摘要:

AbstractThe concentrations of the heavy metals (Cd, Pb, Cu, and Zn) have been determined in oak growth rings from the polluted region of Königstein, Germany, by differential pulse anodic stripping voltammetry and compared to those in soil. The radial distribution was found to be the same for all four metals studied and features a distinct increase in the recent growth rings and a marginal increase in the transition zone between sapwood and heartwood. The toxic metals cadmium and lead are preferentially bound to lower parts of the tree, whereas for essential metals copper and zinc, monotonous axial distribution has been found in the range 0–5 m. This points to different degrees of mobility of heavy metal complexes in wood materi

ISSN:1040-0397    

DOI:10.1002/elan.1140030413

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractLichens have long been used as biomonitors of environmental pollution. We therefore investigated the application of lichen‐modified carbon paste electrodes (CPEs) for the determination of lead(II) and copper(II) using differential pulse anodic stripping voltammetry. These electrochemical biosensors incorporate the biological selectivity of lichen species such asCladonia portentosaandLobaria pulmonaria, and the genusRoccella, with the sensitivity of electrochemical detection. As such, they may offer new reactivity patterns that could be exploited in the determination of trace metal ions in environmental samples and in speciation studies. The voltammetric responses were evaluated with respect to pH of accumulation (carried out under open circuit conditions), pH of electrolyte, solution, metal ion concentration, percentage lichen loading in the carbon paste, interferences, and surface renewa

ISSN:1040-0397    

DOI:10.1002/elan.1140030414

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractWe compared hanging mercury drop electrodes (HMDEs) and carbon paste electrodes (CPEs) for the determination by adsorptive stripping voltammetry (AdSV) of the antibiotic ciprofloxacin in urine. The antibiotic compound could be preconcentrated at both electrode surfaces, with carbon paste electrode yielding a better performance. These electrodes could be used to determine between 6 × 10−7and 4 × 10−6M ciprofloxacin in urine. A cleanup procedure (with 81% recovery), utilizing a C18Sep Pak cartridge, was required to separate ciprofloxacin from the biological matrix prior to adsorptive stripping analysis. The method was applied to the determination of ciprofloxacin in spiked urine samples with a relative standard deviation of

ISSN:1040-0397    

DOI:10.1002/elan.1140030415

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractSimple ion‐selective electrodes of the coated wire type were prepared using an ordinary aluminum wire conductor, coating the central wire with the membrane formed by plasticized poly vinyl chloride. These simple and inexpensive electrodes can be used advantageously as sensors in ion pair formation‐based titrations of surfactants of various types. Cationic surfactants are titrated using sodium tetraphenylborate titrant yielding titration curves with sharp potential breaks. For the determination of nonionic surfactants containing poly oxyalkylene chains, the method used was based on the precipitation of ternary compounds with sodium tetraphenylborate in the presence of bivalent metal ion with an ionic radius higher than 100 pm. Also ampholytic surfactants can be titrated directly with tetraphenylborate in acidic solutions, in which they are cationic; but for the determination of some of them, back‐titration is more convenient. Anionic surfactants are titrated using lipophilic cationic titrants such as quaternary ammonium or pyridinium salts. Some mixed systems can also be analyzed. Several examples are

ISSN:1040-0397    

DOI:10.1002/elan.1140030416

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe implementation of a pH‐ISFET (ion‐selective field effect transistor) planar chip in a flow‐injection system by means of a specially designed flow cell and the application of the sensor to the analysis of volatile compounds is described. Ammonia and sulfur dioxide are determined by exploiting the advantages of the flow techniques combined with continuous gas diffusion. Initial species are converted to gaseous compounds, which diffuse through a microporous hydrophobic membrane into an ammonium chloride or hydrogen sulfite recipient stream, producing a pH variation that is monitored by the semiconductor detector. The linear working range extends from 1 × 10−2to 1 × 10−4M for the ammonium system and from 4 × 10−3to 7 × 10−5for the sulfur dioxide system, with relative standard deviation of about 1 and 0

ISSN:1040-0397    

DOI:10.1002/elan.1140030417

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe construction of a pH‐ISFET (ion‐selective field effect transistor) fabricated with standard negative‐channel MOS technology, compatible with complementary MOS technology, and using silicon nitride as a pH‐sensitive material, is described. Its main analytical characteristics are discussed. The resulting calibration plot is linear over the pH range from 2 to 11; with a slope of 54 mV per

ISSN:1040-0397    

DOI:10.1002/elan.1140030418

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA theoretical kinetic model of a pH‐based enzymatic sensor has been developed. The transport phenomena of substrates and products of enzymatic reactions as well as of buffer components were taken into account. Protolytic equilibria were described by dissociation constants. It was also assumed that the kinetics of the enzymatic reaction is described by the Michaelis–Menten equation. The final equation for the steady‐state response of an enzyme‐based pH sensor describes the form of the calibration curve for this type of biosensor. This equation takes into account sample pH and buffer concentration, as well as kinetic parameters (Vmax,KM) of the enzymatic reaction. The proposed model is particularly useful for describing pH‐based enzyme sensors with thin enzymatic

ISSN:1040-0397    

DOI:10.1002/elan.1140030419

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe pKaof several α‐phenylcarboxilic anti‐inflammatory drugs in both isopropyl andtert‐butyl alcohols have been determined by means of potentiometry. The dissociation constant values of their tetrabutylammonium salts, which are necessary for computation of the acidity constants, have been determined conductometrically. The results show that both the drug acid strength resolution and the pH break in titration curves are greater intert‐butyl than in isopropyl alcohol, but both alcohols can be used in everyday titrations. Titrations in one commercial pharmaceutical preparation have been carried out succ

ISSN:1040-0397    

DOI:10.1002/elan.1140030420

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe performance of a newly synthesized tetramethyl ketone calyx [4]arene ionophore in ion‐selective electrodes has been investigated. Optimization of the plasticized polyvinyl chloride membrane composition has produced electrodes that exhibit a Nernstian response for sodium ions. The best general characteristics exhibited by the electrodes were found when the ionophore mixed with 2‐nitrophenyl octyl ether as plasticizing agent, and potassium tetrakis (p‐chlorophenyl) rate as ion exchanger. Selectivity studies carried out with the electrode have shown excellent discrimination for sodium against potassium and lithium ions. In addition, the electrode displays a rapid response time, a detection limit be low 10−6M for sodium, and a working life of at least 4 months. Determinations of sodium in plasma patient samples have been performed and the results obtained compared to those from flame photometry and two commercial clinical an

ISSN:1040-0397    

DOI:10.1002/elan.1140030421

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA fully automated setup for impedance measurements at the dropping mercury electrode (DME) is described. It is based on the Solartron 1250 frequency response analyzer, and it incorporates an infrared drop‐fall detector. Synchronization with the DME as well as calibration procedures are considered in some detail. Experiments on dummy and electrolytic cells, with and without electroactive species, were performed, and data are compared with earlier results on the same system

ISSN:1040-0397    

DOI:10.1002/elan.1140030422

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY