Yeuk-Ki Tsoi

Highly sensitive and selective organophosphate screening in twelve commodities of fruits, vegetables and herbal medicines by dispersive liquid-liquid microextraction.

The article describes a simple sample pretreatment procedure for the analysis of ten organophosphorus pesticides using dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography-mass spectrometry (GC-MS) in three distinctively different types of matrices: fresh fruits, fresh vegetables and dried herbs. The method was carefully developed, focusing on the chemistry of various dispersive solvents, to achieve simultaneous, comprehensive extraction and preconcentration in a great span of selected matrices. According to matrix-matched validation study, the set of optimized DLLME conditions has been proven robust to determine target OPPs within a wide linear range from 0.1 to 1000 μg L(-1). With limited usage of organic extractants, remarkable enrichment factors up to 100-fold were obtained, enabling ultra-trace pesticide quantification down to sub-ppt levels at 0.12-4.92 ng kg(-1). Practical application of the method was illustrated by quantitative recovery (70-119%) and good precision (2.6-10% R.S.D.) in a representative range of three fruits and four vegetable commodities featured by the CODEX Alimentarius classification as well as their unique matrix compositions. A careful selection of dried herbs was further classified based on their morphological structures to validate analytical ruggedness of the method. Compared with existing methods for food analysis vis-à-vis OPPs, the present method is superior in terms of high sample throughput, minimal solvent consumption, and small sample size requirement. An additional, significant aspect of this universal DLLME method is that it models sample pretreatment methods with wide coverage of analytical matrices that are more effective, more comprehensive, and more flexible than those currently being used.

Selective recognition of arsenic by tailoring ion-imprinted polymer for ICP-MS quantification.

A novel arsenic-ion imprinted polymer (As-IIP) was firstly synthesized for the separation and recovery of trace elemental As from environmental water samples. Polymers prepared from bifunctional monomers with intrinsic metal-binding capability are a platform for tailoring ion-selectivity via imprinting moiety-template interaction, without complex formation and ligand immobilization. In the present study, As-IIPs based on 1-vinylimidazole, 4-vinylpyridine and styrene were designed to investigate the imprinting mechanism in relation to their structural and functional properties. In terms of selectivity as well as imprinting effects compared with the non-imprinted polymer (NIP), 1-vinylimidazole-based As-IIP exhibited superior analyte recognition for As ion among 23 competing elements, with a 25-fold enhancement in the practical dynamic and static adsorption capacity range (0.048-4.925 μmol g(-1)). The robust As-IIP sorbent features good reusability up to 20 cycles and a wide working pH 5-7 for a firstly reported solid-phase extraction (SPE) application. As a result of selective sample clean-up, As-IIP-SPE offered limits of detection (LOD) and quantification (LOQ) down to 0.025 and 0.083 μmol L(-1), respectively, for environmental sample analysis using inductively coupled plasma-mass spectrometry.

Analytical Challenges: Determination of Tetrodotoxin in Human Urine and Plasma by LC-MS/MS

Tetrodotoxin (TTX) is a powerful sodium channel blocker found in puffer fish and some marine animals. Cases of TTX poisoning most often result from puffer fish ingestion. Diagnosis is mainly from patient’s signs and symptoms or the detection of TTX in the leftover food. If leftover food is unavailable, the determination of TTX in the patient’s urine and/or plasma is essential to confirm the diagnosis. Although various methods for the determination of TTX have been published, most of them are for food tissue samples. Dealing with human urine and blood samples is much more challenging. Unlike in food, the amount of toxin in the urine and blood of a patient is generally extremely low; therefore a very sensitive method is required to detect it. In this regard, mass spectrometry (MS) methods are the best choice. Since TTX is a very polar compound, there will be lack of retention on conventional reverse-phase columns; use of ion pair reagent or hydrophilic interaction liquid chromatography (HILIC) can help solve this problem. The problem of ion suppression is another challenge in analyzing polar compound in biological samples. This review will discuss different MS methods and their pros and cons.

Rapid speciation of methylated and ethylated mercury in urine using headspace solid phase microextraction coupled to LC-ICP-MS

Solid-phase microextraction coupled to liquid chromatography-inductively coupled plasma-mass spectrometry (SPME-LC-ICP-MS) is presented as a new approach for the extraction and speciation of methylmercury (MeHg) and ethylmercury (EtHg) in a complex urine matrix. Despite the fact that urine is one of the most easily accessible sources of biological specimens for clinical testing, reports of mercury speciation methods are limited. Without any tedious sample pretreatments or derivatization procedures, headspace SPME offers a clean and convenient one-step extraction followed by direct desorption into HPLC. In this work, the fibre was first exposed to the sample headspace for a 45 min extraction, followed by a 5 min desorption. Experimental parameters including extraction time and temperature, sodium chloride salt concentration, agitation rate and desorption time were optimized to achieve detection limits down to 0.06 μg L−1 for both organomercury species. Sample recoveries in spiked urine matrix ranged from 81.7–109.5%. The accuracy of the method was further validated using a certified reference material (TORT-2) and applied in the organomercury speciation of urine samples collected from patients with suspected mercury poisoning.

Ionic‐liquid‐based dispersive liquid–liquid microextraction for high‐throughput multiple food contaminant screening

This paper describes an innovation of dispersive liquid-liquid microextraction enabling multiple-component analysis of eight high-priority food contaminants in two chemically distinctive families: Sudan dyes and phthalate plasticizers. To provide convenient sample handling for solid and solid-containing matrices, a modified dispersive liquid-liquid microextraction procedure used an extractant precoated frit to perform simultaneous filtration, solvent mixing, and phase dispersion in one simple step. A binary ionic liquid extractant system was carefully tuned to deliver high quality analysis based only on affordable LC with diode array detector instrumentation. The method is comprehensively validated for robust quantification with good precision (6.9-9.8% RSD) in a linear 2-1000 μg/L range. Having accomplished enrichment factors up to 451, the treatment enables sensitive detection at 0.09-1.01 μg/L levels. Analysis of six high-risk solid condiments and sauces further verified its practical applicability within a 70-120% recovery range. Compared to other approaches, the current dispersive liquid-liquid microextraction treatment offers major advantages in terms of minimal solvent (1.5 mL) and sample (0.1 g) consumption, ultra-high analytical throughput (6 min), and the ability to handle complex solid matrices. The idea of performing simultaneous analysis for multiple contaminants presented here fosters a more effective mode of operation in food control routines.

Toward the use of surface modified activated carbon in speciation: Selective preconcentration of selenite and selenate in environmental waters

This paper describes a novel application of tetrabutylammonium hydroxide-modified activated carbon (AC-TBAH) to the speciation of ultra-trace Se(IV) and Se(VI) using LC-ICP-DRC-MS. The anion exchange functionality was immobilized onto the AC surface enables selective preconcentration of inorganic Se anions in a wide range of working pHs. Simultaneous retention and elution of both analytes, followed by subsequent analysis with LC-ICP-DRC-MS, allows to accomplish speciation analysis in natural samples without complicated redox pre-treatment. The laboratory-made column of immobilized AC (0.4 g of sorbent packed in a 6 mL syringe barrel) has achieved analyte enrichment factors of 76 and 93, respectively, for Se(IV) and Se(VI), thus proving its superior preconcentration efficiency and selectivity over common AC. The considerable enhancement in sensitivity achieved by using the preconcentration column has improved the methods detection limits to 1.9-2.2 ng L(-1), which is a 100-fold improvement compared with direct injection. The analyte recoveries from heavily polluted river matrix were between 95.3 and 107.7% with less than 5.0% RSD. The robustness of the preconcentration and speciation method was validated by analysis of natural waters collected from rivers and reservoirs in Hong Kong. The modified AC material is hence presented as a low-cost yet robust substitute for conventional anion exchange resins for routine applications.

Simultaneous determination of seven elemental species in estuarine waters by LC-ICP-DRC-MS

A new multi-elemental speciation method was developed for seven species of three elements namely As(III), As(VI), MMA, Cr(III), Cr(VI), Se(IV) and Se(VI), using liquid chromatography-inductively coupled plasma-mass spectrometry. The use of dynamic reaction cell technique in removing polyatomic interference dramatically extended the detection sensitivity for all seven species with methane as the reaction gas. The developed condition offered low detection limits in ranges of 0.12–0.44 μg L−1, 0.24–0.29 μg L−1 and 0.26 μg L−1 for species of As, Cr and Se, respectively. For concise quantitative speciation, a controlled chelation condition for Cr species was optimized to minimize species interconversion. In the developed method, the seven species were baseline-separated in an 11-minute elution on an anion exchange column using NH4NO3/NH4H2PO4 as the mobile phase at pH 6. This efficient, high-throughput and sensitive method was fully validated and applied in quantitative speciation of river water samples collected from the Shing Mun River of Hong Kong. Most of the species were found as the toxic forms of the elements studied.

Current developments in clinical sample preconcentration prior to elemental analysis by atomic spectrometry: a comprehensive literature review

Sample preconcentration is important for metal analysis in complex clinical matrices due to the low concentration of analytes and high salt content. The limited amount of sample available also increases the challenges of extraction and determination of the analytes. In spite of the increase in sensitivity of instruments, such ultra-trace levels of the metals are still difficult to determine accurately. Researchers have adopted various strategies to improve the efficiency and selectivity of the extraction. The use of chemicals and time for analysis can also be reduced by scaling down the analysis to the micro-level. This review discusses four aspects of the recent development in metal preconcentration in clinical samples, namely the use of ionic liquids (ILs) in extraction, sorption by nanomaterials, preconcentration using surfactants, and automation. The publications reviewed cover the period between 2008 to late 2013.

Current evidence for the hepatoprotective activities of the medicinal mushroom Antrodia cinnamomea

Antrodia cinnamomea (AC) is an endemic mushroom species of Taiwan, and has been demonstrated to possess diverse biological and pharmacological activities, such as anti-hypertension, anti-hyperlipidemia, anti-inflammation, anti-oxidation, anti-tumor, and immunomodulation. This review focuses on the inhibitory effects of AC on hepatitis, hepatocarcinoma, and alcohol-induced liver diseases (e.g., fatty liver, fibrosis). The relevant biochemical and molecular mechanisms are addressed. Overall, this review summarizes the hepatoprotective activities in vitro and in vivo. However, there is no doubt that human and clinical trials are still limited, and further studies are required for the development of AC-related products.