Retention Time of Unretained Compound Calculation and Determination of Retention Indices of Some Monosubstituted Benzenes Using a Multiparametric Method in Binary, Ternary and Quaternary Solvent RP-LC Systems

In reversed phase liquid chromatography (RP-LC), the validity of a multiparametric (MP) non-linear least-squares regression iterative method has been evaluated for 14 different aqueous mobile phases modified with one, two or three organic solvents [acetonitrile (ACN), methanol (MeOH), or tetrahydrofuran (THF)] for calculating the retention time of unretained compound t _M and the regression parameter (slope b), based on the use of alkan-2-ones and alkyl aryl ketones homologous series. The determination of t _M and b has been studied for eight binary (ACN?CH₂O or MeOH?CH₂O), 3 ternary (ACN?CMeOH?CH₂O) and 3 quaternary (ACN?CMeOH?CTHF?CH₂O) mobile phase systems on an Omnispher C₁₈ column. The multiparametric calculated t _M and b values were compared with those obtained by Guardino??s, and Grobler??s methods. The MP retention indices (RI) of ten monosubstituted benzenes with different functionality (hydroxyl, carbonyl, nitro, etc.) based on the alkan-2-ones retention index standards have been determined and compared for the different mobile phase compositions studied. The influence of organic modifier type, the nature of mobile phase system and water content on the variation of retention parameter studied in this work were discussed.     

Separation mechanism of chiral compounds in chiral stationary phase liquid chromatography

In this paper, the concept of reversed- or normal-phase chiral stationary phase liquid chromatography has been put forward according to the polar strength of mobile and stationary phases. The statistical model developed in HPLC has been used to investigate the separation mechanism of D- and L-enantiomer in chiral stationary phase liquid chromatography. It has been observed that the variation of capacity factor of enantiomers with mobile phase composition in both reversed-phase and normal-phase chiral stationary phase liquid chromatography can be described by the fundamental elution equation lnk' = a + blnC_b + _cC_b. The effect of mobile phase composition on the selectivity of enantiomers D and L in normal-phase chiral stationary phase liquid chromatography can be described by the equation lnα = Δa + ΔblnC_b, but in reversed-phase chiral stationary phase liquid chromatography the selectivity is almost independant of the mobile phase composition.     

Well‐defined amphiphilic polymethylene‐b‐poly(acrylic acid) diblock copolymers: New synthetic strategy and their self‐assembly

Well‐defined amphiphilic polymethylene‐b‐poly (acrylicacid) diblock copolymers have been synthesized via a new strategy combining polyhomologation and atom transfer radical polymerization (ATRP). Hydroxyl‐terminated polymethylenes (PM‐OH) with different molecular weights and narrow molecular weight distribution are obtained through the polyhomologation of dimethylsulfoxonium methylides following quantitative oxidation via trimethylamine‐N‐oxide dihydrate. Subsequently, polymethylene‐based macroinitiators (PM‐MIs M_n = 1,300 g mol^?1 [M_w/M_n = 1.11] and M_n = 3,300 g mol^?1 [M_w/M_n = 1.04]) are synthesized by transformation of terminal hydroxyl group of PM‐OH to α‐haloester in ～100% conversion. ATRPs of tert‐butyl acrylate (t‐BuA) are then carried out using PM‐MIs as initiator to construct PM‐b‐P(t‐BuA) diblock copolymers with controllable molecular weight (M_n = 8,800–15,800 g mol^?1 M_w/M_n = 1.04–1.09) and different weight ratio of PM/P(t‐BuA) segment (1:1.7–1:11.2). The amphiphilic PM‐b‐PAA diblock copolymers are finally prepared by hydrolysis of PM‐b‐P(t‐BuA) copolymers and their self‐assembly behavior in water is preliminarily investigated via the determination of critical micelle concentrations, dynamic light scattering, and transmission electron microscope (TEM). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Three‐arm star block copolymers of ε‐caprolactone and acrylic acid: Synthesis and micellization behavior

A series of well‐defined three‐arm star poly(ε‐caprolactone)‐b‐poly(acrylic acid) copolymers having different block lengths were synthesized via the combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, three‐arm star poly(ε‐caprolactone) (PCL) (M_n = 2490–7830 g mol^?1; M_w/M_n = 1.19–1.24) were synthesized via ROP of ε‐caprolactone (ε‐CL) using tris(2‐hydroxyethyl)cynuric acid as three‐arm initiator and stannous octoate (Sn(Oct)₂) as a catalyst. Subsequently, the three‐arm macroinitiator transformed from such PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBuA) to construct three‐arm star PCL‐b‐P^tBuA copolymers (M_n = 10,900–19,570 g mol^?1; M_w/M_n = 1.14–1.23). Finally, the three‐arm star PCL‐b‐PAA copolymer was obtained via the hydrolysis of the PtBuA segment in three‐arm star PCL‐b‐P^tBuA copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared spectroscopy. The aggregates of three‐arm star PCL‐b‐PAA copolymer were studied by the determination of critical micelles concentration and transmission electron microscope. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) triblock copolymer via a combination of polyhomologation,ring‐opening polymerization,and atom transfer radical polymerization

Well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) (PM‐b‐PCL‐b‐PAA) triblock copolymers were synthesized via a combination of polyhomologation, ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). First, hydroxyl‐terminated polymethylenes (PM‐OH; M_n = 1100 g mol^?1; M_w/M_n = 1.09) were produced by polyhomologation followed by oxidation. Then, the PM‐b‐PCL (M_n = 10,000 g mol^?1; M_w/M_n = 1.27) diblock copolymers were synthesized via ROP of ε‐caprolactone using PM‐OH as macroinitiator and stannous octanoate (Sn(Oct)₂) as a catalyst. Subsequently, the macroinitiator transformed from PM‐b‐PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBA) to construct PM‐b‐PCL‐b‐P^tBA triblock copolymers (M_n = 11,000–14,000 g mol^?1; M_w/M_n = 1.24–1.26). Finally, the PM‐b‐PCL‐b‐PAA triblock copolymers were obtained via the hydrolysis of the P^tBA segment in PM‐b‐PCL‐b‐P^tBA triblock copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Porous films of such triblock copolymers were fabricated by static breath‐figure method and observed by scanning electron microscope. The aggregates of PM‐b‐PCL‐b‐PAA triblock copolymer were studied by transmission electron microscope. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of Temperature on the Variation of Retention Time of Unretained Compound and Retention Indices of Some Explosives and Related Compounds Calculated Using a Multiparametric Method in RP-LC

In reversed phase liquid chromatography (RP-LC), a multiparametric non-linear least-squares regression iterative method has been evaluated at different column temperatures (ranging from 30 to 60 °C in 5 °C steps) for calculating the retention time of the unretained compound t _M and the regression parameter (slope b), based on the use of alkan-2-ones, alkyl aryl ketones and 1-nitroalkanes homologous series on two different columns: Spherisorb-ODS2 C₁₈ and Nucleosil C₈. The calculated parameters t _M and b by the multiparametric method (MP) were compared with those obtained by using the iterative method of Guardino’s. The influence of the number of subsets of homologues used for the calculation of t _M and b values was investigated. The retention indices (RI) of some neutral and acidic explosives and related compounds (nitramines, nitroaromatics, aminonitroaromatics and nitrophenols) based on the alkan-2-ones retention index standards have been determined and compared at various temperatures by the MP method. Good agreement was observed between retention data calculated by the MP and GU methods.     

Comparison of Retention Indices of Some Explosives and Related Compounds Calculated by Different Mathematical Methods in Reversed-Phase Liquid Chromatography

In reversed phase liquid chromatography, the retention indices of some neutral and acidic explosives and related compounds (nitramines, nitroaromatics, aminoaromatics, and nitrophenols) based on the alkan-2-one, alkyl aryl ketone, and 1-nitroalkane retention index standards have been determined by the application of a new mathematical adaptation method, viz. a multiparametric least-squares regression iterative method. This method was applied to two types of columns. The first group includes six octadecyl-C₁₈ columns with different packing materials and obtained from different manufacturers, while the second group comprises one octyl-C₈ column. The retention indices have been extensively studied using either methanol-water or methanol-phosphate buffer mobile phase systems. The calculated multiparametric retention indices values were compared with those obtained by Guardino's, Grobler's, and Kovàts' methods. The influences of the concentration of the organic modifier in the mobile phase, aqueous mobile phase pH, and the column packing material on the retention indices of the explosives were also investigated. Good agreement was observed between the retention indices calculated by the use of the four mathematical methods for both neutral and acidic explosives.     

Phase behavior of pseudo-IPN's of polycarbonate-urethane and polystyrene

The pseudo-IPN's of PCU/PS with different M_n and narrow MWD of the linear PS have been synthesized and characterized. The effect of M_n and composition on the phase morphology of the pseudo-IPN's of PCU/PS has been studied by DSC and SEM. The pseudo-IPN's with ultra-high M_n of the linear PS appeared to possess a single T_g and no SEM-resolvable domains at 35 wt % PS and below. This metastable state may reflect the result of a high extent of entanglement of the linear PS chains with the PCU network and the limited molecular mobility of the linear PS chains with high M_n. © 1993 John Wiley & Sons, Inc.     

Lipophilicity of Some Preservatives Estimated by RP-TLC Using Stationary Phases with Different Polarity

Lipophilcity of some preservatives was determined by reversed phase high performance thin layer chromatography (RP-HPTLC) using methanol–water mixtures in different volume proportions as mobile phase on three stationary phases of different polarity: RP-18F_254s, RP-18WF_254s and CNF_254s plates. The R _M values decreased linearly with increasing methanol concentration in the mobile phase in all cases. The regression determination coefficients obtained for all stationary phases were excellent (higher than 0.98 in most cases). The chromatographic behavior of the preservatives on the RP-HPTLC plates used in this study is similar and in a very good agreement with their polarity. Good chromatographic regularities found for retention factors and by applying principal component analysis for all three types of stationary phases indicate that the same lipophilic interactions are dominants in all cases. The relationships between different RP-HPTLC retention parameters (R _M0 , b, scores of R _F -PC1/R _F and scores of R _M -PC1/R _M ) and various calculated log P values of the same preservatives show highly significant correlations for all types of stationary phases.     

Bioluminescent Analysis. The Action of Toxicants: Physical-Chemical Regularities of the Toxicants Effects

Abstract

The physical-chemical regularities of aromatic compounds' effects in luciferase toxicity biotesting have been studied. The structures and physical-chemical characteristics of the toxicants and of the bioluminescent emitter were taken into account. The inhibition constants of bioluminescence intensiy (I) were calculated and interpreted from the viewpoint of the energy (electron) transfer processes. The induction period (P) and the increase of the time of the maximum light intensity (t_M) which take place in the quinones' presence, have been shown to deal with hydrogen transfer processes. The values of I, P and t_M have been shown to be connected with a size of the quinones' aromatic and aliphatic parts. P- and t_M-dependencies on quinone's redox potential have been demonstrated.     

Synthesis and pH-sensitive micellization of doubly hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) triblock copolymer in aqueous solutions

A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M _w/M _n = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and zeta potential. The pK _a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed owing to the ionization of the PAA blocks.     

Synthesis and characterization of two novel star blocks: tCum[poly(isobutylene‐b‐norbornadiene)]3 and tCum[poly(norbornadiene‐b‐isobutylene)]3

Two structurally closely related three‐arm star blocks were synthesized and characterized: tCum(PIB‐b‐PNBD)₃ and tCum(PNBD‐b‐PIB)₃ [where tCum (tricumyl) stands for the phenyl‐1,3,5‐tris(‐2‐propyl) fragment and PIB and PNBD are polyisobutylene and polynorbornadiene, respectively]. The syntheses were accomplished in two stages: (1) the preparation of the first (or inner) block fitted with appropriate chlorine termini capable of initiating the polymerization of the second (or outer) block with TiCl₄ and (2) the mediation of the polymerization of the second block. Therefore, the synthesis of tCum(PIB‐b‐PNBD)₃ was effected with tCum(PIB‐Cl^t)₃ [where Cl^t is tert‐chlorine and number‐average molecular weight (M_n) = 102,000 g/mol] by the use of TiCl₄ and 30/70 CH₃Cl/CHCl₃ solvent mixtures at ?35 °C. PNBD homopolymer contamination formed by chain transfer was removed by selective precipitation. According to gel permeation chromatography, the M_n's of the star blocks were 107,300–109,200 g/mol. NMR spectroscopy (750 MHz) was used to determine structures and molecular weights. Differential scanning calorimetry (DSC) indicated two glass‐transition temperatures (T_g's), one each for the PIB (?65 °C) and PNBD (232 °C) phases. Thermogravimetric analysis thermograms showed 5% weight losses at 293 °C in air and at 352 °C in N₂. The synthesis of tCum(PNBD‐b‐PIB)₃ was achieved by the initiation of isobutylene polymerization with tCum(PNBD‐Cl^sec)₃ (where Cl^sec is sec‐chlorine and M_n = 2900 g/mol) by the use of TiCl₄ in CH₃Cl at ?60 °C. DSC for this star block (M_n = 14,200 g/mol) also showed two T_g's, that is, at ?67 and 228 °C for the PIB and PNBD segments, respectively. It is of interest that the Cl^sec terminus of PNBD, , readily initiated isobutylene polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 740–751, 2003     

Well‐defined polyoxazoline‐based alkoxyamines as efficient macroinitiators in nitroxide‐mediated radical polymerization of styrene

The synthesis of two well‐defined 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide‐terminated poly(2‐methyl‐2‐oxazoline) with narrow dispersity (M_w/M_n = 1.1) has been achieved for the first time. The insertion of the alkoxyamine end groups at one or both ends of poly(2‐methyl‐2‐oxazoline) (PMEOX) chains has been successfully done using a method based on “terminating reagent method.” These macroinitiators have molecular weights ranging from 6.3 × 10³ to 9.4 × 10³ g mol^?1. In contrast, attempt to introduce the alkoxyamine group at one end of PMEOX chain through the “initiator method” has furnished a mixture of alkoxyamine‐graft polyoxazolines because of rearrangement of alkoxyamine occurring during the synthesis of PMEOX. The macroinitiators obtained by terminating reagent method have been used successfully for polymerization of styrene by nitroxide‐mediated radical polymerization (NMP), which exhibited all the expected features of a controlled system. The control of NMP has been proved by a good agreement between theoretical and experimental molecular weights and by narrow dispersity (M_w/M_n < 1.2). Different types of well‐defined multiblock copolymers have been prepared: diblock copolymers poly[(2‐methyl‐2‐oxazoline)‐b‐(styrene)] (PMEOX‐b‐PS) and, for the first time, triblock copolymers poly[(styrene)‐b‐(2‐methyl‐2‐oxazoline)‐b‐(styrene)] (PS‐b‐PMEOX‐b‐PS). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Determination of Iodide and Thiocyanate in Seawater by Liquid Chromatography with Poly(ethylene glycol) Stationary Phase

Novel, simple, rapid, highly sensitive, and direct determination of iodide and thiocyanate ions in seawater has been performed by liquid chromatography (LC) with UV detection at 220 nm. The separation was achieved on a C₃₀ column of conventional size (150 mm × 4.6 mm i.d.) modified with poly(ethylene glycol); an aqueous solution of 300 mM sodium sulfate and 50 mM sodium chloride was used as mobile phase. Detection limits (S/N=3) obtained by injecting a 20-L sample were 0.5 and 6 ng mL^–1 for iodide and thiocyanate, respectively. The method was successfully used for rapid and direct determination of iodide and thiocyanate in seawater samples, collected from the coasts of Japan, without any extra pretreatment.Dedicated to Professor K. Jinno on the occasion of his 60^th birthday     

A sensitive UPLC–MS/MS method for simultaneous determination of polyphenols and theaflavins in rat plasma: Application to a pharmacokinetic study of Da Hong Pao tea

A method based on ultra‐performance liquid chromatography–tandem mass spectrometry has been developed for the rapid and simultaneous determination of five catechins and four theaflavins in rat plasma using ethyl gallate as internal standard. The pharmacokinetic profiles of these compounds were compared after oral administration of five kinds of Da Hong Pao tea to rats. Biosamples processed with a mixture of β‐glucuronidase and sulfatase were extracted with ethyl acetate–isopropanol. Chromatographic separation was achieved by gradient elution using 10 mm HCOONH₄ solution and methanol as the mobile phase. Analytes were detected using negative ion electrospray ionization in multiple reaction monitoring mode. The lower limits of quantification were 1.0, 0.74 and 0.5 ng/mL for theaflavins, two catechins and three catechins, respectively. The validation parameters were well within acceptable limits. The average half‐lives (t_1/2) in blood of the reference solution group was much shorter than those of tea samples. The values of AUC_0–t and C_max of the polyphenols and theaflavins exhibited linear pharmacokinetic characteristics which were related to the dose concentration.     

Gravimetric determination of the diffusion characteristics of polymers using small specimens

An investigation has been undertaken of the factors controlling the rate of ingress of water into relatively small epoxy specimens. The application of a three-dimensional diffusion model, fully acknowledging that the specimen geometry controls the rate of ingress, has successfully resolved the problems of determining the diffusion characteristics—the diffusion coefficient D and the uptake M_∞ corresponding to saturation—and making theoretical predictions of the uptake M_t by small specimens. On the theoretical front, simulations have been carried out to demonstrate that (1) theoretical predictions require two equations to be used to obtain correct relative uptake M_t/M_∞ values for short and long exposure times; (2) a cube of the side h is saturated faster than an infinite slab of the thickness h, and (3) determination of the D value by applying the model derived for an infinite slab to specimens of finite dimensions results in an apparent value that may grossly exceed the true diffusion coefficient. On the experimental front, suggestions are made regarding (4) elimination of a systematic error that might be introduced by single weighing of a specimen prior exposure, (5) determination of the product M_∞ D^1/2 from the gravimetry data for short exposure times, and (6) splitting this product into absolute values D and M_∞ by means of a minimization procedure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42:2122–2128, 2004     

Copolymerization of styrene and methyl methacrylate. Reactivity ratios from conversion–composition data

A method for the determination of reactivity ratios from conversion–composition data has been outlined. The conversion–composition changes during the copolymerization of styrene (M₁) and methyl methacrylate (M₂) have been studied at 60°C. By a method of graphical intersection, the integrated form of Skeist's equation has been used to determine the reactivity ratios (r₁ = 0.54 ± 0.02 and r₂ = 0.50 ± 0.06) in reasonably good agreement with values reported in the literature. The area of intersection was used as a measure of the precision of the data.     

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.     

Novel star‐block polymers: Three polyisobutylene‐b‐poly(methyl methacrylate) arms radiating from an aromatic core

A series of novel three‐arm star blocks consisting of three polyisobutylene‐b‐poly(methyl methacrylate) (PIB‐b‐PMMA) diblocks radiating from a tricumyl core were synthesized, characterized, and tested. The synthetic strategy involved three steps: the synthesis of Cl^t ‐tritelechelic PIB by living cationic isobutylene (IB) polymerization, the conversion of the Cl^t termini to isobutyryl bromide groups, and the initiation of living radical methyl methacrylate (MMA) polymerization by the latter groups. The PIB and PMMA segment lengths (M_n 's) could be controlled by controlling the conditions of the living cationic and radical polymerizations of IB and MMA, respectively. Core destruction analysis directly proved the postulated three‐arm microarchitecture. The structures of the products were analyzed by ¹H NMR and Fourier transform infrared spectroscopies, and their thermal properties were analyzed by differential scanning calorimetry and thermogravimetric analysis. The presence of a low‐ and a high‐temperature glass transition (T_g,PIB ∼ −63°C, T_g,PMMA ∼ 120°C) indicated a phase‐separated micromorphology. Stress/strain analysis showed a tensile strength of up to ∼ 22.9 MPa and an elongation of ∼ 200%. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 706–714, 2000     

Stability-Indicating Chromatographic Methods for Simultaneous Determination of Mosapride and Pantoprazole in Pharmaceutical Dosage Form and Plasma Samples

Simple, sensitive, selective, precise, and stability-indicating thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) methods for the determination of mosapride and pantoprazole in pharmaceutical tablets were developed and validated as per the International Conference on Harmonization guidelines. The TLC method employs aluminum TLC plates precoated with silica gel 60F₂₅₄ as the stationary phase and ethyl acetate/methanol/toluene (4:1:2, v/v/v) as the mobile phase to give compact spots for mosapride (R _f 0.73) and pantoprazole (R _f 0.45) separated from their degradation products; the chromatogram was scanned at 276 nm. The HPLC method utilizes a C18 column and a mobile phase consisting of acetonitrile/methanol/20 mM ammonium acetate (4:2:4, v/v/v) at a flow rate of 1.0 mL min⁻¹ for the separation of mosapride (t _R 11.4) and pantoprazole (t _R 4.4) from their degradation products. Quantitation was achieved with UV detection at 280 nm. The same HPLC method was successfully used in performing calibrations in lower concentration ranges for both drugs in human plasma using ezetimibe as internal standard. The methods were validated in terms of accuracy, precision, linearity, limits of detection, and limits of quantification. Mosapride and pantoprazole were exposed to acid hydrolysis and then analyzed by the proposed methods. As the methods could effectively separate the drugs from their degradation products, these techniques can be employed as stability-indicating methods that have been successively applied to pharmaceutical formulations without interference from the excipients. Moreover the HPLC method was successfully used in the determination of both drugs in spiked human plasma.