Direct detection of nitric oxide in human blood serum by use of 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)difluoroboradiaza-s-indacene with HPLC

To study the relationship between amounts of nitric oxide (NO) in blood and the development of ischemic cardio-cerebrovascular diseases, trace NO in human blood serum has, for the first time, been determined by use of a 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)difluoroboradiaza-s-indacene (TMDABODIPY)-based HPLC method. The proposed method is simple, rapid, and efficient, owing to its high sensitivity and good selectivity for NO. TMDABODIPY and its NO derivative are separated to baseline in 4 min, with simple separation conditions, on a C₁₈ column eluted with 50 mmol L⁻¹ ethanolamine in methanol. The derivative is detected by fluorescence at an emission wavelength of 507 nm with excitation at 498 nm. The response is a linear function of concentration in the range 0.8–800 nmol L⁻¹ NO. The detection limit can reach 2×10⁻¹¹ mol L⁻¹ (signal-to-noise ratio=3). The method has been used to detect NO in the serum of patients with five kinds of ischemic cardio-cerebrovascular disease and two diseases closely connected with ischemic cardio-cerebrovascular diseases. Recoveries of NO from spiked serum samples were between 96.58 and 105.71% and concentrations of NO observed in real samples were at 10⁻⁷ mol L⁻¹ levels. Our studies indicate that the proposed TMDABODIPY-based HPLC technique can be developed into a sensitive and new method for clinical assay and pathology research.     

Fluorimetric determination of traces of europium(III) using a new chelator and acetate or phosphate in dimethylsulfoxide as enhancers

A new Schiff-base ligand [N, N′, N″-Tri- (2,4-dihydroxyacetophenone) – triaminotriethylamine (TDATA)] with a tripodal structure was synthesized. Its fluorescence intensity with the europium(III) complex was increased about 178-fold in the presence of sodium acetate (NaAc) and about 126-fold in the presence of sodium phosphate (Na₃PO₄) solution. After adding the organic solvent dimethylsulfoxide (DMSO) to the above system, which leads to Eu³⁺ the fluorescence was further enhanced about 12-fold. Spectrofluorimetric determination of trace amounts of Eu³⁺ based on the phenomenon was performed. The excitation and emission wavelength is 365 nm and 615 nm, respectively. Under optimum conditions, the fluorescence intensities vary linearly with the concentration of Eu³⁺ in the range of 4.9 × 10⁻¹²–3.2 × 10⁻⁶ mol · L⁻¹ with a detection limit of 4.5 × 10⁻¹² mol · L⁻¹ (for the TDATA-NaAc-DMSO system) or 6.2 × 10⁻¹¹–8.6 × 10⁻⁶ mol · L⁻¹ with a detection limit of 6.0 × 10⁻¹¹ mol · L⁻¹ (for the TDATA-Na₃PO₄-DMSO system). Interferences of some rare earth metals and other inorganic ions are described. The method is a selective, sensitive, rapid and simple analytical procedure for the determination of europium(III) in a high purity yttrium oxide and synthetic sample. The mechanism for the fluorescence enhancement is also discussed.     

Preconcentration and Voltammetric Determination of the Antihypertensive Doxazosin on a C8 Modified Carbon Paste Electrode

 An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based on adsorptive stripping (AdS) of doxazosin at the C₈-modified carbon paste electrode (C₈-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. By means of AdS-DPV and C₈-MCPE, doxazosin can be determined over the 1.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ range with a variation coefficient of 2.2% (2.0 × 10⁻⁸ mol L⁻¹) and a limit of detection of 7.4 ×10⁻¹⁰ mol L⁻¹. If AdS-SWV is used, a linear range from 1.0 × 10⁻⁹ to 4.0 × 10⁻⁸ mol L⁻¹ is obtained, the variation coefficient being 2.8% (2.0 × 10⁻⁸ mol L⁻¹, and the limit of detection reached 7.7 × 10⁻¹⁰ mol L⁻¹. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations. Received March 13, 1999. Revision December 23, 1999.     

Spectrophotometric determination of total protein in serum using a novel near-infrared cyanine dye, 5,5′-dicarboxy-1,1′-disulfobutyl-3,3,3′,3′-tetramethylindotricarbocyanine

The application of near-infrared (NIR) dyes (λ _em > 750 nm) to the analysis of biological samples shows much promise, because the long emission wavelengths of such dyes allow interferences from biomolecule matrices to be minimized. In this paper, a novel NIR dye, 5,5′-dicarboxy-1,1′-disulfobutyl-3,3,3′,3′-tetramethylindotricarbocyanine (DCDSTCY) has been developed for the spectrophotometric determination of total protein in serum. Under acidic conditions, the binding of DCDSTCY to proteins caused a new peak at 878 nm, the height of which was proportional to the concentration of protein. The linear range of the method was found to be 0.04–0.5 μg mL⁻¹ for bovine serum albumin (BSA) and human serum albumin (HSA), and detection limits of 5 ng mL⁻¹ were obtained for these substances. The maximum binding number of BSA with DCDSTCY was measured to be 133. The method proposed here has been applied to the quantitation of total protein in serum, and recoveries of 96.6–104% were achieved. Figure Near-infrared probe for protein determination     

Fluorescence enhancement assay for trace iron(II) using Pyr-tempo as a spin label fluorescent probe

Pyrene-tetramethylpiperidinyl (Pyr-Tempo) as a spin label fluorescent probe for iron(II) was synthesized. It exhibited weak fluorescence (λ_exc/λ_em = 346/399 nm) in aqueous solution due to an intramolecular quenching pathway. A method for determination of iron(II) was proposed based on the fluorescence enhancement of the probe in the presence of iron(II) in acidic medium. Under optimum conditions, the fluorescence enhancement of Pyr-Tempo is linearly proportional to the iron(II) concentration range of 6.0 × 10⁻⁸ to 9.6 × 10⁻⁶ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁹ mol L⁻¹. The relative standard deviation (RSD) of six replicate measurements is 1.95% for 3.0 × 10⁻⁷ mol L⁻¹ iron(II). The developed spin label fluorescence probe is found to be rapidly and sensitively responsive to iron(II) with high selectivity compared to existing fluorescence methods. The proposed method was successfully applied to iron(II) detection in five real samples with satisfactory results obtained by manual UV/Vis spectrophotometry (standard method) with 1,10-phenanthroline.     

Flow-injection analysis for the determination of total inorganic carbon and total organic carbon in water using the H2O2–luminol–uranine chemiluminescent reaction

In the presence of carbonate and uranine, the chemiluminescent intensity from the reaction of luminol with hydrogen peroxide was dramatically enhanced in a basic medium. Based on this fact and coupled with the technique of flow-injection analysis, a highly sensitive method was developed for the determination of carbonate with a wide linear range. The method provided the determination of carbonate with a wide linear range of 1.0 × 10⁻¹⁰–5.0 × 10⁻⁶ mol L⁻¹ and a low detection limit (S/N = 3) of carbonate of 1.2 × 10⁻¹¹ mol L⁻¹. The average relative standard deviation for 1.0 × 10⁻⁹–9.0 × 10⁻⁷ mol L⁻¹ of carbonate was 3.7% (n = 11). Combined with the wet oxidation of potassium persulfate, the method was applied to the simultaneous determination of total inorganic carbon (TIC) and total organic carbon (TOC) in water. The linear ranges for TIC and TOC were 1.2 × 10⁻⁶–6.0 × 10⁻² mg L⁻¹ and 0.08–30 mg L⁻¹ carbon, respectively. Recoveries of 97.4–106.4% for TIC and 96.0–98.5% for TOC were obtained by adding 5 or 50 mg L⁻¹ of carbon to the water samples. The relative standard deviations (RSDs) were 2.6–4.8% for TIC and 4.6–6.6% for TOC (n = 5). The mechanism of the chemiluminescent reaction was also explored and a reasonable explanation about chemical energy transfer from luminol to uranine was proposed. Figure Chemiluminescence profiles in batch system. 1, Injection of 100 μL of K₂CO₃ into 1.0 mL luminol-1.0 mL H₂O₂ solution; 2-3 and 4-5, Injection in sequence of 100 μL of K₂CO₃ and 100 μL of uranine into 1.0 ml luminol-1.0 mL H₂O₂ solution; C_luminol = 1.0 × 10⁻⁷ mol/L, C_H2O2 = 1.0 × 10⁻⁵ mol/L, C_uranine = 1.0 × 10⁻⁵ mol/L, C_K2CO3 = 1.0 × 10⁻⁷ mol/L except for 4-5 where C_K2CO3 = 1.0 × 10⁻⁴ mol/L     

<Emphasis Type="Italic">S,S,S</Emphasis>-Tris(2-ethylhexyl) phosphorotrithioate as an effective solvent mediator for a mexiletine-sensitive membrane electrode

S,S,S-Tris(2-ethylhexyl) phosphorotrithioate proved to be an effective solvent mediator for constructing a mexiletine-sensitive membrane electrode in combination with an ion-exchanger, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate. Among a series of phosphorus compounds containing phosphoryl (P=O) groups, this solvent mediator showed the highest sensitivity to mexiletine in phosphate-buffered physiological saline containing 0.15 mol L⁻¹ NaCl and 0.01 mol L⁻¹ NaH₂PO₄/Na₂HPO₄ (pH 7.4), giving a detection limit of 2 × 10⁻⁶ mol L⁻¹ with a slope of 58.8 mV decade⁻¹. This is the best reported detection limit of any mexiletine-sensitive electrode developed to date. Owing to its high selectivity toward inorganic cations, the electrode was used to determine the level of mexiletine in saliva, the monitoring of which is quite effective for controlling the dose of this drug noninvasively. The mexiletine concentrations determined with the mexiletine-sensitive electrode compared favorably with those determined by high-performance liquid chromatography.     

Simultaneous voltammetric measurement of ascorbic acid and dopamine on poly(caffeic acid)-modified glassy carbon electrode

A poly(caffeic acid) thin film was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The poly(caffeic acid)-modified electrode was used for the determination of ascorbic acid (AA), dopamine (DA), and their mixture by cyclic voltammetry. This modified electrode exhibited a potent and persistent electron-mediating behavior followed by well-separated oxidation peaks toward AA and DA at a scan rate of 10 mV s⁻¹ with a potential difference of 135 mV, which was large enough to determine AA and DA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 × 10⁻⁵−1.2 × 10⁻³ and 1.0 × 10⁻⁶−4.0 × 10⁻⁵ mol L⁻¹ in 0.15 mol L⁻¹ phosphate buffer (pH 6.64). The detection limits for AA and DA were 9.0 × 10⁻⁶ and 4.0 × 10⁻⁷ mol L⁻¹, respectively. The modified electrode shows good sensitivity, selectivity, and stability and has been applied to the determination of DA and AA in real samples with satisfactory results.     

Synthesis and characterization of poly(styrene/α-t-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers with number-average molecular weight Mˉ _n=950 (VB-polyGL950) and Mˉ _n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator (K₂S₂O₈) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10⁻³ to 1.64 × 10⁻² mol/mol and from 3.46 × 10⁻⁴ to 3.47 × 10⁻³ mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters (Dˉ _n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range 1.007≤Dˉ _w/Dˉ _n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene. Received: 26 September 2000/Accepted: 19 February 2001     

Acetylcholinesterase-based biosensors for quantification of carbofuran, carbaryl, methylparaoxon, and dichlorvos in 5% acetonitrile

Amperometric acetylcholinesterase biosensors have been developed for quantification of the pesticides carbofuran, carbaryl, methylparaoxon, and dichlorvos in phosphate buffer containing 5% acetonitrile. Three different biosensors were built using three different acetylcholinesterase (AChE) enzymes—AChE from electric eel, and genetically engineered (B394) and wild-type (B1) AChE from Drosophila melanogaster. Enzymes were immobilized on cobalt(II) phthalocyanine-modified electrodes by entrapment in a photocrosslinkable polymer (PVA-AWP). Each biosensor was tested against the four pesticides. Good operational stability, immobilisation reproducibility, and storage stability were obtained for each biosensor. The best detection limits were obtained with the B394 enzyme for dichlorvos and methylparaoxon (9.6 × 10⁻¹¹ and 2.7 × 10⁻⁹ mol L⁻¹, respectively), the B1 enzyme for carbofuran (4.5 × 10⁻⁹ mol L⁻¹), and both the B1 enzyme and the AChE from electric eel for carbaryl (1.6 × 10⁻⁷ mol L⁻¹). Finally, the biosensors were used for the direct detection of the pesticides in spiked apple samples.     

Tripodal chelating ligand-based sensor for selective determination of Zn(II) in biological and environmental samples

Potassium hydrotris(N-tert-butyl-2-thioimidazolyl)borate [KTt^t-Bu] and potassium hydrotris(3-tert-butyl-5-isopropyl-l-pyrazolyl)borate [KTp^t-Bu,i-Pr] have been synthesized and evaluated as ionophores for preparation of a poly(vinyl chloride) (PVC) membrane sensor for Zn(II) ions. The effect of different plasticizers, viz. benzyl acetate (BA), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tributyl phosphate (TBP), and o-nitrophenyl octyl ether (o-NPOE), and the anion excluders sodium tetraphenylborate (NaTPB), potassium tetrakis(p-chlorophenyl)borate (KTpClPB), and oleic acid (OA) were studied to improve the performance of the membrane sensor. The best performance was obtained from a sensor with a of [KTt^t-Bu] membrane of composition (mg): [KTt^t-Bu] (15), PVC (150), DBP (275), and NaTPB (4). This sensor had a Nernstian response (slope, 29.4 ± 0.2 mV decade of activity) for Zn²⁺ ions over a wide concentration range (1.4 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹) with a limit of detection of 9.5 × 10⁻⁸ mol L⁻¹. It had a relatively fast response time (12 s) and could be used for 3 months without substantial change of the potential. The membrane sensor had very good selectivity for Zn²⁺ ions over a wide variety of other cations and could be used in a working pH range of 3.5–7.8. The sensor was also found to work satisfactorily in partially non-aqueous media and could be successfully used for estimation of zinc at trace levels in biological and environmental samples. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A DNA electrochemical sensor prepared by electrodepositing zirconia on composite films of single-walled carbon nanotubes and poly(2,6-pyridinedicarboxylic acid), and its application to detection of the PAT gene fragment

Carboxyl group-functionalized single-walled carbon nanotubes (SWNTs) and 2,6-pyridinedicarboxylic acid (PDC) were electropolymerized by cyclic voltammetry on a glassy-carbon electrode (GCE) surface to form composite films (SWNTs/PDC). Zirconia was then electrodeposited on the SWNTs/PDC/GCE from an aqueous electrolyte containing ZrOCl₂ and KCl by cycling the potential between −1.1 V and +0.7 V at a scan rate of 20 mV s⁻¹. DNA probes with a phosphate group at the 5′ end were easily immobilized on the zirconia thin films, because of the strong affinity between zirconia and phosphate groups. The sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS was used for label-free detection of the target DNA by measuring the increase of the electron transfer resistance (R _et) of the electrode surface after the hybridization of the probe DNA with the target DNA. The PAT gene fragment and polymerase chain reaction (PCR) amplification of the NOS gene from transgenically modified beans were satisfactorily detected by use of this DNA electrochemical sensor. The dynamic range of detection of the sensor for the PAT gene fragment was from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁶ mol L⁻¹ and the detection limit was 1.38 × 10⁻¹² mol L⁻¹.     

FAD-modified SiO2/ZrO2/C ceramic electrode for electrocatalytic reduction of bromate and iodate

SiO₂/ZrO₂/C carbon ceramic material with composition (in wt%) SiO₂ = 50, ZrO₂ = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image showed that ZrO₂ and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks of the material was 18 S cm⁻¹, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide (FAD) prepared by immersing the solid SiO₂/ZrO₂/C, molded as a pressed disk, inside a FAD solution (1.0 × 10⁻³ mol L⁻¹) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl) were: BrO₃ ⁻, lrr = 4.98 × 10⁻⁵–1.23 × 10⁻³ mol L⁻¹ and dl = 2.33 μmol L⁻¹; IO₃ ⁻, lrr = 4.98 × 10⁻⁵ up to 2.42 × 10⁻³ and dl = 1.46 μmol L⁻¹ for iodate.     

Kinetic Studies on the Complexation of Chromium(III) with some Amino Acids in Aqueous Acidic Medium

Summary.  The kinetics of the formation of the 1:3 complex of chromium(III) with L-glutamic acid and DL-lysine were studied spectrophotometrically at and 550 nm. The reaction was found to be first order in both reactants. Increasing the hydrogen ion concentration from 3.2×10⁻⁵ to 1.0×10⁻³ molċdm⁻³ retarded the reaction rate which is of the form . Values of 28.8 and 63.6 kJċmol⁻¹ were obtained for the energy of activation and −184 and −116 Jċ K⁻¹ċmol⁻¹ for the entropy of activation for L-glutamic acid and DL-lysine. The logarithms of the formation constants of the two complexes were found to be 5.9 and 5.1. Received January 7, 2000. Accepted (revised) March 8, 2000     

Determination of rutin using a CeO2 nanoparticle-modified electrode

CeO₂ nanoparticles approximately 12 nm in size were synthesized and subsequently characterized by XRD, TEM and UV-vis spectroscopy. Then, a gold electrode modified with CeO₂ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode demonstrated strong catalytic effects with high stability towards electrochemical oxidation of rutin. The anodic peak currents (measured by differential pulse voltammetry) increased linearly with the concentration of rutin in the range of 5.0 × 10⁻⁷–5.0 × 10⁻⁴ mol · L⁻¹. The detection limit (S/N = 3) was 2.0 × 10⁻⁷ mol · L⁻¹. The relative standard deviation (RSD) of 8 successive scans was 3.7% for 5.0 × 10⁻⁶ mol · L⁻¹ rutin. The method showed excellent sensitivity and stability, and the determination of rutin in tablets was satisfactory.     

Sorption-Catalytic Determination of Imazapyr on a Copper-Containing Sorbent

 Sorption of copper on filter-paper with chemically attached hexamethylenediamino-groups (HMDA-filter) allows to obtain the sorbent (Cu/HMDA-filter) stable in respect to desorption of copper. A nitrogen-containing herbicide imazapyr (imaz) is retained on Cu/HMDA-filters at pH 5.5–7.0 forming a relatively stable complex. Imazapyr is determined directly on the sorbent by its activating effect in the oxidation of hydroquinone with H₂O₂ catalyzed by Cu(II) with the formation of a product absorbing at 490 nm. The copper ions serve both to preconcentrate imazapyr and to catalyze the indicator reaction. The use of 1-μL sample aliquots pipetted onto the Cu/HMDA-filters allows to determine 1 × 10⁻³–0.03 μmol of imazapyr, whereas preconcentration of the analyte by pumping of its solution through the same sorbent expands the linear range to 1 × 10⁻⁴–1 × 10⁻¹ μmol of imazapyr. When the indicator reaction is carried out in solution, the range of activating action of imazapyr is narrower (0.06–0.1 μmol a for a solution volume of 10 mL). The determination is selective: 5–100-fold amounts of amines, aminoacids, carboxylic acid derivatives and other model compounds do not interfere. Soil extracts and carrot juice samples spiked with imazapyr have been analyzed. Received January 10, 2000. Revision July 28, 2000.     

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (W_m), hexagonal (H₁), bicontinuous cubic (V₁), and lamellar (L_α) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, a _s, in the H₁ phase is almost constant, 0.5 nm², and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10⁻⁵ mol/l that is much lower than that of sodium dodecanoate, 2 × 10⁻² mol/l, or SDS, 8 × 10⁻³ mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. Received: 15 June 2000/Accepted: 27 July 2000     

Ultra-trace level determination of nitrite in human saliva by spectrofluorimetry using 1,3,5,7-tetramethyl-8-(3,4-diaminophenyl)-difluoroboradiaza-s-indacene

A rapid, highly sensitive and selective fluorogenic method for the determination of traces of nitrite is described. It is based on the reaction of weakly fluorescent 1,3,5,7-tetramethyl-8-(3,4-diaminophenyl)-difluoroboradiaza-s-indacence (DAMBO) and nitrite in acidic aqueous solution to give 1,3,5,7-tetramethyl-8-(5-benzotriazolyl)-difluoroboradiaza-s-indacene (DAMBO-T), which is highly fluorescent. The optimum reaction conditions and other analytical parameters are investigated to enhance the sensitivity of the method. The fluorescence enhancement at 507 nm is linearly related to the concentration of nitrite in the range of 6.0 × 10⁻⁹–5.0 × 10⁻⁷ mol L⁻¹ with a correlation coefficient of R = 0.9995 (n = 10) and a detection limit of 1.0 × 10⁻¹⁰ mol L⁻¹. The R.S.D. is 1.12% (n = 10). The method is applied to the determination of nitrite in human saliva samples with the recoveries of 96. 24–105.30%. Correspondence: Ke-Jing Huang, Department of Chemistry, Wuhan University, Wuhan 430072, P.R. China     

Formulas and numerical table for the radial part of overlap integrals with the same screening parameters of Slater-type orbitals

 The numerical properties of the radial part of overlap integrals with the same screening parameters in the form of polynomials in p = ξR over Slater-type orbitals have been studied and obtained by using three different methods. For that purpose, the characteristics of auxiliary functions were used first, then Fourier transform convolution theorem, and recurrence relations for the basic coefficients of A ^s _{n l λ, n ′ l ′λ} were used. The calculations of the radial part of overlap integrals with the same screening parameters were made in the range 1 ≤ n ≤ 75, 1 ≤ n′ ≤ 75, and 10⁻⁶ ≤ p. Received: 18 January 2001 / Accepted: 5 April 2001 / Published online: 27 June 2001     

A Fiber Optode for p-Nitrophenol Based on Covalently Bound 9-Allylaminoacridine

 Using 9-allylaminoacridine synthesized in this laboratory as the fluorescent agent an fiber optode for p-nitrophenol (p-Np) has been prepared. 9-Allylaminoacridine has a polymerizable olefin unit and can be copolymerized with hydrophilic monomer 2-hydroxypropyl methacrylate (HPMA) under UV irradiation. On silanized activated glass surface a 9-allylaminoacridine containing HPMA membrane has been covalently bound forming a stable optode membrane free of leaching problem. The analytical performance characteristics including reversibility, reproducibility, short-term stability and interference have been evaluated. The optode has relatively long lifetime with the spectral response characteristics not changing after one month use. The plot of log(I ₀/I − 1) versus logarithm of the p-NP solution concentration can piecewise be fitted with the straight line of the form of Stern-Volmer equation, with a detection limit of 9.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation obtained from eight separate determinations for two p-NP concentrations, 1.0 × 10⁻⁵ and 4.0 × 10⁻⁴ mol L⁻¹, are 2.36% and 1.34%, respectively. p-Np can be determined in water samples with satisfactory recoveries. Received April 13, 2000. Revision September 28, 2000.