Hans Malissa

Determination of quaternary alkylammonium compounds by capillary zone electrophoresis and indirect UV detection as a real alternative to ion chromatography with suppressed conductivity detection

A capillary electrophoretic (CE) method for the determination of residual mid-chain alkyltrimethylammonium compounds in the pharmaceutical product Welchol (an alkylated, crosslinked polyallylamine) was developed, validated and compared with the existing ion chromatographic (IC) method with suppressed conductivity detection. Excellent reproducibilities of migration times (RSD<0.5% within a series of 55 sample injections) and relative peak areas (RSD<2%) make the method suitable for quality control as a real alternative to IC. Limits of quantification of 0.01% w/w of each impurity in the active substance were achieved. Buffer systems for indirect UV detection based on creatinine as visualization reagent with different inorganic and organic acids (phosphoric, sulfuric, formic, acetic, oxalic and citric acid) and their effect on selectivity to ten quaternary ammonium compounds were studied. Selectivity changes were observed for the di- and trivalent analytes depending on the buffer applied. Also, the influence of acetonitrile, methanol, 1,4-dioxane and tetrahydrofuran on selectivity was investigated. In addition, CE-MS experiments were carried out in order to identify several impurities in the product.

Capillary zone electrophoretic determination of hydroxymetabolites of atrazine in potable water using solid-phase extraction with Amberchrom resins

A CZE-separation system for hydroxyatrazine, desisopropylhydroxyatrazine, desethylhydroxyatrazine and ammeline is presented that allows their determination in environmental waters in the subμgL−1 domain after solid-phase extraction/enrichment with styrene-divinylbenzene and methacrylate macroporous (Amberchrom) resins. The CZE separation and determination system uses the stacking effect and an increased light path for UV-detection (bubble cell). The etching of the bubble cell was done in our laboratory. A ruggedness check of the CZE-system revealed the resolution of theN-dealkylated metabolites to be sensitive to pH, temperature and current variations as well as to changes of capillary dimensions. Fine-tuning of the separation is performed by variation of the current intensity in the constant-current mode. Recoveries from fortified tap-water samples were 95% for hydroxyatrazine, 70% for desethylhydroxyatrazine and approximately 20% for desisopropylhydroxyatrazine at the 0.2 μg L−1 concentration level. Due to its high polarity, ammeline is only slightly adsorbed on Amberchrom resins and cannot be enriched using these materials.

Multiclass/multiresidue method for monitoring widely applied plant protecting agents in air during field dispersion work

A multiclass/multiresidue method for surveying the uptake of plant protecting chemicals by inhalation during field spraying work is described. Eleven nowadays mainly dispersed compounds, which cover a wide range of chemical properties, are analysed in air with personal active sampling and in one single analytical run. This has the advantage, that one basic method only needs to be implemented, calibrated and validated in a laboratory to perform varying monitoring tasks without changing the method itself. Samples were taken with Tenax sorbent tubes operated to collect the active compounds simultaneously in the vapour state, in aerosol state or bound to particles. The procedure consists of four unit operations only: sampling, elution, dilution and HPLC measurement, and is described in SOP-format. The limits of quantification, calculated as method detection limits, were between 1 and 9 microg m(-3) based on 1 m3 air volume sampled (8 h). Method performance was characterised by way of generated test atmospheres and field spraying trials.

Statistical evaluation of uncertainty for rapid tests with discrete readings — examination of wastes and soils

Abstract In the course of the colorimetric determination of analytes using a procedure with discrete readings the measurement uncertainly cannot be calculated in the normally practiced manner. The basic principle of the analytical method used is a stepwise and non-equidistant reading. Based on the fact that half a step can be estimated, a calculation of the measurement uncertainty for the 95% confidence level is possible; this is needed to allow a reliable decision of whether a critical value is exceeded or not.

A rapid toxicological test method with luminous bacteria for laboratory and on-site assessment of wastes and contaminated soils

Comparison between a standard toxicological test with luminous bacteria based on DIN 38 412 L 341, 2 and a rapid test yield similar results. However, the standard deviation of the rapid test was lower than that of the standard test. Costs for material and instruments are low; the test is easy to handle and can be used on site. By appropriate choice of the dilution steps and proper timing by intercalating the individual sets of assays, the overall time required to obtain results can be shortened considerably compared to the standard test. In combination with a recently developed method for aqueous extraction this allows assessment of the risk in contaminated soil on site within 30–45 min.

Verfahren zur kontinuierlichen relativpotentiometrischen Bestimmung von Oxydationsmitteln in Trinkwasser

The method is based on the reaction of the oxidizing agents remaining in the drinking water after processing, with the auxiliary redox system Fe(II)/Fe(III). The difference of redox potentials given by the original and the changed mixing ratio of the auxiliary redox system is proportional to the concentration of the oxidizing agent within an error range of ± 1.5%, if the molar ratio Fe(II)/Fe(III) is held within the limits 7/3 and 3/7.The determination is a relative method for both sample and reagent. A differential amplifier is used to measure the difference of redox potentials between two platinum working electrodes and a platinum reference electrode, which is situated behind the cell.ZusammenfassungEs wird ein neues, kontinuierlich arbeitendes, relativpotentiometrisches Verfahren entwickelt, das auf der Reaktion der nach der Aufbereitung im Trinkwasser verbleibenden Oxydationsmittel mit dem Hilfs-redoxsystem Fe(II)/Fe(III) beruht. Die Differenz der Redoxpotentiale, welche dem ursprünglichen und dem durch das Oxydationsmittel verschobenen Mischungsverhältnis des Hilfsredoxsystems entsprechen, ist der Oxydationsmittelkonzentration innerhalb eines Fehlerbereiches von ± 1,5% vom Skalenendwert proportional, wenn das molare Mischungsverhältnis Fe(II)/Fe(III)=7/3 nicht weiter als bis zum Verhältnis 3/7 verschoben wird.Das Verfahren ist eine Relativmethode für Probe und Reagens, ermöglicht eine diaphragmafreie Messung der Potentialdifferenz und setzt zur Messung dieser Potentialdifferenz zwischen zwei Platin-Meßelektroden einen Differenzverstärker ein, dessen Bezugspunkt eine im Abfluß angeordnete Referenzelektrode darstellt.