Behaviour of nucleotides and oligonucleotides in potentiometric HPLC detection

Potentiometric HPLC detection was studied of mononucleotides (UMP, AMP, UDP, ADP, CTP, UTP, GTP, ATP) and oligonucleotides (a synthetic mixture d(T)_12–18 5′OH, a mixed 21-mer, 33-mer, and 60-mer). Coated-wire electrodes were used. The coatings were of the liquid membrane type containing PVC, DOS and synthetic macrocyclic amine- and podand ureum receptors. Electrodes based on these receptors gave very sensitive responses to triphosphate nucleotides and to oligonucleotides. The molar response of the oligonucleotides was related to their molar mass. The HPLC system consisted of a reversed phase column eluted with a phosphate buffer, triethylammoniumacetate (TEAA), and an acetonitrile gradient. The sensitive potentiometric response of these highly charged ions is discussed.     

Potentiometric detection of organic acids in liquid chromatography using polymeric liquid membrane electrodes incorporating macrocyclic hexaamines

Potentiometric detection employing coated-wire electrodes was applied to the determination of organic acids in liquid chromatography (LC). Poly(vinyl chloride)-based liquid membranes, incorporating lipophilic macrocyclic hexaamines as neutral ionophores were used as electrode coatings. The selectivity and sensitivity of the macrocycle-based electrodes were found to be superior to an electrode based on a lipophilic anion exchanger (a quaternary ammonium salt). Sensitive detection was obtained for the di- and tricarboxylic acids tartaric, malonic, malic, citric, fumaric, succinic, pyruvic, 2-oxoglutaric and maleic acids after separation in reversed-phase LC. Detection limits (signal/4sigmanoise=3) of 6 pmol for malonic acid and 2 pmol for maleic acid were attained. The detection was explained using a molecular recognition model. The hexaamine-based potentiometric electrodes had a 1-s response time at 1 ml min(-1) flow-rates. They were stable for at least 4 months, with an intra-electrode variation of 3.2% (n=5).     

Chirality-organized ferrocene receptor bearing podand dipeptide chains (-L-Ala-L-Pro-NHPyMe) for the selective recognition of dicarboxylic acids

[structure: see text] The ferrocene receptor bearing the podand dipeptide chains (-l-Ala-l-Pro-NHPyMe) was found to provide a chirality-organized binding site through two intramolecular interchain hydrogen bonds between CO (Ala) and NH (another Ala) of each podand dipeptide chain. The size-selective and chiral recognition of dicarboxylic acids was achieved by multipoint hydrogen bonds of the binding site.     

Recognition of Monohydrogen Anions of Geometrical and Positional Isomers of Dicarboxylic Acids Based on Polymeric Liquid Membranes Incorporating Polyamine Host

Macrocyclic lipophilic polyamines were applied as the sensory elements of polymeric liquid membrane electrodes. These hosts gain the anion receptor functionality upon protons uptake from the aqueous solutions. The electrodes studied were able to distinguish potentiometricaly isomers of monocharged and doublecharged forms of ethylene and benzene dicarboxylic acids. The selectivity of interaction between protonated hosts and anionic guests relays not only on the electrostatic interactions, but on hydrogen bounds formations as well. The influence of lipophilicity of protonated hosts on the potential response generation was discussed.     

Potentiometric detection of organic acids in ion-exclusion chromatography using different types of liquid-membrane electrodes

Four different liquid-membrane electrodes were tested in a potentiometric flow-cell, in combination with an LC ion chromatography system (Aminex HPX-87H column). This setup was used for the determination of weak organic acids. The flow-through detector was of the wall-jet type. Conditions were established to achieve the best separation and detection characteristics. The sensitivity, selectivity and response time of the different electrodes were compared. Calibration curves and detection limits were measured for several organic acids, and compared with conductometric, and with low-wavelength UV detection. The detection limits were improved by inserting a post-column ion-suppressor system between the column and the detector. Several biological samples were analyzed to demonstrate the possibilities of the potentiometric detector.     

GC–MS analysis of low-molecular-weight dicarboxylic acids in atmospheric aerosol: comparison between silylation and esterification derivatization procedures

This paper describes methods for the determination of low-molecular-weight (LMW) dicarboxylic acids in atmospheric aerosols as important chemical tracers for source apportionment of aerosol organics and for studying atmospheric processes leading to secondary organic aerosol formation. The two derivatization procedures most widely used in GC analysis of dicarboxylic acids were compared: esterification using BF₃/alcohol reagent and silylation using N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA). The advantages and drawbacks of the two methods are investigated and compared in terms of (1) precision and accuracy of the results and (2) sensitivity and detection limit of the procedure. The comparative investigation was performed on standard solutions containing target C₃–C₉ dicarboxylic acids and on experimental particulate matter (PM) samples. Attention was focused on low-volume sampling devices that collect small amounts of sample for organic speciation. The results show that, overall, both the techniques appear suitable for the analysis of LMW dicarboxylic acids in atmospheric aerosols since they provide low detection limits (≤4 ng m⁻³) and satisfactory reproducibility (RSD% ≤ 15%). Between them, BSTFA should be the reagent of choice under the most limiting conditions of PM filters collected by low-volume air samplers: It provides determination of all the target C₃–C₉ dicarboxylic acids with lower detection limits (≤2 ng m⁻³) and higher reproducibility (RSD% ≤ 10%)      

Macrocyclic antibiotics as chiral selectors in the design of enantioselective, potentiometric membrane electrodes for the determination of l- and d-enantiomers of methotrexate

Three enantioselective, potentiometric membrane electrodes (EPMEs) based on macrocyclic glycopeptide antibiotics—vancomycin and teicoplanin (modified or not with acetonitrile)—were proposed for the determination of l- and d-enantiomers of methotrexate (Mtx). The linear concentration ranges for the proposed enantioselective membrane electrodes were between 10⁻⁶ and 10⁻³ mol l⁻¹ for l- and d- methotrexate. The slopes of the electrodes were 58.00 mV/pl-Mtx for vancomycin-based electrode; 57.60 mV/pd-Mtx for teicoplanin-based electrode and 55.40 mV/pd-Mtx for teicoplanin modified with acetonitrile-based electrode. The detection limits of the proposed electrodes were of 10⁻⁸ mol l⁻¹ magnitude order. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper. All proposed electrodes proved to be successful for the determination of the enantiopurity of Mtx as raw material and of its pharmaceutical formulations (tablets and injections).     

Response of DNA fragments to potentiometric sensors studied using HPLC

Potentiometric sensors are studied as viable candidates for the construction of high throughput DNA arrays. For preliminary investigations, such sensors were used in an HPLC setup in the present work. This avoided errors due to ionic contaminants or additives in the commercial samples. The oligonucleotides dT(10), dT(20) and dT(30) were used as test substances. The potentiometric sensors were of the coated wire type, containing PVC, DOP, MTDDACl and a synthetic podand urea receptor. The HPLC system consisted of a reversed phase column eluted with a phosphate buffer, triethylammoniumacetate (TEAA), and an acetonitrile gradient. Molar responses and sensitivities increased with increasing chain length of oligonucleotides, yielding detection limits as low as 10(-6)M (dT(30), injected concentration). The slopes of the calibration graphs were at least 23 mV/decade (dT(10)), which was much higher than expected. The results are discussed in view of the potential use of this sensor type in high throughput microarrays.     

Molecular Tweezers for Dicarboxylic Acids Based on a Saddle-Shaped Metallomacrocyclic Platform

A new metal containing molecular receptor was prepared from a 15-membered nickel(II) macrocyclic cyclidene platform and two cyclic tetramine (cyclen) recognition cites. In the saddle shaped conformation of the platform, the cyclen receptors are positioned for ditopic binding of difunctional substrates. NMR titration experiments demostrate that the molecule binds dicarboxylic acids in DMSO with apparent equilibrium constants ranging from 10 to 10⁴ M^-1. Incusion of dicarboxylates into the protonated macrocyclic host is shape-selective, with cis-1,2-dicarboxylates (succinate, maleate, and o-phthalate) being the best guests.     

Uranyl-selective PVC membrane electrodes based on some recently synthesized benzo-substituted macrocyclic diamides

Four different recently synthesized macrocyclic diamides were studied to characterize their abilities as uranyl ion carriers in PVC membrane electrodes. The electrodes based on macrocycle 1,18-diaza-3,4;15,16-dibenzo-5,8,11,14,21,24-hexaoxacyclohexaeicosane-2,17-dione resulted in a Nernstian response for UO(2)(2+) ion over wide concentration ranges. The linear concentration range for the polymeric membrane electrode (PME) is 3.0x10(-6)-8.2x10(-3) M with a detection limit of 2.2x10(-6) and that for the coated graphite electrode (CGE) is 5.0x10(-7)-1.5x10(-3) M with a detection limit of 3.5x10(-7) M. The electrodes manifest advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations.     

New Macrocyclic Diamides as Neutral Ionophores for Highly Selective and Sensitive PVC‐Membrane Electrodes for Be2+ Ion

Five recently synthesized macrocyclic diamides were investigated to characterize their ability as beryllium ion carriers in potentiometric PVC‐membrane electrodes. The electrodes based on 1,15‐diaza‐3,4;12,13‐dibenzo‐5,8,11‐trioxabicyclo[13,2,2] heptadecane‐2,14‐dione exhibited a Nernstian response for Be²⁺ ion over wide concentration ranges (from 3.0×10^?6 to 3.0×10^?2 M for polymeric membrane electrode, PME, and from 5.0×10^?7 to 2.0×10^?2 M for coated glassy carbon electrode, CGCE) and very low detection limits (2.0 ×10^?6 M for PME and 4.0×10^?7 M for (CGCE). The electrodes possess low resistances, fast responses, satisfactory reproducibilities and, most importantly, good selectivities relative to a variety of other common cations. The potentiometric response of the electrodes is independent of pH of test solution in the pH range of 4.0–7.5. The proposed sensors were used to determine beryllium ion in water samples.     

Selective transmembrane carriers for hydroxycarboxylic acids: Influence of a macrocyclic calix[4]arene platform

Selective transmembrane carriers for a-hydroxy acids, acyclic a-amino phosphonates and calix[4]arenes containing a-aminophosphonate substituents at the lower rim have been synthesized; analytical HPLC has been used to monitor the selective separation of dicarboxylic, a-hydroxy and a-amino acid mixtures by membrane extraction; the attachment of a-aminophosphonate fragments to the macrocyclic calix[4]arene platform results in receptors with markedly modified efficiency and selectivity relative to those of only aminophosphonates.     

大环多胺型荧光探针的研究进展

大环多胺作为含有多个氮原子和闭合环状结构的一类电子供体,在构筑荧光探针方面具有独特的优势。代表性的大环多胺如四氮环(cyclen、cyclam和pyclen)和三氮环(tacn)等,它们被广泛用于金属离子、阴离子、生物活性小分子和生物大分子探针的识别基团或功能基团。本文依据检测对象的不同,综述近年来大环多胺在荧光探针的设计、制备及应用方面的优秀成果,并对未来其在荧光检测分析领域的进一步发展进行了展望。     

Analysis of size-classified ice crystals by capillary electrophoresis

In order to analyse the main inorganic cations (NH4+, K+, Na+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO4(2-)) as well as carboxylic and dicarboxylic acids in ice crystals by capillary electrophoresis, electrolyte systems were developed and optimised with respect to limits of detection, resolution, reproducibility and analysis time. We applied indirect UV detection, which enables the simultaneous detection of multiple components. Salicylic acid and 4-methylaminophenolsulfate were used as UV-active co-ions for analysis of anions and cations, respectively. The special features of these systems were low limits of detection in the range 0.3-0.9 micromol L(-1), i.e. absolute limits of detection were in the fmol range, and short analyses times. Separations of cations as well as anions including carboxylic and dicarboxylic acids were completed within 4 min allowing a high sample throughput. Furthermore, the applicability of the newly developed electrolyte systems was demonstrated by comparative analyses with ion chromatography and by first field experimental studies.     

On-line, inlet-based trimethylsilyl derivatization for gas chromatography of mono- and dicarboxylic acids

An on-line, inlet-based trimethylsilyl (TMS) derivatization technique was optimized and evaluated for quantitative analysis of mono- and dicarboxylic acids. The technique involves co-injection of sample and reagent followed by gas-phase formation of TMS derivatives and analysis by gas chromatography with flame ionization detection. Derivatization efficiencies were determined by comparing measured and theoretical effective carbon numbers and used to optimize the technique with respect to experimental parameters. For analysis of C5-C17 monocarboxylic acids and C2-C10 dicarboxylic acids under optimized conditions, average derivatization efficiencies were > or = 94%, average measurement uncertainties were < or = 5%, and detection limits were approximately 2 ng. The technique was applied to the analysis of carboxylic acids generated from the ozonolysis of cyclic alkenes in a smog chamber.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

Low nM Detection Limits at Porous 1–3 nm Thick Membrane‐Coated Nanostructured Microdisk Electrodes

Low (15 nM) limits of detection (LOD) of dopamine were obtained at porous 1–3 nm‐thick overoxidized polypyrrole (OPPY) membrane‐coated microdisk carbon fiber electrodes of small size (r=3.5 µm). The excellent mass transport through the porous OPPY membrane (efficiency as good as solution transport) contributes to the low LOD, together with dopamine preconcentration in the membrane. Structural characterization of the membrane coated electrodes confirms the contribution of membrane nanostructure to the high sensitivity and the low LOD.     

Poly(ester sulphonic acid) coated mercury thin film electrodes: characterization and application in batch injection analysis stripping voltammetry of heavy metal ions

Mercury-thin film electrodes coated with a thin film of poly(ester sulphonic acid) (PESA) have been investigated for application in the analysis of trace heavy metals by square wave anodic stripping voltammetry using the batch injection analysis (BIA) technique. Different polymer dispersion concentrations in water/acetone mixed solvent are investigated and are characterised by electrochemical impedance measurements on glassy carbon and on mercury film electrodes. The influence of electrolyte anion, acetate or nitrate, on polymer film properties is demonstrated, acetate buffer being shown to be preferable for stripping voltammetry applications. Although stripping currents are between 30 and 70% less at the coated than at bare mercury thin film electrodes, the influence of model surfactants on stripping response is shown to be very small. The effect of the composition of the modifier film dispersion on calibration plots is shown; however, detection limits of around 5 nM are found for all modified electrodes tested. This coated electrode is an alternative to Nafion-coated mercury thin film electrodes for the analysis of trace metals in complex matrices, particularly useful when there is a high concentration of non-ionic detergents.     

Design and synthesis of a unique ditopic macrocyclic fluorescent receptor containing furan ring as a spacer for the recognition of dicarboxylic acids

A macrocyclic fluorescent receptor was designed and synthesised and the binding study with three different types of dicarboxylic acids was performed with the receptor being found to have appreciable association constants. Downfield shifts of specific amide protons in 1:1 binding by ¹H NMR and the quenching in the fluorescence spectra reveal strong binding and thus unambiguously support the complexation of the receptor 1 with dicarboxylic acids.     

New Validated Potentiometric Determination of Vasodilator Pentoxifylline in its Pharmaceutical Formulations and Biological Fluids

The construction and performance characteristics of pentoxifylline selective electrodes were developed. Two types of electrodes: plastic membrane I and coated wire II were constructed based on the incorporation of pentoxifylline with phosphotungstic acid (PTA). The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time, and foreign ions on the electrodes was investigated. The electrodes showed a Nernstain response with a mean calibration graph slope of 56.77 ± 0.19 and 55.76 ± 0.71 mV decade^‐1 at 25 °C for electrode I and II respectively, over pentoxifylline concentration range from 1.0 × 10^‐5‐1.0 × 10^‐2 and 9.0 × 10^‐6‐1.0 × 10^‐2 mol L^‐1, with detection limits 4.89 × 10^‐6 and 3.90 × 10^‐6 mol L^‐1 for electrode I and II, respectively. The pH range of the constructed electrodes was 4‐6. Interferences from common cations, alkaloids, sugars, amino acids and drug excipients were reported. The results obtained by the proposed electrodes were also applied successfully to the determination of the drug in its pharmaceutical preparations and biological fluids.