Polyelectrolyte titration using fluorescent indicator. II. Analysis of cationic starches and flocculants

In the conventional polyelectrolyte titration, toluidine blue (TB) has been used exclusively as an indicator. This is a very convenient method for analyses of polyelectrolytes with fairly high charge density, but it is very difficult, or impossible, to analyze samples with low charge density such as commercial cationic starches because of the unclear color change of TB at the end point. Also analyses of polyelectrolytes with ultrahigh molecular weights over 10⁷ (such as common flocculants) are often accompanied by serious errors. Usually, the concentration of standard titrant is around 0.2 × 10^?3 N. On the other hand, the standard titrant with very dilute concentration such as 1 × 10^?4 N can be used in the polyelectrolyte titration using a fluorescent indicator because the sensitivity of fluorescence detection is extremely high. It has been elucidated that this method can be employed for accurate analyses of cationic starches, cationic and anionic flocculants, and also for determination of sulfonic and carboxyl groups contained in the same molecule by the titration at pH 2.8 and 9.5, respectively. © 1993 John Wiley & Sons, Inc.     

New Host Molecules with Imidazoliums as Functional Arms:Syntheses and Anion Recognition

The bridged tri-imidazoliums 3.3X^--5.3X^-(X^-=PF6^-,Br^-,I^-)and bis-imidazoliums 6.2PF6^- were synthesized by N-quaternization of imidazole derivative 1 in acetonitrile under reflux.UV spectroscopic titration experiments showed that the halide salts and hexafluorophosphate salts of these imidazoliums exhibited good recognition toward anions in water and in acetonitrile,respectively.     

HTFFR kinetics studies: A chemiluminescence titration method for the determination of absolutes Sn concentrations

Absolute gas phase Sn concentrations in the range 1 × 10¹³ ? [Sn] ? 1 × 10¹⁴ ml^?1 have been determined utilizing a technique based on the rapid (at T ? 900 K) titration reaction Sn + NO₂ → SnO + NO (k(900–1100 K) ≈ 1 × 10^?10 ml molecule^?1 s^?1) and the chemiluminescent indicator reaction Sn + N₂O → SnO + N₂ + hv(SnO a³ Σ-X¹Σ).     

A New Fluorimetric Reagent for Determination of Trace Amounts of Europium

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｃｈｅｍｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆｒａｒｅ ｅａｒｔｈｅｌｅｍｅｎｔｓａｒｅｖｅｒｙｓｉｍｉｌａｒ ,ｃｏｎｓｅｑｕｅｎｔｌｙ ,ｉｔｉｓｄｉｆｆｉｃｕｌｔｔｏｄｅｔｅｃｔａｎｉｎ ｄｉｖｉｄｕａｌｉｏｎｉｎｔｈｅｉｒｍｉｘｔｕｒｅｓｏｗｉｎｇｔｏｔｈｅｉｎｔｅｒｆｅｒｅｎｃｅｏｆｏｔｈｅｒｒａｒｅ ｅａｒｔｈｅｌｅｍｅｎｔｓ .Ｄｕｅｔｏａｈｉｇｈｅｒｓｅｎｓｉｔｉｖｉｔｙａｎｄｓｅｌｅｃｔｉｖｉｔｙ ,ｆｌｕｏｒｉｍｅｔｒｉｃｍｅｔｈｏｄｓｏｆｒａｒｅ ｅａｒｔｈｅｌ…     

Micellar‐Enhanced Spectrofluorimetric Determination of Trazodone Hydrochloride in Human Urine and Serum

Abstract

A novel developed spectrofluorimetric method for the determination of trazodone hydrochloride in the presence of sodium dodecyl sulfate (SDS) surfactant micelles was described. Under optimal conditions, there was a good linear relationship between fluorescence intensity and trazodone hydrochloride concentration in the range of 4.0×10^?9 to 8.0×10^?6 mol · l^?1with the detection limit of 1.3×10^?9 mol · l^?1 (S/N=3). This method has been used to determine trazodone hydrochloride in biological fluids.     

Halide‐Anion Binding by Singly and Doubly N‐Confused Porphyrins

The halide‐binding properties of N‐confused porphyrin (NCP, 1 ) and doubly N‐confused porphyrins (trans‐N₂CP ( 2 ), cis‐N₂CP ( 3 )) were examined in CH₂Cl₂. In the free‐base forms, cis‐N₂CP ( 3 ) showed the highest affinity to each anion (Cl^?, Br^?, I^?) with association constants K_a=7.8×10³, 1.9×10³, and 5.8×10² M ^?1, respectively. As metal complexes, on the other hand, trans‐N₂CP 2–Cu exhibited the highest affinity to Cl^?, Br^?, and I^? with K_a=9.0×10⁴, 2.7×10⁴, and 1.9×10³ M ^?1, respectively. The corresponding K_a values for cis‐N₂CP 3–Cu and NCP 1–Cu were about 1/10 and 1/2, respectively, of those of 2–Cu . With the help of density functional theory (DFT) calculations and complementary affinity measurements of a series of trisubstituted N‐confused porphyrins, the efficient anion binding of NCPs was attributed to strong hydrogen bonding at the highly polarized NH moieties owing to the electron‐deficient C₆F₅ groups at meso positions as well as the ideally oriented dipole moments and large molecular polarizability. The orientation and magnitude of the dipole moments in NCPs were suggested to be important factors in the differentiation of the affinity for anions.     

Spectrophotometric titration of cryptands and compleximetric titration of barium with cryptand (2.2.2)

A spectrophotometric titration of cryptands (2.2.1), (2.2.2), (2_B.2.2) and (2_B.2_B.2) in aqueous medium is described. Titration of the cryptands with standard lead(II) perchlorate allows these cryptands to be quantified down to 1.0 × 10^?5 M. The compleximetric titration of barium(II) with cryptand (2.2.2) using metalphthalein indicator is described and compared with a similar method with EDTA as titrant.     

Post‐chemiluminescence Method of the Determination of Loperamide Hydrochloride in Human Plasma and Pharmaceutical by Using Dichlorofluorescein as Chemiluminescence Reagent

Abstract

A post‐chemiluminescence (PCL) was observed when loperamide hydrochloride solution was injected into the reaction mixture after the finish of CL reaction of alkaline N‐Chlorosuccinimide (NCS) and dichlorofluorescein. Based on this phenomenon, a simple, sensitive and fast flow injection PCL method was established for the determination of loperamide hydrochloride. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the fluorescence spectra. The PCL intensity responded linearly to the concentration of loperamide hydrochloride in the range 8.0×10^?10 to 6.0×10^?7 g · ml^?1 with a linear correlation of 0.9995. The detection limit was 4×10^?10 g · ml^?1. The relative standard deviation was 2.4% for 4.0×10^?8 g · ml^?1 loperamide hydrochloride (n=11). This method has been applied to the determination of loperamide hydrochloride in human plasma and pharmaceutical samples with satisfactory results.     

Direct potentiometric titration of thiosulfate,thiourea, and ascorbic acid with lodate using an iodide ion-selective electrode

A potentiometric method has been developed for the semi-automatic direct titration of thiourea, thiosulfate, and ascorbic acid with potassium iodate in strongly acidic solutions using an iodide ion-selective electrode to monitor the reaction and locate the endpoint. The method is simple, fast, precise, and accurate. Amounts ranging from 0.15–1.5 mg of thiourea (3.9 × 10^?4–3.9 × 10^?3, M), 0.3–3.0 mg of thiosulfate (5.4 × 10^?4–5.4 × 10^?3, M), and 0.5–5.0 mg of ascorbic acid (5.7 × 10^?4–5.7 × 10^?3, M) have been determined with an average error of about 1%. The method has been applied to the determination of ascorbic acid in tablets. Results checked closely with those obtained with a standard titrimetric method.     

Determination of Rifampicin by Peroxomonosulfate‐Cobalt(II) Chemiluminescence System

Rifampicin can enhance the chemiluminescence (CL) of peroxomonosulfate‐cobalt(II) system, and the CL intensity is strongly dependent on the rifampicin concentrations. Based on this phenomenon, a rapid and sensitive flow injection CL method was developed for the determination of rifampicin. The relative CL intensity was linear with the rifampicin concentration over the range of 5×10^?8 to 1×10^?6 g·mL^?1 (r=0.9991), the detection limit was 7×10^?9 g·mL^?1 (S/N=3), and the relative standard deviation was 2.7% for 6×10^?7 g·mL^?1 rifampicin (n=11). Furthermore, this method was successfully applied to the determination of rifampicin in real eye drop and capsules sample.     

PVC matrix membrane sensor for potentiometric determination of dodecylsulfate

The construction and performance characteristics of a new potentiometric PVC membrane sensor for the determination of sodium dodecyl sulfate (SDS) are described. The sensor was based on the use of an N-cetyl-N,N,N trimethyl ammonium (CTA) dodecyl sulfate (DS) ion pair as ion exchange sites in PVC matrix in the presence of o-nitrophenyl octylether as plasticiser. The sensor exhibited a fast, stable, and near-Nernstian response for SDS over the concentration range of 1 × 10^?3 to 10^?6 M at 25°C and the pH range 4–8.5 with anionic slope of 52.5 ± 0.5 mV decade^?1. The lower detection limit was 3 × 10^?6 M, and the response time was 25 s. Selectivity coefficients of SDS with respect to a number of different species were investigated. There were negligible interferences caused by most of the investigated anions. The determination of 1.0–280.0 µg mL^?1 of SDS in aqueous solutions showed an average recovery of 99.1%, and the mean relative standard deviation was 1.4 at 100 µg mL^?1. The results obtained in the determination of SDS in liquid soap, water and in some pharmaceutical preparations compared favourably with those obtained by the Methylene Blue active substance method (MBAS). In the present investigation, the DS sensor has been used as an end-point indicator electrode for some precipitation titration reactions, e.g. titration of SDS with CTMABr and cetylpyridinium chloride with SDS.     

Optimization of a sensitive method for the “switch-on” determination of mercury(II) in waters using Rhodamine B capped gold nanoparticles as a fluorescence sensor

Monodisperse and “naked” gold nanoparticles (GNPs) were modified with thioglycolic acid (TGA). The fluorescence of rhodamine B (RB) is quenched completely by the gold NPs surface with negative charge mainly as a result of fluorescence resonance energy transition (FRET) and collision. The quenching mechanism can be described by a Langmuir isotherm, which was systematically investigated by steady-state fluorescence spectrometry and absorption spectrometry. Hg(II) ion disrupts the GNPs–RB pair, producing a large “switch-on” fluorescence. A low background, highly sensitive and reproducible fluorescence assay for Hg(II) is presented. Under the optimum conditions, the restoration fluorescence intensity is proportional to the concentration of Hg(II). The calibration graphs are linear over the range of 1.0?×?10^?9 to 3.1?×?10^?8 mol L^?1 with a detection limit of 4.0?×?10^?10 mol L^?1. The relative standard deviation was 1.2% for a 5.0?×?10^?9 mol L^?1 Hg(II) solution (N?=?6). This method was applied to the analysis of Hg(II) in environmental water samples, and the results were consistent with those of atomic absorption spectroscopy (AAS).     

Fluorescence Enhancement of Rare Earths by Yttrium and its Application

Abstract

A study of the enhancement effect on the fluorescence intensity of the Eu³⁺–-thenoyltrifluoroacetone (TTA)–-cetyltri–-methylammonium bromide (CTMAB) and the Dy³⁺ pyrocatechol–-3,5-disulphonic acid (Tiron) systems by Y³⁺has been carried out. In the presence of yttrium the fluorescence intensity of the systems was enhanced by a factor of about 100 and 15, respectively. The fluorescence intensity was a linear function of the concentration of europium or dysprosium in the range 1.0 × 10^?10–-1.0 × 10^?8mol dm^?3 and 8.0 × 10^?8–-9.0 × 10^?6mol dm^?3, respectively. The detection limit was 1.0 × 10^?11mol dm^?3 and 1.0 × 10^?10mol dm^?3, respectively. The standard addition method was used for the determination of europium or dysprosium in rare earth oxides and gave satisfactory results. The mechanism of enhanced fluorescence was proposed.     

Axially Chiral TADF‐Active Enantiomers Designed for Efficient Blue Circularly Polarized Electroluminescence

The use of a chiral, emitting skeleton for axially chiral enantiomers showing activity in thermally activated delayed fluorescence (TADF) with circularly polarized electroluminescence (CPEL) is proposed. A pair of chiral stable enantiomers, (?)‐(S)‐Cz‐Ax‐CN and (+)‐(R)‐Cz‐Ax‐CN, was designed and synthesized. The enantiomers, both exhibiting intramolecular π‐conjugated charge transfer (CT) and spatial CT, show TADF activities with a small singlet–triplet energy difference (ΔE_ST) of 0.029 eV and mirror‐image circularly polarized luminescence (CPL) activities with large g_lum values. Notably, CP‐OLEDs based on the enantiomers feature blue electroluminescence centered at 468 nm with external quantum efficiencies (EQEs) of 12.5 and 12.7 %, and also show intense CPEL with g_EL values of ?1.2×10^?2 and +1.4×10^?2, respectively. These are the first CP‐OLEDs based on TADF‐active enantiomers with efficient blue CPEL.     

Lower limits of the potentiometric titration of perchlorate using a perchlorate ion-selective electrode

Three titrants (tetraphenylarsonium chloride, tetraphenylphosphonium chloride, and tetra-n-pentylammonium bromide) were evaluated for the potentiometric determination of perchlorate. The emf levels were monitored with a perchlorate ion-selective indicator electrode and a double-junction reference electrode. The tetraphenylonium salts were equivalent, yielding the same precision and magnitude of potentiometric breaks. Considerably smaller breaks were obtained with tetra-n-pentylammonium bromide, which, therefore, is not recommended as titrant.The lower limits for the potentiometric titration of perchlorate at ambient temperature were extended to ~0.09 mmol per 50 ml (1.7 × 10^?3N) from the previous 0.25 mmol per 50 ml. If Gran plots are used, they can be further extended to ~0.01 mmol per 50 ml (2.1 × 10^?4N).     

Determination of tetraphenylborate by two-phase titration with tetraphenylphosphonium salt

A visual indicator method has been developed for the titration of tetraphenylborate (TPB) with a 5 × 10^?5, M tetraphenylphosphonium (TPP) solution. A hydrophobic dye, tetrabromophenolphthalein ethyl ester (TBPE), is used as an indicator in the presence of 1,2-dichloroethane. The organic phase changes from yellow to blue at the endpoint. This method was applied to the determination of solubility product of TPP perchlorate. The extract of ephedrine, homatropine, perchlorate, or thiocyanate with TPB or TPP was titrated.     

Polymerization of the new double‐charged monomer bis‐1,3(N,N,N‐trimethylammonium dicyanamide)‐2‐propylmethacrylate and ionic conductivity of the novel polyelectrolytes

The achievement of high ionic conductivity in single‐ion conducting polymer electrolytes is one of the important aims for various electrochemical devices including modern lithium batteries. One way to enhance the ionic conductivity in polyelectrolyte systems is to increase the quantity of charge carriers in each monomer unit. Highly charged poly(bis‐1,3(N,N,N‐trimethylammonium)‐2‐propylmethacrylate) with one of the most conducting anions, namely dicyanamide, was prepared via free radical bulk polymerization or using ionic liquids as reaction medium. The cationic polymers of the double‐charged monomer have molar masses up to = 1,830,000 g/mol and the ionic conductivity equal to 5.51 × 10^?5 S / cm at 25°C. The film forming ability, crystallinity, thermal stability, and glass transition temperatures of the new polymeric ionic liquids obtained from detailed studies are presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Novel Ytterbium(III) Selective Membrane Sensor Based on N‐(2‐Pyridyl)‐N′‐(2‐Methoxyphenyl)‐Thiourea as an Excellent Carrier and Its Application to Determination of Fluoride in Mouth Wash Preparation Samples

The construction, performance, and applications of a novel ytterbium(III) sensor based on N‐(2‐pyridyl)‐N′‐(2‐methoxyphenyl)‐thiourea (PMT), as an excellent carrier, in plasticized poly(vinyl chloride) PVC matrix, is described. The influences of membrane composition and pH on the potentiometric response of the sensor were investigated. The sensor exhibits a nice Nernstian response for Yb(III) ion over a wide concentration range of 4 decades of concentration (1.0×10^?6–1.0×10^?2 M), and a detection limit of 5.0×10^?7 M. The response time of the electrodes is between 8 and 10 s, depending on the concentration of ytterbium(III) ions. The proposed sensor can be used for about 8 weeks without any considerable divergence in potential. The sensor revealed very good selectivity for Yb(III) in the presence of several metal ions. The best performance was observed for the membrane containing; 30% PVC, 59% o‐nitrophenyloctyl ether (NPOE) as solvent mediator, 7% PMT, and 4% sodium tetraphenyl borate (NaTPB). It was successfully applied as indicator electrodes in the potentiometric titration of Yb(III) with EDTA and for the determination of fluoride ion in two mouth wash formulations. The proposed La(III) sensor was found to work well under laboratory conditions. It was also used as an indicator electrode in titration of a 1.0×10^?4 M of Yb(III) with a standard EDTA solution (1.0×10^?2 M). It was also used for determination of Yb(III) ion in Xenotime .     

Polyelectrolytes containing dihydronicotinamide. III. Fluorescence quenching by nicotinamide-containing polymers in aqueous solution

Charge-transfer (CT) interaction of N-benzyl-1,4-dihydronicotinamide (BNAH) and poly(sodium styrene-p-sulfonate) containing 6 mol % of BNAH groups (PNAH) with several types of nicotinamide-containing polyelectrolytes in aqueous solution was investigated by fluorescence quenching. The experimental data were analyzed in terms of a kinetic model including both static and dynamic quenching. Hydrophobic association of BNAH with the polymers led to more effective quenching than the monomer [N-benzylnicotinamide (BNA)] system. Electrostatic attraction of PNAH and BNA also resulted in the remarkably large value of apparent quenching constant (K′ = 1.4 × 10⁴M^?1). Further, the fluorescence of PNAH was quenched far more effectively by poly[N-(p-vinylbenzyl)nicotinamide] (PBNA) and poly(acrylamide)s containing nicotinamide (NA) groups (PAm) due to the formation of a polyelectrolyte complex (PEC). In this case, the K′ value depended on the BNA content in the copolymer, suggesting the structural matching effect of the interacting pair on the intermacromolecular interaction.     

Fluorescence enhancement of the europium-yttrium-diphacinone-ammonia system

A study of the enhanced (ca. 100 ×) fluorescence intensity of the Eu³⁺-diphacinone-ammonia system by Y³⁺ was made using a colloidal suspension. The excitation and emission wavelengths were 330 and 612 nm, respectively. The fluorescence intensity was a linear function of the concentration of europium in the range 6.0 × 10^?11–8.0 × 10^?7 M. The detection limit was 8.0 × 10^?14 M. The standard addition method was used for the determination of europium in rare earth oxides, with satisfactory results.