Analysis of methylparaben in cosmetics based on a chemiluminescence H2 O2 -NaIO4 -CNQDs system.

In this article, a simple, effective chemiluminescence (CL) method for the detection of methylparaben (MP) in cosmetic samples was developed based on an IO4 - -H2 O2 -carbon nitrogen quantum dots (CNQDs) system without a separation process. The results indicated that the redox reaction between periodate and hydrogen peroxide released hydroxide radicals and superoxide radical anions in the presence of bicarbonate. These two radicals were responsible for the formation of excited luminophor CNQD* with a maximum wavelength at 480 nm. Due to the competitive reaction with hydroxide radicals, CL intensity was markedly diminished in the presence of MP. The relative standard deviation in the intraday assay was below 5.5% (n = 9), and the detection limit was as low as 0.50 µmol/L. The proposed method allowed for the successful, selective determination of MP in cosmetics.

Ultrasensitive high-performance liquid chromatography determination of tetracycline antibiotics and their 4-epimer derivatives based on dual effect of methanesulfonic acid.

In reversed-phase liquid chromatography, tetracycline antibiotics yield broad and asymmetrical peaks, as a result of their ionic interaction with the anionic free silanol groups and metal ion present in the silica-based stationary phases (commonly derivatized with C18 groups). These frequently encountered difficulties were absolutely eliminated based on dual effect when methanesulfonic acid was employed as an eluent additive. The study revealed that the performance of methanesulfonic acid to minimize the "silanol effect" is mainly explained by both direct neutralization of the anionic silanol sites and electrostatic attraction with analytes. Based on these dual action mechanisms, an ultrasensitive method has been successfully developed for the simultaneous determination of tetracycline antibiotics and their derivatives (minocycline, oxytetracycline, tetracycline, chlortetracycline, metacycline, doxycycline, 4-epitetracycline, and 4-epichlortetracycline) in bovine milk with convenient ultraviolet detection within 15 min. Under the optimal conditions, the calibration curves showed good linearity (r2  > 0.999) for all analytes in the range of 1∼200 ng/mL with the instrument limits of detection as low as 0.3 ng/mL. The study sheds new light on suitable additives to analyze basic compounds with the advantage of good compatibility with MS detection.

Class-specific determination of fluoroquinolones based on a novel chemiluminescence system with molecularly imprinted polymers.

A ultrasensitive chemiluminescence (CL) method for the determination of fluoroquinolones (FQs) in milk was proposed based on the enhancement effect of FQs on the CL reaction between cerium(IV) and methoxylated Cypridina luciferin analogs (MCLA). Prior to the CL determination, molecularly imprinted polymers (MIPs) with superior recognition performances were adopted to the clean-up and extraction of the family of FQs. Then the developed CL system coupling with MIPs (MIP-CL) was applied to the selective determination of FQs in milk. Under the optimized conditions, the method was validated with respect to linearity, precision, accuracy, limits of detection and quantification. The relative standard deviation (RSD) on intra-day assay was below 5.1%, and detection limit was as low as 0.10 nmol/L. The consistency of this method and HPLC method was compared and validated by the paired t-test. The results indicated that the proposed method allowed class-specific determination of FQs in complex matrices.

Effect of selenite on organic selenium speciation and selenium bioaccessibility in rice grains of two Se-enriched rice cultivars.

The accumulation of organic selenium (Se) in grains is helpful in understanding its bioaccessibility in various Se-enriched rice cultivars after soil selenite treatments. In the present study conducted with two rice cultivars, the organic Se as well as the glutelin-derived Se and the selenomethionine (SeMet) percentage in grains increased with soil Se levels. The available Se that was detected in the forms of SeMet (∼40%) and selenite (∼12%) accounted for more than 50% of the total Se in grains, and no significant differences were observed between the two rice cultivars (P > 0.05). Simulated gastrointestinal digestion showed that the digested grain SeMet increased with the soil Se treatment levels, whereas there were minimal changes in the percentages of selenite in the grain. Furthermore, approximately half of the available SeMet was derived from the grain glutelin. These results suggest that the non-glutelin-derived Se in rice should be further studied.

Determination of bromate via the chemiluminescence generated in the sulfite and carbon quantum dot system.

The authors describe a chemiluminescence (CL)-based assay for the determination of bromate. The method is based on the use of a solution of carbon quantum dots (CQDs) and sulfite. Strong CL (peak at 490 nm) is observed when bromate is injected into the solution. The CL increases linearly in the 0.3 to 10 µmol L-1 bromate concentration range, giving a 0.1 µmol L-1 limit of detection (at an S/N ratio of 3). A possible CL mechanism is suggested that involves a redox reaction between the CQDs, bromate and sulfite in the acidic medium. This leads to the formation of hole-injected and electron-injected CQDs. Radiative recombination of oxidant-injected holes and electrons in the CQDs accounts for the occurrence of CL. This mechanism contradicts the previous assumption that the transfer of energy occurs from SO2* to the CQDs. Although nitrite may interfere in the determination of bromate, its effect can be eliminated by adding sulfamic acid. The assay is sensitive and represents a new tool for the determination of bromate, which is a carcinogen. Graphical abstract Under acidic condition, carbon quantum dots (CQDs) can react with sulfite and bromate transforming to hole-injected CQDs (CQDs•-) and electron-injected CQDs (CQDs•+), respectively. Thereafter, strong chemiluminescence (490 nm) aroused from the radiative electron-hole annihilation between CQDs•- and CQDs•+.

Simultaneous determination of anabolic steroids and ß-agonists in milk by QuEChERS and ultra high performance liquid chromatography tandem mass spectrometry.

A simple, accurate and highly sensitive multiresidues method was developed for the determination of 9 anabolic steroids and 16 ß-agonists in milk. Target compounds were extracted and separated by a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method with Primary secondary amine (PSA) and Zinc oxide (ZnO) nanoparticles as adsorbents. The analytes were determined by ultra high performance liquid chromatography coupled to an electro-spray ionization tandem mass spectrometer (UHPLC-MS/MS) operating in negative/positive multiple reaction monitoring mode. The effect of QuEChERS including organic solvent, amount of ZnO nanoparticle was evaluated. Good linearity was obtained for the analytes in the concentration range of 0.1-200µg/L with a correlation coefficients higher than 0.994. Decision limits (CCα) was from 0.007µg/kg-0.1µg/kg, and detection capabilities (CCß) was in the range of 0.02-0.4µg/kg. The recoveries of these compounds were between 63% and 126% at three fortified levels. Reproducibility represented by RSD was with 10% or less. The method was successfully applied to screening of real milk samples obtained from local markets and confirmation of the suspected target analytes.

Sensitive monitoring of humic acid in various aquatic environments with acidic cerium chemiluminescence detection.

In this research, a simple, sensitive chemiluminescence (CL) method for the determination of humic acid (HA) in water samples was first developed based on the redox reaction between humic acid and cerium(IV) in the acidic condition. Different with the former redox CL reaction which occurred in alkaline solution, no enhancers were needed and neither precipitation nor a second contamination would occur in the present CL system. Comparing with other spectrometric methods, we find that the proposed analysis system had better applicability and accuracy. Under the optimal experiment conditions, the CL peak height was linear with the concentration of HA in the range of 0.03 to 10.0 microg mL(-1). The detection limit is 0.01 microg mL(-1) (S/N = 3), and the relative standard deviation was 2.3% for 0.5 microg mL(-1) HA solution with eleven repeated measurements. The present CL method was successfully applied to the determination of HA in tap water, spring water and river water samples with good recovery from 90.0 to 110.0%. A possible CL mechanism was proposed based on the results of UV and fluorescence spectrometry and the CL spectrum of HA. It was speculated that the semi-quinone radicals in the excited state were the emitters.

On-line preparation of peroxymonocarbonate and its application for the study of energy transfer chemiluminescence to lanthanide inorganic coordinate complexes.

It has been shown that peroxymonocarbonate ion (HCO(4) (-)) is a potent oxidant. In this study, a flow-injection system was developed in order to prepare on-line HCO(4) (-) ion and the optimum conditions for the on-line preparation of HCO(4) (-) were studied in detail. We used 99% (13)C-enriched NaHCO(3) to examine peroxymonocarbonate by (13)C-NMR at 25 degrees C. An ultra-weak chemiluminescence (CL) was observed after mixing H(2)O(2) and sodium bicarbonate in an organic co-solvent that can accelerate the formation of HCO(4) (-) ion. When lanthanide inorganic coordinate complex, Eu(II)-EDTA, was added into this HCO(4) (-) system, the CL intensity was significantly enhanced. The CL mechanism was investigated by various methods. The experimental results indicate that peroxymonocarbonate oxidizes Eu(II) to Eu(III) and produces singlet oxygen; meanwhile, the energy originating from dimers of singlet oxygen is accepted by the Eu(III)-EDTA(-) complex. The excited Eu(III) ions undergo radiative deactivation and emit CL.