Approximation of Parametric Derivatives by the Empirical Interpolation Method

We introduce a general a priori convergence result for the approximation of parametric derivatives of parametrized functions. We consider the best approximations to parametric derivatives in a sequence of approximation spaces generated by a general approximation scheme, and we show that these approximations are convergent provided that the best approximation to the function itself is convergent. We also provide estimates for the convergence rates. We present numerical results with spaces generated by a particular approximation scheme—the Empirical Interpolation Method—to confirm the validity of the general theory.     

Immobilized 2-(4-hydrazinocarbonylphenyl)-4,5-diphenylimidazole as solid phase luminophore in peroxyoxalate chemiluminescence

A new luminophore for application in peroxyoxalate chemiluminescence is presented. An analogue of the well-known chemiluminescence compound lophine, i.e. 2-(4-hydrazinocarbonylphenyl)-4,5-diphenylimidazole (HCPI), has been covalently immobilized to controlled pore glass and a porous methacrylate resin. By using this reagent in a solid phase detection reactor, sensitive determinations of hydrogen peroxide have been demonstrated. In homogeneous solution HCPI emits poorly as a result of 1,1-oxalyldiimidazole excitation, but when immobilized its efficiency is almost comparable to highly efficient luminophores such as 3-aminofluoranthene. Linearity extends in the single stream flow system over several orders of magnitude with both materials. The limit of detection was 1 nmol/l (10 fmole injected), when using the porous methacrylate support.     

Potentiometric micro-titration of potassium

Summary The potentiometric micro titration of potassium tetraphenylborate in acetone/water mixtures using a silver nitrate solution gives a sharper end-point than with indicators. The silver nitrate titer obtained against K(Ph)₄B in acetone/water mixtures varies with the acetone concentration. This applies particularly for solutions which contain less than ca. 40 Vol.% acetone.

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Zusammenfassung Die potentiometrische Mikrotitration von Kaliumtetraphenylborat in Aceton-Wasser-Gemischen mit Silbernitrat gibt einen schärferen Endpunkt als bei Verwendung eines Indikators. Der Silbernitrattiter gegen K(Ph)₄B in Aceton-Wasser-Gemischen variiert mit der Acetonkonzentration, besonders wenn der Acetongehalt der Lösungen geringer ist als 40 Vol.-%.

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Résumé Le microtitrage potentiométrique du tétraphénylborate de potassium dans des mélanges d'eau et d'acétone à l'aide d'une solution titrante de nitrate d'argent donne un point final de titrage plus net que les indicateurs. Le titre du nitrate d'argent déterminé à l'aide de K(Ph)₄B dans des mélanges acétone-eau varie avec la concentration en acétone. Cette observation s'applique particulièrement aux solutions qui contiennent moins de 40% environ en volume d'acétone.

     

Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: gas phase reactions between ammonia and R1R2COCH3+ oxonium ions

The reactivity of carbonyl substituted methyl oxonium ions (R1R2COCH3+) towards ammonia has been investigated using an FT-ICR mass spectrometer and ab initio calculations. The monosubstituted ions (R1 = H; R2 = H, CH3, C2H5 and i-C3H7) show different reaction patterns with variable degree of: (1) nucleophilic substitution, (2) addition-elimination and (3) proton transfer, when reacted with ammonia. In all cases addition-elimination dominates over nucleophilic substitution, and the observed reactions are slow. The trends in reactivity are consistent with the alkyl group's electronic properties, as expressed by a single parameter linear or slightly non-linear model.     

Structures and thermochemistry of ions formed by methane chemical ionization of Fe(CO)5. Site of protonation and determination of Fe?H and Fe?CO bond dissociation energies of HFe(CO)n+ ions

High-energy collisional activation mass spectrometry of HFe(CO)₅⁺ ions shows that Fe(CO)₅ is protonated on the iron atom rather than on one of the ligands. This finding is supported by ab initio quantum chemical calculations. The value of the proton affinity of Fe(CO)₅ was measured by high-pressure mass spectrometry to be 857 kJ mol^?1. The Fe? CO bond dissociation energies for HFe(CO)_n⁺ (n = 1–5) were measured by energy-variable low-energy collisional activation mass spectrometry. The Fe? H bond dissociation energies in HFe(CO)_n⁺ ions were also determined. A synergistic effect on the strengths of the Fe? H and Fe? CO bonds in HFe(CO)⁺ is noticed. It is demonstrated that the electronically unsaturated species HFe(CO)_n⁺ (n = 3, 4) formed in exothermic proton-transfer reactions with Fe(CO)₅ form adducts with CH₄. Adducts between C₂H₅⁺ or C₃H₅⁺ and Fe(CO)_n are observed. These adducts are probably formed in direct reactions between the respective carbocations and Fe(CO)₅.     

Low-voltage electromembrane extraction of basic drugs from biological samples

The present work has for the first time demonstrated electromembrane extraction (EME) at voltages obtainable by common batteries. Five basic drugs were extracted from acidified aqueous sample solutions, across a supported liquid membrane (SLM) consisting of 1-isopropyl-4-nitrobenzene impregnated in the walls of a hollow fiber, and into an acidified aqueous acceptor solution present inside the lumen of the hollow fiber with potential differences of 1-10 V applied over the SLM. Extractions from 1 ml standard solutions prepared in 10mM HCl for 5 min and with a potential of 10 V demonstrated analyte recoveries of 50-93% in 25 microl of 10mM HCl as acceptor solution. This corresponds to enrichment factors of 20-37. Similar results were obtained with a common 9 V battery as power supply. Recoveries from low-voltage EME on human plasma, urine, and breast milk diluted with acetate buffer (pH 4) demonstrated recoveries in the range of 37-55% after 5 min of extraction. Excellent selectivity was demonstrated as no interfering peaks were detected. Standard curves in the range of 0.0625-0.62 5 microg/ml demonstrated correlation coefficients of 0.994-0.999. Extraction recoveries from human plasma, urine or breast milk were not found to be sensitive towards individual variations. The results show that low-voltage EME has a future potential as a simple, selective, and time-efficient sample preparation technique of biological fluids.     

Structures,fragmentation, and protonation of trideoxynucleotide CCC mono- and dianions

Both quantum chemical calculations and ESI mass spectrometry are used here to explore the gas-phase structures, energies, and stabilities against collision-induced dissociation of a relatively small model DNA molecule--a trideoxynucleotide with the sequence CCC, in its singly and doubly deprotonated forms, (CCC-H)(-) and (CCC-2H)(2-), respectively. Also, the gas-phase reactivity of these two anions was measured with HBr, a potential proton donor, using an ESI/SIFT/QqQ instrument. The computational results provide insight into the gas-phase structures of the electrosprayed (CCC-2H)(2-) and (CCC-H)(-) anions and the neutral CCC, as well as the proton affinities of the di- and monoanions. The dianion (CCC-2H)(2-) was found to dissociate upon CID by charge separation via two competing channels: separation into deprotonated cytosine (C-H)(-) and (CCC-(C-H)-2H)(-), and by w(1)(-)/a(2)(-) cleavage of the backbone. The monoanion (CCC-H)(-) loses a neutral cytosine upon CID, and an H/D-exchangeable proton, presumably residing on one of the phosphate groups, is transferred to the partially liberated (C-H)(-) before dissociation. This was confirmed by MS/MS experiments with the deuterated analog. The reaction of (CCC-2H)(2-) with HBr was observed to be rapid, k=(1.4+/-0.4) x 10(-9) cm(3) molecule(-1) s(-1), and to proceed both by addition (78%) and by proton transfer (22%) while (CCC-H)(-) reacts only by HBr addition, k=(7.1+/-2.1) x 10(-10) cm(3) molecule(-1) s(-1). This is in accord with the computed proton affinities of (CCC-2H)(2-) and (CCC-H)(-) anions that bracket the known proton affinity of Br(-).