Guoying Chen

SPE speciation of inorganic arsenic in rice followed by hydride-generation atomic fluorescence spectrometric quantification.

Due to high toxicity, inorganic arsenic (iAs) species are the focus of monitoring effort worldwide. In this work arsenic was first extracted from rice by microwave-assisted digestion in HNO3-H2O2, during which As(III) was oxidized to As(V). Silica-based strong anion exchange cartridges were used to separate As(V) from organic forms. After prereduction by iodide, iAs was quantified by hydride-generation atomic fluorescence spectrometry (HG-AFS). This method achieved 1.3 ng g(-1) limit of detection (LOD), and 94 ± 3% and 93 ± 5% recoveries, respectively, for As(III) and As(V) at 100 ng g(-1). Validation was performed using standard reference material NIST 1568a (102 ng g(-1)) and ERM BC211 (124 ng g(-1)) rice flour. By eliminating chromatography, SPE speciation gained throughput and cost advantages. HG-AFS, at 10% budget and operation cost of a typical inductively-couple plasma mass spectrometer (ICPMS), proved highly sensitive and specific for iAs quantification.

Europium-sensitized luminescence determination of oxytetracycline in catfish muscle

An europium-sensitized time-resolved luminescence (TRL) method was developed to determine oxytetracycline (OTC) in cultivated catfish muscle. Extraction of OTC from fish muscle was performed with pH 4.0 ethylenediaminetetraacetic acid (EDTA)-McIlvaine buffer and clean up with hydrophilic-lipophilic balanced copolymer solid phase extraction (SPE) cartridges. The eluate was used without further concentration for TRL measurement in pH 9.0 micellar tris(hydroxylmethyl)aminomethane (TRIS) buffer. Cetyltrimethylammonium chloride (CTACl) was used as surfactant and EDTA as a co-ligand. The excitation and emission wavelengths were set at 388 and 615nm, respectively. The linear dynamic range was 0-1000ngg(-1) (R(2)=0.9995). The recovery was 92-112% in the fortification range of 50-200ngg(-1) and the limits of detection (LOD) ranged from 3 to 7ngg(-1). Incurred catfish samples were used to demonstrate the performance of the method around 100ngg(-1), the European Union maximum residue level.

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.

Time‐Resolved Luminescence Screening Assay for Tetracyclines in Chicken Muscle

Abstract A time‐resolved luminescence (TRL) assay was developed for effective screening of tetracyclines in chicken muscle at the European Union (EU) maximum residue level of 100 ng g−1. The method involves extraction of the tetracyclines with McIlvaine–ethylenediamine tetraacetic acid (EDTA) buffer, centrifugation, solid‐phase extraction (SPE) clean‐up, formation of an Eu(III) complex, and then measurement of the TRL signal at 615 nm (excitation at 388 nm). Samples fortified with tetracycline (TC), oxytetracycline (OTC) or chlortetracycline (CTC) gave a linear response over the range of 0–1000 ng g−1, with relative sensitivities 5.4×, 2.4×, and 1×, respectively. Limits of detection for TC, OTC, and CTC were 3.5, 8, and 19 ng g−1, respectively. Examination of the least sensitive case, CTC, showed no overlap between the TRL of control chicken extracts and those that had been fortified with 100 ng g−1 CTC. The within‐day variation for these samples averaged 3.1% relative standard deviation (RSD), as did the day‐to‐day variation. The method was tested with blind control and fortified samples over the range of 20–500 ng g−1 CTC to illustrate its utility. Other veterinary drugs approved for chickens in the US (enrofloxacin, nicarbazin, tylosin) did not interfere. This method can provide a useful alternative to microbial screening assays for tetracyclines. #Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.

Continuous arsine detection using a Peltier- effect cryogenic trap to selectively trap methylated arsines

Hydride generation (HG) is an effective technique that eliminates interfering matrix species and enables hydride separation. Arsenic speciation analysis can be fulfilled by cryogenic trapping (CT) based on boiling points of resulting arsines using liquid nitrogen (LN2) as a coolant. In this work, LN2 was replaced by the thermoelectric effect using a cryogenic trap that consisted of a polytetrafluoroethylene (PTFE) body sandwiched by two Peltier modules. After the trap was precooled, the arsines flew along a zigzag channel in the body and reached a sorbent bed of 0.2 g of 15% OV-3 on Chromosorb W-AW-DMCS imbedded near the exit of the trap. CH3AsH2 and (CH3)2AsH were trapped, while AsH3, that passed the trap unaffected, was detected by atomic fluorescence spectrometry. Continuous operation led to enhanced throughput. For inorganic As, the limit of detection (LOD) was 1.1 ng/g and recovery was 101.0 ± 1.1%. Monomethylarsonic acid and dimethylarsinic acid did not interfere with 0.2 ± 1.2% and -0.3 ± 0.5% recoveries, respectively.

Reflux open-vessel digestion system can overcome volatilization loss in mercury speciation analysis

Volatilization loss of analytes in open-vessel digestion is a concern for mercury speciation analysis. Loss of Hg0 vapour can be overcome by using oxidative digestion media, while loss of aerosols can be circumvented by complete condensation under sub-boiling-point heating. Using a simple system that consisted of a block heater and culture tubes, two digestion protocols were developed for determination of total Hg (tHg) and inorganic Hg (iHg). The resulting Hg++ was selectively reduced by SnCl2 to Hg0, which was detected by atomic fluorescence spectrometry (AFS). MeHg+ was oxidized to Hg++ to yield tHg and calculated from the difference. These methods were validated using certified reference material (CRM) DORM-4, and applied to seafood analysis with 3.6 and 3.2u202fngu202fg-1 (dry weight) limit of detection for iHg and tHg, respectively. Using only off-the-shelf components, these methods gained cost, simplicity, and parallel operation advantages.

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.