Determination of bromophos residues by fluorogenic labelling with dansyl chloride and thin-layer. Chromatography

The use of a highly sensitive and inexpensive method for determination of residues of bromophos (an organophosphate pesticide) in peanut crops, by fluorogenic labelling and thin-layer chromatography (TLC) is described. The bromophos is hydrolysed and the product 4-bromo-2,5-dichlorophenol (BDCP) dansylated with dansyl chloride. The fluorescent dansylated BDCP is separated by TLC and detected fluorimetrically. Linear fluorimetric analytical curves are obtained for bromophos weights ranging between 0.5 and 50 ng. The minimum detectable quantity is estimated to be 0.5 ng. The method can be used to recover as little as 400 ng of bromophos residue from 25 g of peanut seeds.     

Room-temperature phosphorimetry studies of some addictive drugs following dansyl chloride labelling

A room-temperature phosphorimetric (RTP) method for the analysis of barbital, codeine, morphine and practolol after labelling with dansyl chloride (DNS-Cl) is described. The drug-DNS derivatives were obtained by refluxing with drug-ethyl acetate solutions and solid DNS-Cl in the presence of anhydrous potassium carbonate. The reaction conditions were investigated in detail. The fluorescence emission of drug-DNS derivatives shifted to longer wavelengths compared with that of DNS-Cl. The RTP phenomena observed for these derivatives by using a micellar stabilized room-temperature phosphorescence technique were examined and optimum conditions for their RTP emission were studied using an orthogonal array design. Derivative RTP spectra were obtained and successfully used to determine practolol by the established method without further separation.     

Determination of the xenoestrogens 4-nonylphenol and bisphenol A by high-performance liquid chromatography and fluorescence detection after derivatisation with dansyl chloride

An easily performable and highly selective method for the determination of the xenoestrogens bisphenol A (BPA) and technical 4-nonylphenol (mixture of isomers) from environmental samples was developed. The method consists of fluorigenic labelling of the substances by dansylation followed by HPLC separation of the derivatives. Specific wavelengths (lembda(ex)=354 nm, lambda(em)=545 nm) for detection of the dansylated phenols were determined in order to reduce the signals of interfering compounds. The applicablility of the method for environmental samples was demonstrated by using sewage sludge spiked with BPA and 4-n-nonylphenol (as internal standard).     

Determination of hydrogen peroxide by photoinduced fluorogenic reactions

4-Hydroxyproline, 8-hydroxyquinoline, 4-hydroxyquinoline-2-carboxylic acid and 4-hydroxyphenylacetic acid (HPA) react with H₂O₂ when irradiated with UV light to yield fluorescent products. Sub-micromolar detection limits of H₂O₂ are possible with HPA. The fluorescent product is the same as that formed in the peroxidase enzyme-mediated H₂O₂ oxidation of HPA. Several compounds that participate in the photomediated reaction do not react in the enzyme-mediated system. A mechanism for the photomediated reaction involving an aryloxy radical derived from the substrate is suggested. Although the limits of detection for H₂O₂ do not equal the best achievable with the enzyme-mediated systems, the simplicity of a single-step reaction and an ability to “photodevelop” the product offer a range of novel analytical possibilities.     

Determination of serotonin and bufotenin as their dansyl derivatives.

A method is described which permits the determination of serotonin and bufotenin in the same tissue sample. It comprises the following steps: (a) tissue extraction with acetone-0.1 M hydrochloric acid (19:1); (b) reaction of the tissue extract with dansyl (Dns) chloride; (c) pre-separation of O-Dns-bufotenin from O,N-bis-Dns-serotonin and other Dns-amides on a small silica gel column (this step is dispensable if only serotonin or bufotonin is being determined); (d) TLC separation of O-Dns-bufotenin and O,N-bis-Dns-serotonin from other Dns derivatives; (e) quantitative evaluation of the separated compounds by fluorimetry for O-Dns-bufotenin and by fluorimetry or mass spectrometry for the serotonin derivative. The photometer response is linear within the range 0.1-300 nmole. With the mass spectrometric method, 2 pmole of O,N-bis-Dns-serotonin could be determined with a standard deivation of +/-9%. The recovery of the amines from tissue was better than 85%. Reserpine treatment of toads caused a concomitant decrease in serotonin and bufotenin in the brain, but not in the skin of the animals. Repletion of bufotenin in the brain occurs at a higher rate than the repletion of the serotonin pool.     

Fluorimetric determination of oxidised and reduced glutathione in cells and tissues by high-performance liquid chromatography following derivatization with dansyl chloride.

A high-performance liquid chromatographic method utilising fluorimetric detection of oxidised and reduced glutathione, following derivatization with dansyl chloride is described. Dansyl derivatives are separated on an aminopropyl silica column with a methanol-sodium acetate gradient system giving detection limits (signal-to-noise ratio = 2) of 1 pmol. This is in the order of 100-fold more sensitive than established methods based on the ultraviolet detection of dinitrophenylglutathione derivatives. The present procedures have been used to determine oxidised and reduced glutathione in rat lung tissues and in alveolar macrophages.     

Determination of plasma and urinary cortisol by high-performance liquid chromatography using fluorescence derivatization with dansyl hydrazine

A method is described for the determination of cortisol in human plasma and urine by high-performance liquid chromatography using fluorophotometric detection. After extraction with methylene chloride, cortisol is labelled with dansyl hydrazine, and then separated by high-performance chromatography. The eluate is monitored by a fluorophotometer at 350 nm (excitation) and 505 nm (emission). The optimum conditions for the determination, such as HCl and dansyl hydrazine concentrations, reaction time and reaction temperature, and for the eluent of high-performance liquid chromatography, are discussed. Linearity of the fluorescence intensity (peak height) with the amount of cortisol was obtained between 0.5 and 60 ng. The recoveries for 50 and 100 ng of added cortisol were 98.7 and 95.4% for plasma, and 96.4 and 90.6% for urine, respectively. Comparison with a radioimmunoassay gave a correlation coefficient of 0.978. The proposed method is suitable for the routine analysis of cortisol in plasma and urine.     

Determination of chloride by stripping chronopotentiometry with silver-film electrode

The experimental parameters of cathodic stripping chronopotentiometry of chloride at a silver-film electrode are investigated and optimized. The chloride preconcentration is achieved in the form of silver chloride by a controlled potential oxidation of the working electrode under vigorous stirring. Cathodic stripping of the deposit is obtained by the constant current, under the condition of diffusive mass transfer. Deaeration of the solution is not necessary. A detection limit of 35 μ dm⁻³ (10⁻⁶ mol dm⁻³) is obtained at a deposition time of 180 s, with a reproducibility of 6.7 % (expressed as relative standard deviation, RSD).     

Precolumn fluorogenic labelling of carboxylic acids with the use of N-(1-pyrenyl)-bromoacetamide and phase-transfer catalysis

Summary N-(1-Pyrenyl)-bromoacetamide, which is readily synthesized from 1-aminopyrene and bromoacetyl bromide, has proved to be an excellent derivatization reagent for carboxylic acids. A technique has been developed, based upon a reaction with the carboxylate as an ion pair in ethylene dichloride at 90 °C, which gives highly fluorescent ester derivatives, permitting quantitative determination by liquid chromatography of less than one pmol using conventional fluorimetric detection. Further, the method is highly reproducible and of general utility.     

Determination of cysteine concentration by fluorescence increase: reaction of cysteine with a fluorogenic aldehyde

A fluorogenic method for the determination of cysteine concentration has been developed.     

Automated pre-column derivatization of amines in biological samples with dansyl chloride and with or without post-column chemiluminescence formation by using TCPO-H2O2.

On-line automation of two different liquid chromatographic procedures, a pre-column derivatization system and a pre- and post-column system, in order to generate chemiluminescence is reported. Dansyl chloride (Dns-Cl) was used as a pre-column reagent to form fluorophores and bis(2,4,6-trichlorophenyl) oxalate (TCPO) and hydrogen peroxide (H2O2) as a post-column reagent to generate chemiluminescence. This procedure is based on the employment of a primary column packed with C18 material inserted in a multi-dimensional assembly for sample clean-up and derivatization with Dns-Cl. The dansyl derivatives formed are transferred and separated in a LiChrospher 100 RP18 analytical column (125 x 4 mm id, 5 microns film thickness) using acetonitrile-imidazole buffer (pH 6.8) (70 + 30) as eluent. The separated derivatives were transferred to the detector for fluorescence detection or to the post-column system where the chemiluminescence response was generated by using TCPO-H2O2 and the products were detected by chemiluminescence. The procedure was optimised for amphetamine and related compounds. A comparison between the on-line pre-column and pre- and post-column systems was performed. The results show that the sensitivity of chemiluminescence detection can be higher than that of fluorescence detection. The recoveries obtained ranged from 98 +/- 8 up to 108 +/- 8% for amphetamine and methamphetamine, respectively. The accuracy and precision of these methods were evaluated.     

Simultaneous determination of the binding of amantadine and its analogues to synthetic melanin by liquid chromatography after precolumn derivatization with dansyl chloride

For the determination of amantadine (1-ADA), 2-adamantanamine (2-ADA), memantine (MEM), and rimantadine (RIM) in melanin binding studies, the simultaneous determination of 1-ADA or 2-ADA, MEM, and RIM is investigated by high-performance liquid chromatographic assay with dansyl chloride as a fluorescent derivative reagent. Dansyl derivatives with fluorescent intensity are detected at an excitation wavelength of 370 nm and an emission wavelength of 506 nm. Retention times of 1-ADA, 2-ADA, MEM, and RIM derivatives are 12.2, 12.2, 15.2, and 16.6 min, respectively. The peak of 1-ADA derivative coelutes with the 2-ADA derivative. The limits of detection for 1-ADA, 2-ADA, MEM, and RIM are 0.014, 0.007, 0.012, and 0.020microM, respectively (signal-to-noise ratio of 3:1). In the intra- and interday assay, the range of standard deviation to the average of 1-ADA, 2-ADA, MEM, and RIM is 4.6-12.7%. Their recovery is also good. The ranking order for synthetic melanin binding among these compounds is RIM > MEM > 2-ADA = 1-ADA. The method is simple, sensitive, and reproducible for simultaneously measuring 1-ADA or 2-ADA, MEM, and RIM. Also, it is useful to investigate their binding kinetics to melanin.