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A 2D-separation of 16 polyaromatic hydrocarbons (PAHs) according to the Environmental Protecting Agency (EPA) standard was introduced. Separation took place on a TLC RP-18 plate (Merck, 1.05559). In the first direction, the plate was developed twice using n-pentane at −20°C as the mobile phase. The mixture acetonitrile-methanol-acetone-water (12:8:3:3, v/v) was used for developing the plate in the second direction. Both developments were carried out over a distance of 43 mm. Further on in this publication, a specific and very sensitive indication method for benzo[a]pyrene and perylene was presented. The method can detect these hazardous compounds even in complicated PAH mixtures. These compounds can be quantified by a simple chemiluminescent reaction with a limit of detection (LOD) of 48 pg per band for perylene and 95 pg per band for benzo[a]pyrene. Although these compounds were separated from all other PAHs in the standard, a separation of both compounds was not possible from one another. The method is suitable for tracing benzo[a]pyrene and/or perylene. The proposed chemiluminescence screening test on PAHs is extremely sensitive but may indicate a false positive result for benzo[a]pyrene.
We present a two dimensional (2D) planar chromatographic separation of estrogenic active compounds on RP-18 (Merck, 1.05559) and silica gel (Merck, 1.05721) phase. A mixture of 13 substances was separated using a solvent mix consisting of methanol–acetonitrile–water (2 + 2 + 1, v/v/v) on RP-18 phase in the first direction and cyclohexane–butylacetate–methanol (8 + 6 + 1, v/v/v) in the second direction on silica gel plate. Both developments were carried out over a distance of 70 mm. We used the grafted method to combine both plates in a 2D-separation. This 2D-separation method can be used to quantify 17α-ethinylestradiol (EE2) in an effect-directed analysis using the yeast strain Saccharomyces cerevisiae BJ3505. The test strain (according to McDonnell) contains the estrogen receptor. Its activation by estrogen active compounds is measured by inducting the reporter gene lacZ that encodes the enzyme ß-galactosidase. This enzyme activity is determined on plate by using the fluorescent substrate MUG (4-methylumbelliferyl ß-D-galactopyranoside).
We present a video-densitometric quantification method in combination with diode-array quantification for the methyl-, ethyl-, propyl-, and butylparaben in cosmetics. These parabens were separated on cyanopropyl bonded plates using water-acetonitrile-dioxane-ethanol-NH3 (25%) (8:2:1:1:0.05, v/v) as mobile phase. The quantification is based on UV-measurements at 255 nm and a bioeffectively-linked analysis using Vibrio fischeri bacteria. Within 5 min, a Tidas S 700 diode-array scanner (J&M, Aalen, Germany) scans 8 tracks and thus measures in total 5600 spectra in the wavelengths range from 190 to 1000 nm. The quantification range for all these parabens is from 20 to 400 ng per band, measured at 255 nm. In the V. fischeri assay a CCD-camera registers the white light of the light-emitting bacteria within 10 min. All parabens effectively suppress the bacterial light emission which can be used for quantifying within a linear range from 100 to 400 ng. Measurements were carried out using a 16-bit MicroChemi chemiluminescence system (biostep GmbH, Jahnsdorf, Germany), using a CCD camera with 4.19 megapixels. The range of linearity is achieved because the extended Kubelka-Munk expression was used for data transformation. The separation method is inexpensive, fast, and reliable.
Limits of quantification of some neonicotinoid insecticides measured by thin-layer chromatography
(2012)
A simple method to quantify the neonicotinoid insecticides nitenpyram, thiamethoxam, acetamiprid, imidacloprid, thiacloprid and clothianidin directly on an HPTLC-plate is presented. As stationary phase silica gel 60 RP-18WF254 s plates were used and a mixture of methyl-t-butyl ether, 2-butanone, NH3 (25%) (5 + 2+0.1, v/v) was used as solvent. All neonicotinoid insecticides show light absorptions below 300 nm. The calculated limits of quantification (LOQ) by UV-detection are in the range from 12 ng to 26 ng on plate depending on the different insecticides.Nitenpyram can be stained using fast blue salt B, forming red zones. The observed LOQ is 25 ng on plate. Acetamiprid can be specifically stained using phenylglyoxylic acid forming a yellow/green fluorescent compound. The LOQ is 52 ng per spot.The compounds thiamethoxam, acetamiprid, thiacloprid and clothianidin can be transformed into blue fluorescing zones, using a relatively new staining solution. This consists of tetraphenylborate and HCl. This is the first publication mentioning that neonicotinoids undergo this reaction. The calculated limits of quantification are in the range from 10 ng to 27 ng on plate.A simple pre-treatment procedure using an acetonitrile extraction and a Chromabond SiOH clean up procedure leads to overall LOQs for bee samples of 48 to 108 µg/Kg. The method can be used to measure neonicotinoid contaminations of bees.
Improved separation of highly toxic contact herbicides paraquat (1,1′-dimethyl-4-4′-bipyridinium), diquat (6,7-dihydrodipyridol[ 1,2-a:2′,1′-c]pyrazine-5,8-di-ium), difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium-methyl sulfate), mepiquat (1,1-dimethyl-piperidinium), and chloromequat (2-chloroethyltrimethylammonium) were presented by high-performance thin-layer chromatography (HPTLC). The quantification is based on a derivatization reaction, using sodium tetraphenylborate. Measurements were made in the wavelength range from 500 to 535 nm, using a light-emitting diode (LED) for excitation purposes, which emits very dense light at 365 nm. For calculations, a new theory of standard addition method was used, thus leading to a minimal error if exactly the same amount of sample content is added as a standard. The method provides a fast and inexpensive approach to quantification of the five most important quats used for plant protection purposes. The method works reliably because it takes into account losses during pre-treatment procedure. The method meets the European legislation limits for paraquat and diquat in drinking water according to United States Environmental Protection Agency (US EPA) method 549.2 which are 680 ng L−1 for paraquat and 720 ng L−1 for diquat. The method of standard addition in planar chromatography can be beneficially used to reduce systematic errors. Although recovery rates of 33.7% to 65.2% are observed, calculated contents according to the method of standard addition lie between 69% and 127% of the theoretical amounts.
We present a video-densitometric quantification method for the pain killer known as diclofenac and ibuprofen. These non-steroidal anti-inflammatory drugs were separated on cyanopropyl bonded plates using CH2Cl2, methanol, cyclohexane (95 + 5 + 40, v/v) as mobile phase. The quantification is based on a bio-effective-linked analysis using Vibrio fisheri bacteria. Within 10 min a CCD-camera registered the white light of the light-emitting bacteria. Diclofenac and ibuprofen effectively suppressed the bacterial light emission which can be used for quantification within a linear range of 10 to 2000 ng. The detection limit for ibuprofen is 20 ng and the limit of quantification 26 ng per zone. Measurements were carried out using a 16-bit ST-1603ME CCD camera with 1.56 megapixels (from Santa Barbara Instrument Group, Inc., Santa Barbara, USA). The range of linearity covers more than two magnitudes because the extended Kubelka-Munk expression is used for data transformation. The separation method is inexpensive, fast, and reliable.