Head-column field-amplified sample stacking in presence of siphoning. Application to capillary electrophoresis-electrospray ionization mass spectrometry of opioids in urine

Capillary electrophoresis (CE) with head-column field-amplified sample stacking (FASS) in presence of a water plug inserted at the capillary tip is a robust approach providing a more than 1000-fold sensitivity enhancement when applied to low-conductivity samples that are analyzed in an integrated instrument. Employing modular systems comprising a small hydrodynamic buffer flow (siphoning) towards the capillary end and featuring UV absorption or electrospray ionization mass spectrometric (MS) detection, insertion of a water plug is demonstrated to deteriorate the performance of head-column FASS or making it unfunctional. Electroinjection in the absence of the water plug can be employed instead and is shown to provide a ng/ml sensitivity when applied to low conductivity samples. With some suction of sample into the capillary during electroinjection, contamination of the sample vial with buffer is thereby largely avoided. Electroinjection applied to the CE-ion trap MS-MS and MS-MS-MS analysis of twofold diluted urines, urinary solid-phase extracts and urinary liquid-liquid extracts is shown to provide much improved sensitivity compared to hydrodynamic injection of these samples. With electroinjection from diluted urine and urinary solid-phase extracts, the presence of free opioids and their glucuronic acid conjugates can be unambiguously confirmed in urines that were collected after single-dose administration of small amounts of opioids (tested with about 7 mg codeine and 25 mg dihydrocodeine, respectively). Thus, CE-multiple MS with direct electroinjection of opioids from untreated urines could prove to become a rapid and simple approach for unambiguous urinary testing of drug abuse. Procedures leading to the reduction of siphoning in modular CE setups are briefly discussed as well.     

Sterically demanding diporphyrin ligands and rhodium(II) porphyrin bimetalloradical complexes

A series of sterically demanding diporphyrins H2(por)-X-(por)H2 ligands that contain spacers (X) with different degrees of flexibility were synthesized from the trimesitylporphyrin derivatives 5-(4-hydroxyphenyl)-10,15,20-trimesitylporphyrin (TMP-OH)H2 (1a) and 5-(2,6-dimethyl-4-hydroxyphenyl)-10,15,20-trimesityl-porphyrin, (DMTMP-OH)H2 (1b). The monomeric porphyrins 1a,b, which have steric demands similar to that of tetramesitylporphyrin, (TMP)H2, and carry a hydroxyl functional group at the para position of one of the mesophenyl substituents, were constructed from reaction of pyrrole with two aromatic aldehydes by a mixed aldehyde condensation approach. The diporphyrins with alkyl diether tethers were obtained stepwise from reactions of the hydroxy functionalized porphyrins 1a,b with dibromides Br(CH2)nBr. The diporphyrin which contains a more rigid m-xylylene spacer, was made directly from reaction of 1b with alpha,alpha'-dibromo-m-xylene. Rhodium was inserted into the porphyrins using Rh2(CO)2Cl2 and converted to dimethyl complexes Me-Rh(Por)-X-(Por)Rh-Me. The dirhodium(II) derivatives .Rh(por)-X-(por)Rh.) were generated by photolysis of the dimethyl complexes and observed to occur as stable bimetalloradicals because the ligand steric demands prohibit Rh(II)-Rh(II) bonding. EPR spectra of the dirhodium(II) derivatives, triphenyl phospine adducts, and dioxygen complexes are reported. The kinetic advantage of bimetalloradical complexes for substrate reactions that have two metal-centered radicals in the transition state is demonstrated by reactions of dihydrogen with dirhodium(II) bimetalloradical complexes.     

Growth transition and morphology change in polypropylene

The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 C and interpreted as a Regime III Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II Regime I transition is also theoretically predicted at 155 C, i. e. at a temperature outside the investigated temperature range. The Regime III Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae atT _c < 138 C (Regime III) and preferentially radiating lamellae atT _c > 138 C (Regime II). It is suggested that such a morphological change could be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites.     

A spin-dependent unitary group approach to many-electron systems

In this article we derive a segment-level formula for the matrix elements of the U(2n) generators in a basis symmetry adapted to the subgroup U(n) × U(2) (i.e., spin-orbit basis), for the representations appropriate to many-electron systems. This enables the direct evaluation of the matrix elements of spin-dependent Hamiltonians.     

Wave mechanics - the first fifty years : edited by W.C. Price,S.S. Chissick and T. Ravensdale,Butterworths, London, 1973, pp. 435, price £12.00

The free NH₃ molecule and the [Zn(NH₃)₄]²⁺ ion were studied by the kinematic coupling approach. The pure effects of this coupling were found to be small, and some modifications had to be introduced in order to get a reasonable force field. The force constants deduced for the skeletal vibrations are comparable with those of a quasi-exact force field. Calculated frequencies for [⁶⁸Zn(NH₃)₄]²⁺ and [⁶⁴Zn(ND₃)₄]²⁺ are reported in addition to those of [⁶⁴Zn(NH₃)₄]²⁺. Mean amplitudes of vibration for [⁶⁴Zn(NH₃)₄]²⁺ are given.     

Reactions of methylniobium(V) and methyltantalum(V) chlorides with carbodiimides

The chlorides Me_xMCl_5-x, M = Nb, Ta, x = 1, 2, 3 react with carbodiimides RNCNR (R = isopropyl, cyclohexyl, p-tolyl) to give products of the types MCl₄[NR-C(Me)=NR], MeMCl₃[NR-C(Me)=NR], MCl₃[NR-C(Me)=NR]₂, Me₂MCl₂[NR-C(Me)=NR], MeMCl₂[NR-C(Me)=NR]₂, which cóntain bidentate acetamidine groups arising from insertion of the carbodiimide into the metal-carbon bond. The products have been characterised by elemental analysis IR and proton NMR spectra.     

Microwave spectra of transient species — cyclopentadienone

The microwave spectrum of the main isotopic species of cyclopentadienone has been measured and assigned. The rotational constants imply an essentially planar geometry and that the ring is rather “fatter” than the analogous ring in fulvene.The dipole moment, derived from Stark-effect measurements, is 10.4 × 10^?30 C m (3.13 D). A vibrational satel- lite spectrum, which, from its inertial defect, corresponds to an out-of-plane vibration has also been assigned.The life time of cyclopentadienone under our spectroscopic conditions is approximately 15 sec.     

Untersuchung der Wechselwirkung von Eiweißen mit Polysacchariden im Wassermedium

Zusammenfassung Die komplexe Koazervation im SystemG-A-H₂O kann als zweistufiger Prozeß aufgefaßt werden. Das erste Stadium ist die Bildung des elektrisch neutralen Komplexes zwischen G und A unter Einfluß der elektrostatischen Anziehungskräfte. Die Stöchiometrie der gewonnenen Verbindung wird durch die Äquivalenz der Makroionen bestimmt.Nur elektrisch neutrale Komplexe können die neue Phase, d. h. das komplexe Koazervat bilden. Deshalb muß die Zusammensetzung der koazervaten Phase von p_H abhängen und bei Veränderung des Verhältnisses der Polymere im Gemisch unveränderlich bleiben.Bei einem Verhältnis der Polymere, kleiner als das stöchiometrische, ist die Bildung geladener Komplexe möglich.Den Prozeß der komplexen Koazervation kann man mittels der Methode der Trübungsmessung bei C_s<6·10^{–3 g}/100 g untersuchen. Hierbei ist die optische Dichte proportional der Menge des komplexen Koazervats oder des elektrisch neutralen Komplexes im System.     

Pyrimidines

The condensation of -substituted acetophenones with benzylidenebisurea in an acid medium has given 5-R-2-oxo-4,6-diphenyl-1,2,3,4-tetrahydropyrimidones. The analogous condensation of propiophenone forms 5-methyl-2-hydroxy-4,6-diphenylpyrimidine. The tetrahydro derivatives obtained are readily dehydrogenated to 5-R-2-hydroxy-4,6-diphenylpyrimidines.For part XX, see [1].