix with a 400 mL min−1 carrier gas of 10% H2/Ar (v/v) mixture through trapping Pb on the inner surface of the QTAT without heating. Finally, Pb was released from the QTAT by heating to 800 °C with the carrier gas switch-off and was then swept by the carrier gas into the AFS for measurement. The method LOD and the RSD of repeated measurements were 2 pg and 1.5%, respectively, indicating sufficient analytical sensitivity and precision. The Pb concentrations measured in reference materials by the proposed QT-ETV-QTAT-AFS method were within the certified values, and the spiked recoveries ranged from 95% to 106%, which demonstrated satisfactory accuracy for rapid and on-site determination of Pb in food samples. Furthermore, the vapourization, trapping and releasing mechanisms for Pb by QT-ETV-QTAT-AFS were also studied via tungsten coil ETV-QTAT-AFS, in situ atomic absorption spectrometry, X-ray photoelectron spectroscopy and other means. We deduced that the formation of atom clusters played a crucial role in Pb transportation to the detector. [ABSTRACT FROM AUTHOR]

A novel method of ultraviolet vapour generation (UVG) coupled with atomic fluorescence spectrometry (AFS) was developed for the determination of ultratrace inorganic arsenic (iAs) in surface water. In this work, different ferric species were utilised for the first time as an enhancement reagent for the ultraviolet vapour generation of As(iii), and their UVG efficiencies for volatile species of arsenic were investigated. 15 mg L−1 of ferric chloride provided the greatest enhancement of approximately 10-fold, using 20% acetic acid combined with 4% formic acid with 30 s ultraviolet irradiation at 200 mL min−1 Ar/H2 flow rate. Under the optimised conditions, the linear range was 1.0 μg L−1–100.0 μg L−1, and the spiked recoveries were 92%–98%. The limit of detection was 0.05 μg L−1 for iAs, and the relative standard deviation (RSD) value of the repeated measurements was 2.0% (n = 11). This method was successfully applied to the determination of ultratrace iAs in tap water, river water, and lake water samples using 0.2% H2SO4 (v : v) as the sample preserver. The obtained values for the water samples of certified reference materials (CRMs) including GSB-Z50004-200431, GBW08605 and GBW(E)080390 were all within the certified ranges. [ABSTRACT FROM AUTHOR]