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Previous studies of the hyphenation of gas chromatographic separation and spectrophotometric detection in the ultraviolet wavelength range between 168 and 330 nm showed a high potential for applications where the analysis of complex samples is required. Within this paper the development of a state-of-the-art detection system for compounds in the vapour phase is described, offering an improved behaviour compared to previous systems: Dependent on the requirements of established detection systems hyphenated with gas chromatography, the main components of the system have to be designed for optimum performance and reliability of the spectrophotometric detector: A deuterium lamp as a broadband light source has been selected for improved stability in the measurements. A new-type absorption cell based on fiber-optics has been developed considering the dynamic necessary to compete with existing techniques. In addition, the influence of the volume of the cell on the chromatogram needs to be analyzed. Tests for determining the performance of the absorption cell in terms of chemical and thermal influences have been carried out. A new spectrophotometer with adequate spectral resolution in the wavelength range, offering improved stability and dynamic for an efficient use in this application was developed. Furthermore, the influence of each component on the performance, reliability and stability of the sensor system will be discussed. An overview and outlook over the potential applications in the environmental, scientific and medical field will be given.
In thin-layer chromatography, fiber-bundle arrays have been introduced for spectral absorption measurements in the UV-region. Using all-silica fiber bundles, the exciting light will be detected after re-emission on the plate with a fiberoptic spectrometer. In addition, fluorescence light can be detected which will be masked by the re-emitted light. Therefore, it is helpful to separate the absorption and fluorescence on the TLC-plate. A modified three-array assembly has been developed: using one array for detection, the two others are used for excitation with broadband band deuterium-light and with UV-LEDs adjusted to the substances under test. As an example, the quantification of glucosamine in nutritional supplements or spinach leaf extract will be described. Using simply heating of the amino-plate for derivation, the reaction product of Glucosamine can be detected sensitively either by light absorption or by fluorescence, using the new fiber-optic assembly. In addition, the properties of the new 3-row fiber-optic array and the commercially available UV-LEDs will be shown, in the interesting wavelength region for excitation of fluorescence, from 260 nm to 360 nm. The squint angle having an influence on coupling efficiency and spatial resolution will be measured with the inverse farfield method. Some properties of UV-LEDs for analytical applications will be described and discussed, too.
The main focus of this chapter is the theoretical and instrumental processes that underpin densitometric methods widely used in thin-layer chromatography (TLC). Densitometric methods include UV–vis, luminescence and fluorescence optical measurements as well as infrared and Raman spectroscopic measurements. The chapter is divided in two general parts: a theoretical part and a practical part. The systems for direct radioactivity measurements and the combination of TLC with mass spectrometry are also discussed. All these systems allow measuring an intensity distribution directly on a TLC plate. We call this “in situ detection” because no analyte is removed from the plate.
The main focus of this chapter is the theoretical and instrumental processes that underpin densitometric methods widely used in thin-layer chromatography (TLC). Densitometric methods include UV–vis, luminescence, and fluorescence optical measurements as well as infrared and Raman spectroscopic measurements. The chapter is divided in two general parts: a theoretical part and a practical part. The systems for direct radioactivity measurements and the combination of TLC with mass spectrometry are also discussed. All these systems allow measuring an intensity distribution directly on a TLC plate. We call this “in situ detection” because no analyte is removed from the plate.
Die quantitative Dünnschichtchromatographie (HPTLC) mit einem Graustufen-Handscanner ist eine preiswerte, schnelle und präzise Methode zur Schwermetallbestimmung. Als Alternative zu teuren Densitometern wird ein Grünlichtscanner mit einer Auflösung von 256 Graustufen benutzt. Die Ortsauflösung beträgt maximal 400 dpi (dots per inch). Die Chromatogramme werden mit 300 dpi aufgenommen. Zur Entwicklung wird eine Camag-Linearkammer verwendet. Zur Probenvorbereitung werden die zu bestimmenden Schwermetallionen bei pH 4,2 mit Dithizon komplexiert. Nur die Metallkationen Zn(2+), Co(2+), Hg(2+), Cd(2+) und Ni(2+) reagieren zu einem farbigen Metallkomplex, wobei sich Zn(2+)- und Co(2+)-Komplexe chromatographisch abtrennen lassen. Nach Komplexierung der Wasserprobe wird mit Essigsäureethylester ausgeschüttelt, Probe- und Standardlösung auf eine Platte aus Kieselgel SI-60 aufgetragen, mit Essigsäureethylester fokussiert und nach der Trocknung der Platte mit Toluol entwickelt. Die HPTLC-Platte wird mit scannereigener Software eingelesen und im PCX-Format (PC PaintBrusch der Fa. ZSoft) auf die Festplatte abgelegt. Zur Auswertung wird eine Leseroutine benutzt. Die ganze Chromatographiebahn ist mit 150 Einzeldioden aufgenommen, die eine Strecke von 48 mm in 564 Einzelmessungen auflösen. Die Summe aller 150 Einzelaufnahmen liefert das Densitogramm aus dem der Schwermetallgehalt bestimmt wird.
Eine einfache Bestimmung von Mineraloel-KWstoffen - Ersatz des FCKW-haltigen Extraktionsmittels
(1996)
Die Messung von KWstoffen in Abwaessern nach DIN ist eine in der Umweltanalytik haeufig geforderte Bestimmung. Die Abwasserprobe wird dabei mit 1,1,2-Trichlortrifluorethan extrahiert. Anschliessend wird der Extrakt mittels IR-Spektroskopie vermessen. Neben einigen Schwaechen ist bei dieser Bestimmungsmethode besonders die Verwendung des ozonschaedigenden FCKW-Loesemittels heute nicht mehr zeitgemaess. - Die Verf. beschreiben ein schnelles robustes Bestimmungsverfahren, das alle Schwaechen der alten Methode vermeidet.
Nativ-organische Abfälle bilden mit ca. 30 Gew. % den Hauptteil des Hausmülls. Daher leistet die Bioabfallkompostierung einen bedeutenden Schritt hin zu einer sinnvollen Abfallverwertung. Bundesweit werden derzeit jährlich etwa 750 000 t Bioabfallkompost erzeugt. Mit Ausnahme von sieben Land- und Stadtkreisen planen die Landkreise Baden-Württembergs die getrennte Sammlung von Bioabfällen: Einwohner von 23 Landkreisen waren 1993, zum Teil versuchsweise, an Biotonnen angeschlossen. Die Notwendigkeit der Bioabfallkompostierung scheint außer Frage zu stehen, intensiv erörtert werden jedoch die Verfahrenskonzepte, die der Bioabfallkompostierung zugrunde liegen. Kern der Diskussion ist, ob einfache Kompostierungsverfahren wie die dezentrale Kompostierung den technisch aufwendigeren Verfahren zentraler Anlagen gleichwertig sind.
Als erster Landkreis in Baden Württemberg hat der Landkreis Sigmaringen bei der Entsorgung des bei 120 000 Einwohnern im Kreis anfallenden organischen Abfalls neue Wege beschritten und die Landwirtschaft in den Stoffkreislauf miteinbezogen, anstatt das anfallende Material zu deponieren. Auf dem Hintergrund der TA-Siedlungsabfall, die vorschreibt, daß nach einer Übergangszeit organische Abfälle nicht mehr deponiert werden dürfen, sondern kompostiert oder thermisch behandelt werden müssen, hat der Landkreis Sigmaringen im Jahr 1992 ein Konzept zur dezentralen Kompostierung verabschiedet.
High performance thin layer chromatography (HPTLC) is a frequently used separation technique which works well for quantification of caffeine and quinine in beverages. Competing separation techniques, e.g. high-performance liquid chromatography (HPLC) or gas chromatography (GC), are not suitable for sugar-containing samples, because these methods need special pretreatment by the analyst. In HPTLC, however, it is possible to separate ‘dirty’ samples without time-consuming pretreatment, because disposable HPTLC plates are used. A convenient method for quantification of caffeine and quinine in beverages, without sample pretreatment, is presented below. The basic theory of in-situ quantification in HPTLC by use of remitted light is introduced and discussed. Several linearization models are discussed.
A home-made diode-array scanner has been used for quantification; this, for the first time, enables simultaneous measurements at different wavelengths. The new scanner also enables fluorescence evaluation without further equipment. Simultaneous recording at different wavelengths improves the accuracy and reliability of HPTLC analysis. These aspects result in substantial improvement of in-situ quantitative densitometric analysis and enable quantification of compounds in beverages.
A new diode-array scanner in combination with a computer-controlled application system meets all the demands of modern HPTLC measurement. Automatic application, simultaneous measurements at different wavelengths, and different linearization models enable appropriate evaluation of all analytical questions. The theory of error propagation recommends quantification at reflectance values smaller than 0.8; this can be verified only by use of diode-array scanning. The same theory also recommends quantification by use of peak height data, because the theory predicts best precision only for peak height evaluation. Diode-array scanning with reflectance monitoring enables appropriate validation in TLC and HPTLC analysis. All these aspects result in substantial improvement of in-situ quantitative densitometric analysis, and simultaneous recording at different wavelengths opens the way for chemometric evaluation, e.g. peak purity monitoring, which improves the accuracy and reliability of HPTLC analysis.
Fluorescence Enhancement of Pyrene Measured by Thin-Layer Chromatography with Diode-Array Detection
(2003)
In-situ densitometry for qualitative or quantitative purposes is a key step in thin-layer chromatography. It offers a simple way of quantifying by measuring the optical density of the separated spots directly on the plate. A new TLC scanner has been developed which is able to measure TLC plates or HPTLC plates, at different wavelengths simultaneously, without destroying the plate surface. The system enables absorbance and fluorescence measurements in one run. Fluorescence measurements are possible without filters or other adjustments.
The measurement of fluorescence from a TLC plate is a versatile means of making TLC analysis more sensitive. Fluorescence measurements with the new scanner are possible without filters or special lamps. Improvement of the signal-to-noise ratio is achieved by wavelength bundling. During plate scanning the scattered light and the fluorescence are both emitted from the surface of the TLC plate and this emitted light provides the desired spectral information from substances on the TLC plate. The measurement of fluorescence spectra and absorbance spectra directly from a TLC plate is based on differential measurement of light emerging from sample-free and sample-containing zones.
The literature recommends dipping TLC plates in viscous liquids to enhance fluorescence. Measurement of the fluorescence and absorbance spectra of pyrene spots reveals the mechanism of enhancement of plate dipping in viscous liquids—blocked contact of the fluorescent molecules with the stationary phase or other sample molecules is responsible for the enhanced fluorescence at lower concentrations.
In conclusion, dipping in TLC analysis is no miracle. It is based on similar mechanisms observable in liquids. The measured TLC spectra are also very similar to liquid spectra and this makes TLC spec-troscopy an important tool in separation analysis.
A new formula is presented for transforming fluorescence measurements in accordance with Kubelka-Munk theory. The fluorescence signals, the absorption signals, and data from a selected reference are combined in one expression. Only diode-array techniques can measure all the required data simultaneously to linearize fluorescence data correctly. To prove the new theory HPTLC quantification of the analgesic flupirtine was performed over the mass range 300 to 5000 ng per spot. The fluorescence calibration curve was linear over the whole range. The transformation of fluorescence measurements into linear mass-dependent data extends the technique of in-situ fluorescence analysis to the high concentration range. It also extends Kubelka-Munk theory from absorption to fluorescence analysis. The results presented also emphasize the importance of Kubelka-Munk theory for in-situ measurements in scattering media, especially in planar chromatography.
We will present the first example of a two-dimensional scanned TLC-plate, measured by use of a diode-array scanner. A spatial resolution of 250 µm was achieved on plate. The system provides real 2D fluorescence and absorption spectra in the wavelength-range from 190 to 1000 nm with a spectral resolution of greater than 1 nm. A mixture of 12 sulphonamides was separated by using a cyanopropyl-coated silica gel plate (Merck, 1.16464) with the solvent mix of methyl tert-butyl ether-methanol-dichloromethane-cyclohexane-NH3 (25%) (48:2:2:1:1, v/v) in the first and with a mixture of water-acetonitrile-dioxane-ethanol (8:2:1:1, v/v) in the second direction. Both developments were carried out over a distance of 70 mm. A separation number (spot capacity) of 259 was calculated. We discussed a new formula for its calculation in 2D-TLC separations. The drawback of this method is that measuring a 2D-TLC plate needs more than 3 h measurement time.
Vorgestellt wird die Dioden-Array-Dünnschichtchromatographie als eine moderne und preiswerte Messmethode zur densitometrischen Erfassung von Substanzen auf einer DC- oder einer HPTLC-Platte. Sicher identifizierbar sind auch Substanzen mit schwachem Chromophor. Die Kubelka-Munk-Gleichung beschreibt einen linearen Zusammenhang zwischen Remissionslicht und lichtabsorbierender Stoffmenge auf der Platte. Die Auswertung im Spektralbereich von 316 bis 334 nm zeigt den Zusammenhang zwischen transformiertem Messsignal und aufgetragener Substanzmasse. Die schnelle Aufnahme von UV/vis-Spektren eröffnet der HPTLC den gesamten Bereich der Methodenvalidierung auf dem Niveau, auf welchem heute die HPLC-Analytik durchgeführt wird.
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Rudolf E. Kaiser
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Enzyme‐assisted HPTLC method for the simultaneous analysis of inositol phosphates and phosphate
(2023)
Background
The analysis of myo‐inositol phosphates (InsPx) released by phytases during phytic acid degradation is challenging and time‐consuming, particularly in terms of sample preparation, isomer separation, and detection. However, a fast and robust analysis method is crucial when screening for phytases during protein engineering approaches, which result in a large number of samples, to ensure reliable identification of promising novel enzymes or target variants with improved characteristics, for example, pH range, thermal stability, and phosphate release kinetics.
Results
The simultaneous analysis of several InsPx (InsP1‐InsP4 and InsP5 + 6) as well as free phosphate was established on cellulose HPTLC plates using a buffered mobile phase. Inositol phosphates were subsequently stained using a novel enzyme‐assisted staining procedure. Immobilized InsPx were hydrolyzed by a phytase solution of Quantum® Blueliquid 5G followed by a molybdate reagent derivatization. Resulting blue zones were captured by DAD scan. The method shows good repeatability (intra‐day and intra‐lab) with maximum deviations of the Rf value of 0.01. The HPTLC method was applied to three commercially available phytases at two pH levels relevant to the gastrointestinal tract of poultry (pH 5.5 and pH 3.6) to observe their phytate degradation pattern and thus visualize their InsPx fingerprint.
Conclusion
This HPTLC method presents a semi‐high‐throughput analysis for the simultaneous analysis of phytic acid and the resulting lower inositol phosphates after its enzymatic hydrolysis and is also an effective tool to visualize the InsPx fingerprints and possible accumulations of inositol phosphates.
High-performance thin-layer chromatography (HPTLC), as the modern form of TLC (thin-layer chromatography), is suitable for detecting pharmaceutically active compounds over a wide polarity range using the gradient multiple development (GMD) technique. Diode-array detection (DAD) in conjunction with HPTLC can simultaneously acquire ultraviolet‒visible (UV‒VIS) and fluorescence spectra directly from the plate. Visualization as a contour plot helps to identify separated zones. An orange peel extract is used as an example to show how GMD‒DAD‒HPTLC in seven different developments with seven different solvents can provide an overview of the entire sample. More than 50 compounds in the extract can be separated on a 6-cm HPTLC plate. Such separations take place in the biologically inert stationary phase of HPTLC, making it a suitable method for effect-directed analysis (EDA). HPTLC‒EDA can even be performed with living organism, as confirmed by the use of Aliivibrio fischeri bacteria to detect bioluminescence as a measure of toxicity. The combining of gradient multiple development planar chromatography with diode-array detection and effect-directed analysis (GMD‒DAD‒HPTLC‒EDA) in conjunction with specific staining methods and time-of-flight mass spectrometry (TOF‒MS) will be the method of choice to find new chemical structures from plant extracts that can serve as the basic structure for new pharmaceutically active compounds.
Two solvent mixtures for high-performance thin-layer chromatographic (HPTLC) separation of some compounds showing estrogenic activity in the yeast estrogen screen (YES) assay are presented. The new method, planar yeast estrogen screen (pYES) combines the YES assay and a chromatographic separation on silica gel HPTLC plates with the performance of the YES assay. For separation, the analytes were applied bandwise to HPTLC plates (10 × 20 cm) with fluorescent dye (Merck, Germany). The plates were developed in a vertical developing chamber after 30 min of chamber saturation over a separation distance of 70 mm, using cyclohexane‒methyl-ethyl ketone (2:1, V/V) or cyclohexane‒CPME (3:2, V/V) as solvents. Both solvents allow separation of estriol, daidzein, genistein, 17β-estradiol, 17α-ethinyl estradiol, estrone, 4-nonylphenol and bis(2-ethylhexyl) phthalate.
Alle Materie strebt nach maximaler Unordnung. Diese Erkenntnis wird durch die thermodynamische Funktion der Entropie beschrieben. Auch bei jeglicher Art menschlichen Handelns wird die Entropie immer erhöht. Wird in der Technik Materie in geordnete Formen gebracht (z. B. beim Herstellen von Pfandflaschen), findet in diesem Produkt eine Entropieerniedrigung statt. Gleichzeitig wird aber an anderer Stelle die Unordnung beträchtlich vergrößert. Diese Entropieerhöhung nennen wir Abfall. Jede Entropieerhöhung ist mit dem Verbrauch wertvoller Ressourcen verbunden. Durch eine optimale Recyclingtechnik kann einer Entropieerhöhung von Materie entgegengearbeitet werden. Aber nur Recyclingraten von über 90 % erlauben eine wirksame Streckung der Ressourcen.
The NaSiO Institute (Institute for Sustainable Silicate Research in Offenburg, https://inasio.hs-offenburg.de/) has been working for years on climate-friendly alternatives to insulation materials and inorganic binders, as well as the reasonable use of construction waste in the building industry. The aim of research is to realize the enormous CO 2 saving potential of the construction sector worldwide. A stopping of climate heating will only succeed if these climate-friendly alternatives are used in the construction industry. This is the only way to realize the enormous CO2 savings that will be needed in future to comply with the Paris Agreement.
Described is a solid body formed with Si, Al, Ca, O and at least one of Na and K, said body exhibiting in the 27Al MAS NMR spectrum a signal additional to the 27Al MAS NMR spectrum of pure calcium aluminate, with a chemical shift sited between that of the main peak of calcium aluminate and the peak next upfield to the main peak of calcium aluminate. Possible uses of the solid body include use as a building material with aggregates, as a coating, as an adhesive for joining two components for sanitary ceramic units, for high-temperature applications, for renovating existing edifices, especially for underwater renovation, for the erection and/or repair of built structures, particularly when high compressive strengths are needed or chemically aggressive conditions arise. It can be produced by bringing waterglass, sodium hydroxide and/or potassium hydroxide, calcium aluminate, one or more aggregates and optionally water, especially sea water, into contact, even at temperatures below 0°C without heating.
We present a densitometric quantification method for triclosan in toothpaste, separated by high-performance thin-layer chromatography (HPTLC) and using a 48-bit flatbed scanner as the detection system. The sample was band-wise applied to HPTLC plates (10 × 20 cm), with fluorescent dye, Merck, Germany (1.05554). The plates were developed in a vertical developing chamber with 20 min of chamber saturation over 70 mm, using n-heptane–methyl tert-butyl ether–acetic acid (92:8:0.1, V/V) as solvent. The RF value of triclosan is hRF = 22.4, and quantification is based on direct measurements using an inexpensive 48-bit flatbed scanner for color measurements (in red, green, and blue) after plate staining with 2,6-dichloroquinone-4-chloroimide (Gibbs' reagent). Evaluation of the red channel makes the measurements of triclosan very specific. For linearization, an extended Kubelka–Munk expression was used for data transformation. The range of linearity covers more than two orders of magnitude and is between 91 and 1000 ng. The separation method is inexpensive, fast and reliable.
We present a video-densitometric high-performance thin-layer chromatography (HPTLC) quantification method for patulin in apple juice, developed in a vertical chamber from the starting point to a distance of 50 mm, using MTBE, n-pentane (9 + 5, v/v) as mobile phase. After separation the plate is sprayed with methyl-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH) solution (40 mg in 20 mL methanol) and heated at 105 °C for 15 min. Patulin zones are transformed into yellow spots. The quantification is based on direct measurements using an inexpensive 48-bit flatbed scanner for color measurements (in red, green, and blue). Evaluation of the blue channel makes the measurements very specific. Quantification in fluorescence was also done by use of a 16-bit CCD-camera and UV-366 nm illumination as well as using a HPTLC DAD-scanner. For linearization the extended Kubelka–Munk expression for data transformation was used. The range of linearity covers more than two magnitudes and lies between 5 and 800 ng patulin. The extraction of 20 g apple juice and an extract application on plate up to 50 µL allows statistically defined checking the limit of detection (LOD) of 50 ng patulin per track, which is equivalent to 50 µg patulin per kg apple juice.
A Simple and Reliable HPTLC Method for the Quantification of the Intense Sweetener Sucralose®
(2003)
This paper describes a simple and fast thin layer chromatography (TLC) method for the monitoring of the relatively new intense sweetener Sucralose® in various food matrices. The method requires little or no sample preparation to isolate or concentrate the analyte. The Sucralose® extract is separated on amino‐TLC‐plates, and the analyte is derivatized “reagent‐free” by heating the developed plate for 20 min at 190°C. Spots can be measured either in the absorption or fluorescence mode. The method allows the determination of Sucralose® at the levels of interest regarding foreseen European legislation (>50 mg/kg) with excellent repeatability (RSD = 3.4%) and recovery data (95%).
Quantification of astaxanthin in salmons by chemiluminescence and absorption after TLC separation
(2018)
Astaxanthin is a keto-carotenoid, belongs to the chemical class of terpenes and is a yellow lipid soluble compound. The compound is present in marine animals like salmons and crustacean. Its colour is due to conjugated double bonds and these double bonds are responsible for its antioxidant effect. Its antioxidant activity is ten times stronger than other carotenoids and nearly 500 fold stronger than vitamin-E. We present a new thin layer chromatography (TLC) method to measure astaxanthin on TLC-plates (Merck, 1.05554) in the visible absorption range as well as by using chemiluminescence. For separation a solvent mixture of cyclohexane and acetone (10 + 2.4, v/v) was used. The RF-value of astaxanthin is 0.14.The limit of detection in vis-absorption is 64 ng / band and the limit of quantification is 92 ng/band. In chemiluminescence the values are 90 ng / band and 115 ng/band. The method offers two independently working measurement modes on a single plate which increase the accuracy of the quantification.
We present a planar chromatographic separation method for the compounds caffeine, artemisinin, and equol, separated on high-performance thin-layer chromatography (HPTLC) silica gel plates. As solvents for separation, methyl t-butyl ether and cyclohexane (1:1, V/V) have been used for equol, cyclohexane and ethyl acetate (7:3, V/V) for artemisinin, and ethyl acetate and acetone (7:3, V/V) for caffeine. After separation, the plate was scanned with a very specific time of flight-direct analysis in real time-mass spectrometry (TOF-DART-MS) system using the (M + 1)+ signals of equol, artemisinin, and caffeine. The (M + 1) peak of artemisinin at 283.13 m/z is clearly detectable, which is the proof that DART-MS is applicable for the quantitative determination of rather instable molecules. The planar set-up of DART source, HPTLC plate and detector inlet in a line showed higher sensitivities compared to desorption at an angle. The optimal detector voltage increases with the molar mass of the analyte, thus an individual determination of optimal detector voltage setting for the different analyte is recommended to achieve the best possible measurement conditions. In conclusion, DART-MS detection in combination with an HPTLC separation allows very specific quantification of all three compounds.
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.
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.
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.
Thin-layer chromatography is a rapid and reliable working method for quantification of mycotoxins which is suitable for checking EC legislation aflatoxin limits for dried figs without an RP-18 pre-column cleaning step. We describe normal-phase chromatography on silica gel plates with 2.4:0.05:0.1:0.05 ( v/v ) methyl t -butyl ether-water-methanol-cyclohexane as mobile phase and reversed-phase chromatography on RP-18 plates with methanol-4% aqueous ZnSO 4 solution-ethyl methyl ketone 15:15:3 ( v/v ) as mobile phase. Sample pretreatment was by modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) extraction with tetrahydrofuran or acetone. NaCl was used as QuEChERS salt. Response was a linear function of amount chromatographed in the ranges 3 to 100 pg per zone for aflatoxins B 2 and G 2 , 10 to 350 pg per zone for the aflatoxins B 1 and G 1 , and 0.25 to 2.5 ng per zone for ochratoxin A. Quantification limits for the aflatoxins were between 13 and 35 pg per zone (equivalent to 1.5 and 2.4 ppb, taking the pre-treatment procedure into account). Ochratoxin A was detectable with a limit of quantification of 970 pg per zone, corresponding to 56 ppb in the sample. Normal phase and RP-18 separations work rapidly, reliably, and at low cost. They are also suitable for checking the content of the mycotoxins patulin, penicillic acid, zearalenone, and deoxynivalenol.