Retention behaviour of 1,n-halo(alkylthio)alkanes in HPLC

The RPLC retention of 1,n-halo(alkylthio)alkanes on an ODS phase with methanol/water (95%/5%) has been investigated. Replacement of a methyl group in a dialkyl sulphide R-S-R by a halogen atom X, to yield the title compounds X-(CH₂)_n-S-R, generally results in a retention decrease. This retention loss results either from the halogen atom proper, or from its immediate vicinity, or from a reduced retention contribution of the alkyl units. The methylene groups (n) between halogen and sulphur produce somewhat greater retention than the methylene groups in the alkyl groups R.     

Formation of cyclic ions in the electron impact induced fragmentation of 1,n-bis-(alkylthio) alkanes

Fragmentation of molecular ions of 1,n-bis(alkylthio)alkanes (R¹-S-(CH₂)_n-S-R²) occurs mainly by α- or β-cleavage to a sulphur atom. The ratio of fragments derived by α- or β-cleavage depends on the number of methylene groups (n) between the two sulphur atoms and on the alkyl groups R¹ and R². Generally β-cleavage induced fragmentation dominates for 1,2-bis(alkylthio)ethanes (n=2) leading to formation of thiiranium ions. Fragmentations derived by α-cleavage are predominant for all compounds with n=3; base peaks corresponding to [M-(R)]⁺ or [M-(2R)+(H)]⁺ are found which gives evidence for formation of five membered cyclic ions. Such fragmenss are less intense in compounds with n=4 whereas m all other compounds β-cleavage predominates if R = methyl, ethyl, n-propyl.     

Gaseous cation chemistry and chain-length effects in electron ionization and collision-induced dissociation mass spectra of symmetric 1,n-bis(9-anthracenyl)alkanes

The behavior of the gaseous cations resulting from EI (30 and 70 eV) of the bichromophoric title compounds 1–5 (for n = 1–5, respectively) is examined by ion‐trap mass spectrometry, including collision‐induced dissociation (CID) with variation in collision energy. These results are compared with those from anthracene and 9‐methylanthracene and with previously reported mass spectrometric results for 3 and dicarbazolylalkanes. Rather than using the kinetic method to obtain ion energetics where the fragmentation mechanism is clear, as commonly done, the method is used here with relative complementary‐ion abundances from CID to test the proposed fragmentation mechanisms using B3LYP calculations of relative ionization energies and optimized geometries of ionic and neutral fragments. Hydrogen migrations are common, and skeletal rearrangements including formation of expanded, fused and spiro rings are proposed in several cases. Of the chain cleavages, α‐homolysis giving C₁₅H₁₁⁺, likely as dibenzotropylium, is most important for each of 1–5 except 3, where β‐cleavage to C₁₆H₁₃⁺ dominates with a proposed methyldibenzotropylium structure. α‐Cleavage was important also in the dicarbazolylalkanes. A previous inference of a McLafferty rearrangement to explain C₁₅H₁₂^+? from 3 is not supported by the present results. The fragmentation behavior of 1–5 depends strongly on n and implies significant interchromophoric interaction between anthracenyl groups. Copyright © 2011 John Wiley & Sons, Ltd.     

气相色谱法测定除草剂吡嘧黄隆

A gas chromatography method for the quantitative analysis of pyrazosulfuron is described. Analytical conditions were as follows:column:OV-225 (5% )on Chromosorb W AW DMCS(60-80 mesh),2m column with 3mm i.d.at 172℃;FID at 260℃;N2 as carrier gas with flow rate of 30mL/min.     

Diffusion coefficients of bolaform alkane-1,n-bis(trimethylammonium bromide) surfactants

Mutual diffusion coefficients of alkane-1,n-bis(trimethylammonium bromide), C_nMe₆Br₂ (n = 8, 10, 12), surfactants have been measured using the Taylor dispersion technique, at T = 298.15 K, at concentrations from (0.000 to 0.0380) mol · dm⁻³. The dependence of mutual diffusion coefficients on the concentration has been discussed in the framework of Onsager–Fuoss and Pikal models. On the basis of this discussion, it is suggested that these surfactants behave as associated electrolytes. From limiting mutual diffusion coefficient values, extrapolated from experimental values for c → 0, limiting ionic conductance, tracer diffusion coefficients, and hydration radii of alkane-1,n-bistrymethyl ammonium ions have been estimated. For the case of dodecane-1,12-bis(trimethylammonium bromide), no aggregation has been noticed up to 0.04 mol · dm⁻³.     

Chromatographic separation of benzo(a)pyrene isomers on nematic liquid crystal GC and polymeric reversed-phase HPLC phases

Summary The use of two nematic liquid crystals (BABT and BPhBT) as GC stationary phases for the separation of monohydroxybenzo(a)pyrenes. as their TMS ethers, and monomethylbenzo(a)pyrenes was developed and compared with the separation of these isomers by HPLC using a polymeric ODS reversed-phase column. It was found that while HPLC and GC gave comparable separation of the hydroxy isomers, 10 out of 12 separated, better separation of the methyl isomers was obtained using HPLC. A simultaneous use of both HPLC and GC would resolve the twelve hydroxy isomers in about 70min. The results indicated that HPLC, using polymeric reversed-phase columns, is as powerful a tool as GC using nematic liquid crystal phases, for the separation of benzo(a)pyrene isomers. A discussion of the effect of solute length-to-breadth ratio on elution order is presented.Presented in part at the 1981 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Atlantic City, NJ; paper No. 51.     

气相气谱测定土壤中的糖

气相气谱测定土壤中的糖王彦中,穆惠玲,仇津苹（南开大学中心实验室天津３０００７１）１前言糖是土壤有机质的重要组成,它的测定对认识土壤质量无疑是重要的。以往大多仅测定土壤有机质总量,而单独测定其中糖含量的报道甚少￣［１～３］,在国内尚未见到。近年来气相...     

Chromatographic behaviour of flavonoid compounds in reversed-phase HPLC systems

Summary Reversed-phase HPLC retention behaviour of different flavonoid compounds in different columns and with a range of methanol-buffer eluents was examined. Repeatibility and reproducibility of logk′ and Δlogk′ values were analyzed. Sharp group contributions, expressed as Δlogk′, were observed. These did not depend significantly on acid modifier type, column packing characteristics (C8 and C18) and dimensions (5,7 and 10μm) or the percentage of methanol in the mobile phase. A list of twelve group contributions is presented which is in agreement with literature data.     

Chromatographic characteristics of poly(1-vinylimidazole)-grafted silica in normal-phase HPLC

A stationary phase based on poly(1-vinylimidazole)-grafted silica has been prepared by the surface radical chain-transfer reaction. The stationary phase was characterized by infrared spectra, X-ray photoelectron spectroscopy and elemental analysis. Chromatographic characteristics of the stationary phase were investigated in normal-phase HPLC. The results showed that both weak polar compounds (polycyclic aromatic hydrocarbons, dialkyl phthalates) and polar compounds (anilines, phenols) could be successfully separated on this stationary phase, implying better separation performance than blank silica and conventional aminopropyl-bonded silica under the same conditions. The excellent performance can be attributed to multiple interactions between surface modifier and the analytes that might include dipole, hydrogen bonding, H-π, electrostatic and inductive interactions.     

Trennqualität in der Chromatographie (GC,HPLC, HPDC)

Zusammenfassung Es werden die Grundlagen eines offensichtlich allgemeingültigen Bewertungsverfahrens in der Gas- und Flüssig-Chromatographie (GC, HPLC, DC, HPDC) vorgestellt und die Schlußfolgerungen für die Praxis diskutiert. Das Bewertungsverfahren ist einfach, es zeigt aber den ganz außerordentlich wichtigen Einfluß instrumenteller und methodischer Feinheiten (unterschiedliche Optimierung, schärfste Startkonzentration vor Trennbeginn der zu trennenden Stoffe) auf, welche Voraussetzung sind für hohe Trennleistungen und ein hohes Trennvermögen in allen chromatographischen Techniken. Das Bewertungsverfahren erlaubt einen ehrlichen praxisgerechten Methodenvergleich und dient damit der Optimierung experimenteller Arbeit.

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True quality of separation in chromatography (GC, HPLC, HPTLC)

Summary The basis of a procedure to measure, calculate and discuss true separation-quality indices is given and discussed. The procedure is simple and shows the most important role of components of the instrument and the technique used—optimization for different conditions, highest injection concentration per inlet volume prior to start of a separation—which are responsible for high separating efficiency and high separating power in all chromatographic techniques. The procedure allows a true comparison of separation methods and helps in the optimization of experimental work. This paper is a supplment to the green pages in Chromatographia9, 335 (1976) (German version) which will appear in English in a forthcoming issue.

     

硒半胱氨酸和硒胱氨酸的间接气相色谱测定──溴化氰－气相色谱法

将硒半胱氨酸（ＳｅＣｙｓＨ）甲基化，对硒胱氨酸（ＳｅＣｙｓ）需还原后再甲基化。它们生成的甲基硒半胱氨酸（ＣＨ＿３ＳｅＣｙｓＨ）能与溴化氰（ＣＮＢｒ）发生专一性反应，定量生成的硒氰酸甲酯（ＣＨ＿３ＳｅＮ）可用气相色谱法（ＧＣ）测定。此法简称ＣＮＢｒ－ＧＣ法，检测限４×１０￣（－８）克ＳｅＣｙｓ，准确度８９．５％，相对标准差１２．１％，非含硒氨基酸不干扰。此法适于样品中微量硒氨基酸（硒蛋氨酸ＳｅＭｅｔ，ＳｅＣｙｓＨ和Ｓｅｃｙｓ）的测定。     

气相色谱法测定油脂中棕榈酸单甘油酯与油酸单甘油酯含量

建立了一种利用气相色谱法测定油脂中棕榈酸单甘油酯与油酸单甘油酯含量的方法。样品中加入六甲基二硅氨烷,于９５℃水浴中完成硅烷化反应。样品的平均加标回收率分别为９６．３０％与９７．８２％,ＲＳＤ分别为１．８％与２．１％。最低检出限分别为０．０１μｇ／ｇ与０．１μｇ／ｇ。     

Intramolecular excimer of DI(1-pyrenylmethyleneoxycarbonyl) alkanes

Intramolecular excimer emission of a series of di(1-pyrenylmethyleneoxycarbonyl)alkanes (n = 0–22) has been studied under photostationary conditions. The intramolecular excimer formation rate constant decreases monotonously with increasing number of methylene units of the chains in the low temperature region. The temperature dependence of the rate constant for each sample was studied to give an apparent activation energy of ca. 5 kcal/mol.     

Improved High-Performance Liquid Chromatographic (HPLC) Assay Method for Ceftizoxime

Abstract

We improved a high-performance liquid chromatographic method for the quantitative determination of ceftizoxime in human serum and urine using cefotaxime as internal standard. It employs a μ Bondapak Alkyl Phenyl column, elution with acetonitrile-phosphate buffer and measurement of UV absorption at 254 nm. Results obtained using the HPLC assay were compared to those obtained using a microbiological assay. The correlation coefficient was 0.987 (n:25). The method is rapid, accurate and reproducible with a sensitivity of 2.5 μg/ml of ceftizoxime. Cefotaxime and its major metabolite, the desacetylcefotaxime, can also be quantitated by this procedure.     

毛细管气相色谱法测定油田水中短链有机酸

The evaporation of water phase has been used to remove a vast amount of inorganic salts and interferingorganic components. The distillate concentrated by rotary evaporator was directly analyzed by means of wide-bore capillary GC column, The coefficients of variation for C_2～C_5 organic acids were 1.9～6.4%. The recov-eries of the acids in the oilfield water were 81.0～106%.     

Characterization of a Road Asphalt by Chromatographic Techniques (GPC and HPLC)

Abstract

There has long been a need to fractionate asphalt into as well-defined entities as possible. It is known that asphalt consists of a mixture of a very great number of components, too numerous and complex to isolate in the chemically pure state, in appreciable quantities. Consequently, attention has begun to turn towards fractionation of this binder into generic groups, the recombination of which, in varying proportions, should permit experimental evaluation of the influence of a particular fraction on one or another technological property (susceptibility, hardness, etc.) (1). It is also understood that the chemical structures of these generic groups, and their relative proportions, have a fundamental effect on the colloidal structure of asphalt (2, 3), a colloidal structure responsible for rheological behavior (4, 5). Molecular weight distribution has been shown to be a parameter of prime importance (6).

It is, therefore, of interest to compare two modern fractionatoin techniques – gel permeation chromatography (GPC), and high performance liquid chromatography (HPLC) – and to characterize, by means of the latter, the fractions of bitumen isolated by the former. Only the key experimental results are given in this paper. Their interpretation, aimed at a deeper knowledge of the physico-chemical structure of asphalts in connection with their colloidal structure and their rheological behaviour, will no doubt require further long experiments with other samples of different origin.     

1-(alkylthio)-polyfluoroalkynes. Reactions with mercaptans and thermal transformations

1-(Alkylthio)difluoropropynes regioselectively add dialkylamines and mercaptans with formation of 1-(alkylthio)-2-dialkylamino(alkylthio)ethenes, which exist only in the form of one (presumably the trans isomer) geometrical isomer. Thermal transformation of 1-(alkylthio)difluoropropynes occurs at a temperature of under 100°C and leads to the formation of 2,4-bis(polyfluoroalkyl)-3-(alkylthio)thiophenes. © 1998 John Wiley & Sons, Inc.Heteroatom Chem 9:151–154, 1998