Predicting the performance of molecularly imprinted polymers: Selective extraction of caffeine by molecularly imprinted solid phase extraction

A rational design approach was taken to the planning and synthesis of a molecularly imprinted polymer capable of extracting caffeine (the template molecule) from a standard solution of caffeine and further from a food sample containing caffeine. Data from NMR titration experiments in conjunction with a molecular modelling approach was used in predicting the relative ratios of template to functional monomer and furthermore determined both the choice of solvent (porogen) and the amount used for the study. In addition the molecular modelling program yielded information regarding the thermodynamic stability of the pre-polymerisation complex. Post-polymerisation analysis of the polymer itself by analysis of the pore size distribution by BET yielded significant information regarding the nature of the size and distribution of the pores within the polymer matrix. Here is proposed a stepwise procedure for the development and testing of a molecularly imprinted polymer using a well-studied compound—caffeine as a model system. It is shown that both the physical characteristics of a molecularly imprinted polymer (MIP) and the analysis of the pre-polymerisation complex can yield vital information, which can predict how well a given MIP will perform.     

Comparison of Different Sorbents for Solid-Phase Extraction of Phenoxyalkanoic Acid Herbicides

An HPLC procedure for determination of phenoxyalkanoic acid herbicides in water samples is proposed. The analytical column Phenomenex C18(2) Luna 5 µm and UV detection at 225 nm were applied. Baseline resolution was achieved in isocratic mode with a mobile phase consisting of acetonitrile/acetic acid (40/60, v/v), adjusted to pH 2.5. SPE sorbents – C₁₈ BondElut, phenyl-silica, LiChrolut SAX and polymeric sorbents – were compared for isolation and preconcentration of 6 phenoxyalkanoic acid herbicides. Higher (above 95%) and more reproducible recoveries were obtained with polymeric and phenyl-silica sorbents using pure methanol for elution. The method was tested for river water samples with the limit of detection in the range of 2–3 µg L⁻¹ (for 50 mL sample) and a reproducibility of 5% RSD.     

Development and validation of a capillary electrophoresis method for the determination of phenothiazines in human urine in the low nanogram per milliliter concentration range using field-amplified sample injection

A capillary zone electrophoresis (CZE) method with ultraviolet-visible detection has been established and validated for the determination of five phenothiazines: thiazinamium methylsulfate, promazine hydrochloride, chlorpromazine hydrochloride, thioridazine hydrochloride, and promethazine hydrochloride in human urine. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 150 mM tris(hydroxymethyl)aminomethane and 25% acetonitrile at pH 8.2, with temperature and voltage of 25 degrees C and 20 kV, respectively. Naphazoline hydrochloride was used as an internal standard. Field-amplified sample injection (FASI) has been applied to improve the sensitivity of the detection. Considering the influence of parameters affecting the on-line preconcentration (nature of preinjection plug, sample solvent composition, injection times, and injection voltage) and due to the significant interactions among them, in this paper we propose for the first time the application of a multivariate approach to carry out the study. The optimized conditions were as follows: preinjection plug of water for 7 s at 50 mbar, electrokinetic injection for 40 s at 6.2 kV, and 32 microm of H3PO4 in the sample solvent. Also, a solid-phase extraction (SPE) procedure is developed to obtain low detection limits and an adequate selectivity for urine samples. The combination of SPE and FASI-CZE-UV allows adequate linearities and recoveries, low detection limits (from 2 to 5 ng/mL), and satisfactory precisions (3.0-7.2% for an intermediate RSD %).     

Simple route to secondary amides of phosphorylacetic acids and their use for extraction and sorption of actinides from nitric acid solutions

An efficient method for the synthesis of secondary alkylamides of phosphorylacetic acids (APA) was proposed. The method involves amidation of ethyl phosphorylacetates with primary aliphatic amines. The scope of reaction was determined. Reactions with ethylenediamine and 1,4-diaminobutane yield the corresponding bisamides; in the case of 1,3-diaminopropane, N-(3-aminopropyl)diphenylphosphorylacetamide or N,N-propylenebis(diphenylphosphorylacetamide) was obtained, depending on the reaction conditions. The extraction of americium(III) complexes and the sorption of uranium(VI) by sorbents with physically sorbed APA from nitric acid solutions were studied. There is no correlation between the partition coefficient of americium(III) and the structure of APA; in the sorption of uranium(VI), the degree of extraction depends on the complexone structure.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2394–2402, November, 2004.     

Development of an analytical procedure for determination of selected estrogens and progestagens in water samples

An analytical procedure has been developed for determination of eight selected natural and synthetic hormonal steroids in surface water and in effluent samples. Several methodological points have been investigated and are discussed; they include the choice of the solid-phase extraction sorbent, the influence of flow rate on recovery, the breakthrough volume for a given sorbent (Env+ and Oasis HLB), sample clean up, and sample storage. As regards the latter point, it was found that when no preservative was added to effluent from a sewage-treatment plant, severe loss of steroids occurred—85% of progesterone and about 30% of both estrone and estradiol were found to be degraded in 24 h. The procedure developed was applied to samples from the Seine river estuary. Sex steroids were not detected in surface water; estrone was the most commonly detected steroid in sewage-treatment plant effluent, with levels ranging from 1.8 to 8.3 ng L^–1. Synthetic estrogens (ethynylestradiol and mestranol) and progestagens (levonorgestrel and norethindrone) were never detected, whatever the sampling season. Overall, for 162 out of 168 measurements levels were below the detection limits of the developed procedure.     

阴阳离子型表面活性剂双水相萃取色氨酸衍生物和牛血清白蛋白

溴化十二烷基三乙胺（Ｃ１２ＮＥ）和十二烷基硫酸钠（ＳＤＳ）在一定条件下混合可以形成具有清晰界面的两个水相，称为阴阳离子型表面活性剂双水相。作者研究了利用该双水相萃取３种色氨酸衍生物和牛血清白蛋白的可能性．文中采用工作曲线校正扣除表面活性剂背景的影响，萃取结果准确可信。     

On line trace enrichment for isolation of vitamin B2 in food samples

Summary Vitamin B₂ was enriched by liquid-solid extraction from large volumes of aqueous samples on a short precolumn. The enriched compounds were transferred onto an analytical reversed-phase column and separated by ion-pair chromatography. The equipment used provides the possibility of automation for routine analysis.Dedicated to Professor J. F. K. Huber on the occasion of the 60th birthday.     

Simple and versatile operational fractionation of Fe and Zn in dietary products by solid phase extraction on ion exchange resins

A simple and versatile protocol, based on use of solid phase extraction on strong ion exchangers and off-line detection by flame atomic absorption spectrometry, was devised to fractionate iron and zinc in common dietary food and beverages products, i.e., bee honeys, fruit juices and tea infusions. In the procedure proposed, cation exchanger Dowex 50Wx4 and anion exchanger Dowex 1x4 were used separately for distinguishing broadly meant the cationic metal fraction and the fraction of stable anionic metal complexes, respectively, after retention of metal species and their exhaustive elution by means of a 4.0 mol l⁻¹ HCl solution. The third fraction, referred to the residual metal species, was retrieved by difference between total soluble metal contents and sum of metal quantities in separated cationic and anionic fractions. The fractionation pattern observed for both metals was described and discussed.     

超临界流体萃取-胶束电动毛细管色谱法分离测定大黄中蒽醌类组分的含量

采用ＳＴＥ－ＭＥＣＣ法分离测定大黄中的芦荟大黄素，大黄素和大黄酸。萃取条件为压 力４１．４ＭＰａ，温度５０℃，改性剂量０．４ｍＬ。被测组分在１０ｍｉｎ得到全部分离。本法准确、简 便、快速、结果令人满意。     

Determination of Low Contents of Fenpiverine Bromide by Extraction Spectrophotometry

An ion-pair extraction spectrophotometry method was developed for the determination of fenpiverine bromide in tablets. To determine this substance it was necessary to find experimental conditions that would allow eliminating the influence of other components of the tablets. Attention was paid to the fact that a suitable pH of water phase was necessary to achieve high selectivity.Received December 11, 2002; accepted April 24, 2003 Published online July 28, 2003