Yiu Chung Yip - Academia.edu (original) (raw)

Papers by Yiu Chung Yip

Accreditation and Quality Assurance

Journal of AOAC INTERNATIONAL, 2007

A method was validated for the direct determination of As(III) and As(V) in water samples by ion ... more A method was validated for the direct determination of As(III) and As(V) in water samples by ion chromatography/inductively coupled plasma-mass spectrometry. Sample preservation required only dilution with a mobile phase containing a sufficient amount of ethylenediaminetetraacetic acid and acetic acid. Analyses of 6 certified reference materials (CRMs) of various water matrixes, including seawater, demonstrated good method accuracy. The matrixes included 2 natural water samples National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1643e and NIST SRM 1640, 1 fortified standard solution (TMDA-64), 1 fortified water sample (TM-DWS), and 2 seawater samples (CASS-4 and NASS-5). The sum of As(III) and As(V) in each CRM agreed with the respective certified value for the total amount of As within its stated uncertainty. Quantitative recoveries (96.7-102.1%) were obtained. Satisfactory results were achieved for intraday repeatability relative standard deviatio...

Journal of AOAC INTERNATIONAL, 2006

A method was developed for high-throughput determinations of 7 elements in food samples, namely a... more A method was developed for high-throughput determinations of 7 elements in food samples, namely antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and tin (Sn). The samples were digested by closed-vessel microwave-assisted digestion using concentrated nitric acid (HNO3) as the medium, followed by microwave- assisted evaporation to concentrate the sample solutions before dilution to the desired volume. The microwave-assisted evaporation procedure effectively reduced the final acid concentration to around 8 before analysis by inductively coupled plasmamass spectrometry (ICPMS). This reduction allows determination by ICPMS to proceed without further sample dilution, which would affect the detection limit. The method was validated, and method recoveries for As, Cd, Cr, Pb, and Hg were within the certified ranges of the chosen certified reference materials. Recoveries of the 7 elements from spiked samples ranged from 93.1 to 103.6. The standard uncertainti...

Accreditation and Quality Assurance, 2017

$Research paper thumbnail of APMP.QM-S8: determination of mass fraction of benzoic acid, methyl paraben and n-butyl paraben in soy sauce$

Metrologia, 2017

The supplementary comparison APMP.QM-S8: determination of mass fraction of benzoic acid, methyl p... more The supplementary comparison APMP.QM-S8: determination of mass fraction of benzoic acid, methyl paraben and n-butyl paraben in soy sauce was coordinated by the Health Sciences Authority, Singapore under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM). Ten national metrology institutes (NMIs) or designated institutes (DIs) participated in the comparison. All the institutes participated in the comparison for benzoic acid, while six NMIs/DIs participated in the comparison for methyl paraben and n-butyl paraben. The comparison was designed to enable participating institutes to demonstrate their measurement capabilities in the determination of common preservatives in soy sauce, using procedure(s) that required simple sample preparation and selective detection in the mass fraction range of 50 to 1000 mg/kg. The demonstrated capabilities can be extended to include other polar food preservatives (e.g. sorbic acid, propio...

TrAC Trends in Analytical Chemistry, 2007

Abstract The combination of a collision/reaction cell (C/RC) with a quadrupole/single focusing ma... more Abstract The combination of a collision/reaction cell (C/RC) with a quadrupole/single focusing magnetic sector inductively coupled plasma mass spectrometer has been regarded as promising in reducing interfering ions while maintaining ample sensitivity for ultra-trace measurements of analytes, even in complicated matrices. Commonly used reagent gases, such as H2, He and NH3, have been successful in the determinations of a number of elements using isotope dilution mass spectrometry (IDMS). This review focuses primarily on recent applications of C/RC technology in IDMS. We also cover other issues, including equations for IDMS, currently available instrumentation and potential areas for future development.

Topics in Organometallic Chemistry, 2011

ABSTRACT Chiral ketones have been developed as efficient catalysts for asymmetric alkene epoxidat... more ABSTRACT Chiral ketones have been developed as efficient catalysts for asymmetric alkene epoxidation in the past decades. The development of different classes of chiral ketones for asymmetric epoxidation of unfunctionalized alkenes will be discussed. In addition, studies on diastereoselective epoxidation are also covered. Keywords Asymmetric epoxidation-Chiral ketones-Dioxiranes-Epoxides

Organic Syntheses, 2003

trans-2-Methyl-2,3-diphenyloxirane R trans-α-Methylstilbene P trans-2-Methyl-2,3-diphenyloxirane ... more trans-2-Methyl-2,3-diphenyloxirane R trans-α-Methylstilbene P trans-2-Methyl-2,3-diphenyloxirane Keywords: ethers, epoxides; heterocycles, three-membered, one oxygen; epoxide formation; oxidation, miscellaneous; catalytic epoxidation with oxone

TrAC Trends in Analytical Chemistry, 2009

... Permissions &amp; Reprints. Commonly used methodologies for inorganic analysis in int... more ... Permissions &amp; Reprints. Commonly used methodologies for inorganic analysis in international key comparisons. Yiu-chung Yip Corresponding Author Contact Information , a , E-mail The Corresponding Author , James Chung-wah Lam b and Wai-fong Tong a [Author vitae]. ...

TrAC Trends in Analytical Chemistry, 2009

This review addresses the assessment of laboratory performance in intercomparisons for inorganic ... more This review addresses the assessment of laboratory performance in intercomparisons for inorganic analysis. Three types of intercomparisons in question are proficiency testing schemes, measurement evaluation programs, and international key comparisons. Evaluation of intercomparisons focuses primarily on purposes of participation, participants involved, sample matrices encountered, methods commonly used for analysis, traceability of assigned values to SI, calculation of performance statistics, reporting

TrAC Trends in Analytical Chemistry, 2008

... Applications of lead isotope ratio measurements. ... Abstract. Lead isotope ratio measurement... more ... Applications of lead isotope ratio measurements. ... Abstract. Lead isotope ratio measurements (Pb-IRM) have been widely used for identification purposes for several decades. This article reviews current analytical techniques available for Pb-IRM, including: ...

TrAC Trends in Analytical Chemistry, 2011

This review evaluates commonly used methodologies for assessing the chemical purity of organic re... more This review evaluates commonly used methodologies for assessing the chemical purity of organic reference materials. Direct assay of the principal component can be established by methodologies such as gas chromatography, liquid chromatography (LC), quantitative nuclear magnetic resonance (NMR), elemental analysis and titrimetry. Measurements of detectable impurity components mainly include determination of water or moisture content, and analysis of residual solvents,

Tetrahedron Letters, 1997

Metrologia, 2013

ABSTRACT The supplementary comparison APMP.QM-S5 was undertaken to demonstrate the capability of ... more ABSTRACT The supplementary comparison APMP.QM-S5 was undertaken to demonstrate the capability of participating national metrology institutes (NMIs) and designated institutes (DIs) in measuring the contents of the incurred essential elements (iron and zinc) and toxic elements (total arsenic and cadmium) at µg/g levels in a test sample of dried shrimp by various analytical techniques.

Journal of the American Chemical Society, 1998

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