Axel Meyer

COMPARISON OF AMPEROMETRIC AND UV-SPECTROPHOTOMETRIC MONITORING IN THE HPLC ANALYSIS OF PESTICIDES

SummaryStudies have been carried out to compare different detection techniques including amperometric detection in the reductive and oxidative mode and UV detection following the HPLC separation of pesticides. By the example of 4,6-dinitro-o-cresol (DNOC), 2-sec-butyl-4,6-dinitrophenol (Dinoseb) and 2-tert-butyl-4,6-dinitrophenol (Dinoterb), it is shown that the electrochemical detection exhibits higher sensitivities than the UV-technique. The detection limits are in case of the oxidative amperometric technique 0.1 ng for all pesticides, in the reductive mode 0.3 ng for DNOC and 1 ng for Dinoseb and Dinoterb. By UV-monitoring the detection limits were found to be 2 ng for DNOC and 24 ng for Dinoseb and Dinoterb.

Determination of polycyclic aromatic hydrocarbons in water samples using high-performance liquid chromatography with amperometric detection

Abstract The determination of polycyclic aromatic hydrocarbons (PAHs) using high-performance liquid chromatography (HPLC) with UV and fluorescence detection has been well established. Although most of the PAHs can be detected by these methods, some environmentally important polyaromatic compounds, such as acenaphthylene, do not show fluorescence and can only be determined by UV detection at higher concentrations. A sensitive and selective determination of acenaphthylene, acenaphthene and the six PAHs listed in the TVO, the German drinking water standard, is also possible by amperometric detection following HPLC separation. The method was applied to the determination of PAHs in different water samples after solid-phase extraction (SPE). The efficiency of the amperometric determination was found to be superior to UV detection (λ = 300 nm).

Determination of p-phenylenediamine and its metabolites MAPPD and DAPPD in biological samples using HPLC-DAD and amperometric detection

A sensitive and selective HPLC method using a diode array detector (DAD) and an electrochemical detector (ECD) in series has been developed and validated for the quantitative measurement of p-phenylenediamine and its acetylated metabolites N-acetyl-p-phenylenediamine (MAPPD) and N,N-diacetyl-p-phenylenediamine (DAPPD) in biological samples. The separation was carried out on a hydrophilic modified AQUA C(18) column and the mobile phase was composed of acetonitrile: ammonium acetate solution (5:95, 25 mM, v/v). Spectrophotometric detection was performed at 240 or 255 nm and amperometric detection was carried out using a positive oxidation potential of 400 mV. The quantification of the three analytes was validated in the range of 0.05-50 microM and the established limits of determination were 0.5 microM for PPD and MAPPD and 1 microM for DAPPD. The standard deviations (N=9) were lower than 7.5% at a concentration of 1 microM. The samples were stabilised with ascorbic acid to prevent PPD from oxidizing. Pretreatment of samples or analyte enrichment before sample injection is not required. The method proved to be accurate, sensitive and sufficiently specific. It was applied to the ecotoxicological study of the kinetics of the PPD N-acetylation in cell lysates in two different media.

Untersuchungen zur HPLC-Bestimmung von Pesticiden mit amperometrisch detektierbaren Hydroxylgruppen

SummaryFor the sensitive determination of pesticides in soil and water samples, the possibility of using h.p.l.c. with amperometric detection was investigated. The polarographic and voltammetric behaviour of some selected compounds (bromofenoxim, bromoxynil, dimethirimol, dinoseb, dinoterb, DNOC, ethirimol, ioxynil, maleic hydrazide, pentachlorophenol) was tested.After separation by h.p.l.c. the detection of all these pesticides may be done in the voltammetric cell by the anodic signal of their hydroxyl group. The sensitivity of the determination lies in all cases in the pg-range.The simultaneous determination of the metabolites in presence of the pesticide is shown with the example of bromofenoxim and its photolytic decomposition products.

Oxidative transformation processes and products of para-phenylenediamine (PPD) and para-toluenediamine (PTD)—a review

Abstractpara-Phenylendiamine (PPD) and its ring-methylated analogue, para-toluenediamine (PTD), are primary intermediates (precursors) for azo dye synthesis. Particularly, they are used in oxidative hair dye formulations and in henna tattoo inks. In the hair coloration process, the final permanent color develops during complex chemical reactions in the presence of an oxidant, e.g., hydrogen peroxide, and a coupler, e.g., resorcinol (benzene-1,3-diol). PPD is well known as the most important allergen associated with hair dye-related allergic contact dermatitis. PPD acts as a pre- or pro-hapten. It is (aut)oxidatively transformed into haptens, e.g., benzoquinone diimine, benzoquinone, or Bandrowski’s Base. In the presence of adequate amounts of couplers, some haptens, e.g., Bandrowski’s Base, are not formed, and others, e.g., benzoquinone diimine, are converted into non-sensitizing products, e.g., the desired dye. Under toxicological aspects, the illegal use of henna tattoo inks containing aryldiamines but no couplers is of high concern. Nevertheless, even during hair coloration at comparably high coupler concentration, the aryldiamines are not completely scavenged and transformed by the couplers. To understand and to assess the reactive and toxicological potential of PPD and PTD, a sound knowledge of their (aut)oxidation reactions and of the nature of formed intermediates and (by)products is crucial. Thus, this review pursues the aim to provide a synopsis of the current state of knowledge of (aut)oxidative reactions of PPD and PTD in the absence of a coupler. Monomeric and oligomeric reaction products of each compound are presented together with the reaction conditions and analytical techniques applied for their generation and identification. Analytical data of these transformation products, e.g., electrochemical potentials, UV/VIS absorbance maxima, and mass spectrometric data, are tabulated. The certainty of the substance identification is rated with respect to the performance of the applied analytical techniques, to the concordance of results achieved by different methods, and to the traceability of the analytical procedure. Reaction pathways are outlined for both compounds. An integrated reaction scheme is drawn for PPD. Finally, intrinsic difficulties of process and product elucidation are discussed, and some conclusions are drawn pointing to several knowledge gaps and to new analytical approaches, potentially helpful to fill them.

Determination of the phenylurea herbicide linuron and its metabolites in environmental samples by HPLC with serial ultraviolet and amperometric detection

SummaryProcedures were developed for the determination of the herbicide linuron and its main metabolites using reversed-phase high performance liquid chromatography with serial ultravoilet-amperometric detection. For the application to water and soil analysis solid-phase extraction with cyclohexyl cartridges was found to be useful for the separation and enrichment of these compounds at trace level. By amperometric detection at +1.3 V down to approximately 0.5 ng of the tested metabolites could be determined. This is about 5-times more sensitive than the ultraviolet detection by the selected wavelength of 247 nm. Only for linuron the UV-detection proved to be more sensitive under the described conditions; the detection limit was found to be 5 ng.

Polarographisches Verhalten von Pesticiden mit Organohalogenbindungen

SummaryThe dp-polarographic behaviour of different pesticides with carbon-halogen bonds was investigated in dimethylsulfoxide and methanol/water as solvents; the peak-potentials are demonstrated graphically. From peak-height the pesticides are detectable up to 100 ng · ml−1. The investigations are of interest for the development of multistage-combined procedures by h.p.l.c. with amperometric detection.

Photometrische Bestimmung von Bor im Grund- und Oberflächenwasser

SummaryThe coloured complex “rosocyanin” which is formed after reaction with curcumin is suited for the photometric determination of boron in water. An optimised procedure is described, which is superior to the usually applied standard method. Boron is separated from interfering matrix components in ground- and surface water by extraction with 2-ethyl-1,3-hexanediol in methylisobutylketone. Another advantage, in comparison with other methods, is the immediate formation of the curcumin complex in the extraction phase. For the determination of 1 ppb boron the relative standard deviation was calculated to ±4.3%, for 100 ppb to ±1.1%.The boron contents of tap water, mineral water and river water of different origin were investigated; reference measurements were carried out using emission spectrometry with ICP excitation.ZusammenfassungFür Wasseruntersuchungen ist die photometrische Borbestimmung mit Curcumin über den Farbkomplex „Rosocyanin“ geeignet. Es wird ein optimiertes Verfahren beschrieben, welches leistungsfähiger ist als die empfohlenen Standardverfahren. Durch die Extraktion mit 2-Ethyl-1,3-hexandiol in Methylisobutylketon wird Bor von allen störenden Bestandteilen abgetrennt, die im Grundund Oberflächenwasser enthalten sein können. Gegenüber anderen Verfahren ist es auch vorteilhaft, daß der Bor-Curcumin-Komplex unmittelbar im Extrakt gebildet wird. Für die Bestimmung von 1 ppb Bor wurde die relative Standardabweichung zu ±4,3% berechnet, für 100 ppb Bor zu ±1,1%.Es wurden die Borgehalte im Leitungswasser, Mineralwasser und Flußwasser verschiedener Herkunft ermittelt; die Referenzuntersuchungen erfolgten emissionsspektrometrisch mit ICP-Anregung.

Determination of zinc, cadmium, lead and copper in soils and sewage sludges by microprocessor-controlled voltammetry in comparison with atomic absorption spectrometry

SummaryInformation on the heavy metal contents in soils and sewage sludges is of strong ecological interest. For control of the maximum allowed concentrations photometric and atomic absorption spectrometric methods have been developed for the determination of the single elements; sample digestion is carried out using hydrochloric acid and nitric acid.Differential pulse polarography and differential pulse anodic stripping voltammetry allow the simultaneous determination of different heavy metals in one digestion solution according to their electrochemical behaviour. This possibility is given, for instance, for zinc, cadmium, lead and copper. The adequate procedure was tested with a microprocessor-controlled polarograph. Flame atomic absorption spectrometry was used as reference method.

Comparison of HPLC Methods for the Determination of Amino Sugars in Soil Hydrolysates

A study on the suitability of chromatographic techniques such as high performance anion exchange chromatography (HPAEC) with fluorescence detection (FL) and pulsed amperometric detection (PAD) and reversed phase (RP) chromatography for the determination of galactosamine, glucosamine, mannosamine, and muramic acid in soil hydrolysates was carried out. The reversed phase fluorescence method was rapid, provided good validation parameters, and employed relatively inexpensive instrumentation. The HPAEC methods had slightly higher limits of quantification, 0.6–5.0 µmol L−1 (HPAEC-FL) and 1.0–10.0 µmol L−1 (HPAEC-PAD), compared to the reversed phase fluorescence method (0.5–5.0 µmol L−1). Various sample pretreatment methods and chromatographic methods were investigated and the advantages and disadvantages of the HPLC methods are discussed.