Sharp Endpoint Research Articles

Potentiometric determination of some food additives and their binding to a polycationic species using polyion sensors

Polycation-sensitive membrane electrodes based on dinonylnaphthalene sulfonate (DNNS) were examined for the determination of some polyanions, namely xanthan (Xanth), alginate (Alg), carboxymethyl cellulose (CMC), and carrageenan (Carr). The potentiometric titrations of polyanionic analytes yielded sharp end points and correlative stoichiometries. After the determinations were successfully performed in saline, these polyanions were also determined in some food products consumed in Bolu (Turkey). In addition, the titration data were used to estimate the interactions between titrant and polyanionic analytes. The equilibrium constants, K_{eq}, and the number of titrant binding sites (n) per mole of analyte polyanion were calculated using Scatchard plots. The accuracy of the assayed method was confirmed by recovery experiments in spiked samples. Dynamic ranges for the determination of polyanionic analytes were 2--20 \mu g/mL for CMC, 1--8 \mu g/mL for Xanth, 0.5--4 \mu g/mL for Alg, and 2--20 \mu g/mL for Carr. LOD values were

Phenomenology of excited doubly charged heavy leptons at the LHC

We consider the production at the LHC of exotic composite leptons of charge Q=+2e. Such states are allowed in composite models which contain extended isospin multiplets (Iw=1 and Iw=3/2). These doubly charged leptons couple with Standard Model [SM] fermions via gauge interactions, thereby delineating and restricting their possible decay channels. We discuss the production cross section at the LHC of L++ (p p --> L++, l-) and concentrate on the leptonic signature deriving from the cascade decays L++ --> W+, l+ --> l+, l+, \nu_l i.e. p p --> l-, l+, l+, \nu_l showing that the invariant mass distribution of the like-sign dilepton has a sharp end point corresponding to excited lepton mass m*. We find that the sqrt{s}=7 TeV run is sensitive at the 3-sigma (5-sigma) level to a mass of the order of 600 GeV if L=10 fb^-1 (L=20 fb^-1). The sqrt{s}=14 TeV run can reach a sensitivity at 3-sigma (5-sigma) level up to m*=1 TeV for L=20 fb^-1 (L=60 fb^-1).

Application of Ion-Association Titration for the Assay of Cyproheptadine Hydrochloride in Pharmaceuticals

Two simple and rapid titrimetric methods are described for the determination of cyproheptadine hydrochloride (CPH) in pharmaceuticals. The proposed methods are based on the solvent extraction-titration of CPH with two ion association reagents, sodium lauryl sulphate (SLS), (method A), and tetraphenylborate (TPB), (method B). In method A, SLS was used as titrant and the titration was carried out in the presence of dilute sulphuric acid and chloroform using dimethyl yellow as indicator, whereas, in method B, the titrant was TPB and the titration was done in Walpole buffer of pH 4.5 and 1, 2-dichloroethane using tetrabromophenolphthalein ethyl ester as indicator. The proposed procedures give sharp end points as the color of the organic phase changes from yellow to pink in method A, and from red-violet to yellow in method B. The methods are applicable over the ranges of 1.0–20.0 and 2.0–9.0 mg of CPH for method A and method B, respectively. The accuracy and precision of the methods are good. The methods were applied successfully to the determination of CPH in tablets, and the results were in agreement with the label claim and those of the reference method.

Silver ion recognition using potentiometric sensor based on recently synthesized isoquinoline-1,3-dione derivatives

The four derivatives of isoquinoline-1,3-dione based on β-lactum (I-IV), have been explored as neutral ionophores for preparing poly(vinylchloride) based polymeric membrane electrodes (PME) selective to silver(I) ions. The addition of sodium tetraphenylborate (NaTPB) and dioctylsebacate (DOS) as a plasticizer was found to improve the performance of ion selective electrodes. The best performance was obtained with PME-1 based on ionophore I having composition: ionophore (9.2 mg), PVC (100.1 mg), DOS (201.1 mg) and NaTPB (1.5 mg) in 5 mL tetrahydrofuran. The electrode response was linear with Nernstian slope of 58.44 mV/decade in the concentration range of 1.0 x 10 -1 M to 5.0 x 10 -6 M and detection limit of 5.83 x 10 -6 M. It performs satisfactorily over wide pH range of 1.0-5.5. The proposed sensor can be used over a period of more than three months without any significant drift in potential and shows good selectivity to silver(I) ion over a number of cations especially with no interference of mercury(II) ions. Sharp end point was obtained when the sensor was used as an indicator electrode for the potentiometric titration of silver(I) ions with chloride ions and therefore this electrode (PME-1) could be used for quantitative determination of silver(I) ion in synthetic water, silver foil and dental amalgam samples.

Application of ion-association titration for the assay of bupropion hydrochloride in pharmaceuticals

Two simple and rapid titrimetric methods are described for the determination of bupropion hydrochloride (BUPH) in pharmaceuticals. The proposed methods are based on the solvent extraction-titration of BUPH with two ion-association reagents, i.e. sodium lauryl sulphate (SLS) and tetraphenylborate (TPB). In method A, SLS was used as titrant and the titration was carried out in the presence of dilute sulphuric acid and chloroform using dimethyl yellow as indicator whereas in method B, the titrant was TPB and the titration was done in borate-phosphate buffer of pH 6.0 and 1,2-dichloroethane with tetrabromophenolphthalein ethyl ester (TBPE) as indicator. In the two-phase titrations, the proposed procedures give sharp end points as the color of the organic phase changes from yellow to pink in method A and from red-violet to yellow in method B. The methods are applicable over the ranges of 1.0-20.0 and 3.0-10.0 mg of BUPH for method A and method B, respectively. The accuracy and precision of the methods are good. The methods were applied successfully to the determination of BUPH in tablets and the results were in agreement with the label claim and those of the comparison method.

Denoising of Two-Dimensional Geometric Discontinuities

Accurate reduction of two-dimensional curve noises at sharp edges, corners, or C0 discontinuous end points is crucial to the fast and accurate metrology, because more severe measurement errors of various sensors are frequently observed near sharp edges and corners of the objects to be measured. In this paper we explore three schemes (interior-point, polynomial extrapolation-and reflection-point methods) for handling C0 discontinuity. We also propose a new interior-point method for dealing with the accurate denoising of C1 discontinuity. Numerical experiments have been conducted for demonstrating the efficacy of our new approach in terms of denoising accuracy.

DENOISING OF TWO-DIMENSIONAL GEOMETRIC DISCONTINUITIES

Accurate reduction of two-dimensional curve noises at sharp edges,corners, or C0 discontinuous end points is crucial to the fast andaccurate metrology, because more severe measurement errors ofvarious sensors are frequently observed near sharp edges and cornersof the objects to be measured.

Microfabrication of colloidal scanning probes with controllable tip radii of curvature

We report the first batch-fabrication method to create colloidal scanning probes based on standard micromachining processes. Microfabrication of colloidal probe arrays having smooth surface profiles with radius of curvature ranging from nanometers to tens of microns is successfully demonstrated. A new mold filling technology is developed where bulk-etched cavities with sharp endpoints are transformed into cavities with curved endings via spin coating of a liquid filling material (photoresist). The curved profile is then replicated into a stable metallic mold by evaporating a layer of aluminum, after which mold-transfer scanning probe (SP) fabrication is conducted to create colloidal probes. Multiple control knobs were developed and characterized for accurate control of the tip radius of curvature. By adjusting the solid content of the filling material, the number of spin-coat cycles, and the cavity geometry, different mold profiles and thereby tip radii of curvature were achieved. The new controllable technology allows rapid microfabrication of singular or arrayed colloidal scanning probes with different tip radii of curvature which will be useful for many biological and nanotechnology applications.

Restriction of Fourier transforms to curves and related oscillatory integrals

We prove sharp endpoint results for the Fourier restriction operator associated to nondegenerate curves in ${\Bbb R}^d$, $d\ge 3$, and related estimates for oscillatory integral operators. Moreover, for some larger classes of curves in ${\Bbb R}^d$ we obtain sharp uniform $L^p\to L^q$ bounds with respect to affine arclength measure, thereby resolving a problem of Drury and Marshall.

New maximal functions and multiple weights for the multilinear Calderón–Zygmund theory

A multi(sub)linear maximal operator that acts on the product of m Lebesgue spaces and is smaller than the m-fold product of the Hardy–Littlewood maximal function is studied. The operator is used to obtain a precise control on multilinear singular integral operators of Calderón–Zygmund type and to build a theory of weights adapted to the multilinear setting. A natural variant of the operator which is useful to control certain commutators of multilinear Calderón–Zygmund operators with BMO functions is then considered. The optimal range of strong type estimates, a sharp end-point estimate, and weighted norm inequalities involving both the classical Muckenhoupt weights and the new multilinear ones are also obtained for the commutators.

THE FEASIBILITY OF USING TANTALUM METAL AS INDICATOR ELECTRODE IN PRECIPITATION TITRATION REACTIONS

Tantalum metalwas found to serve as an excellent indicator for potentiometric precipitation titrations. The experimental results were discussed in terms of the potential arrests and potential shifts upon addition of the titrant. The obtained results for 0.05M halogen solutions revealed that when tantalum electrode is coupled with SCE or Pt electrodes, sharp potential jumps and distinct end points were obtained in the titration of Cl, Br and I solutions against 0.057M AgNO3 solution in both forward and backward titration techniques. On the other hand, Ta/Ag systems in forward titrations of Br and Cl solutions behave similarly. While in backward titration, the end point is determined by presence of a sharp potential peak in the positive direction. In I solutions, Ta/Ag system illustrates a sharp potential peak in both forward and backward titration curves. Results for 0.1M halogen solutions revealed that the equivalence volumes in forward titrations for Br and I solutions in the four systems are very near to the calculated ones. Concerning Cl solutions, the volume magnitudes corresponding to the potential jumps are so far from calculated values in all systems used. For I solution, in backward titration, the order of increasing potential jumps of tantalum systems was as follows: Ta/ Pt < Ta/ Ag < Ta/SCE system. The shape of the titration curves depends upon the kind of halogen and its concentration as well as on the type of system used and type of titration when the experiment is carried out.

Polyelectrolyte complex characterization with isothermal titration calorimetry and colloid titration

Abstract Isothermal titration calorimetry (ITC) and colloid titration (CT) were used to characterize aqueous polyelectrolyte complex formation between strong polyelectrolytes, poly(diallyldimethylammonium chloride) and potassium poly(vinyl sulfate) and between weak polyelectrolytes, polyvinylamine (PVAm) and carboxymethyl cellulose (CMC). ITC gives information about the evolution of polyelectrolyte complex properties but does not give good measure of the charge balance composition. By contrast, CT determines the charge balance endpoint but reveals nothing about the path to the endpoint. For strong polyelectrolyte complexes based on fixed charge polymers, the CT curves are very clean giving a sharp endpoint. The corresponding ITC curves are relatively simple although the endpoints are not as distinct as CT. ITC does, however, indicate the onset of phase separation. For weak polyelectrolyte complexes (PVAm/CMC) based on polymers with labile charges, ITC gives complicated curves which are sensitive to pH, ionic strength and the order of addition. The most dramatic effects occur at pH 5–5.9 where we propose that complex formation induces the CMC to ionize further during the titration.

Mercury(II) Ion‐Selective Electrodes Based on Heterocyclic Systems

Mercury ion-selective electrodes (ISEs) were prepared with a polymeric membrane based on heterocyclic systems: 2-methylsulfanyl-4-(4-nitro-phenyl)-l-p-tolyl-1H-imidazole (I) and 2,4-diphenyl-l-p-tolyl-1H-imidazole (II) as the ionophores. Several ISEs were conditioned and tested for the selection of common ions. The electrodes based on these ionophores showed a good potentiometric response for Hg2+ ions over a wide concentration range of 5.0 x 10(5-) - 1.0 x 10(-1)M with near-Nernstian slopes. Stable potentiometric signals were obtained within a short time period of 20 s. The detection limits, the working pH range of the electrodes were 1.0 x 10(-5) M and 1.6-4.4 respectively. The electrodes showed better selectivity for Hg2+ ions over many of the alkali, alkaline-earth and heavy metal ions. Also sharp end points were obtained when these sensors were used as indicator electrodes for the potentiometric titration of Hg2+ ions with iodide ions.

Multi-Sensor Monitoring System in Chemical Mechanical Planarization (CMP) for Correlations with Process Issues

In this paper, three different sensors were used to measure multi-scale phenomena in chemical mechanical planarization. A piezoelectric force sensor, Hall effect sensor and acoustic emission sensor (AE) were installed in CMP equipment and the signals were measured simultaneously during the polishing process. The results showed that the sensors measuring frictional behaviour, such as the Hall effect sensor and force transducer, produced a clear end point signal in the case of the friction characteristics are distinguishable for each material. Also, if there is difference in hardness between materials, then a sharp end point signal is detected with the AE sensor even though the friction characteristic is similar between the two materials. Therefore, using multi-sensors having different bandwidths is complementary for not only process monitoring but also end point detection.

Titrimetric method for determination of O-desulfated heparin in physiological samples using protamine-sensitive membrane electrode as endpoint detector

O-Desulfated heparin (ODSH) is a promising new anti-inflammatory agent for the prevention of reperfusion injury following myocardial infarction or stroke. This partially desulfated heparin derivative has less anticoagulant activity than unfractionated heparin but retains the inherent anti-inflammatory properties of heparin. Thus, ODSH could be administered at the high doses needed to achieve desired anti-inflammatory function without risk of hemorrhage. However, given the very low anticoagulant activity of this species, traditional methods for heparin determination in clinical samples might not be well suited for ODSH measurements. In this article, a novel titrimetric method for detection of ODSH in buffer and plasma is described using a protamine-sensitive polymer membrane electrode as the detector. Titrations of ODSH with the heparin antagonist protamine yield sharp endpoints with sensitivity to ODSH in the micrograms per milliliter range for plasma samples. The stoichiometry for protamine interaction with ODSH is determined to average 1.39 μg protamine/μg ODSH in plasma. This technology is further applied to a toxicokinetic study of ODSH in an animal model, demonstrating the ability to detect the changes in ODSH concentrations in biological samples.

Application of Dipon, (1,4,8,11-Tetraazacyclotetradecane-4,11-bis(methylphosphonic acid) as Selective Complexing Agent for Determination of Copper(II)

A new macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid)(dipon), is selective complexing agent for copper(II) over other transition metal ions. The ligand was tested for analytical applications of copper(II) determination. Spectrophotometric determination under optimal experimental conditions (−log [H+]= 5.5, cL≈ 5 × 10−4 mol L−1, λ= 310 nm) is valid in dynamic range (5–200)× 10−6 mol L−1 with detection limit 2.2 × 10−6 mol L−1, i.e. 0.14 μg ml−1. Volumetric determination of copper(II) with standardized dipon solution was used for copper(II) determination at micromolar concentration level without any necessity to sequester interfering metal ions. A sharp end point of titration was detected by UV/VIS spectrophotometry. Both methods were tested on artificial and real samples (spiked mineral water, alloys) and gave satisfactory results without any systematic error. The advantage of both methods is their simplicity, rapidity and no sensitivity to the presence of other metal ions.

Sharp endpoint inequality for multilinear Littlewood-Paley operator

Sharp endpoint inequality for multilinear Littlewood-Paley operator

Mercury(II) ion-selective electrodes based on p-tert-butyl calix[4]crowns with imine units.

A PVC membrane incorporating p-tert-butyl calix[4]crown with imine units as an ionophore was prepared and used in an ion-selective electrode for the determination of mercury(II) ions. An electrode based on this ionophore showed a good potentiometric response for mercury(II) ions over a wide concentration range of 5.0 x 10(-5) - 1.0 x 10(-1) M with a near-Nernstian slope of 27.3 mV per decade. The detection limit of the electrode was 2.24 x 10(-5) M and the electrode worked well in the pH range of 1.3 - 4.0. The electrode showed a short response time of less than 20 s. The electrode also showed better selectivity for mercury(II) ions over many of the alkali (Na+, -1.69; K+, -1.54), alkaline-earth (Ca2+, -3.30; Ba2+, -3.32), and heavy metal ions (Co2+, -3.67; Ni2+, -3.43; Pb2+, -3.31; Fe3+, -1.82). Ag+ ion was found to be the strongest interfering ion. Also, sharp end points were obtained when the sensor was used as an indicator electrode for the potentiometric titration of mercury(II) ions with iodide and dichromate ions.

Use of 9-Methylfluorene as an Indicator in the Titration of Common Group IA and Group IIA Organometallic Reagents

9-Methylfluorene was tested as an indicator in the titration of commonly used organometallic reagents. This indicator is readily prepared in three steps from fluorenone. In THF solution the deprotonated indicator is red and exhibits a sharp endpoint. The highly basic reagents sec-butyllithium and tert-butyllithium can be titrated in ether solution, where the color of the deprotonated indicator is yellow.

Determination of pentosan polysulfate and its binding to polycationic species using polyion-sensitive membrane electrodes

The use of previously developed polyanion and polycation-sensitive membrane electrodes to determine pentosan polysulfate (PPS), an anti-osteoarthritis drug chemically derived from a natural polysaccharide, in buffered saline and biological samples is examined. Owing to PPS’s very high anionic charge density, an extremely large non-equilibrium EMF response to PPS is observed over the concentration range of 0.3–10 μg/ml using polyanion-sensitive electrodes based on tridodecylmethylammonium chloride (TDMAC) as the membrane ion-exchanger. However, optimal quantitative determinations of PPS at μg/ml levels are accomplished via simple potentiometric titrations with polycationic protamine or poly- l-arginine using a membrane electrode formulated with dinonylnapthalene sulfonate (DNNS) as the potentiometric end point detector. Such titrations yield sharp end points and provide consistent mass stoichiometries for the complexation between the polycation species and PPS (1.55:1 protamine:PPS; 1.20:1 poly- l-arginine:PPS). It is shown that similar titrations with protamine can be utilized to detect PPS quantitatively in undiluted plasma at concentrations ≥0.5 μg/ml. Fundamental studies regarding the binding of PPS to various polycations can also be accomplished using the TDMA-based polyanion sensor as a detector. Scatchard analysis of the EMF data for the titration of protamine and poly- l-arginine with PPS indicate that both species bind PPS with relatively high affinity (4.4 and 9.4 μM −1, respectively).