Melamine contamination

In the summer of 2008, serious illnesses and deaths of babies in China were linked to melamine-tainted powdered infant formula. Melamine contains several metabolites, such as ammeline, ammelide, and cyanuric acid, and has been used for the adulteration of foods or milk to increase their apparent protein content. It is assumed that melamine and its metabolites are absorbed in the gastrointestinal tract, and precipitate in the kidney to form crystals. A new tolerable daily intake of 0.2 mg kg^?1 body weight was adapted by the World Health Organization in 2008. This paper reviews the variety of analytical methods that have been used for the analysis of melamine in food. The limit of detection of these various methods is 0.05–100 ppm. The maximum acceptable concentration in food has been set at 50 ppb by the US FDA. A fast and ultrasensitive procedure for screening, detection, and characterization of melamine and its derivative compounds needs to be established. Currently, mass-spectrometry technologies provide an alternative to derivatization for regulatory analysis of food.     

The Infrared Spectrum of Solid Chlorotrifluoromethane

The Infrared spectrum of solid chlorotrifluoromethane (CF₃Cl) has been studied and compared with that of matrix-isolated CF₃Cl. Crystal field splitting patterns of the strongest modes ν₁ and ν₄ suggest the crystal structure to be orthorhombic with a C_2v factor group and two molecules per unit cell located on C_s sites.     

Oligomeric guanidine synthesis assisted by TFA-sensitive arylsulfonylthiourea

Through arylsulfonyl activation of thiourea, efficient synthesis of oligomeric guanidines can be achieved in either solution or solid-phase. Incorporation of TFA-sensitive arylsulfonyl groups, such as Pbf, during the synthesis greatly simplifies deprotection procedures for obtaining the final oligomeric guanidine products.     

Development and validation of an isotope-dilution electrospray ionization tandem mass spectrometry method with an on-line sample clean-up device for the quantitative analysis of the benzene exposure biomarker S-phenylmercapturic acid in human urine

An isotope-dilution electrospray ionization tandem mass spectrometry (ESI-MS/MS) method with an on-line sample clean-up device, for the quantitative analysis of human urine for the benzene exposure biomarker S-phenylmercapturic acid (SPMA), was developed and validated. The sample clean-up system was constructed from an autosampler, a reversed-phase C18 trap cartridge, a two-position switching valve, and controlling computer software and hardware. The sample clean-up system was interfaced via 1/20 splitting to the ESI source of a triple-quadrupole mass spectrometer using negative ion mode and multiple reaction monitoring for SPMA and the isotope-labeled internal standard. A strategy was adopted to acquire pooled blank urine matrix and quality control samples spiked with standards. Validated procedures and data on method specificity, detection limits, standard curves, precision and recovery, sample storage stability, and inter-laboratory comparison are presented. The analytical system was fully automated. No tedious manual sample clean-up procedures are required. With the selectivity and the sensitivity provided by ESI-MS/MS detection, the analytical system can be used for high-throughput and accurate determination of SPMA levels in human urine samples, as a biomarker for environmental as well as occupational benzene exposure.     

Synthesis and characterization of (smif)2M(n) (n = 0, M = V, Cr, Mn, Fe, Co, Ni, Ru; n = +1, M = Cr, Mn, Co, Rh, Ir; smif =1,3-di-(2-pyridyl)-2-azaallyl)

A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)(2)M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe(3))(2)(THF)(n) (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated ((o)Mesmif)(2)Fe (2-Fe) and ((o)Me(2)smif)(2)Fe (3-Fe) were similarly prepared. Metatheses of MX(2) variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru). Metathesis of VCl(3)(THF)(3) with 2 Li(smif) with a reducing equiv of Na/Hg present afforded 1-V, while 2 Na(smif) and IrCl(3)(THF)(3) in the presence of NaBPh(4) gave [(smif)(2)Ir]BPh(4) (1(+)-Ir). Electrochemical experiments led to the oxidation of 1-M (M = Cr, Mn, Co) by AgOTf to produce [(smif)(2)M]OTf (1(+)-M), and treatment of Rh(2)(O(2)CCF(3))(4) with 4 equiv Na(smif) and 2 AgOTf gave 1(+)-Rh. Characterizations by NMR, EPR, and UV-vis spectroscopies, SQUID magnetometry, X-ray crystallography, and DFT calculations are presented. Intraligand (IL) transitions derived from promotion of electrons from the unique CNC(nb) (nonbonding) orbitals of the smif backbone to ligand π*-type orbitals are intense (ε ≈ 10,000-60,000 M(-1)cm(-1)), dominate the UV-visible spectra, and give crystals a metallic-looking appearance. High energy K-edge spectroscopy was used to show that the smif in 1-Cr is redox noninnocent, and its electron configuration is best described as (smif(-))(smif(2-))Cr(III); an unusual S = 1 EPR spectrum (X-band) was obtained for 1-Cr.     

The development and application of capillary electrophoresis methods for food analysis

Capillary electrophoresis (CE) offers the analyst a number of key advantages for the analysis of the components of foods. CE offers better resolution than, say, high-performance liquid chromatography (HPLC), and is more adept at the simultaneous separation of a number of components of different chemistries within a single matrix. In addition, CE requires less rigorous sample cleanup procedures than HPLC, while offering the same degree of automation. However, despite these advantages, CE remains under-utilized by food analysts. Therefore, this review consolidates and discusses the currently reported applications of CE that are relevant to the analysis of foods. Some discussion is also devoted to the development of these reported methods and to the advantages/disadvantages compared with the more usual methods for each particular analysis. It is the aim of this review to give practicing food analysts an overview of the current scope of CE.     

Synthesis, spectroscopy, and X-ray structures of fac-(CO)3(dppe)MnSC(S)H, fac-(CO)3(dppe)ReSC(S)H, fac-(CO)3(dppp)ReSC(S)H, and fac-(CO)3(dppb)ReSC(S)H

The monodentate dithioformato complexes, fac-(CO)₃(dppe)MnSC(S)H (1), fac- (CO)₃(dppe)ReSC(S)H (2), fac-(CO)₃(dppp)ReSC(S)H (3), and fac-(CO)₃ (dppb)ReSC(S)H (4), where dppe is 1,2-bis(diphenylphosphino)ethane, dppp is 1,3-bis(diphenylphosphino)propane, and dppb is 1,4-bis(diphenylphosphino)butane, were synthesized from the treatment of the corresponding hydrides, fac-(CO)₃ (P-P)MSC(S)H with CS₂. Compounds 1–4 crystallize in the monoclinic crystal system: for 1, space group = P2₁/c, a = 15.3139(3) Å, b = 9.7297(4) Å, c = 19.0991(6) Å, = 105.928(1), V = 2736.5 ų, Z = 4; for 2, space group = P2₁/c, a = 15.6395(8) Å, b = 9.8182(5) Å, c = 19.4153(11) Å, = 106.741(1), V = 2854.9(3) ų, Z = 4; for 3, space group = P2₁/n, a = 11.3570(10) Å, b = 19.465(2) Å, c = 15.5702(14) Å, = 104.776(2), V = 3328.3(5) ų, Z = 4; and for 4, space group = C2/c, a = 32.078(2) Å, b = 10.4741(6) Å, c = 19.0608(9) Å, = 94.315(2), V = 6386.1(6) ų, Z = 8.     

Compositional dependence of the electrical conductivity of vanadium phosphate glass

The bulk resistivities of vanadium phosphate glasses in the compositional range from 65 to 85 mole % V₂O₅ were measured and fitted as a function of composition to the equation for conductivity as proposed by Mott and later modified by Sayer and Mansingh for n, the number of unoccupied mearest sites surrounding the final hopping site of the small polaron. The fit to the experimental data was found to be best if the number n is chosen to be proportional to the total number of V⁵⁺ sites in the glass. Also n is found to be non-integer and can be regarded as the effective number of unoccupied sites surrounding the final site in the sense of eqn (24) developed in this paper. Values for n ranged from 0.2 to 5 for different compositions of the glass. A model for the structure of vanadium phosphate glass is proposed to explain the data.     

Characterization of a class of bivariate distribution functions

Let F_X,Y(x,y) be a bivariate distribution function and P_n(x), Q_m(y), n, m = 0, 1, 2,…, the orthonormal polynomials of the two marginal distributions F_X(x) and F_Y(y), respectively. Some necessary conditions are derived for the co-efficients c_n, n = 0, 1, 2,…, if the conditional expectation E[P_n(X) ∥ Y] = c_nQ_n(Y) holds for n = 0, 1, 2,…. Several examples are given to show the application of these necessary conditions.     

Acoustic imaging of objects buried in soil

In this study, we demonstrate an acoustic system for high-resolution imaging of objects buried in soil. Our goal is to image cultural artifacts in order to assess in a rapid manner the historical significance of a potential construction site. We describe the imaging system and present preliminary images produced from data collected from a soil phantom. A mathematical model and associated computer software are developed in order to simulate the signals acquired by the system. We have built the imaging system, which incorporates a single element source transducer and a receiver array. The source and receiver array are moved together along a linear path to collect data. Using this system, we have obtained B-mode images of several targets by using delay-and-sum beamforming, and we have also applied synthetic aperture theory to this problem.