Testing green coffee for ochratoxin A, part I: estimation of variance components

The variability associated with testing lots of green coffee beans for ochratoxin A (OTA) was investigated. Twenty-five lots of green coffee were tested for OTA contamination. The total variance associated with testing green coffee was estimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased with an increase in OTA concentration. Using regression analysis, mathematical expressions were developed to model the relationship between OTA concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific OTA concentration. Testing a lot with 5 microg/kg OTA using a 1 kg sample, Romer RAS mill, 25 g subsamples, and liquid chromatography analysis, the total, sampling, sample preparation, and analytical variances were 10.75 (coefficient of variation [CV] = 65.6%), 7.80 (CV = 55.8%), 2.84 (CV = 33.7%), and 0.11 (CV = 6.6%), respectively. The total variance for sampling, sample preparation, and analytical were 73, 26, and 1%, respectively.     

New refinement of the crystal structure of 1,3-diaminopropane dihydrochloride

The structure of C₃H₁₀N₂·2HCl,M _r =147.05,a=8.567(3),b=9.341(2),c=9.444(9) Å,V=755.7 ų,Pbcn,d ₀=1.30,d _c =1.29 Mg m^–3,Z=4,F(000)=312e, which had been previously solved (Hirokawa etal., 1968), has been refined by full matrix to a finalR value of 0.034 as compared to 0.196 in the work cited above.     

Crystal structures of baclofen analogs: 3-thienyl- and 3-furylaminobutyric acids

X-ray crystal structures of 4-amino-3-(2-thienyl) butyric acid (compound1), 4-amino-3-(4-bromo-2-thienyl) butyric acid (compound2), and 4-amino-3-(5-methyl-2-furyl) butyric acid (compound3) are reported. Space groups and unit/cell parameters are: compound1, monoclinic,P2₁ c,a=13.288(3),b=5.231(1),c=12.388(2)Å,=92.3(1)°; compound2, monoclinic,P2₁/c,a=12.610(7),b=5.156(1),c=15.814(8)Å,=101.8(1)°; compound3, orthorhombic, Pccn,a=11.461(1),b=25.284(2),c=6.977(1)Å. FinalR indices are: compound1, 0.057; compound2, 0.069; compound3, 0.060. Conformations of their -aminobutyric chains are compared with the one of -amino--(p-chlorophenyl)-butyric acid (baclofen, compound4). Two different types of conformations are observed, i.e., conformations (i) with folding (compound3) or (ii) without folding (compounds1,2, and4) of the ammonium group toward the heteroaromatic or aromatic ring. However, distances between ionized groups are constant.     

Analysis by fast-atom bombardment tandem mass spectrometry of phosphatidylcholine isolated from heart mitochondrial fractions: Evidence of incorporation of monohydroxylated fatty acyl moieties

Phosphatidylcholine (PC) is one of the main phospholipids present in mitochondrial membranes. According to current knowledge, the predominant fatty acyl moieties in this phospholipid are 16, 18, 20, or 22 carbon atoms long with chains that contain only carbon and hydrogen atoms. We have conducted a detailed analysis of the fatty acid substituents of the phospholipids present in mitochondrial fractions by using fast-atom bombardment tandem PC extracted from mitochondrial fractions of rat heart. The structure of one of these monohydroxylated fatty acids has been elucidated and corresponded to 12-hydroxy 9-octadecenoic acid. Indications that concern the structure of the five other monohydroxylated fatty acids are presented. These monohydroxylated fatty acyl groups are preferentially associated in the PC molecule with C-18 and C-20 fatty acyl moieties. We present arguments to suggest that the formation of these compounds is probably not due to a free-radical initiated mechanism. The potential implication of these monohydroxylated fatty acids in several physiological functions is suggested by the fact that free hydroxylated fatty acids that are identical or closely related to those found in the mitochondrial fractions possess various biological activities.     

Homogeneous N doping of thick polyacetylene films by chemical way

The kinetics of reduction (n doping) of fibrillar films of polyacetylene (PA) by a large excess of organoalkaline electron donors in solution was studied. The doping rate is proportional to dopant concentration and inversely proportional to the square of film thickness (in a range 100–1000 microns). This means that the kinetics of reduction is entirely controlled, in these experiments, by the interfibrillar diffusion of dopants, leading to macroscopic doping inhomogeneity if the reaction is stopped before completion. The maximum doping level achieved at the end of the reaction is mainly controlled by the redox potential of the dopant. Homogeneously doped thick films, at various doping levels, were prepared using a suitable set of dopants in various solvents.     

Study of interference in the flame atomic absorption spectrometric determination of lithium by using factorial design

The severe interference of a number of metallic ions found in brines, marine sediments and sea water in the determination of lithium is demonstrated. Calcium, iron and sodium significantly depressed the absorption signal on lithium in an air/acetylene flame. Aluminium, magnesium and strontium up to 1500, 1000 and 200 μg/mL, respectively, showed no interference in the determination of lithium under the same conditions. Potassium produced some suppression of the lithium signal at levels in excess of 1500 μg/mL. Experimental data were examined using the factorial design method. Interference was demonstrated in two synthetic samples (models of “brine” and “marine sediments” ) and natural marine sediment. It was possible to eliminate all interferences using a higher temperature (nitrous oxide/acetylene flame). In addition, by using the standard addition method the interference disappeared, which confirmed the interference as a proportional systematic error. Received: 4 December 1998 / Revised: 3 March 1999 / Accepted: 6 March 1999     

Hydrogenation of oleic acid over sol-gel ruthernium catalysts

The hydrogenation of oleic acid to oleyl alcohol over Ru-alumina and Ru−Sn-alumina sol-gel catalysts has been studied. It was found that, besides its hydrogenation activity, the Ru−Sn-alumina catalyst promotes thecis-trans isomerization of the unsaturated acid. This effect is used to explain some kinetic features of the system, like the high induction time observed in the formation of alcohols, and to re-examine the role of tin.     

Poly(ethylene oxide) macromonomer based hydrogels as a template for the culture of hepatocytes

Macromonomer based poly(ethylene oxide) (PEO) hydrogels were tested with respect to their ability to serve as a template for the survival and the growth of hepatocytes. Two systems were considered : either the surface of preexisting hydrogels, with controlled structural parameters, were seeded with isolated rat hepatocytes or the hepatocytes were dispersed in physiological medium containing the macromonomer/initiator and heated to 37°C. In the first case, cells were examined at given times after spreading over two days. The results were compared to those observed for the dispersion of fibroblasts onto a surface of the same type of hydrogels. The effects of the structure of the hydrogels and its chemical nature on the extent of hepatocyte attachment (or encapsulation) and the morphology were investigated.     

The packing property

A clutter (V, E) packs if the smallest number of vertices needed to intersect all the edges (i.e. a minimum transversal) is equal to the maximum number of pairwise disjoint edges (i.e. a maximum matching). This terminology is due to Seymour 1977. A clutter is minimally nonpacking if it does not pack but all its minors pack. An m×n 0,1 matrix is minimally nonpacking if it is the edge-vertex incidence matrix of a minimally nonpacking clutter. Minimally nonpacking matrices can be viewed as the counterpart for the set covering problem of minimally imperfect matrices for the set packing problem. This paper proves several properties of minimally nonpacking clutters and matrices. Received: December 1, 1997 / Accepted: April 6, 1999?Published online October 18, 2000     

Electrochemical impedance spectroscopy as a probe for wet chemical silicon oxide characterization

The kinetics of the chemical growth of silicon oxide in H₂O₂-containing ammonia solutions and its break-up by dilute ammonia solutions was investigated using electrochemical techniques and more specifically electrochemical impedance spectroscopy. The recording of the open circuit potential (OCP), complemented by successive impedance diagrams, demonstrates clearly the build-up of a silicon oxide passivating layer when hydrophobic Si surfaces are immersed in NH₃+H₂O₂ solutions. The thickening of the chemical oxide coating mainly results in the decrease of the capacitance value together with the enhancement of the ohmic surface resistance. On the other hand, pure ammonia dilute solutions lead to the progressive destruction of this hydrophilic passivating surface oxide, which is revealed by the simultaneous decay of the real component of the impedance. Finally, we observed the break-up of the passive layer, characterized by a sudden drop of the OCP to a value quite identical to that obtained with a bare Si surface. This process resulted in a dramatic corrosion of the substrate surface. Electronic Publication