Kinetic Fluorimetric Method Research Articles

Kinetic fluorimetry for determination of bisphenol S in plastics based on its promoting effect on the Fenton process

The environmental contaminant bisphenol S (BPS) was determined by a kinetic fluorimetric method combined with Fenton process in the presence of rhodamine B (RhB). In acidic solution, the fluorescent RhB was oxidized by hydroxyl radical generated in Fenton process and produced fluorescence quenching, which was obviously accelerated by BPS added into the system. The decrease in fluorescence intensity (ΔF) was proportional to the concentration of BPS with the maximum excitation and emission wavelengths of 554 nm and 578 nm, respectively. Under the optimal conditions, the ΔF was good linear with the concentration of BPS over the range of 0.004–2.0 mg/L with a correlation coefficient of 0.9991. The detection limit of 0.73 μg/L was obtained for the determination of BPS by the proposed method. The general coexisting substances did not interfere to the reactions of BPS with Fenton reagent and RhB. The proposed method has been successfully applied to determine BPS migrated from plastic package with satisfactory results. This new method is environmentally friendly and easy to popularize.

Intraindividual changes of dipeptidyl peptidase-IV in peripheral blood of patients with rheumatoid arthritis are associated with the disease activity.

BackgroundDipeptidyl peptidase-IV (DPP-IV) is suggested to contribute to the pathogenesis of several autoimmune diseases. The aim of this study was to evaluate the association of DPP-IV presence in blood plasma and mononuclear cells with the disease activity in rheumatoid arthritis (RA).MethodsPatients with active RA (n = 27) were examined at the study enrolment and a follow-up examination was performed after the regression of the joint effusions and at least 6 months after the first investigation. The control group comprised patients with a noninflammatory joint disease, i.e. osteoarthritis (OA; n = 15). The DPP-IV-like enzymatic activity was measured by a kinetic fluorimetric method, the concentration of DPP-IV in the blood plasma was determined using ELISA and the expression of DPP-IV in leukocytes was assayed by flow cytometry.ResultsBlood plasma DPP-IV-like enzymatic activity (median ± SD 220.15 ± 83.6 pkat/mL in RA vs. 376.9 ± 144.9 pkat/mL in OA, p < 0.001) and concentrations (median ± SD 465.1 ± 215.6 ng/mL in RA vs. 953.3 ± 368.4 ng/mL in OA, p < 0.001) were lower in patients with active RA compared to OA. In RA patients, the blood plasma DPP-IV-like enzymatic activity negatively correlated with the CRP concentration (r = −0.39, p = 0.044). No significant differences were observed in the DPP-IV-like enzymatic activity and DPP-IV expression in blood mononuclear cells between the RA and OA groups. At follow-up, 18 RA patients had a less active disease as demonstrated by an improved DAS28 score. In this group, comparison of the entry and the follow-up values in individual patients revealed an increase of the blood plasma DPP-IV-like enzymatic activity (median ± SD 141 ± 46 % of the patient’s entry values, p = 0.011) and DPP-IV concentration (median ± SD 168 ± 25 %, of the patient’s entry values, p = 0.033). In contrast to the blood plasma, the DPP-IV expression in blood mononuclear cells was reduced in these patients as evidenced by a decrease in the cell surface DPP-IV-like enzymatic activity as well as the median fluorescence intensity of DPP-IV staining in lymphocytes (median ± SD 66 ± 56 %, p = 0.018 and 63 ± 31 % of the patient’s entry values, p = 0.005, respectively).ConclusionsThe association between RA activity and the changes in blood plasma and blood mononuclear cell DPP-IV in individual patients supports the possible relationship of DPP-IV to RA pathophysiology.

Simple and Sensitive Synchronous- Fluorescence Method for the Determination of Trace Bisphenol S Based on its Inhibitory Effect on the Fluorescence Quenching Reaction of Rhodamine B

An inhibitory kinetic fluorimetric method is reported for the determination of trace bisphenol S (BPS). The proposed method is based on the inhibitory effect of BPS on the fluorescence quenching of rhodamine B (RhB) caused by potassium bromate in a dilute phosphoric acid medium. Under the optimal conditions of the experiment, the detection limit for BPS was 0.021mg/L, and the linear range of determination was from 0.035mg/L to 0.750mg/L. The relative standard deviations of 11 measurements for 0.20mg/L and 0.40mg/L BPS solutions were 2.74% and 1.87%, respectively. The method was successfully applied to the determination of bisphenol S derived from commercially available plastic film samples in hot water. A possible reaction mechanism of the inhibitory effect of BPS on the fluorescence quenching of RhB was proposed.

Dipeptidyl peptidase-IV in synovial fluid and in synovial fluid mononuclear cells of patients with rheumatoid arthritis

Dipeptidyl peptidase-IV (DPP-IV) enzymatic activity controls biological halftime of multiple local mediators. Its deregulation is associated with pathogenesis of several autoimmune diseases, including rheumatoid arthritis (RA). Although DPP-IV is the canonical representative of the group, a number of other proteins have been shown to have similar enzymatic activity. This study was aimed to identify the molecular source of DPP-IV activity in synovial fluid (SF) and fluid mononuclear cells (FMNC) in patients with RA and osteoarthritis (OA). In addition, the association of DPP-IV and the concentration of stromal cell-derived factor-1alpha (SDF), DPP-IV substrate, were evaluated. DPP-IV activity was measured by the kinetic fluorimetric method. The expression of studied molecules in FMNC and their concentrations in SF were assayed using flow cytometry and ELISA respectively. DPP-IV activity in SF, dominantly derived from the canonical DPP-IV, does not significantly differ between RA and OA. However, a significantly lower DPP-IV activity and expression in FMNC was found in RA as opposed to OA patients. Negative correlation between SDF concentration in SF and the relative amount of CD3+CD26+ cells was observed. We report decreased presence of DPP-IV/CD26 in CD3+ FMNC in RA, which also may participate on impaired balance of SDF concentration in SF.

A novel inhibitory kinetic fluorimetric method for the determination of trace methomyl in environmental samples

A novel inhibitory kinetic fluorimetric method for the determination of trace methomyl was proposed. It was shown that the Fenton reagent oxidized rhodamine B in acid medium which enabled the fluorescence quenching of the latter. The presence of trace methomyl clearly inhibited the reaction. Upon addition of EDTA, a good linear relationship between the inhibitory effect and the concentration of methomyl was observed, together with improved stabilization and sensitivity. Factors affecting the determination of trace methomyl were investigated systematically. Under the optimum conditions, the linear range for the determination of methomyl was 0.04-2.2 microg/mL; the detection limit and the quantification limit for methomyl were 0.011 and 0.037 microg/mL, respectively. The proposed method was applied to the determination of methomyl in four environmental soil samples, six environmental water samples and one synthetic sample; the results were compared with those determined by the HPLC method. The recoveries and the relative errors were 83.5-101.2 and 0.47-2.02%, respectively. The possible reaction mechanism has also been discussed.

Simple and sensitive fluorimetric method for determination of environmental hormone bisphenol A based on its inhibitory effect on the redox reaction between peroxyl radical and rhodamine 6G

Peroxyl radical produced by Fenton-like reagent (Fe(III) + H 2O 2) oxidizes Rhodamine 6G and produces the quenching of its fluorescence. It is also found that bisphenol A has an inhibitory effect on the redox reaction. Based on this observation, an inhibitory kinetic fluorimetric method is reported for the determination of trace bisphenol A. The fluorescent inhibition of rhodamine 6G is measured by fix-time method. Under the optimum experimental conditions, the detection limit and the quantification limit for bisphenol A is 2.0 and 6.7 ng mL −1, respectively; and the linear range of the determination is 0.024–0.4 μg mL −1. The proposed method has been used for the determination of bisphenol A in environmental waters, river bottom sediment, generic soil, polycarbonate products and teeth filling samples with recoveries of 92.5–110.0%. The possible mechanism of the reaction has also been discussed.

A surfactant enhanced stopped-flow kinetic fluorimetric method for the determination of trace DNA

A novel and high-sensitive stopped-flow kinetic fluorimetric method for determining the concentration of DNA (calf thymus DNA), in the presence of SDS, based on monitoring the variation of fluorescence within a very short period has been developed. The optimum conditions for various parameters, on which the binding of YOYO-1 to DNA depends, were investigated. It was found that the initial reaction rate increased linearly with increasing DNA concentration in the range from 8.0 × 10 −10 to 9.0 × 10 −8 M. The detection limit was calculated to be 3.0 × 10 −10 M. This method was used for determining the concentration of DNA in synthetic samples and real samples extracted from leaves of Arabidopsis thaliana, tobacco and rice with satisfactory results. The kinetics of the interaction under pseudo first-order conditions was established by the aid of single-mixing stopped-flow techniques.

Inhibitory Kinetic-Fluorimetric Determination of Trace Aniline

A novel inhibitory kinetic-fluorimetric method is reported for the determination of trace aniline. The method is based on the inhibitory effect of aniline on the oxidation of rhodamine B by potassium iodate in hydrochloric acid. The detection limit for aniline is 0.872 ng/mL; the linear range of determination is 4.10∼41.0 ng/mL. Every parameter has been optimized. Some ions which seriously interfere with the determination can be removed by means of pre-distillation in basic condition. The proposed method is simple, rapid and reliable. It has been applied to the determination of trace aniline in waste and tap waters.

Spectrofluorimetric determination of tannins based on their activative effect on the Cu(II) catalytic oxidation of rhodamine 6G by hydrogen peroxide

A simple and highly sensitive kinetic fluorimetric method is proposed for the determination of trace tannins, based on the activation of tannins on the oxidation of rhodamine 6G (Rh 6G) by hydrogen peroxide catalyzed by Cu(II) ion. The calibration graph was rectilinear in the range 0.08–1.28mgl−1 for tannin, the 3σ detection limit for tannin is 0.0455mgl−1. The relative standard deviation for 11 determinations of 0.4mgl−1 tannin is 0.96%. The proposed method has been successfully used to determine tannins in tea and Chinese gall. The results obtained were compared with those provided by the Folin–Ciocalteu method. This is the first procedure to be reported for the determination of tannins based on fluorimetric measurements.

Determination of Formaldehyde Traces in Fabric and in Indoor Air by a Kinetic Fluorimetric Method

A simple and sensitive kinetic fluorimetric method is reported for the determination of trace amount of formaldehyde. The proposed method is based on the catalytic effect of formaldehyde on the oxidation reaction of rhodamine B with potassium chlorate in sulfuric acid solution. Formaldehyde in the range of 0.020-0.340 µg/mL can be determined with a limit of detection of 5.73 ng/mL. The method has been used to determine trace formaldehyde in fabric and in indoor air. The results thus obtained show good agreement with those determined by acetyl acetone method.

Kinetic fluorimetric study of the oxidation reaction of folinic acid (leucovorin) with potassium permanganate. Determination in human urine

In this study a kinetic fluorimetric method for the determination of folinic acid (leucovorin, LV) in human urine has been developed. The fluorescence emission generated by the oxidation reaction between LV and potassium permanganate in alkaline medium has been monitored at 360 nm (excitation wavelength 290 nm). The effect of instrumental and experimental variables on the reaction was investigated and a 0.17 M sodium hydroxide, 3.3×10 −5 M KMnO 4 concentration and a temperature of 70 °C were selected for the reaction. The concentration range has been optimized between 10 and 700 ng ml −1 of LV. The correlation coefficient was 0.9989. The sensitivity of the proposed method is 9.5 ng ml −1 (expressed as limit of detection in accordance with the Clayton criterion). The determination time per sample is smaller than 200 s. The proposed kinetic fluorimetric method has been applied to the direct determination of this compound in human urine. Recovery values from urine samples, containing LV, range from 82 to 110% (mean 96%).

KINETIC–FLUORIMETRIC DETERMINATION OF ETHYLENETHIOUREA BY THE STOPPED–FLOW TECHNIQUE

A simple, sensitive, and rapid kinetic-fluorimetric method based on the oxidation of ethylenethiourea with cerium (IV) is proposed for the determination of ethylenethiourea. The rate of formation of fluorescent cerium (III) is high, while the stped flow mixing technique allows this initial rate to be easily measured and facilitates the automation of the method. The calibration graph is linear over the range 0.1–2 μg mL−1 and the precision (% RSD) is close to 1.1%. The usefulness of the method was tested for the determination of ethylenethiourea in water, milk, and fruit.

Inhibitory Kinetic Fluorimetric Determination of Trace Phenols

An inhibitory kinetic fluorimetric method is reported for the determination of trace phenols. The proposed method is based on the inhibitory effect of phenols on the reaction of H2O2 oxidation of Rh6G catalyzed by Fe(III) in perchloric acid medium. The detection limit for phenol is 8.45 ng/ml. The linear range of the determination is 0.013∼0.192 μg/ml. This method has been successfully used to determine phenols in crude carbolic acid, synthetic samples and industrial wastewaters. A comparison is made between the proposed and the 4-aminoantipyrine (4-AAP) methods. It is found that the method proposed in this paper is superior to the 4-AAP method.

An impregnated filter sampling approach for determination of hydrogen cyanide in air by a kinetic-fluorimetric micellar method

A new hydrogen cyanide collecting device based on the use of borosilicated micro-fibreglass filters impregnated with sodium hydroxide was proposed and its performance assessed. It was used for the determination of hydrogen cyanide in air by a kinetic-fluorimetric method within the 5–600 ng ml–1 range. The proposed method is based on the catalytic effect of cyanide on the oxidation of pyridoxal-5′-phosphate (PALP) by dissolved oxygen in the cationic micellar medium afforded by dodecyltrimethylammonium bromide (DTAB). The reaction was monitored by measuring the fluorescence of the oxidation product [4-pyridoxic acid 5-phosphate (PAP)]. The improved sensitivity provided by DTAB micelles was due to an increase in the quantum yield of PAP when it was concentrated on the DTAB micellar surface, resulting in an apparently increased reaction rate. The relative standard deviation for 50 ng ml–1 of cyanide was 1.7%. Common interferences, such as those arising from carbon dioxide, nitrogen oxides (NOx) and sulfur oxides (SOx), were found not to affect the hydrogen cyanide determination. The interference from hydrogen sulfide could be detected (e.g. the kinetic curve recorded showed an induction period) and amended.

Detection of Human Serum Albumin by a Photoinduced Fluorogenic Reaction

ABSTRACT 9,10-anthraquinone (AQ), a photochemically reactive substrate, has been conjugated together with human serum albumin (HSA), and the photoinduced fluorogenic reaction of the HSA-AQ conjugate was studied. This conjugate shows a greatly enhanced photochemical fluorimetric activity compared with that of free AQ. The spectral characteristics of the photoreduction product of the HSA-AQ conjugate was investigated and large blue shifts in both the excitation and emission bands, compared with those of free AQ, were observed. The kinetic behavior of the photoinduced fluorogenic reaction and the effects of some experimental conditions were also investigated. The enhancement in the photoinduced fluorogenic reactivity of HSA-AQ was utilized in the sensitive detection of HSA by a simple in-situ photoinduced kinetic fluorimetric method. The calibration graph was linear over the range 0-1.0x10−6 mol/L HSA. The detection limit was 6.5x10−10 mol/L HSA and the relative standard deviation was 2.7% for 6.0x10−8 mol/L HSA (n=6).

Fluorimetric Kinetic-FIA Determination of Ag(I) Based on Its Catalytic Effect on the Reduction Reaction of Safranine with Iodide

Abstract A sensitive kinetic fluorimetric flow injection method has been developed for the determination of Ag(I) over the range 100–2500 ng. The method is based on the catalytic effect of Ag(I) on the reduction reaction of safranine by iodide. Method development includes optimization of reagent concentration, pH, reaction temperature, and flow variables. The optimized flow injection manifold yielded a detection limit of 50 ng of Ag(I). Chemical interference studies showed that the method also has good selectivity. The method was applied to the determination of silver in expired black and white photographic film.

In-situ photochemical spectrofluorimetric detection of 9,10-anthraquinone-labeled bovine serum albumin

Bovine serum albumin (BSA) labeled with 9,10-anthraquinone (AQ) shows a greatly enhanced photochemical luorimetric activity compared with that of free AQ. The spectral characteristics of the photoreduction product of conjugated AQ were investigated and large blue shifts in the excitation and emission bands compared with those of free AQ were observed. The enhancement in the photochemical reactivity can be employed for sensitive detection of labeled BSA by a simple in-situ photochemical kinetic fluorimetric method. The kinetic behavior of the photochemical reaction and the effects of some experimental conditions were investigated. The calibration graph was linear over the range 0–1.8 × 10 −7 M BSA. The detection limit was 1.2 × 10 −10 M BSA and the relative standard deviation was 2.24% for 1.42 × 10 −8 M BSA ( n = 7).

In-situ photochemical spectrofluorimetric detection of 9,10-anthraquinone-labeled bovine serum albumin

Bovine serum albumin (BSA) labeled with 9,10-anthraquinone (AQ) shows a greatly enhanced photochemical fluorometric activity compared with that of free AQ. The spectral characteristics of the photoreduction product of conjugated AQ was investigated and large blue shifts in the excitation and emission bands compared with those of free AQ were observed. The enhancement in the photochemical reactivity can be employed for sensitive detection of labeled BSA by a simple in-situ photochemical kinetic fluorimetric method. The kinetic behavior of the photochemical reaction and the effects of some experimental conditions were investigated. The calibration graph was linear over the range 0–1.8 × 10 −7 M BSA. The detection limit was 1.2 × 10 −10 M BSA and the relative standard deviation was 2.24% for the 1.42 × 10 −8 M BSA ( n = 7).

Determination of trace thiocyanate in body fluids by a kinetic fluorimetric method

A simple and very sensitive kinetic fluorimetric method is reported for the determination of trace amount of thiocyanate. The proposed method is based on the inhibition effect of thiocyanate on oxidation of rhodamine 6G by potassium bromate in sulfuric acid solution. The detection limit for thiocyanate is 1.63 × 10 −6 mmol/l. The linear range of the determination is 4.82 × 10 −6−4.13 × 10 −5 mmol/l. This method has been used to determine trace thiocyanate in urine and saliva of smokers and non-smokers. The results obtained are satisfactory.

Cyclodextrin enhanced fluorimetric determination of malonaldehyde by the thiobarbituric acid method

The enhancement effects of α-, β-, γ;- and hydroxypropyl-β-cyclodextrins on the fluorescence of a 2:1 thiobarbituric acid/malonaldehyde adduct in acid aqueous solutions have been studied. The best characteristics as a fluorescence enhancement agent showed hydroxypropyl-β-cyclodextrin which bound the adduct sufficiently tightly (K = 180 1 mol −1) mol −1) and caused a five-fold increase in its fluorescence. A kinetic-fluorimetric method of determination of malonaldehyde in the range 0.1–10 μM at room temperature with hydroxypropyl-β-cyclodextrin as the enhancement agent is proposed and applied for the analysis of raw and cooked meat samples.