Evaluation of dead time calculation in liquid chromatography using a linearization procedure for homologous series

A mathematical method for the calculation of the dead time (t_m) in HPLC was evaluated using a computer simulation approach, in which artificial perturbations were introduced to Simulated homolog retention times. The calculation was based on a modified and extended Grobler and Bálisz (GB) method. Investigated wav how the precision of the calculated t_M is affected by: statistical fluctuations in retention times and which, and how many homolog retention times are used. Based on these simulations a two-step procedure for the t_M calculation is proposed: In the first step the linearity of log t_{R, n} vs carbon number n is checked using as many homolog retention times as possible. The slope value b^o of the first linear regression in the GB method is used for the selection of homolog retention times in the final t_M calculation. In the second step the optimal selection of homologs is made and the final t_M calculation is carried out. Guidelines for homolog selection are given.     

Ionic Association and Mobility IV. Ionophores in Dimethylsulfoxide at 25°C

The results of conductance measurements on pyridinium picrate, tetraphenylo-sonium picrate, potassium picrate, tetraphenylantimony picrate, tetrapropylam-monium, tetrafluoroborate, tetramethylammonium hexafluorophosphate ion association noncoulombic interaction in dimethyl sulfoxide (DMSO) at 25°C in the concentration range 1–15×10^–4 M are reported. The data were analyzed by the Justice modification of the Fuoss–Hsia equation. Except for pyridinium picrate all salts studied were found to be associated.Application of the Justice Barthel–Bjerrum model of ion association permitted calculation of the noncoulombic portion of the potential of mean force, W _±. Ionic limiting conductances were calculated for six ions using known values of previously determined transport numbers. A table of most current limiting ionic conductances for a variety of ions in DMSO at 25°C has been established.     

Preparation of a sulfonated fused-silica capillary and its application in capillary electrophoresis and electrochromatography

In the present paper, two new methods, sol-gel and chemical bonding methods, were proposed for preparation of sulfonated fused-silica capillaries. In the sol-gel method, a fused-silica capillary was coated with the sol solution obtained by hydrolysis of 3-mercaptopropyltrimethoxysilane (MPTS) and tetramethoxysilane, and followed by age; while in the chemical bonding method, a capillary was chemically bonded directly with MPTS. Then, both the resulting capillaries were oxidized with an aqueous solution of hydrogen peroxide solution (H2O2) (30%, m/m) to obtain the sulfonated capillaries. The electroosmotic flow (EOF) for the sulfonated capillaries was found to remain almost constant within the studied pH range, and greater than that of the uncoated capillary. However, the coating efficiency of the capillary prepared by chemical bonding method was higher than that by sol-gel method, by comparing their magnitude of the EOF, the degree of disguise of the silanol and reproducibility of preparation procedure. The effects of the electrolyte's concentration and the content of methanol (MeOH) on the EOF were also studied. Especially, the study of the apparent pH (pH*) on the EOF in a water-MeOH system was reported. Finally, capillary electrophoretic separation of seven organic acids was achieved within 6.5 min under optimal condition using the chemically bonded sulfonated capillary. Moreover, separation of four alkaloids on the sulfonated capillary was compared with that on uncoated capillary in different conditions. Ion-exchange mechanism was found to play a key role for separation of these four basic analytes on the sulfonated capillary.     

火焰原子吸收光谱法测定奶类食品中铜锌铁锰

对火焰原子吸收光谱法(FAAS)测定乳品中铜、锌、铁、锰的条件进行了试验和优化。对方法的干扰因素,准确度和精密度也作了试验。乳品试样用HNO3-HClO4混合酸消化处理。所得溶液蒸发至近干,用稀硝酸(1 99)溶解盐类,溶液经定容后供作FAAS测定。对4元素的测定时,吸光度与浓度之间呈良好线性关系,所求得的线性回归方程及其相关系数可作佐证。应用所提出的方法测定了3种不同的乳制品中的铜、锌、铁及锰,测定值的RSD值均小于3.5%,回收率在93.0%~103.0%之间。     

Cycloarsanes (AsCF3)n (n = 4, 5) – Precursors for the Highly Reactive Diarsene F3CAs=AsCF3

Tetrakis(trifluoromethyl) cyclotetraarsane (F₃CAs)₄ ( 2 ) was used to repeat the UV initiated [4+2]‐cycloaddition reaction of the diarsene F₃CAs=AsCF₃ ( 1 ) with cyclohexa‐1,3‐diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X‐ray diffraction analysis. 4 crystallizes in the space group and contains the diarsene group in its E‐configuration. 2 was also applied for [2+2]‐cycloaddition reactions of 1 with tBuC≡P and MeC≡CNⁱPr₂, but in contrast to positive results with (F₃CP)₄ the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π‐donor ligand to the Pd(PPh₃)₂ complex fragment yielding η²‐bis(trifluoromethyl)diarsene‐bis(triphenylphosphane)‐palladium(0) 5 , which was characterized by X‐ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1 , generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]‐cycloadduct with 1‐di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3‐dimethyl‐1,3‐butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F₃CP=PCF₃.     

Matrix effects and selectivity issues in LC-MS-MS

Summary Chlorobenzenes, triazine and phenylurea herbicides were separated by normal micellar electrokinetic chromatography (MEKC) and by micellar electrokinetic chromatography with reversed flow (RF-MEKC) in running buffers containing organic solvents. The relationship between the two techniques is similar to that between reversed-phase and normal-phase HPLC. Using RF-MEKC, the separation of lipophilic compounds is often improved compared to normal MEKC. The migration in MEKC and in RF-MEKC was characterised by lipophilic and polar indices. The experimental values of the lipophilic indices of the compounds tested in the two techniques were close to the indices in reversed-phase HPLC (RP-HPLC). This enables the use of the indices determined in RP-HPLC for predicting the effects of changing composition of the running buffers on migration times in MEKC and in RF-MEKC. Presented at Balaton Symposium '01 on High-Performance Separation Methods, siófok, Hungary, September 2–4, 2001     

Electronic structure of axially ligated rhodium carboxylates: π back-bonding revisited

Fenske-Hall molecular orbital calculations have been applied to a new, structurally isolable analog of the intermediate involved in catalytic rhodium carboxylate carbenoid transformations. Results from the structural characterization of axially ligated rhodium acetate phenylisonitrile complexes have been utilized in approximate molecular orbital calculations. The results from the calculations suggest that a significant degree of π back-bonding exists between the metal and isonitrile fragments which, by analogy, implies that π back-bonding should also exist in the rhodium carbenoid intermediate. Sensitivity of the Fenske-Hall method to the magnitude of π back-donation in these complexes was gauged through calculations involving different phenylisonitrile groups in which the π back-bonding ability was modulated through derivativization. The reliability of the Fenske-Hall method was evaluated through a comparison to a high-level calculation. Received: 13 December 1996 / Accepted: 18 March 1997     

Reaction of hexafluoropropylene and its oligomers with acetone oxime

Reactions of perfluoropropylene and its oligomers with acetone oxime in the presence of a base afford perfluoroalkyl and/or perfluoroalkenyl ethers of acetone oxime. When heated to 100 °C, the 3-perfluoro-2-methyl-2-pentenyl ether of acetone oxime (3) is quantitatively converted to 4-hydroxy-3-methyl-5,5-bistrifluoromethyl-4-pentafluoroethyl-1-pyrroline (4), the structure of which was established by X-ray diffraction analysis. A convenient one-stage synthesis of perfluoro-3-isopropyl-4-methyl-3-penten-2-one (7) was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1068–1072, June, 1994.     

Reaction ofo-aminobenzohydroxamic acid with aldehydes

The reaction of o-aminobenzohydroxamic acid with aliphatic, aromatic, or heterocyclic aldehydes leads to the formation of derivatives of 3-hydroxy-1,2-dihydroquinazolin-4-one. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 115–117, January, 1997.     

Further studies on dppm-stabilized mixed-metal clusters: X-ray structure of PdPtCoCl(CO)3(μ-dppm)2 1

The metalloligated mixed-metal cluster [PdPtCo₂(CO)₇(-dppm)₂] (2) (dppm = -Ph₂PCH₂PPh₂) possesses numerous potential reaction centers (e.g., metal(s), metal-metal bonds, CO, and dppm ligands) and this has previously led to an investigation of the site selectivity of reactions with nucleophiles. The exocyclic CO(CO)₄ fragment was substituted with a chloride ligand and the resulting chiral, triangular cluster PdPtCoCl(CO)₃(-dppm)₂ (4) has been structurally characterized. The Pd-Co and Pt-Co edges of this almost equilateral triangle are bridged by a dppm ligand, and two of the three carbonyls borne by the Co atom are semi-triply bridging above and below the plane of the metals. The Co(CO)₃P fragment behaves as an anionic 4-electron donor organometallic bridging group toward thed ⁹-d ⁹ Pd(I)-Pt(I) unit. Crystal data for4, monoclinic space groupP2₁/n with Z=4 in a unit cell of dimensionsa=12.291(3),b=19.321(4),c=23.680(5) Å,=100.05(2)°. The structure has been solved from diffractometer data by Patterson, Fourier methods and refined by full-matrix least squares on the basis of 3512 observed reflections (l>3) toR(F) andR _w(F) values of 0.059 and 0.061.Dedicated to Professor L. F. Dahl on the occasion of his 65th birthday, with our sincere congratulations and best wishes.