Synthesis, Electrochemistry, Photophysics, and Photochemistry of a Discrete Tetranuclear Copper(I) Sulfido Cluster.

A tetranuclear copper(I) complex, [Cu4{µ-(Ph2P)2NH}4(µ4-S)](PF6)2 (1), was synthesized. It was found to display intense and long-lived phosphorescence in the solid and solution states. The lowest-energy excited state was assigned as ligand-to-metal charge transfer (LMCT) [S2- → Cu4] mixed with some metal-centered (ds/dp) character. In addition, the phosphorescent state of this complex was found to be quenched by pyridinium acceptors via an oxidative electron-transfer quenching process. An excited-state reduction potential of -1.74 V versus saturated salt calomel electrode was estimated through oxidative quenching studies with a series of structurally related pyridinium acceptors, indicative of its strong reducing power in the excited state. From the transient absorption difference spectrum of the tetranuclear copper(I) sulfido complex and 4-(methoxycarbonyl)-N-methylpyridinium hexafluorophosphate, in addition to the characteristic absorption of the pyridinyl radical at ca. 395 nm, two absorption bands at ca. 500 and 660 nm were also observed. The former was assigned as an LMCT absorption [S2- → Cu4] and the latter as an intervalence charge-transfer transition, associated with the mixed-valence species CuI/CuI/CuI/CuII.

Isotope dilution gas chromatography/mass spectrometry method for determination of pyrethroids in apple juice.

This paper presents the development of a highly precise and accurate analytical method for the determination of three matrix-bound pyrethroids, namely, cypermethrin, permethrin, and bifenthrin, using an isotope dilution gas chromatography/mass spectrometry technique. Identification of the analytes was confirmed under selective ion monitoring mode by the presence of two dominant ion fragments within specific time windows and matching of relative ion intensities of the ions concerned in samples and calibration standards. Quantitation was based on the measurement of concentration ratios of the natural and isotope analogues in the sample and calibration blends. Intraday and interday repeatabilities of replicate analyses of the pyethroids in an apple juice sample were below 0.5%. The expanded relative uncertainty ranged from 3 to 6%, which was significantly lower than the range obtained using internal or external calibration methods. As a labeled analogue is not available for bifenthrin, bifenthrin was determined using labeled cis-permethrin as the internal standard. The results were counterchecked by a gas chromatography-electron capture detection technique using PCB 209 as the internal standard. The method developed was applied to a recent pilot study organized by CCQM and the results were consistent with those of other participants.

Development of an Analytical Method for Analyzing Pyrrolizidine Alkaloids in Different Groups of Food by UPLC-MS/MS.

Suspected nontargeted pyrrolizidine alkaloids (PAs), without analytical reference standard, were observed and interfered with the determination of targeted PAs in complex food matrices, especially for spices samples. Selectivity and applicability of multiple reaction monitoring (MRM) transitions, multistage fragmentation (MS3), and MRM with differential ion mobility spectrometry (DMS) for eliminating false positive identifications were evaluated. Afterward, a selective and sensitive LC-MS/MS method for the determination of 15 PAs and 13 PA N-oxides in foodstuffs was developed. The sample preparation and cleanup are applicable to a wide range of foodstuffs, including cereal products, dairy products, meat, eggs, honey, tea infusion, and spices. Freezing-out of the raw extract and the water/acetonitrile washing steps in a solid phase extraction was found to efficiently remove complex matrices. The method was validated at 0.05 µg kg-1 for general food and 0.5 µg kg-1 for spices, with reference to the Eurachem Guide. The estimated limit of quantifications of different PAs was in the range of 0.010-0.087 µg kg-1 for general food and 0.04-0.76 µg kg-1 for spices. Isotopically labeled PAs were used as internal standards to correct the variation of PAs/PANs performance in different food commodities. Matrix effects observed in complex food matrices could be reduced by solvent dilution. Recoveries of PAs and PA N-oxides were all seen within 50-120%.

Dietary exposure to mycotoxins of the Hong Kong adult population from a Total Diet Study.

Dietary exposure of Hong Kong adults to mycotoxins and their metabolites including aflatoxins (AFs), ochratoxin A (OTA), fumonisins (FNs), deoxynivalenol (DON), acetyldeoxynivalenols (AcDONs) and zearalenone (ZEA) was estimated using the Total Diet Study (TDS) approach to assess the associated health risk to the local people. Sixty commonly consumed food items, collected in four seasons, were sampled and prepared as consumed. These mycotoxins were primarily found at low levels. The highest mean levels (upper bound) were: AFs, 1.50 µg kg(-)(1) in legumes, nuts and seed; OTA, 0.22 µg kg(-)(1) in sugars and confectionery; FNs, 9.76 µg kg(-)(1) in cereals and their products; DON and AcDONs, 33.1 µg kg(-)(1) in cereals and their products; and ZEA, 53.8 µg kg(-)(1) in fats and oils. The estimated dietary exposures of Hong Kong adults to the mycotoxins analysed were well below the respective health-based guidance values, where available. For AFs, the upper-bound exposure for high consumers is 0.0049 µg kg bw(-)(1) day(-)(1), which was estimated to contribute to about 7.7 (< 1%) of liver cancer cases when compared with 1222 liver cancer cases per year in Hong Kong. The percentage contributions of the estimated 95th percentile dietary exposures (lower and upper bound) to the health-based guidance values of individual mycotoxins were: ochratoxin A, 3.6-9.2%; fumonisins, 0.04-8.5%; deoxynivalenol and acetyldeoxynivalenols, 21.7-28.2%; and zearalenone 3.3-34.5%. The findings indicate that dietary exposures to all the mycotoxins analysed in this study were unlikely to pose an unacceptable health risk to the Hong Kong population.

An oscillating C2(2-) unit inside a copper rectangle.

[Cu4(mu-dppm)4(mu4-eta1,eta2-C[triple bond]C-)]2+ has been shown by 31P and 1H NMR studies to undergo two fluxional processes in solution, the oscillation of the C[triple bond]C2- unit inside the copper rectangle and the flipping of the diphosphines, and this has been supported by DFT(B3LYP) calculations.

Development of an ultraperformance liquid chromatography-tandem mass spectrometry method for the analysis of perfluorinated compounds in fish and Fatty food.

This paper reports the development of a method for the quantitative analysis of perfluorinated compounds (PFCs), including C6-C14 perfluorinated carboxylic acids (PFCAs) and C4-C12 perfluorinated sulfonates (PFSAs), in fish and fatty foods by ultraperformance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) in which the UPLC was equipped a PFC Analysis Kit to eliminate background contamination. Rapid baseline separation was achieved for 17 PFCs within 12 min, and PFCs were well-resolved from potential interferences from taurodeoxycholic acid and branched isomers of PFCs. The method was validated according to Commission Regulation 2002/657/EC of the European Commission with matrices including salmon, beef, egg, and butter. Average spiked recoveries, measured at concentration levels of 0.02 (method limit of quantification (MLOQ)), 0.2, and 2 µg/kg, were in the range of 68-117% with relative standard deviations below 20%. Matrix effects were evaluated and found to be correctable by internal standardization, especially for short- and long-chained PFCs. Trueness was verified against two certified reference materials. The method has also been successfully applied to the analysis of more than 200 food samples of a risk assessment study.

Total and inorganic arsenic in foods of the first Hong Kong total diet study.

Arsenic (As) is a metalloid that occurs in different inorganic and organic forms, which are found in the environment from both natural occurrence and anthropogenic activity. The inorganic forms of As (iAs) are more toxic as compared with the organic As, but so far most of the occurrence data in food collected in the framework of official food control are still reported as total As without differentiating the various As species. In this paper, total As and iAs contents of 600 total diet study (TDS) samples, subdivided into 15 different food groups, were quantified by high-resolution inductively coupled plasma mass spectrometry (HR-ICP/MS) and hydride generation (HG) ICP/MS respectively. The method detection limits for both total As and iAs were 3 µg As kg(-1). As the samples were prepared for TDS, food items were purchased directly from the market or prepared as for normal consumption, i.e. table ready, in the manner most representative of and consistent with cultural habits in Hong Kong as far as practicable. The highest total As and iAs content were found in 'fish, seafood and their products' and 'vegetables and their products' respectively. Besides, this paper also presents the ratios of iAs and total As content in different ready-to-eat food items. The highest ratio of iAs to total As was found in 'vegetables and their products'. It is likely that iAs in vegetables maintained its status even after cooking.

Dietary exposure of Hong Kong adults to acrylamide: results of the first Hong Kong Total Diet Study.

Acrylamide is a processing contaminant in food formed during cooking at high temperature, such as frying and baking. To assess the associated health risk of the Hong Kong population, the dietary exposure of Hong Kong adults to acrylamide was estimated in the first Hong Kong Total Diet Study (TDS), where food samples were collected and prepared "as consumed". A total of 532 composite food samples were analysed for acrylamide using LC-MS/MS. Dietary exposures were estimated by combining the analytical results with the food consumption data of the Hong Kong adults. The mean and 95th percentile exposures to acrylamide of the Hong Kong population were 0.213 and 0.538 µg kg⁻¹ body weight (bw) day⁻¹, respectively, and their margins of exposure (MOEs) were all below 10,000. The main dietary source of acrylamide was "Vegetables and their products" (52.4% of the total exposure), particularly stir-fried vegetables (44.9%), followed by "Cereals and their products" (14.7%) and "Mixed dishes" (9.43%). The study findings suggest that the relatively low figures for MOE for a genotoxic carcinogen may indicate human health concern of the Hong Kong population. Efforts should continue to be made in the interest of reducing acrylamide levels in food locally.

Dietary exposure of Hong Kong adults to pesticide residues: results of the first Hong Kong Total Diet Study.

The use of pesticides and other chemicals has become a common practice in modern agriculture to enhance and stabilise crop yield, protect the nutritional integrity of food, facilitate food storage to assure year-round supplies, and provide attractive and appealing food products. With the adoption of strict good agricultural practice (GAP), only minimal amounts of pesticide residues should remain on the crops or in connected foods of animal origin up the food chain. To assess their associated health risk to local people, the dietary exposure of Hong Kong adults to residues of four groups of pesticides or their metabolites - organophosphorus pesticides (OPPs), carbamates, pyrethrins and pyrethroids, and dithiocarbamate (DTC) metabolites - is estimated in the first Hong Kong Total Diet Study (TDS). A total of 150 commonly consumed food items were collected and prepared "as consumed". A total of 600 composite food samples were analysed for 85 pesticides or their metabolites by liquid chromatography-tandem mass spectrometry (LC-MS/MS). These pesticides were primarily found at low levels (highest mean = 350 µg kg⁻¹) in food samples of plant origin such as vegetables and fruits. Dietary exposures to pesticide residues were estimated based on the analytical results and the food consumption data of the local residents. The estimated dietary exposures of Hong Kong adults to all individual pesticides were well below their respective acceptable daily intakes (ADIs). The percentage contributions of the estimated mean and 95th percentile dietary exposures to the ADIs of individual pesticides were <6% and <24% for the OPPs, <1% for the carbamates and pyrethrins and pyrethroids, and <1% and <4% for the DTC metabolites, respectively. The findings indicate that dietary exposures to all the pesticide residues analysed in this study were unlikely to pose unacceptable health risks to the Hong Kong population.

Measurement of carbonaceous aerosols: validation and comparison of a solvent extraction-gas chromatographic method and a thermal optical transmittance method.

A solvent extraction-gas chromatographic method was developed for the measurement of four classes of solvent-extractable organic compounds (SEOC), viz., aliphatic hydrocarbons, polynuclear aromatic hydrocarbons, fatty acids and alkanols, in ambient carbonaceous aerosols. The selectivity and recovery of the method using different solvents commonly used in the analysis of SEOC was evaluated. The composition of SEOC in aerosol and urban dust samples was found to vary with the choice of solvent. Such variation was not observed in filters spiked with standards of SEOC. The developed method was validated by the analysis of reference urban dust SRM 1649a from the National Institute of Standards and Technology. The concentrations of selected polynuclear aromatic hydrocarbons in the reference dust were found to fall within the certified and reference concentrations. The thermal characteristics of aerosol samples collected in an urban area of Hong Kong and the four classes of identified SEOC were also studied using a thermal optical transmittance (TOT) method as specified in NIOSH Method 5040. Correlations were made to compare the method-dependent SEOC content obtained by the solvent extraction method and the results for total carbon, organic carbon and elemental carbon obtained by the TOT method.

Synthesis, photophysics, electrochemistry, theoretical, and transient absorption studies of luminescent copper(I) and silver(I) diynyl complexes. X-ray crystal structures of [Cu3(micro-dppm)3(micro3-eta1-C triple bond CC triple bond CPh)2]PF6 and [Cu3(micro-dppm)3(micro3-eta1-C triple bond CC triple bond CH)2]PF6.

A series of soluble trinuclear copper(I) and silver(I) complexes containing bicapped diynyl ligands, [M(3)(micro-dppm)(3)(micro(3)-eta(1)-C triple bond CC triple bond CR)(2)]PF(6) (M = Cu, R = Ph, C(6)H(4)-CH(3)-p, C(6)H(4)-OCH(3)-p, (n)C(6)H(13), H; M = Ag, R = Ph, C(6)H(4)-OCH(3)-p), has been synthesized and their electronic, photophysical, and electrochemical properties studied. The X-ray crystal structures of [Cu(3)(micro-dppm)(3)(micro(3)-eta(1)-C triple bond CC triple bond CPh)(2)]PF(6) and [Cu(3)(micro-dppm)(3)(micro(3)-eta(1)-C triple bond CC triple bond CH)(2)]PF(6) have been determined.