Screen-Printed Carbon Electrodes Modified with Cobalt Phthalocyanine for Selective Sulfur Detection in Cosmetic Products

Cobalt phthalocyanine (CoPc) films were deposited on the surface of a screen-printed carbon electrode using a simple drop coating method. The cyclic voltammogram of the resulting CoPc modified screen-printed electrode (CoPc/SPE) prepared under optimum conditions shows a well-behaved redox couple due to the (CoI/CoII) system. The CoPc/SPE surface demonstrates excellent electrochemical activity towards the oxidation of sulfur in a 0.01 mol·L−1 NaOH. A linear calibration curve with the detection limit (DL, S/N = 3) of 0.325 mg·L−1 was achieved by CoPc/SPE coupled with flow injection analysis of the sulfur concentration ranging from 4 to 1120 mg·L−1. The precision of the system response was evaluated (3.60% and 3.52% RSD for 12 repeated injections), in the range of 64 and 480 mg·L−1 sulfur. The applicability of the method was successfully demonstrated in a real sample analysis of sulfur in anti-acne creams, and good recovery was obtained. The CoPc/SPE displayed several advantages in sulfur determination including easy fabrication, high stability, and low cost

Preconcentration of organic compounds at a diphenyl ether graphite paste electrode and determination of vanillin by adsorptive-extractive stripping voltammetry

A carbon paste electrode containing diphenyl ether (dp-CPE) as a paste liquid was prepared and the preconcentration of various electroactive aromatic compounds at this electrode was studied and compared with the commonly used carbon paste electrode containing Nujol as paste liquid (nu-CPE). All compounds tested showed a much greater tendency for preconcentration at the dp-CPE than the nu-CPE, and many compounds proved to be readily preconcentrated exclusively at the dp-CPE, thus allowing their sensitive determination by adsorptive-extractive stripping voltammetry (typical concentration range 0.6-4 μmol dm-3). The selectivity of these determinations was enhanced by applying the 'medium-exchange' procedure. Based on these findings, a simple procedure was developed for the electrochemical determination of vanillin in food samples

Flow injection amperometric determination of thiocyanate and selenocyanate at a cobalt phthalocyanine modified carbon paste electrode

Inorganic anions containing sulfur (SO32-, S 2O32-, and SCN-), selenium (SeO 32- and SeCN-), nitrogen (NO2 -), and arsenic (AsO2-) oxidize readily at a carbon paste electrode (CPE) modified with cobalt phthalocyanine (CoPC-CPE). All of these anions are virtually non-electroactive (with the exception of SeCN-) towards the CPE. The CoPC-CPE was used as an amperometric flow sensor for the direct determination of SCN- and SeCN-. The application of a potential alternating between an anodic detection potential and a cathodic reactivation potential provided a more stable detector response for both anions. Potentials alternating in the ranges +0.85 to -0.30 V and +0.60 to -0.30 V were used for SCN- and SeCN-, respectively. The linear response ranges and the detection limits were 2-50 μmol l -1 and 0.8 μmol l-1 (at pH 2.0), respectively, for SCN-, and 0.2-20 μmol l-1 and 0.1 μmol l -1 (at pH 7.0), respectively, for SeCN-. Thiocyanate can be readily determined in saliva samples following 100-fold dilution with the supporting electrolyte solution. The results are comparable to those obtained using a standard spectrophotometric method

Flow injection-pulse amperometric detection of ephedrine at a cobalt phthalocyanine modified carbon paste electrode

Direct detection of ephedrines and other underivatized amino compounds (amines, alicyclic amines, alkanolamines, and amino acids) can be carried out via electrocatalytic oxidation at a carbon paste electrode (CPE) modified with cobalt phthalocyanine (CoPC) in alkaline solution (0.10 mol L-1 NaOH). Most of the amino compounds tested could be determined using the CoPC/CPE in an amperometric flow detector. The analytical signal of ephedrine was stabilised by alternating the potential between an anodic detection potential of +0.30 V (+0.45 V for other amino compounds) applied for 220 ms and a cathodic reactivation potential of -0.30 V applied for 100 ms (potentials versus SCE). The linear response range for ephedrine was within 1-100 μmol L-1 and the detection limit was 0.8 μmol L-1 with 100 μL sample loop and a typical sampling raw of 60 h-1. The signal (oxidation peak current) reproducibility was 2-3%. The method was applied to the determination of ephedrine in pharmaceutical formulations with results comparable to those obtained with a standard spectrophotometric method

Doping control analysis: the 6th World Championships of Athletics, Athens, Greece

The first official report on the organization, analytical methodologies, and the results of the doping control analysis performed by the International Olympic Committee (IOC)-accredited Doping Control Laboratory of Athens, Greece, during the 6th World Championships of Athletics, held in Athens on 1-10 August 1997, is presented. The significance of the various analytical parameters of the doping control is shown. The results include 20 positive cases, of which two were detected in screening procedures and confirmed exclusively by high resolution mass spectrometry. The screening results and analytical data on the excretion of a new black-market doping agent, phenylpiracetam or carfedon, which was unknown in the literature, are also presented. Copyright (C) 1999 Elsevier Science B.V