Jixin Liu

Assessment of homogeneity and minimum sample mass for cadmium analysis in powdered certified reference materials and real rice samples by solid sampling electrothermal vaporization atomic fluorescence spectrometry.

To optimize analytical quality controls of solid sampling electrothermal vaporization atomic fluorescence spectrometry (SS-ETV-AFS), the homogeneity (H(E)) of rice samples and their minimum sample mass (M) for cadmium analysis were evaluated using three certified reference materials (CRMs) and real rice samples. The effects of different grinding degrees (particle sizes <0.85, <0.25, <0.15, and >1 mm) on H(E) and M of real rice samples were also investigated. The calculated M values of three CRMs by the Pauwels equation were 2.19, 19.76, and 3.79 mg. The well-ground real rice samples (particle size <0.25 mm) demonstrated good homogeneity, and the M values were 3.48-4.27 mg. On the basis of these results, the Cd concentrations measured by the proposed method were compared with the results by microwave digestion graphite furnace atomic absorption spectrometry with a 0.5 g sample mass. There was no significant difference between these two methods, which meant that SS-ETV-AFS could be used to accurately detect Cd in rice with several milligrams of samples instead of the certified value (200 mg) or the recommended mass (200-500 mg) of the methods of the Association of Official Analytical Chemists.

Ambient-Temperature Trap/Release of Arsenic by Dielectric Barrier Discharge and Its Application to Ultratrace Arsenic Determination in Surface Water Followed by Atomic Fluorescence Spectrometry

A novel dielectric barrier discharge reactor (DBDR) was utilized to trap/release arsenic coupled to hydride generation atomic fluorescence spectrometry (HG-AFS). On the DBD principle, the precise and accurate control of trap/release procedures was fulfilled at ambient temperature, and an analytical method was established for ultratrace arsenic in real samples. Moreover, the effects of voltage, oxygen, hydrogen, and water vapor on trapping and releasing arsenic by DBDR were investigated. For trapping, arsenic could be completely trapped in DBDR at 40 mL/min of O2 input mixed with 600 mL/min Ar carrier gas and 9.2 kV discharge potential; prior to release, the Ar carrier gas input should be changed from the upstream gas liquid separator (GLS) to the downstream GLS and kept for 180 s to eliminate possible water vapor interference; for arsenic release, O2 was replaced by 200 mL/min H2 and discharge potential was adjusted to 9.5 kV. Under optimized conditions, arsenic could be detected as low as 1.0 ng/L with an 8-fold enrichment factor; the linearity of calibration reached R(2) > 0.995 in the 0.05 μg/L-5 μg/L range. The mean spiked recoveries for tap, river, lake, and seawater samples were 98% to 103%; and the measured values of the CRMs including GSB-Z50004-200431, GBW08605, and GBW(E)080390 were in good agreement with the certified values. These findings proved the feasibility of DBDR as an arsenic preconcentration tool for atomic spectrometric instrumentation and arsenic recycling in industrial waste gas discharge.

Direct Determination of Ultratrace Cadmium in Spinach by Electrothermal Vaporization Atomic Fluorescence Spectrometry Using On-line Atom Trap of Tungsten Coil

A novel solid sampling method of detecting cadmium in spinach by electrothermal vaporization atomic fluorescence spectrometer(SS-ETV-AFS) was established,which made use of a tungsten-coil as a Cd trap at room temperature to remove matrix interferences and foam graphite as a electrothermal vaporizer and a sample boat.In our wok,it was proven that the foam graphite vaporizer had a stable performance and different sample boats had no difference for testing;there was good homogeneity and representativeness for fresh spinach sample grinded with liquid nitrogen,16.3mg was calculated by the Pauwels equation as the minimum sample mass which satisfied microsampling of SS-ETV-AFS.After optimization,the ashing(50 W for 50 s then 70 W for 80 s) and evaporating(70 W for 30 s) procedures were separated,and 600 mL/min Ar/H2(9∶1,V/V) was chosen as the carrier gas.Under the optimized conditions,the limit of detection was 0.2 μg/kg;the recovery was 90.1%-106.1%,the relative standard deviation was less than 10%,and the analysis time was within 5 min.There was no interference from the other elements and organic matrix,and there was no significant difference(p0.05) between the methods of SS-ETV-AFS and microwave digestion graphite furnace atomic absorption spectrometer.

Simultaneous trapping of Zn and Cd by a tungsten coil and its application to grain analysis using electrothermal inductively coupled plasma mass spectrometry

For the first time, a tungsten coil (TC) was employed to trap Zn and Cd at room temperature and release them simultaneously by heating. In this study, using porous carbon as a vaporizer and a tungsten coil as a Zn and Cd trap, a novel method of solid sampling electrothermal vaporization (SS-ETV) coupled with inductively coupled plasma mass spectrometry (ICP-MS) was developed for the direct detection of Zn and Cd in grain samples. The optimal ashing, vaporization, and releasing conditions as well as the flow rate of the 4% H2 (v/v) and Ar mixture as the extra and carrier gases were investigated. Under the optimized conditions, the detection limits (LOD) were 1 pg for Zn and 0.1 pg for Cd; the relative standard deviations (RSD) of 11 repeated measurements were 4.7% for Zn and 7.9% for Cd using 2 mg of rice powder samples; the spiked recoveries ranged from 88% to 113%. The concentrations of Zn and Cd in wheat, corn and rice samples measured by the established method were all found to be in the range of the certified values of reference materials. Furthermore, it was proven that the vaporized and trapped species of Zn and Cd were almost atoms by atomic fluorescence spectrometry (AFS) and X-ray photoelectron spectrometry (XPS).

An integrated quartz tube atom trap coupled with solid sampling electrothermal vapourization and its application to detect trace lead in food samples by atomic fluorescence spectrometry

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.

Direct determination of trace mercury and cadmium in food by sequential electrothermal vaporization atomic fluorescence spectrometry using tungsten and gold coil traps

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.

In Situ Dielectric Barrier Discharge Trap for Ultrasensitive Arsenic Determination by Atomic Fluorescence Spectrometry

The mechanisms of arsenic gas phase enrichment (GPE) by dielectric barrier discharge (DBD) was investigated via X-ray photoelectron spectroscopy (XPS), in situ fiber optic spectrometer (FOS), etc. It proved for the first time that the arsenic species during DBD trapping, release, and transportation to the atomic fluorescence spectrometer (AFS) are probably oxides, free atoms, and atom clusters, respectively. Accordingly, a novel in situ DBD trap as a GPE approach was redesigned using three-concentric quartz tube design and a modified gas line system. After trapping by O2 at 9.2 kV, sweeping for 180 s, and releasing by H2 at 9.5 kV, 2.8 pg detection limit (LOD) was achieved without extra preconcentration (sampling volume = 2 mL) as well as 4-fold enhancement in absolute sensitivity and ∼10 s sampling time. The linearity reached R2 > 0.998 in the 0.1-8 μg/L range. The mean spiked recoveries for tap, river, lake, and seawater samples were 100-106%; and the measurements of the certified reference materials (CRMs) were in good agreement with the certified values. In situ DBD trap is also suitable to atomic absorption spectrometry (AAS) or optical emission spectrometry (OES) for fast and on-site determination of multielements.

Determination of inorganic arsenic in algae using bromine halogenation and on-line nonpolar solid phase extraction followed by hydride generation atomic fluorescence spectrometry

Accurate, stable and fast analysis of toxic inorganic arsenic (iAs) in complicated and arsenosugar-rich algae matrix is always a challenge. Herein, a novel analytical method for iAs in algae was reported, using bromine halogenation and on-line nonpolar solid phase extraction (SPE) followed by hydride generation atomic fluorescence spectrometry (HG-AFS). The separation of iAs from algae was first performed by nonpolar SPE sorbent using Br- for arsenic halogenation. Algae samples were extracted with 1% perchloric acid. Then, 1.5mL extract was reduced by 1% thiourea, and simultaneously reacted (for 30min) with 50μL of 10% KBr for converting iAs to AsBr3 after adding 3.5mL of 70% HCl to 5mL. A polystyrene (PS) resin cartridge was employed to retain arsenicals, which were hydrolyzed, eluted from the PS resin with H2O, and categorized as iAs. The total iAs was quantified by HG-AFS. Under optimum conditions, the spiked recoveries of iAs in real algae samples were in the 82-96% range, and the method achieved a desirable limit of detection of 3μgkg-1. The inter-day relative standard deviations were 4.5% and 4.1% for spiked 100 and 500μgkg-1 respectively, which proved acceptable for this method. For real algae samples analysis, the highest presence of iAs was found in sargassum fusiforme, followed by kelp, seaweed and laver.