Effects of ammonium fluoride on the decomposition of geochemical samples as fluorinating agent and its analytical application.

In this work, the effects of ammonium fluoride on the decomposition of geochemical samples were investigated by analyzing some certified reference materials (CRM). The major and minor elements were detected by inductively coupled plasma optical emission spectrometry (ICP-OES), while trace and ultra-trace elements were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Decomposition time, temperature and the amount of ammonium fluoride were studied in detail. In the process of sample decomposition, on one hand, ammonium fluoride was used as the fluorinating agent because ammonium fluoride can be dissociated under acid medium to yield fluoride ions to attack silicon compound effectively. On the other hand, ammonium fluoride was used as a latent solvent since ammonium salt may dissolve insoluble fluorine compounds. The removal of insoluble fluorine compounds decreased the memory effect on digestion vessels caused by fluoride coprecipitation. By testing CRMs and many real samples, it was found that trace and ultra-trace elements could be digested using ammonium fluoride instead of hydrofluoric acid and the dissolution ratios of major and minor elements, for example Al, Ca, Mg, Fe, Na and K, improved noticeably. Moreover, the use of ammonium fluoride instead of hydrofluoric acid contributes to a greener environment and safer for operators.

Construction of a controllable Förster resonance energy transfer system based on G-quadruplex for DNA sensing.

Conjugations of oligonucleotides, chromophores, and gold nanoparticles (GNPs) can be used for energy transfer assays to detect DNA. Herein, a homogenous Förster resonance energy transfer (FRET) system employing two-step modification of oligonucleotide on GNPs was reported. The distance between the donor (fluorescein attached onto DNA) and the acceptor (GNPs) was controlled by using the G-rich DNA. In the presence of porphyrin or berberine, which can act as ligands of G-quadruplexes, the G-rich DNA spacer can result into G-quadruplex structure. Therefore, the intimate contact between the fluorophore and the GNP results in efficient energy transfer and fluorescence quenching. After hybridization with target DNA, the G-quadruplex stretched and resulted in an enhancement of fluorescence. So the present FRET system can be used for target DNA sensing with detection limit as low as 40 pM (S/N=3). In this study, a relation between the fluorescence quenching efficiency and GNP sizes was found and bigger GNPs had higher fluorescence enhancement after hybridization with target DNA.

Sensitive chemiluminescence assay for risperidone in pharmaceutical preparations.

A sensitive chemiluminescence (CL) method to determine the antipsychotic risperidone (RSP) is proposed, based on the catalytic effect of risperidone on the CL reaction between luminol and hydrogen peroxide in flow system. The increment of CL intensity was correlated with risperidone concentration in the range of 10pg ml(-1) to 1.0ng ml(-1) with a relative standard deviation of less than 5.0% (n = 5); and a limit of detection of 4pg ml(-1) (3sigma). At a flow rate of 2.0ml min(-1), the flow injection CL method exhibited both high sensitivity and excellent selectivity giving a throughput of 120 samples per hour. The proposed method was applied successfully to the determination of risperidone in pharmaceutical preparations.

Flow injection chemiluninescence for detecting picogram amounts of dobesilate in human urine.

A sensitive method for the determination of dobesilate in pharmaceutical preparations and human urine is described by using controlled-reagent-release technology. The method entailed the use of luminol and periodate, which are immobilized on anion exchange resin and react in alkaline medium, giving chemiluminescence (CL) at 425 nm. Dobesilate was detected by measuring the decrease of CL intensity, and which was observed linear over the dobesilate concentration range of 10-600 pg ml(-1), and the limit of detection was 3.5 pg ml(-1) (3sigma) and a relative standard deviation of less than 3.0%. At a flow rate of 2.0 ml min(-1), the determination of dobesilate, including sampling and washing, could be performed in 0.5 min, giving a throughput of about 120 times per hour. The proposed method has an extremely low limit of detection down to 3.5 pg ml(-1), thus it can be applied directly in the assay of human urine without any pre-treatment. It was also found that the dobesilate concentration reached its maximum after orally administrated for 3.5h, and the excretion ratio in 24h was 58.8% in the body of volunteers.

In vitro monitoring of nanogram levels of puerarin in human urine using flow injection chemiluminescence.

A rapid and sensitive chemiluminescence (CL) determination of puerarin with the flow injection technique was presented. It was found that puerarin could enhance the CL generated from luminol-KIO(4) system significantly. The increment of CL intensity was linear over the concentration of puerarin ranging from 0.3 to 100.0 ng mL(-1) (r(2)=0.9963), offering a detection limit as low as 0.1 ng mL(-1) (3 sigma). At a flow rate of 2.0 mL min(-1), one analysis cycle, including sampling and washing, could be accomplished in 20 s with a relative standard deviation of less than 5.0%. The experimental results demonstrated that the excretive amounts of puerarin reached its maximum in 3 h after taking 250 mL green drink containing 275 mg puerarin, and the puerarin excretive ratio during 24 h was 9.70% in the body of volunteers.

Ultrasensitive assay of azithromycin in medicine and bio-fluids based on its enhanced luminol-H(2)O(2) chemiluminescence reaction using flow injection technique.

A simple flow injection chemiluminescence method with synergistic enhancement has been investigated for the rapid and sensitive determination of azithromycin. The synergistic action was significant in the chemiluminescence system of luminol-hydrogen peroxide with azithromycin as an enhancer. The enhanced chemiluminescence intensity was linear with the concentration of azithromycin over the range from 0.1 pg x mL(-1) to 1.0 ng x mL(-1) (r(2=)0.9988) with a detection limit (3sigma) of 0.04 pg x mL(-1). At a flow rate of 2.0 mL x min(-1), a complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 3.0%. The proposed method was applied successfully in the assay of azithromycin in pharmaceutical preparations, human urine and serum without any pre-treatment procedure.