Study of the heavy atom-induced room temperature phosphorescence properties of melatonin and its analytical application

Liquid phase room temperature phosphorescence (RTP) properties of melatonin were studied using heavy atom induced-room temperature phosphorescence (HAI-RTP) technique. 1.2 M potassium iodide was used as a heavy atom reagent together with 0.002 M sodium sulphite as deoxygenating agent to produce the RTP signal. The maximum phosphorescence emission and excitation wavelengths of melatonin were 290 and 457 nm, respectively. The effect of potassium iodide concentration on the RTP lifetime of melatonin was also investigated and based on the results, the rate constants for phosphorescence decay (k(p)) and radiationless deactivation through reaction with heavy atom (k(h)) were determined. Based on the obtained results, a simple and sensitive room temperature phosphorimetric method was developed for the determination of melatonin. The method allowed the determination of 10.0-200 ng ml(-1) melatonin in aqueous solution with the limits of detection and quantification of 3.6 and 12 ng ml(-1), respectively. The proposed method was satisfactorily applied to the determination of melatonin in commercial pharmaceutical formulations.     

Development of a Novel Versatile Method for Determination of two Antihistamines in Association with Naphazoline Using Cathodically Pretreated Boron‐doped Diamond Electrode

Antihistamines such as pheniramine (PHN) or chlorpheniramine (CPH) are commonly associated with naphazoline (NPZ) in eye drops and nasal decongestants. In this work, a batch‐injection analysis system with multiple pulse amperometric (BIA‐MPA) detection has been applied for the first time for fast simultaneous determination of naphazoline (NPZ) and pheniramine (PHN) or NPZ and chlorpheniramine (CPH). PHN or CPH was selectively detected at +1.1 V and both PHN and NPZ or CPH and NPZ were detected at +1.3 V using boron doped diamond (BDD) as working electrode and Britton‐Robinson (BR) buffer (pH=10.0) as supporting electrolyte. The current of NPZ can then be obtained by subtraction of the currents detected at both potential pulses and applying a correction factor (CF). The proposed method presented good intra‐day repeatability (RSD between 0.7 and 3.2 % for PHN; 0.7 and 2.1 % for CPH; 1.5 and 4.0 % for NPZ; n=20), high analytical frequency (>80 injections h⁻¹), and limits of detection of 0.64, 0.47 and 0.11 μmol L⁻¹ for PHN, CPH and NPZ, respectively. The results obtained with the proposed method are in agreement with those obtained by HPLC (95 % confidence level).     

Simple and rapid determination of the drug naproxen in pharmaceutical preparations by heavy atom-induced room temperature phosphorescence

A simple, selective and sensitive heavy atom-induced room temperature phosphorimetric method (HAI-RTP) is described for the determination of naproxen (NAP) in pharmaceutical preparations. The phosphorescence signals are a consequence of intermolecular protection when analytes are, exclusively, in presence of a heavy atom salt and sodium sulfite as an oxygen scavenger to minimize RTP quenching. These variables selection constitute the basis of a HAI-RTP method for the determination of naproxen (detection limit 17.6 ng ml(-1); 1.71% relative standard deviation at 250 ng ml(-1)). The method has been applied satisfactorily to the analysis of pharmaceutical preparations.     

Analytical study of the phosphorescence of pyrimidine derivatives in frozen aqueous solution

Phosphorescence excitation and emission spectra, phosphorescence lifetimes, phosphorimetric analytical curves and limits of detection were determined at 77K in 10/90 v/v methanol/water solution for seven pyrimidine derivatives. The effect of pH on the phosphorescence intensity indicated an improvement of the sensitivity of the method in basic medium (pH reverse similar11). Low limits of detection, between 10(-5) and 10(-8)M, were obtained. The effect of sodium iodide on the phosphorescence efficiency led to heavy-atom enhancement factors ranging from 1.1 to 9.6, depending on the molecular structure and the pH conditions.     

Study of the substituent groups effect on the room-temperature phosphorescent emission of fluorene derivatives in solution

We present here the first study of the effect of substituent groups and the chemical structure of fluorene derivatives on phosphorescent emission. A group of fluorene derivatives have been studied with a new methodology of room-temperature phosphorescence emission called heavy atom induced room-temperature phosphorescence (HAI-RTP). This methodology makes use of RTP emission directly from the compound in fluid solution, without a protective medium but only with the presence of high concentrations of heavy atom perturbers and an oxygen scavenger. These experimental conditions permit sufficient interaction between the perturbers and the phosphors to produce effective population of the triplet states of the latter and, consequently, intense phosphorescent emission. Good deoxygenation conditions are obtained using sodium sulfite as the oxygen scavenger. We show here that it is possible that many fluorene derivatives can exhibit RTP emission in aqueous solutions in the absence of a protective medium. Phosphorescence spectral characteristics of these compounds (excitation and emission wavelengths and lifetime) and the optimization of the chemical variables involved in the phosphorescence phenomenon are reported. Under optimal experimental conditions, calibration graphs and detection and quantification limits in the ng ml⁻¹ level have been established.     

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.     

叶酸的低温磷光分析

叶酸有光、酸中强、碱中弱、HCl浓度高,光强,但不稳定。叶酸经紫外光照射后光增强,增强量与叶酸含量成比例,建立了叶酸的低温光分析法,并用作小鼠,豚鼠肝中叶酸含量分析     

The use of modified simplex method to optimize the room temperature phosphorescence variables in the determination of an antihypertensive drug

In the present paper, the modified simplex method (MSM) has been applied, for the first time, to determine compounds by a luminescence technique. The method was based on the optimization of chemical and instrumental variables affecting phosphorescence using a geometric simplex in two and three dimensions of space, respectively. As application, we have determined a novel antihypertensive drug, naftopidil, in urine and serum, by heavy atom induced room temperature phosphorescence (HAI-RTP); this technique enables us to determine analytes in complex matrices, biological fluids, without the need for a tedious prior separation process. With the proposed method, the maximum signal of phosphorescence appears instantly once the sample has been prepared and the intensity was measured at lambda(ex)=287 nm and lambda(em)=525 nm. Overall least-squares regression was used to find the straight line that fitted the experimental data. The detection limit, as well as the repeatability and the standard deviation (S.D.) for replicate sample, were also determined.     

水溶液中丙酮的敏化室温磷光测定

测定水溶液中微量丙酮,常用吸光光度法^[1～3]和色谱法^[4,5]等,这些方法固然灵敏度较高,但样品的预处理比较复杂,分析速度慢,线性范围窄.本文以丁二酮为能量受体,建立了水溶液中微量丙酮的敏化室温磷光测定法.方法简便快速,重现性好,灵敏度亦高.     

Construction and performance characterization of screen printed and carbon paste ion selective electrodes for potentiometric determination of naphazoline hydrochloride in pharmaceutical preparations

This paper describes the development of screen-printed (SPE) and carbon paste (CPE) sensors for the rapid and sensitive quantification of naphazoline hydrochloride (NPZ) in pharmaceutical formulations. This work compares the electroactivity of conventional carbon paste and screen-printed carbon paste electrodes towards potentiometric titration of NPZ. The repeatability and accuracy of measurements performed in the analysis of these pharmaceutical matrices using new screen printed sensors were evaluated. The influence of the electrode composition, conditioning time of the electrode and pH of the test solution, on the electrode performance were investigated. The drug electrode showed Nernstain responses in the concentration range from 1 × 10(-6) to 1 × 10(-2) mol L(-1) with slopes of 57.5 ± 1.3 and 55.9 ± 1.6 mV per decade for SPE and CPE, respectively, and was found to be very precise and usable within the pH range 3-8. These sensors exhibited a fast response time (about 3 s for both SPE and CPE, respectively), a low detection limit (3.5 × 10(-6) and 1.5 × 10(-6) M for SPE and CPE, respectively), a long lifetime (3 and 2 months for SPE and CPE, respectively) and good stability. The selectivity of the electrode toward a large number of inorganic cations, sugars and amino acids was tested. It was applied to potentiometric determination of NPZ in pure state and pharmaceutical preparation under batch conditions. The percentage recovery values for the assay of NPZ in tablets (relative standard deviations ≤0.3% for n = 4) were compared well with those obtained by the official method.     

The determination of natural uranium in human tissues by recovery corrected kinetic phosphorescence analysis

Two typical methods used for the determination of uranium in human autopsy tissues are kinetic phosphorescence analysis (KPA) and alpha-spectrometry, both of which have significant limitations and advantages. KPA is limited because of the amount of sample used (1–10 ml for sample digestion followed by one ml KPA aliquots), no isotopic information is provided, phosphorescence degradation by salts in solution, and even more importantly, it does not provide chemical recovery information. For samples with sub ng uranium concentrations per g of inorganic material, preconcentration is necessary, which may require chemical recovery (other than simple evaporation). While alpha-spectrometry has very good radiometric detection limits for ²³⁸U, the very long half-life of ²³⁸U (4.468·10⁹ y) restricts its mass detection limit (27 ng). KPA, on the other hand, has a detection limit three orders of magnitude lower (0.02 ng) for natural uranium. A recovery corrected method for the determination of natural uranium in human tissues was developed combining preconcentration of human tissues dissolved in 6M HCl by anion exchange with alpha-spectrometry and kinetic phosphorescence analysis, utilizing ²³²U as a tracer. Solution aliquots containing up to 6 g of bone ash were pre-concentrated for KPA measurement thereby allowing the use of up to 25% of the original sample solution weight for analysis by KPA. The radiochemical yield of ²³²U was determined by alpha-spectrometry and the uranium content was determined by KPA. The mean radiochemical yields obtained for human tissue samples range from 65% to 106% with a mean of 85%±8%.     

Direct determination of 1-naphthoxylactic acid in biological fluids by non-protected fluid room temperature phosphorimetry

A selective and sensitive room-temperature phosphorimetric method for the direct determination of 1-naphthoxylactic acid (NA) in biological fluids is described. It is based on obtaining a phosphorescence signal from NA using TlNO₃ as a heavy atom perturber and Na₂SO₃ as a deoxygenator without a protective medium. This technique is named non-protected room-temperature phosphorescence (NP-RTP), which allows to determine analytes in complex matrices without the need for tedious prior separation. Optimization of the operational conditions resulted in a detection limit for NA of 9.6 ng/mL according to the error propagation theory. The repeatability and standard deviation were also determined. This method was successfully applied to the determination of NA in urine and human serum.     

Determination of oxolinic acid in cow's milk and human urine by means of a single-use phosphorimetric sensor

A single-use phosphorimetric drop plane sensor for the determination of oxolinic acid (OXA) is proposed. The sensor was formed by a 30x16 mm(2) rectangular strip of Mylar type polyester as solid support that contained a circular sensing zone, 6 mm in diameter and 20 mum in thickness, formed by PVC plasticized with tributylphosphate adhered to its surface. When the strip was introduced for 1 hour into a sample solution, the analyte was retained in the sensing zone, making it possible to directly measure the phosphorescence intensity emitted by the OXA in the solid phase, at lambda(exc)=330 nm and lambda(em)=449 nm. The variables that affect the construction of the sensor have been studied, along with the experimental variables that influence the fixation of the analyte in the sensor. The method's detection limit was 0.01 mg l(-1) with an applicable concentration range from 0.04 to 1.50 mg l(-1) and a repeatability of 2.6% at the concentration range of 0.8 mg l(-1). The method was applied to samples of human urine and cows' milk, with recovery percentages ranging between 97.6 and 108.7%.     

Direct determination of 1-naphthoxylactic acid in biological fluids by non-protected fluid room temperature phosphorimetry

A selective and sensitive room-temperature phosphorimetric method for the direct determination of 1-naphthoxylactic acid (NA) in biological fluids is described. It is based on obtaining a phosphorescence signal from NA using TlNO3 as a heavy atom perturber and Na2SO3 as a deoxygenator without a protective medium. This technique is named non-protected room-temperature phosphorescence (NP-RTP), which allows to determine analytes in complex matrices without the need for tedious prior separation. Optimization of the operational conditions resulted in a detection limit for NA of 9.6 ng/mL according to the error propagation theory. The repeatability and standard deviation were also determined. This method was successfully applied to the determination of NA in urine and human serum.     

Determination of carbaryl in foods by solid-phase room-temperature phosphorimetry

A phosphorimetric solid phase assay is proposed for the determination of the pesticide carbaryl (CBL) at room temperature. CBL was spotted on filter paper together with Tl(I) as heavy metal, and dried for 3 min, after which the diffuse transmitted phosphorescence was measured using two quartz plates to avoid the quenching effect produced by atmospheric oxygen. The linear dynamic range was 0.5–4.0 μg/mL and the detection and quantification limits were 0.09 and 0.31 μg/mL, respectively. The precision of the method, expressed as relative standard deviation, was 2.3% for a sample containing 2.0 μg/mL of CBL. The method was applied to the determination of CBL residues in cereals, potatoes and waters, obtaining recoveries ranging between 92 and 105%. Received: 10 October 1997 / Revised: 2 February 1998 / Accepted: 7 February 1998     

Sensitive and simple determination of the vasodilator agent dipyridamole in pharmaceutical preparations by phosphorimetry

The applicability of heavy atom-induced room-temperature phosphorescence to pharmaceutical samples is demonstrated in this work. Thus a new, simple, rapid, and selective phosphorimetric method for dipyridamole determination is proposed. The phosphorescence signals are a consequence of intermolecular protection when analytes are exclusively in the presence of heavy atom salts and sodium sulfite as an oxygen scavenger to minimize RTP quenching. The determination was performed in 0.1 mol L^–1 thallium(I) nitrate and 8 mmol L^–1 sodium sulfite at a measurement temperature of 20 °C. The phosphorescence intensity was measured at 635 nm, with excitation at 305 nm. Phosphorescence was easily developed; a linear concentration range was obtained between 0 and 100 ng mL^–1 with a detection limit of 940 ng L^–1, an analytical sensitivity of 2.5 ng mL^–1, and a standard deviation of 2.7% at 60 ng mL^–1 concentration. The method has been successfully applied to the analysis of dipyridamole in a unique Spanish commercial formulation containing 100 ng mL^–1 per capsule. The recovery was 101.6% with 6.5% standard deviation of analytical measurement. The method using the standard addition methodology has been validated.     

Determination of carbaryl in foods by solid-phase room-temperature phosphorimetry

A phosphorimetric solid phase assay is proposed for the determination of the pesticide carbaryl (CBL) at room temperature. CBL was spotted on filter paper together with Tl(I) as heavy metal, and dried for 3 min, after which the diffuse transmitted phosphorescence was measured using two quartz plates to avoid the quenching effect produced by atmospheric oxygen. The linear dynamic range was 0.5–4.0 μg/mL and the detection and quantification limits were 0.09 and 0.31 μg/mL, respectively. The precision of the method, expressed as relative standard deviation, was 2.3% for a sample containing 2.0 μg/mL of CBL. The method was applied to the determination of CBL residues in cereals, potatoes and waters, obtaining recoveries ranging between 92 and 105%.     

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.     

Solid-phase spectrophosphorimetric determination of the pesticide <Emphasis Type="Italic"> o</Emphasis>-phenylphenol in water and vegetables

A phosphorimetric method for the determination of o-phenylphenol (OPP) using filter paper as solid support and Tl(I) as heavy metal enhancer of the phosphorescent signal is proposed. The phosphorescence measurements were carried out by placing the paper with the sample between two plates of quartz, thus avoiding the quenching effect produced by atmospheric oxygen and moisture. The linear dynamic range of the method was 0.5-4.0 mg L(-1) and the detection and quantification limits were 0.03 and 0.11 mg L(-1), respectively. The precision of the method (expressed as relative standard deviation) was 1.7% for a sample containing 2.0 mg L(-1) of analyte. The method has been applied to the determination of OPP in different types of water, lettuce, string beans and peppers, with recoveries ranging between 97.1 and 100.7%     

Fast simultaneous spectrophotometric determination of naphazoline nitrate and methylparaben by sequential injection chromatography

Fast simultaneous determination of naphazoline nitrate and methylparaben in pharmaceuticals using separation method based on a novel reversed-phase sequential injection chromatography (SIC) is described in this contribution as an alternative to classical HPLC. A Chromolith™ Flash RP-18e (25 mm × 4.6 mm) column (Merck^®, Germany) and a FIAlab^® 3000 system (USA) with a six-port selection valve and 5.0 ml syringe pump were used for sequential injection chromatographic separations in our study. The mobile phase used was methanol/water (40:65, v/v), pH 5.2 adjusted with triethylamine 0.8 μl ml⁻¹ and acetic acid, at flow rate 0.9 ml min⁻¹. UV detection provided by DAD detector and two wavelengths were simultaneously monitored for increasing sensitivity of determination. Detector was set up at 220 nm for naphazoline nitrate and 256 nm for methylparaben and ethylparaben (IS). There is no necessity to use pre-adjustment of sample of nasal drops (only dilution with mobile phase) so the time of the whole analysis is very short. The validation parameters have shown good results: linearity of determination for both components (naphazoline nitrate and methylparaben), correlation coefficient >0.999; repeatability of determination (R.S.D.) in the range 0.5-1.6% at three different concentration levels, detection limits 0.02 μg ml⁻¹ (naphazoline nitrate) and 0.20 μg ml⁻¹ (methylparaben and ethylparaben), and recovery from the pharmaceutical preparations in the range 100.06-102.55%. The chromatographic resolution between peaks of compounds was more than 4.0 and analysis time was less than 4 min under the optimal conditions. The advantages and drawbacks of SIC against classical HPLC are discussed showing that SIC can be an advantageous alternative in many cases.