Adsorptive voltammetric procedure for the determination of platinum baseline levels in human body fluids

Summary An extremly sensitive procedure for the determination of platinum in human body fluids is presented. A high pressure decomposition of the samples is followed by adsorptive voltammetric measurement. A detection limit down to 0.2 ng Pt/l sample allowed baseline levels of platinum in body fluids (urine: 0.5–15 ng/l, blood and blood plasma: 0.8–6.9 ng/l) to be evaluated. The concentration ranges in body fluids of occupationally exposed people were determined to 21–2900 ng/l (urine), 32–180 ng/l (blood) and 95–280 ng/l (blood plasma).     

Optimierung der gas-chromatographischen Elementanalyse über Di(trifluorethyl)dithiocarbamate

Analytical and Bioanalytical Chemistry -     

Asymmetric Syntheses of New Polyhydroxylated Quinolizidines: Cross‐Aldol Reactions of 7‐Oxabicyclo[2.2.1]heptan‐2‐one and 3a,4a,7a,7b‐Tetrahydro[1,3]dioxolo[4,5]furo[2,3‐d]isoxazole‐3‐carbaldehyde Derivatives

The cross‐aldolization of (−)‐(1S,4R,5R,6R)‐6‐endo‐chloro‐5‐exo‐(phenylseleno)‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((−)‐ 25 ) and of (+)‐(3aR,4aR,7aR,7bS)‐ ((+)‐ 26 ) and (−)‐(3aS,4aS,7aS,7bR)‐3a,4a,7a,7b‐tetrahydro‐6,6‐dimethyl[1,3]dioxolo[4,5]furo[2,3‐d]isoxazole‐3‐carbaldehyde ((−)‐ 26 ) was studied for the lithium enolate of (−)‐ 25 and for its trimethylsilyl ether (−)‐ 31 under Mukaiyama's conditions (Scheme 2). Protocols were found for highly diastereoselective condensation giving the four possible aldols (+)‐ 27 (`anti'), (+)‐ 28 (`syn'), 29 (`anti'), and (−)‐ 30 (`syn') resulting from the exclusive exo‐face reaction of the bicyclic lithium enolate of (−)‐ 25 and bicyclic silyl ether (−)‐ 31 . Steric factors can explain the selectivities observed. Aldols (+)‐ 27 , (+)‐ 28 , 29 , and (−)‐ 30 were converted stereoselectively to (+)‐1,4‐anhydro‐3‐{(S)‐[(tert‐butyl)dimethylsilyloxy][(3aR,4aR,7aR,7bS)‐3a,4a,7a,7b‐tetrahydro‐6,6‐dimethyl[1,3]dioxolo[4,5]‐furo[2,3‐d]isoxazol‐3‐yl]methyl}‐3‐deoxy‐2,6‐di‐O‐(methoxymethyl)‐α‐D ‐galactopyranose ((+)‐ 62 ), its epimer at the exocyclic position (+)‐ 70 , (−)‐1,4‐anhydro‐3‐{(S)‐[(tert‐butyl)dimethylsilyloxy][(3aS,4aS,7aS,7bR)‐3a,4a,7a,7b‐tetrahydro‐6,6‐dimethyl[1,3]dioxolo[4,5]furo[2,3‐d]isoxazol‐3‐yl]methyl}‐3‐deoxy‐2,6‐di‐O‐(methoxymethyl)‐α‐D ‐galactopyranose ((−)‐ 77 ), and its epimer at the exocyclic position (+)‐ 84 , respectively (Schemes 3 and 5). Compounds (+)‐ 62 , (−)‐ 77 , and (+)‐ 84 were transformed to (1R,2R,3S,7R,8S,9S,9aS)‐1,3,4,6,7,8,9,9a‐octahydro‐8‐[(1R,2R)‐1,2,3‐trihydroxypropyl]‐2H‐quinolizine‐1,2,3,7,9‐pentol ( 21 ), its (1S,2S,3R,7R,8S,9S,9aR) stereoisomer (−)‐ 22 , and to its (1S,2S,3R,7R,8S,9R,9aR) stereoisomer (+)‐ 23 , respectively (Schemes 6 and 7). The polyhydroxylated quinolizidines (−)‐ 22 and (+)‐ 23 adopt `trans‐azadecalin' structures with chair/chair conformations in which H−C(9a) occupies an axial position anti‐periplanar to the amine lone electron pair. Quinolizidines 21 , (−)‐ 22 , and (+)‐ 23 were tested for their inhibitory activities toward 25 commercially available glycohydrolases. Compound 21 is a weak inhibitor of β‐galactosidase from jack bean, of amyloglucosidase from Aspergillus niger, and of β‐glucosidase from Caldocellum saccharolyticum. Stereoisomers (−)‐ 22 and (+)‐ 23 are weak but more selective inhibitors of β‐galactosidase from jack bean.     

Sub‐Picosecond Singlet Exciton Fission in Cyano‐Substituted Diaryltetracenes

Thin films of 5,11‐dicyano‐6,12‐diphenyltetracene ( TcCN ) have been studied for their ability to undergo singlet exciton fission (SF). Functionalization of tetracene with cyano substituents yields a more stable chromophore with favorable energetics for exoergic SF (2E(T₁)?E(S₁)=?0.17 eV), where S₁ and T₁ are singlet and triplet excitons, respectively. As a result of tuning the triplet‐state energy, SF is faster in TcCN relative to the corresponding endoergic process in tetracene. SF proceeds with two time constants in the film samples (τ=0.8±0.2 ps and τ=23±3 ps), which is attributed to structural disorder within the film giving rise to one population with a favorable interchromophore geometry, which undergoes rapid SF, and a second population in which the initially formed singlet exciton must diffuse to a site at which this favorable geometry exists. A triplet yield analysis using transient absorption spectra indicates the formation of 1.6±0.3 triplets per initial excited state.     

Separation of antidepressants by capillary electrophoresis with in-line solid-phase extraction using a novel monolithic adsorbent

The separation of three selective serotonin reuptake inhibitors (SSRIs) by capillary electrophoresis (CE) with fully integrated solid-phase extraction (SPE) is described. Polymeric monolithic SPE modules were prepared in situ within a fused silica capillary from either butyl methacrylate-co-ethylene dimethacrylate or 3-sulfopropyl methacrylate-co-butyl methacrylate-co-ethylene dimethacrylate. Using a 1 cm SPE module placed at the inlet of the capillary, a mixture of sertraline, fluoxetine and fluvoxamine was extracted from aqueous solution by applying a simple pressure rinse. Under pressure-driven conditions, efficient elution was possible from both SPE materials investigated using 50 mM phosphate buffer, pH 3.5 in acetonitrile (20/80, v/v). Two different strategies were investigated for the efficient elution and subsequent CE separation. Injection of an aqueous sample plug directly into the non-aqueous elution/separation buffer was found to be unsuitable with poor elution profiles observed in the electrodriven mode. Alternatively, a sample plug equivalent to several capillary volumes could be injected by pressure followed by filling the capillary with the non-aqueous elution/separation buffer from the outlet end using a combination of pressure and electrodriven flow. Using a neutral monolith, efficient elution/separation was not possible due to an unstable electroosmotic flow (EOF), however, by adding the ionisable monomer, 3-sulfopropyl methacrylate to the SPE module to increase and stabilise the EOF, it was possible to achieve efficient elution from the SPE module, followed by baseline separation by CE using a 200 mM acetate buffer, pH 3.5 in acetonitrile (10/90, v/v). With enrichment factors of over 500 achieved for each of the analytes this demonstrates the potential of in-line SPE-CE for the sensitive analysis of these drugs.     

Analytical validity of the determination of mercury in whole blood and urine--results of the German external assurance programme for toxicological analysis in biological materials

The determination of mercury concentrations in blood and urine is currently the best way of monitoring individual uptake of organic and inorganic mercury. In Germany these determinations must be carried out under the conditions of an external quality assurance programme. The German performance evaluation, based on reference values established by reference laboratories yields success rates in percent for the participants in the intercomparison programme of about 60%. A Canadian evaluation system based on two evaluations scores, yields success rates of 25-50% for "good performance" and of 65-80% for "acceptable performance". The determination of mercury in blood and urine is at present not carried out with the necessary reliability.     

Flie?injektionsanalyse in der Bodenuntersuchung und Pflanzenanalyse

Summary It could be shown that the flow injection technique can be well introduced in labs which need a high sample throughput without any loss of precision. For normal labs with agrochemical tasks it is possible to adapt the proposed flow injection methods for nitrogen and phosphorus. For the determination of ammonia in juices and musts flow injection is better in precision and faster than the conventional methods. The determination of nitrate in plant extracts can be performed without any clean-up of the crude extract by introducing a dialysis cell in the normal flow injection system. For the determination of proline and arginine methods were developed for flow injection. Both are selective with a high precision and crude plant extracts can be injected for determination. Flow diagrams and equipment parameters are described.     

Characterisation of regioselectively functionalized 2,3-O-carboxymethyl cellulose by enzymatic and chemical methods

The determination of the molecular structure of 2,3-O-carboxymethyl cellulose (2,3-O-CMC), prepared via 6-O-(4-monomethoxy)triphenylmethyl cellulose, was carried out in detail by means of enzymatic and chemical methods. The 2,3-O-CMCs had degrees of substitution (DS) in the range of 0.5–1.2 showing a narrow molar mass distribution as revealed by SEC. As a result of an endoglucanase treatment, an intensive depolymerization of the samples occurred which was more pronounced for 2,3-O-CMC with comparatively low DS. All degraded samples could be separated into 18 fractions by preparative SEC and the proportion of each individual repeat unit was analysed by anion exchange chromatography (AEC) following complete hydrolytic chain degradation. The results indicated a homogeneous distribution of the functional groups within the polymer chain. Moreover, it became obvious that a preferred carboxymethylation of O-2 compared with O-3 occurred and that a preferred functionalization of already carboxymethylated units occurred as the reaction progressed. AEC with pulsed amperometric detection, which was used to separate and analyse the differently functionalized repeating units as well as glucose, had to be calibrated. Therefore, a method to determine the response factors of the individual carboxymethylated glucose units was developed using ¹³C NMR spectroscopic measurements (inverse gated decoupling) of depolymerised 2,3-O-CMC.