Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l⁻¹ HNO₃ and in 1+1 v/v diluted wine using mixtures of Pd(NO₃)₂+Mg(NO₃)₂ and NH₄H₂PO₄+Mg(NO₃)₂ as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l⁻¹ HNO₃, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l⁻¹ Cd and 5.0–50 μg l⁻¹ Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l⁻¹ for Cd, 0.8 μg l⁻¹ for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l⁻¹ and for Pb at 500 μg l⁻¹. The relative standard deviations (n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.     

Tungsten coil devices in atomic spectrometry: absorption, fluorescence, and emission.

In this work, tungsten coil (W-Coil) devices are used as atomizers for electrothermal atomization atomic absorption spectrometry (ETAAS), electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS), and electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES). For most cases in ETAAS and ETA-LEAFS, limits of detection (LODs) using the W-Coil are within a factor of ten of those observed with commercial graphite furnace systems. LOD for Cd by W-Coil AAS is 10 pg, while LODs for As, Se, Cr, Sb and Pb by W-Coil LEAFS are 950, 320, 1400, 330, and 160 fg, respectively. The compact W-Coil device makes it an ideal atomizer for portable atomic spectrometry instrumentation, especially when coupled with a miniature charge coupled device spectrometer. Alternatively, the atomizer can be used as an inexpensive, modular add-on to an existing commercial ICP-AES system; and the thermal separation of Pb with interference elements Al, Mn, and Fe is demonstrated.     

Smooth Dependence of Thermodynamic Limits¶of SRB-Measures

The thermodynamic limits of SRB-measures for uniformly hyperbolic sets are smoothly dependent on the map in an appropriate functional space. Received: 26 April 1999 / Accepted: 17 November 1999     

Thermal stability of ionic liquid BMI(BF4) in the presence of nucleophiles

We have found that a common ionic liquid--one containing a N-N′-dialkylimidazolium cation--decomposes in the presence of nucleophiles at much lower temperatures than previously believed. The decomposition occurs through S_N2 attack of the nucleophile on the electrophilic alkyl groups attached to the imidazolium ring.     

Highly strained dihydroanthraquinones: oxidation versus elimination

The chemistry of strained dihydroanthraquinones was investigated for the purpose of developing syntheses for highly strained anthraquinones. The reaction of (1,4-dihydro-9,10-dioxo-anthracen-1-yl)-acetates with triethylamine under aerobic conditions was found to be dependent on the degree of substitution on the acetate. Dihydroanthraquinones bearing dimethylacetates underwent elimination of enolate exclusively, while those without acetate substitution dehydrogenated as expected. Furthermore, oxidation of the cyclohexadiene ring using iodine failed due to a competitive iodolactonization reaction. The desired strained anthraquinones could be prepared, in low yield, by treatment of the resulting lactones with acidic ethanol.     

Death,taxes, and the genetic code?

The genetic code is an enduring feature of biology: only rare circumstances result in changes to translation of the code, at least in nature. Researchers are devising methods to engineer ribosome-synthesized polypeptides containing novel and potentially useful amino acids.     

Standard dilution analysis of beverages by microwave-induced plasma optical emission spectrometry

In this work, standard dilution analysis (SDA) is combined with microwave-induced plasma optical emission spectrometry (MIP OES) to determine seven elements in coffee, green tea, energy drink, beer, whiskey and cachaça (Brazilian hard liquor). No sample preparation other than simple dilution in HNO₃ 1% v v⁻¹ is required. Due to relatively low plasma temperatures, matrix effects may compromise accuracies in MIP OES analyzes of complex samples. The method of standard additions (SA) offers enhanced accuracies, but is time-consuming and labor intensive. SDA offers a simpler, faster approach, with improved accuracies for complex matrices. In this work, SDA's efficiency is evaluated by spike experiments, and the results are compared to the traditional methods of external calibration (EC), internal standard (IS), and standard additions (SA). SDA is comparable to the traditional calibration methods, and it provides superior accuracies for applications involving ethanol-containing beverage samples. The SDA-MIP OES procedure is effective. Using only two calibration solutions, it may be easily automated for accurate and high sample throughput routine applications.     

Deviations of discrete distributions and a question of Móri

In this note, we consider a question of Móri regarding estimating the deviation of the kth terms of two discrete probability distributions in terms of the supremum distance between their generating functions over the interval [0,1]. An optimal bound for distributions on finite support is obtained. Properties of Chebyshev polynomials are employed.     

Simple and effective method for the deracemization of ethyl 1-hydroxyphosphinate using biocatalysts with lipolytic activity

The kinetic resolution of ethyl (1-hydroxyethyl)phenylphosphinate was carried by enzymatic esterification with vinyl butyrate or by hydrolysis of ethyl (1-butyryloxyethyl)phenylphosphinate either by the use of lipases or whole cells of microorganisms (bacteria and fungi). Since no stereodifferentiation of the phosphinate moiety was observed, the biotransformations gave diastereoisomers of ethyl (1-hydroxyethyl)phenylphosphinate with excellent enantiomeric excesses above 98%, while the percentage conversion ranged from 10% to 49% depending upon the procedure and conditions of the biocatalysis.