A Simple and Rapid High Performance Liquid Chromatographic Method with Fluorescence Detection for the Estimation of Amikacin in Plasma ‐ Application to Preclinical Pharmacokinetics

A simple and sensitive reversed‐phase liquid chromatographic method has been developed for the determination of amikacin by derivatization. The method is based on the pre‐column derivatization of amikacin with 9‐fluorenylmethyl chloroformate (FMOC‐Cl). Isepamicin was used as the internal standard. The derivatization reaction proceeds in aqueous solution at room temperature with a borate buffer of pH 7.3. The formation of the corresponding derivative of amikacin is instantaneous and it is stable for more than 48 h. Detection was performed by fluorescence. Several factors influencing the derivatization reaction yields were studied and optimized. The system offered the following analytical parameters: limit of detection (LOD) of 90 ng mL^?1 (3σ), linear correlation coefficient of 0.9998 and linear range response from 0.45 to 21.60 μg‐mL^?1. The precision of the method was < 6%. As a preliminary application, the method has been successfully applied to the amikacin determination in parenteral pharmaceutical formulations.     

Determination of octylphenol and nonylphenol in aqueous sample using simultaneous derivatization and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A simple and fast sample preparation method for the determination of nonylphenol (NP) and octylphenol (OP) in aqueous samples by simultaneous derivatization and dispersive liquid–liquid microextraction (DLLME) was investigated using gas chromatography–mass spectrometry (GC/MS). In this method, a combined dispersant/derivatization catalyst (methanol/pyridine mixture) was firstly added to an aqueous sample, following which a derivatization reagent/extraction solvent (methyl chloroformate/chloroform) was rapidly injected to combine in situ derivatization and extraction in a single step. After centrifuging, the sedimented phase containing the analytes was injected into the GC port by autosampler for analysis. Several parameters, such as extraction solvent, dispersant solvent, amount of derivatization reagent, derivatization and extraction time, pH, and ionic strength were optimized to obtain higher sensitivity for the detection of NP and OP. Under the optimized conditions, good linearity was observed in the range of 0.1–1000 μg L⁻¹ and 0.01–100 μg L⁻¹ with the limits of detection (LOD) of 0.03 μg L⁻¹ and 0.002 μg L⁻¹ for NP and OP, respectively. Water samples collected from the Pearl River were analyzed with the proposed method, the concentrations of NP and OP were found to be 2.40 ± 0.16 μg L⁻¹ and 0.037 ± 0.001 μg L⁻¹, respectively. The relative recoveries of the water samples spiked with different concentrations of NP and OP were in the range of 88.3–106.7%. Compared with SPME and SPE, the proposed method can be successfully applied to the rapid and convenient determination of NP and OP in aqueous samples.     

Experimental and theoretical study of the electronic structure of methyl chloroformate and methyl cyanoformate

The HeI photoelectron spectra of methyl chloroformate (CH₃OC(O)Cl) and methyl cyanoformate (CH₃OC(O)CN) in the gas phase have been obtained for the first time. A complete theoretical study involving the calculation of the ionization energies using outer valence Green’s functional (OVGF) was performed, based on the calculated and previously reported energetically favorable cis-conformer (the carbonyl group eclipses the methyl group). Calculations of cationic-radical forms were carried out in order to interpret the main characters of the first six highest occupied molecular orbitals (HOMOs). The first vertical ionization potentials are 11.36 eV for CH₃OC(O)Cl and 11.65 eV for CH₃OC(O)CN, each attributed to {19a′(n_O(CO), n_Cl)}⁻¹ and {18a′(n_O(CO))}⁻¹, respectively.     

Liquid–liquid phase behaviour,liquid–liquid density,and interfacial tension of multicomponent systems at 298 K

Experimental liquid–liquid phase diagrams are presented for the multicomponent systems isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol (2-methyl-1-propanol) and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol, at 298.15 K. The density and interfacial tension of conjugate phases of concentration located in the isothermal binodal have been determined at 298.15 K for the partially miscible systems: isooctane–benzene–methanol, isooctane–benzene–(80 mass% methanol + 20 mass% water), isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol, and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol. The experimental tie-line data define the binodal or coexistence curve of the two studied multicomponent systems and depending on the initial isobutyl alcohol concentration the liquid–liquid phase diagram is either of type II, with low alcohol concentration, or type I, with high concentration of alcohol, which is a clear indication that the solubility of the partially miscible systems is greatly enhanced via the co-solvency phenomenon. It is observed that both the density of each conjugate phase and the interfacial tension of each tie-line are valuable indicators of the degree of solubility of the multicomponent systems. Furthermore the experimental tie-lines data were correlated with the NRTL and UNIQUAC solution models with satisfactory quantitative results.     

Determination of amines using 2-(11H-benzo[a]carbazol-11-yl) ethyl chloroformate (BCEC-Cl) as labeling reagent by HPLC with fluorescence detection and identification with APCI/MS

A pre-column derivatization method for the sensitive determination of amines using a labeling reagent 2-(11H-benzo[a]-carbazol-11-yl) ethyl chloroformate (BCEC-Cl) followed by high-performance liquid chromatography with fluorescence detection has been developed. Identification of derivatives was carried out by LC/APCI/MS in positive-ion mode. The chromophore of 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC-Cl) reagent was replaced by 2-(11H-benzo[a]-carbazol-11-yl) ethyl functional group, which resulted in a sensitive fluorescence derivatizing reagent BCEC-Cl. BCEC-Cl could easily and quickly label amines. Derivatives were stable enough to be efficiently analyzed by HPLC and showed an intense protonated molecular ion corresponding m/z [M + H]⁺ under APCI/MS in positive-ion mode. The collision-induced dissociation of the protonated molecular ion formed characteristic fragment ions at m/z 261.8 and m/z 243.8 corresponding to the cleavages of CH₂O-CO and CH₂-OCO bonds. Studies on derivatization demonstrated excellent derivative yields over the pH 9.0-10.0. Maximal yields close to 100% were observed with three- to four-fold molar reagent excess. In addition, the detection responses for BCEC-derivatives were compared to those obtained using 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC-Cl) and 9-fluorenyl methylchloroformate (FMOC-Cl) as labeling reagents. The ratios I_BCEC/I_BCEOC = 1.94-2.17 and I_BCEC/I_FMOC = 1.04-2.19 for fluorescent (FL) responses (here, I was relative fluorescence intensity). Separation of the derivatized amines had been optimized on reversed-phase Eclipse XDB-C₈ column. Detection limits calculated from 0.50 pmol injection, at a signal-to-noise ratio of 3, were 1.77-14.4 fmol. The relative standard deviations for within-day determination (n = 11) were 1.84-2.89% for the tested amines. The mean intra- and inter-assay precision for all amines levels were <3.64% and 2.52%, respectively. The mean recoveries ranged from 96.6% to 107.1% with their standard deviations in the range of 0.8-2.7. Excellent linear responses were observed with coefficients of >0.9996.     

A New Initiator Cholesteryl Chloroformate for Cupper-Based Atom Transfer Radical Polymerization of Methyl Methacrylate

The polymerization of metyl methacrylate (MMA) was studied in detail by use of CuCI/L as a catalyst and cholesteryl chloroformate (CC) as an initiator. It was found that the atom transfer radical polymerization of MMA could proceed when L equals to a multidentate aliphatic amine ligand, N,N,N‘,N“,N“-penta(methyl acrylate)diethylenetriamine (MA5-DETA), and no polymerization was occurred while L=2,2‘-bipyridine and 1,10phenanthroline. The linear proportionality of the molecular weights to the conversions and straight lines observed in ln[M]0/[M] versus time plots indicated that the present polymerization system had the typical controlled polymerization characteristics.     

钒取代三元钼杂多化合物对异丁酸氧化脱氢的催化作用

研究了钒取代钼杂多化合物对异丁酸氧化脱氢生成甲基丙烯酸的催化行为。用ＩＲ、ＤＴＡ方法研究了钒对催化剂稳定性、酸性的影响。ＥＳＲ和循环伏安法研究结果表明，钒不仅改变了催化剂的物化性质，而且参与了反应，成为新的催化活性中心。     

以固体光气为原料合成氯代甲酸(2-乙基)己酯

氯代甲酸(2-乙基)己酯是一种化工中间体,主要用来制备过氧化二碳酸二(2-乙基)己酯(简称EHP),EHP是一种高活性聚合引发剂。由固体光气和2-乙基己醇为原料合成氯代甲酸(2-乙基)己酯的研究未见报道。本文以固体光气和2-乙基己醇为原料合成了氯代甲酸(2-乙基)己酯,研究了反应物加入顺序、反应时间、反应温度、催化剂种类及用量对氯代甲酸(2-乙基)己酯收率和纯度的影响,得到了优化的合成工艺,对产物结构进行了分析,进一步用其合成了常用的高活性聚合引发剂过氧化二碳酸二(2-乙基)己酯(EHP)。     

氯甲酸2-(9-咔唑)乙基酯柱前衍生化HPLC法用于环境水中脂肪胺测定

利用一种新型的衍生化试剂氯甲酸2-(9-咔唑)乙基酯柱前衍生10种脂肪胺,建立了脂肪胺类化合物的梯度洗脱高效液相色谱分离分析方法,在紫外254nm条件下检测,线性检测范围为50-500μmol／L,检出(S／N=3)为9．5—25μmol／L;对海水及河水中脂肪胺的试验结果表明,建立的方法快速、灵敏度高,可以满足环境检测等方面的需要。     

LC Determination of Amino Acids in Rat Plasma with Fluorescence Detection: Application to Exercise Physiology

An LC method for the determination of 20 amino acids (AAs), using 1,2-Benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC) as fluorescent labeling reagent, has been validated and applied for the analysis of AAs in rat plasma at three different states concerning exercise physiology. Identification of AA derivatives was carried out by LC-MS with electrospray ion (ESI), and the MS-MS cleavage mode of the representative tyrosine (Tyr) derivative was analyzed. Gradient elution on a Hypersil BDS C₁₈ column gave good separation of the derivatives. Excellent linear responses were observed and good compositional data could be obtained from as little as 50–200 μL of plasma samples. The contents of 20 AAs in rat plasma of three groups (24 rats, group A: quiet state, group B: at exercising exhaust, group C: 12 h after exercising exhaust) exhibited evident difference corresponding to the physiological states. Facile BCEOC derivatization coupled with LC-FLD-ESI-MS analysis allowed the development of a highly sensitive method for the quantitative analysis of trace level of AAs from plasma or other biochemical samples.