Micellar-stabilized room-temperature phosphorimetric determination of the fungicide thiabendazole in canned pineapple samples

A method for the determination of the fungicide thiabendazole (TBZ) by micellar-stabilized room-temperature phosphorescence is described. It does not require any separation step and allows the direct determination of the fungicide in canned pineapple samples. The effect of various experimental conditions is discussed in detail. The analytical curve of thiabendazole gives a linear dynamic range of 23.8–500.0 ng mL^–1 and a detection limit of 23.8 ng mL^–1. Recoveries of 103.9 and 89.2% for syrup and canned pineapple pulp, respectively, were obtained for 250 ng mL^–1 thiabendazole. Received: 30 April 1997 / Revised: 18 July 1997 / Accepted: 23 July 1997     

A new analytical application of nylon-induced room-temperature phosphorescence: determination of thiabendazole in water samples

This paper discusses the first analytical determination of the widely used fungicide thiabendazole by nylon-induced phosphorimetry. Nylon was investigated as a novel solid-matrix for inducing room-temperature phosphorescence of thiabendazole, which was enhanced under the effect of external heavy-atom salts. Among the investigated salts, lead(II) acetate was the most effective in yielding a high phosphorescence signal. An additional enhancement of the phosphorescence emission was attained when the measurements were carried out under a nitrogen atmosphere. There was only a moderate increase in the presence of cyclodextrins. The room-temperature phosphorescence lifetimes of the adsorbed thiabendazole were measured under different working conditions and, in all cases, two decaying components were detected. On the basis of the obtained results, a very simple and sensitive phosphorimetric method for the determination of thiabendazole was established. The analytical figures of merit obtained under the best experimental conditions were: linear calibration range from 0.031 to 0.26 μg ml⁻¹ (the lowest value corresponds to the quantitation limit), relative standard deviation, 2.4% (n = 5) at a level of 0.096 μg ml⁻¹, and limit of detection calculated according to 1995 IUPAC Recommendations equal to 0.010 μg ml⁻¹ (0.03 ng/spot). The potential interference from common agrochemicals was also studied. The feasibility of determining thiabendazole in real samples was successfully evaluated through the analysis of spiked river, tap and mineral water samples.     

Non-protected fluid room-temperature phosphorimetric procedure for the direct determination of naftopidil in biological fluids

Non-protected fluid room temperature phosphorescence, NPRTP, has been applied to the determination of naftopidil in biological fluids. The proposed method is based on obtaining a phosphorescence signal from naftopidil using potassium iodide as heavy atom perturber and sodium sulfite as a deoxygenating reagent without a protected medium. Optimized conditions for the determination were 1.4 mol L= KI, 5.0 x l0(-3) mol L(-1) sodium sulfite, pH 6.5 (adjusted with sodium hydrogen phosphate-dihydrogen phosphate buffer solution, 5.0 x 10(-2) mol L(-1). The delay time, gate time, and time between flashes were 70 micros, 400 micros, and 5 ms, respectively. The maximum phosphorescence signal appeared instantly and the intensity was measured at lambda(ex)=287 nm and lambda(em)=525 nm. The response obtained was linearly dependent on concentration in the range 50 to 600 ng mL(-1). The detection limit, according to error-propagation theory, was 7.93 ng mL(-1) and the detection limit as proposed by Clayton was 11.12 ng mL(-1). The repeatability was studied by using ten solutions of 400 ng mL(-1) naftopidil; if the theory of error propagation is assumed the relative error is 0.88%. The standard deviation of replicates was found to be 3.5 ng mL(-1). This method was successfully applied to the analysis of naftopidil in human serum and urine with recoveries of 104.0 +/- 0.6% for serum and 106.0 +/- 1.0% for urine.     

Highly sensitive and selective room-temperature phosphorescence determination of thiabendazole by the supramolecular interaction of thiabendazole/beta-cyclodextrin/triton X-100

A strong and stable room temperature phosphorescence (RTP) signal (lambda(ex)/lambda(em) = 298/481 nm) resulting from a 1:1:1 beta-cyclodextrin (beta-CD)/thiabendazole (TBZ)/triton X-100 (TX-100) supramolecular ternary inclusion complex was induced by KI as a heavy atom perturber. Based on the heavy-atom induced RTP, a new phosphorescence method for TBZ determination was established. The analytical curve of TBZ gave a linear range of 20-820 ng mL(-1) with a detection limit and relative standard deviation of 2.1 ng mL(-1) and 1.9%, respectively. The interference of 46 coexisting substances was studied. Compared with the method using a chemical oxygen scavenger, this method is simpler as deoxygenation of the solution is not required. The detection limit and the heavy-atom concentration of the proposed method were decreased about 8 and 4 times, respectively. The lifetime of the phosphorescence was prolonged 9 times and the pH range was greatly broadened. The proposed method has been successfully applied to the determination of TBZ in tap water, lake water and pineapples.     

Molecularly imprinted capillary electrochromatography for selective determination of thiabendazole in citrus samples

In this work, the suitability of the combination of molecular imprinting and capillary electrochromatography (MIP-CEC) to be used as powerful tool in environmental or food analysis has been for the first time studied and successfully demonstrated. A molecularly imprinted monolith (MIM) has been synthesised and evaluated as stationary phase for the selective determination of the fungicide thiabendazole (TBZ) in citrus samples by non-aqueous capillary electrochromatography. The influence of the mobile phase composition, the voltage of the power supply and the separation temperature on the recognition of TBZ by the imprinted polymer has been evaluated, and the imprint effect in the MIM was clearly demonstrated. Once optimum recognition conditions were established, other variables affecting mechanical properties and chromatographic performance of MIM were adjusted using computational approach. The high selectivity achieved by the MIP-CEC developed procedure allowed unambiguous detection and quantification of TBZ in citrus samples by direct injection of the crude sample extracts, without any previous clean-up, in less than 6 min. The developed method was properly validated and the calculated detection limits were below the established maximum residue limits (MRLs), clearly demonstrating the suitability of the method to be used for the control of the selected fungicide.     

Solid-surface room-temperature phosphorimetric detection of caffeine,theophylline and theobromine in liquid chromatography

Solid-surface room-temperature phosphorimetry (SSRTP) is proposed as an alternative detection technique for the liquid chromatographic determination of caffeine, theophylline and theobromine. The measurements are performed in a continuous mode with a two-nebulizer automated system for SSRTP detection. The analytical figures of merit obtained with the proposed detector are compared with those obtained by UV absorption detection. The SSRTP and UV chromatograms of spiked urine samples are compared, and the possibility of keeping the SSRTP substrates as permanent records of analyzed samples is discussed.     

Application of partial least-squares calibration to phosphorimetric data for determination of polycyclic aromatic hydrocarbons in spiked environmental samples

A partial least-squares calibration method is proposed, for the first time, for phosphorescence signals. The proposed method is based on the determination of phenanthrene, fluoranthene, and benz[a]anthracene by room temperature phosphorimetry, using microemulsion solutions. The emission and first-derivative emission spectra of the ternary mixtures were tested to perform the calibration matrix. Improved recoveries were found for the prior differentiation step in the analysis of ternary mixtures of these polycyclic aromatic hydrocarbons in road dust samples. The proposed method yielded recoveries ranging from 93.2 to 115.3%, with relative standard deviations of < 6.8%.     

Polarographic determination of thiabendazole

Summary Polarographic Determination of Thiabendazole Thiabendazole is used as a fungistat on citrus fruit to protect it from decay.In order to work out a polarographic determination the electrochemical behaviour of thiabendazole was investigated by sampledd c polarography and differential pulse polarography. Thiabendazole shows one wave or peak in the polarogram, when a short drop time (0.4 s) is used. Detection is most sensitive at pH 8. The current measured is proportional to the concentration. The detection limit is 0.5 ppm.By evaluating further experimental data it was possible to conclude, that mercury is first oxidised. Thereby two electrons are exchanged. Then mercury(II) ions formed in this way react with two molecules thiabendazole. Two protons are involved in this chemical process.Applying drop times greater than 0.4 s and concentrations higher than 1.5·10^–4 M a polarogram with two peaks is formed. This is due to the adsorption of the reaction product.For quantitative determination several citrus fruits were peeled and the peels were extracted with ethylacetate. After removing interfering substances by shaking with sodium hydroxide solution, thiabendazole was extracted by diluted hydrochloric acid and quantitatively determined by differential pulse polarography. The recovery of thiabendazole is 70.0% with a relative standard deviation of 2.9%. For all samples investigated the thiabendazole concentrations were below the permitted value.Cordially dedicated to Univ.-Prof. Dr. Dr. h. c. K. Kratzl on the occasion of his 70th birthday.     

Determination of thiabendazole in foods and waters by solid-phase transmitted room-temperature phosphorescence

A new method for the determination of thiabendazole (TBZ) is proposed, based on enhanced native phosphorescence at room temperature when the pesticide is fixed on paper and using Pb (CH₃-COO)₂ as the enhancer. The sample and enhancer solutions were deposited on a slip of paper (Whatman No. 4), previously humidified with pH 4.0 acetic/acetate buffer solution, after which the paper was dried and placed between two quartz plates. The diffuse transmitted phosphorescence intensity was measured directly at _ex = 303 nm and _em = 472 nm. The applicable concentration range was 160.0–1200.0 ng/ml, with a relative standard deviation of 1.2%. The detection and quantification limits were 47.7 and 158.9 ng/ml, respectively. This simple method was used to measure the levels of this pesticide in potatoes, green beans, lettuce and different types of waters, showing good selectivity in all instances.     

A sensitive spectrophotometric method for the determination of dithiocarbamate fungicide and its application in environmental samples

A sensitive spectrophotometric method based on the evolution of CS₂ and colour development by leuco crystal violet is described for the determination of dithiocarbamate fungicides, e.g. thiram, ziram and zineb. Dithiocarbamate fungicides release CS₂ on acid hydrolysis. This CS₂ is absorbed in ethanolic sodium hydroxide and forms xanthate. The xanthate formed is subsequently treated with potassium iodate and N-chlorosuccinimide, during which free iodine is liberated. Crystal violet dye was formed through selective oxidation of leuco crystal violet by liberated iodine, which has an absorbance maxima at 595 nm. The colour systems obey Beer's law in the range of 0.02–0.20, 0.02–0.24 and 0.04–0.32 ppm for thiram, ziram and zineb respectively. The molar absorptivity of the colour system were found to be 9.6×10⁵, 1.1×10⁶ and 6.8×10⁵±100 l mol⁻¹ cm⁻¹ for thiram, ziram and zineb respectively. The method has been successfully applied to the determination of these dithiocarbamate fungicides in various environmental samples.     

Single-use phosphorimetric sensor for the determination of nalidixic acid in human urine and milk

A single-use phosphorimetric sensor to determine the germicide nalidixic acid is proposed. The sensing action is based on the absorption of the analyte into the sensing zone and the subsequent measurement of the phosphorescence intensity emitted by the analyte fixed in the sensor. This plane drop sensor is made up of a 3 x 1.6 cm sheet of the polyester Mylar as solid support, and a circular film 5 mm in diameter and 20 microns in thickness, formed by poly(vinyl chloride) and tributyl phosphate as the plasticizer, adhered to its surface. The sensor is introduced for 2 h into the sample solution, after which it is dried and the phosphorescence intensity is measured directly at lambda ex = 332 nm, lambda em = 412 nm, with a delay time of 0.15 ms and a gate time of 10 ms, under a dry nitrogen stream. The characteristic parameters of the construction of the sensing zone and of the processes of fixing the analyte along with the emission of phosphorescence were studied. The applicable concentration range was from 60 to 1500 ng ml-1, with a detection limit of 20 ng ml-1 and a precision of 2% expressed as relative standard deviation. The method was applied to the determination of nalidixic acid in milk and human urine with recoveries ranging between 96.0 and 103.7%. The calibration process was carried out by applying a mathematical method of finite elements that expresses the analytical signal as a function of the analyte concentration and equilibration time between the sensor and the sample solution.     

Spectrofluorimetric determination of thiabendazole in a micellar medium

A sensitive, selective Spectrofluorimetric method has been developed for the determination of thiabendazole in a sodium dodecylsulphate micellar medium. The method features a linear determination range of 0.020-15 g and a detection limit of 0.2 ng/ml, with a relative standard deviation of less than 3%. By using a straightforward extraction procedure with ethyl acetate and hydrochloric acid, the method provided average thiabendazole recoveries above 96% from apple, pear and potato samples.     

Dispersive liquid-liquid microextraction combined with high performance liquid chromatography-fluorescence detection for the determination of carbendazim and thiabendazole in environmental samples

A rapid and sensitive method for the determination of carbendazim (methyl benzimidazole-2-ylcarbamate, MBC) and thiabendazole (TBZ) in water and soil samples was developed by using dispersive liquid-liquid microextraction (DLLME) coupled with high performance liquid chromatography with fluorescence detection. The water samples were directly used for the DLLME extraction. For soil samples, the target analytes were first extracted by 0.1 mol L⁻¹ HCl. Then, the pH of the extract was adjusted to 7.0 with 2 mol L⁻¹ NaOH before the DLLME extraction. In the DLLME extraction method, chloroform (CHCl₃) was used as extraction solvent and tetrahydrofuran (THF) as dispersive solvent. Under the optimum conditions, the enrichment factors for MBC and TBZ were ranged between 149 and 210, and the extraction recoveries were between 50.8 and 70.9%, respectively. The linearity of the method was obtained in the range of 5-800 ng mL⁻¹ for water sample analysis, and 10-1000 ng g⁻¹ for soil samples, respectively. The correlation coefficients (r) ranged from 0.9987 to 0.9997. The limits of detection were 0.5-1.0 ng mL⁻¹ for water samples, and 1.0-1.6 ng g⁻¹ for soil samples. The relative standard deviations (RSDs) varied from 3.5 to 6.8% (n = 5). The recoveries of the method for MBC and TBZ from water samples at spiking levels of 5 and 20 ng mL⁻¹ were 84.0-94.0% and 86.0-92.5%, respectively. The recoveries for soil samples at spiking levels of 10 and 100 ng g⁻¹ varied between 82.0 and 93.4%.     

Room temperature phosphorimetric determination of cyanide based on triplet state energy transfer

The determination of cyanide ions in water samples by room temperature phosphorescence (RTP) detection is described. The method is based on the measurement of the RTP emission of α-bromonaphthalene (BrN). The principle of the RTP cyanide determination involves the energy transfer (ET) from the BrN phosphor molecule insensitive to the presence of cyanide (acting as a donor) to a cyanide-sensitive dye (acceptor).The RTP emission spectrum of BrN overlaps significantly with the absorption spectrum of the complex formed between copper and Cadion 2B, giving rise to a non-radiative ET from the phosphor molecules to the metal complex. The sensing of cyanide ions is based on the displacement by cyanide of the copper ions from its complex with Cadion 2B (the free chelating molecule presents a low absorbance in the region of maximum emission of the BrN phosphor). An increase in the concentration of cyanide causes a decrease on the concentration of the Cadion 2B-copper complex (acceptor) with the subsequent decrease of the absorbance in the overlapping region with the RTP spectra, resulting in higher RTP emission signals measured. Both, RTP intensities and triplet lifetimes of the BrN increased with the increase of the cyanide concentration.The calibration graphs were linear up to a concentration of 500 mg l⁻¹ cyanide and a precision of ±2 and ±0.5% for five replicates of 50 μg l⁻¹ of cyanide has been obtained when measuring intensities and triplet lifetimes values, respectively. A detection limit of 3 μg l⁻¹ of cyanide was achieved under optimal reaction conditions and pH 11. The use of phosphorescence measurements (low background noise signals) resulted in an important improvement on the sensitivity of the cyanide detection higher than eight times as compared to the molecular absorption spectrophotometric method for cyanide detection based on the use of Cadion 2B-copper as cyanide-indicator.Interference studies were performed with cations and anions present in drinking water samples which could affect the analytical response. Finally, the method has been successfully applied to the determination of trace levels of labile cyanide in spiked drinking water samples.     

Determination of lead in fresh and canned pineapple by isotope dilution mass spectrometry and isotope systematics

Pineapple stored in welded and soldered can was analysed for lead to assess the extent to which it is contaminated during processing and storage. To avoid contamination during analysis the samples were prepared in clean laboratory using ultra-clean procedures. The lead concentration was determined by isotope dilution mass spectrometry and the sources of lead were identified by their isotopic signature and quantified by isotope systematics. The results showed that the lead concentration in pineapple stored in the soldered cans (ca. 150 ng g^?1) was about 2.5 times that found in the welded cans and 60–80% of this lead was traced to the soldered joint using isotope systematics. The edible portion of a fresh pineapple contained < 0.85 ng g^?1 lead, showing that even pineapple in welded cans may be contaminated 80 times more than the natural level.     

Fluorimetric determination of the fungicide benomyl after solvolysis

A simple spectrofluorimetric method for the determination of the fungicide benomyl in grapes is described. Benomyl is rapidly solvolysed in organic solvents to give the highly fluorescent metabolite carbendazim. Solvent effects on the spectral shape and their influence on analytical performance are studied. DMF was found to be the best solvent. The method is sensitive to 12 ng/ml benomyl, and has an RSD at the 0.5 g/ml level of 2.2%. The method is suitable for determining benomyl in spiked grapes, with recoveries in the range 97 to 104%.     

A novel flow-through fluorescence optosensor for the determination of thiabendazole

This paper presents the development of a new flow-injection system combined with solid-surface fluorescence detection for the determination of the widely used fungicide thiabendazole. Nylon powder was probed as a novel solid support for building the optosensor. The method is based on the on-line immobilization of thiabendazole onto nylon in a continuous flow system, followed by the measurement of its native fluorescence. Aqueous samples are directly injected in a water carrier, resulting in a very simple and economical method. The analytical figures of merit obtained using 1500 μL of sample and 75% methanol (v/v) as eluting solution were: linear calibration range from 8 to 120 ng mL⁻¹ (the lowest value corresponds to the quantitation limit), relative standard deviation, 0.9% (n = 5) at a level of 64 ng mL⁻¹, limit of detection calculated according to 1995 IUPAC recommendations is to 2.8 ng mL⁻¹, and sampling rate of 14 samples h⁻¹. The potential interference from other agrochemicals, metal ions and common anions, and the viability of determining thiabendazole in real water samples were also evaluated.     

Synchronous-derivative phosphorimetric determination of 1- and 2-naphthol in irrigation water by employing beta-cyclodextrin

A room-temperature phosphorimetric (RTP) study of the inclusion process between 1- and 2-naphthol, beta-cyclodextrin (beta-CD) and 3-bromo-1-propanol as heavy atom pertuber has been performed. Experimental conditions were optimized for the formation of trimolecular complexes with lifetimes of 10.82 and 9.41 ms for 1- and 2-naphthol, respectively. A synchronous-derivative room-temperature phosphorimetric method has been proposed to the analysis of both naphthols in synthetic mixtures and irrigation water in the ratio 1:10 to 10:1; the limit of detection is 0.02 mug ml(-1) and the relative standard deviation (RSD) is about 6%.     

Molecularly imprinted stir bars for selective extraction of thiabendazole in citrus samples

Stir‐bar sorptive extraction is based on the partitioning of target analytes between the sample (mostly aqueous‐based liquid samples) and a stationary phase‐coated magnetic stir bar. Until now, only PDMS‐coated stir bars are commercially available, restricting the range of applications to the non‐selective extraction of hydrophobic compounds due to the apolar character of PDMS. In this work, a novel stir bar coated with molecularly imprinted polymer as selective extraction phase for sorptive extraction of thiabendazole (TBZ) was developed. Two different procedures, based on physical or chemical coating, were assessed for the preparation of molecularly imprinted stir bars. Under optimum conditions, recoveries achieved both in imprinted and non‐imprinted polymer stir bars obtained by physical coating were very low, whereas TBZ was favourably retained by imprinted over non‐imprinted polymer stir bars obtained by chemical coating and thus the latter approach was used in further studies. Different parameters affecting both stir‐bars preparation (i.e. cross‐linker, porogen, polymerization time) and the subsequent selective extraction of TBZ (i.e. washing, loading and elution solvents, extraction time) were properly optimized. The molecularly imprinted coated stir bars were applied to the extraction of TBZ from citrus samples (orange, lemon and citrus juices) allowing its final determination at concentrations levels according to current regulations.     

Room-temperature phosphorimetric determination of biogenic indole compounds adsorbed on a thin-layer chromatographic plate

A simple and sensitive method is described for the determination of biogenic indole compounds adsorbed on cellulose or alumina plates for thin-layer chromatography by room-temperature phosphorimetry. The optimum conditions were investigated for 5-hydroxyindole-3-acetic acid and indole-3-acetic acid. The compounds are spotted on the plates, which are then sprayed successively with sodium citrate or sodium acetate, and sodiu iodide solutions. The plates are dried completely under a stream of dry nitrogen, and immediately dipped in molten paraffin. The phosphorescence is stable for at least 3 h even in moist air. The limits of detection for nine biogenic indole compounds tested are between 2 and 300 pmol per sample spot.