Analytical Letters

Sun, Wenliang; Kong, Jilie; Deng, Jiaqi

doi: 10.1080/00032719608002781pmid: N/A

Abstract A chemically modified electrode (CME) exhibiting electrocatalytic response toward dioxygen was constructed by adsorbing the mediator riboflavin onto spectroscopic graphite. The electron transfer between the riboflavin functionality and the graphite was fast. The surface apparent coverage was at most 9.6 × 10−10 mol cm−2. The modified electrode permitted the dioxygen electroreduction to take place at the reduction potential of the mediator molecule. Dioxygen accepted two electrons from a reduced mediator to form hydrogen peroxide. Characterisation of the performance of the CME was carried out. After 30 min of continuous electrochemical cycling of pH 6.8, 30% of the original coverage remained for the CME. The effect of the solution pH and temperature on the electrocatalytic activity of the CME for oxygen reduction was also investigated.

Zhilong, Gong; Zhujun, Zhang

doi: 10.1080/00032719608002782pmid: N/A

Abstract A flow-through optosensor for phenylalanine and tyrosine is described in this paper. The sensor is developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The analytical performance characteristics of the proposed sensor for analysis of very low levels of phenylalanine and tyrosine were as follows: the detection limits for phenylalanine and tyrosine were 0.20 μg ml−1 and 8.9 ng ml−1, respectively. The observed relative standard deviations were 1.03% for 50 μg ml−1 of phenylalanine (n = 7) and 3.6% for 0.1 μg ml−1 of tyrosine (n = 7), respectively.

Nakamura, Junko; Igarashi, Shukuro

doi: 10.1080/00032719608002783pmid: N/A

Abstract When cationic 5, 10, 15, 20-tetrakis(4-N-trimethylaminophenyl)porphine (TTMAPP) and anionic 5, 10, 15, 20-tetrakis(4-sulfophenyl)porphine (TSPP) were mixed in aqueous solution, these compounds were rapidly aggregated due mainly to their electrostatic interaction. The fluorescences of both porphyrins were quenched. However, if small amounts of a bulky molecule such as a polymer electrolyte coexisted in this reaction system, the aggregation of TTMAPP and TSPP was inhibited and their fluorescences reappeared. Based on these findings, a new highly sensitive spectrofluorometric determination of nucleic acids (DNA, RNA) was developed. Each calibration curve was linear in the concentration range of 0.03–0.4 μg/ml (DNA) and 0–05–0.6 μg/ml (RNA). Further, the detection limit (S/N = 3) was 0.016 μg/ml for DNA and for RNA, 0.020 μg/ml. The relative standard deviations were DNA: 1.70% and RNA: 1.83% (5 determinations). When the proposed method was applied to the determination of DNA originating from a bacteriophage, the results were satisfactory.

He, Ya-nan; Chen, Hong-yuan

doi: 10.1080/00032719608002784pmid: N/A

Abstract An improved ELISA for the determination of Thyroglobulin(TG) in human serum with differential pulse voltammetry(DPV) has been developed. The enzymatic product 2,2′-diaminoazobenzene(DAA), produced from horseradish peroxidase(HRP) catalyzing the oxidation of H2O2 with orthophenylene diamine(OPD), yielded a sensitive differential pulse voltammetric response at - 0.18V(Vs Ag/AgCL) in pH2.0 0.2mol/L phosphate-0.1mol/L citrate buffer at a gold electrode. The small three-electrode system was directly inserted in the well of an ELISA plate for detection. The detection limit for TG was 3.8 ng/mL, which was about four times lower than that obtained by measuring the absorbance of DAA.

Starczewska, B.; Karpiñska, J.

doi: 10.1080/00032719608002785pmid: N/A

Abstract Chlorpromazine reacts with Eriochrome Cyanine R forming an ion association compound, insoluble in water but fairly soluble in buthyl alcohol. In this work the optimal reaction and extraction conditions were established. The spectroscopic studies of the formed compound were performed by UV, VIS, IR, 1H NMR and 13C NMR spectrometry. The new extractive-spectrophotometric method for chlorpromazine hydrochloride determination is proposed. Using this method it is possible to determine chlorpromazine hydrochloride concentration in the range 7.0–70 μg/ml. This method was verified against the method of Blazek and applied to determination of chlorpromazine hydrochloride in pharmaceuticals.

El-Koussi, Nawal A.; El-Maaboud, Abd; Mohamed, I.; Mohamed, Horria A.; Fargaly, Zeinab S.

doi: 10.1080/00032719608002786pmid: N/A

Abstract A colorimetric method for the determination of certain 8-hydroxyquinolines has been developed. The method is based on the coupling of 8-quinolinols with diazotriazole carboxylic acid in the presence of sodium carbonate (0.5% w/v) at ambient temperature (around 30°C). The resulting azo dyes are stable and give intense absorption in the range of 486–540 nm. Beer's law is valid in the concentration ranges of 1 – 8, 2.5 – 17.5, 5 – 35, 2 – 20, and 2 – 20 mcg/ml for 8-hydroxyquinoline (HQ), 5,7-diiodo-8-hydroxyquinoline (DIQ), 5,7-dibromo-8-hydroxyquinoline (DBQ), 5-chloro-7-iodo-8-hydroxyquinoline (CIQ) and 8-hydroxy-7-iodo-5-quinoline sulfonic acid (SIQ), respectively. The proposed method has been successfully applied for the determination of the studied compounds in pure form and in commercial formulations. The obtained results are in good agreement with those obtained from reported methods.

Hayashi, Kenji; Okugawa, Takuji; Kozuka, Yoshiaki; Sasaki, Satoshi; Ikebukuro, Kazunori; Karube, Isao

doi: 10.1080/00032719608002787pmid: N/A

Abstract A dual channel chemiluminescence FIA system for the rapid measurement of the fish freshness index KI where [IMP], [HxR] and [Hx] are, respectively, the inosine 5′-monophosphate, inosine and hypoxanthine contents of fish meat was developed. The system consisted of a pair of chemiluminescence FIAs (CL-FIA); one for the measurement of [IMP] + [HxR] + [Hx], and the other for [HxR] + [Hx]. IMP, HxR or Hx were measured using a reactor comprising immobilized alkaline phosphatase, purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD). The calibration curves for IMP, HxR or Hx were linear from 0.06 μM to 100 μM for a sample volume of 20 μl. The time for a single KI measurement was less than 1 min. This fish freshness FIA system is rapid, convenient and applicable for fish freshness measurements in real fish samples.

Lee, Y. I.; Indurthy, S.; Smith, M. V.; Sneddon, J.

doi: 10.1080/00032719608002788pmid: N/A

Abstract An evaluation of the parameters which effect the collection efficiency of metals in an aerosol via an improved impaction-graphite furnace atomic absorption spectrometric system showed that an optimum could be obtained at a jet diameter of 1.50 mm, and a jet exit -to-impaction surface distance of 3 mm. Low flow rates gave poor precision at low concentrations except when a large jet diameter was used. Preliminary studies by electron microscopy of particle size collected showed that the higher the flow rate and smaller the jet diameter, leads to a more dense concentration of particle sizes. 1 Presented, in part, at Pittcon '96, in Chicago, Illinois on March 3–8 th, 1996. 2 Permanent address, Department of Chemistry, Konyang University, Nonsan, 320–800, Korea.

Salinas, F.; Espinosa-Mansilla, A.; Zamoro, A.; de la Peña, A. Muñoz

doi: 10.1080/00032719608002789pmid: N/A

Abstract Difference spectrophotometry, based on the utilization of difference absorption spectra corresponding to the same compound obtained at two different pH's, has been investigated for the analysis of binary mixtures. The method has been applied to the simultaneous determination of bromophenol blue and methyl orange, and two different binary mixtures of sulfonamides i.e., sulfamethoxazole (SX)-sulfaquinoxaline (SQ) and sulfathiazole (ST)-sulfamethoxazole (SX). In addition, the determination of SX, SQ and ST in the presence of sulfanilamide (SB) has been performed. For the determination of ST and SX, first-derivative difference spectrophotometry was applied. A comparative study of the advantages of the pH-induced difference method with respect to first-derivative spectrophotometry is presented.

Uchiyama, Katsumi; Xhing-Zhen, Wu; Hobo, Toshiyuki; Sato, Jyunya; Imaeda, Kazuo; Ohsawa, Keiko

doi: 10.1080/00032719608002790pmid: N/A

Abstract To obtain surface layer thickness easily, a simple pseudo pulse excited photoacoustic spectrometric method was proposed. An argon ion laser was chopped mechanically to generate a pseudo pulse (pulse width; 6.6 ms, duty 1.67%), which was then led to a sample enclosed in photoacoustic cell. Two layer samples made of polymethyl methacrylate (PMMA) were used as model samples. The photoacoustic signal waveform observed showed a maximum from the negative edge of the pseudo pulse of the laser. The delay of the signal increased concomitant with the sample surface thickness. The delay time of the signal was calculated by a cross-correlation method. A linear relationship was obtained between the delay time of the photoacoustic signal from the input pseudo pulse and the surface transparent layer thickness in the range of 0–90 mm. The regression line between the film thickness x (cm) and the delay time was expressed with the thermal diffusivity of the film k, as follows; Δτ (s) = 1.16 × 10−1 κ−½ x + 0.006. Using this result, the method proposed was successfully applied to the measurement of the thickness for laminated polyethylene film on papers. The method proposed is simple and easy to perform without any modification of usual photoacoustic instrumentation.