Solid-phase extraction of alkylphosphonic and O-alkyl alkylphosphonic acids followed by HPLC separation using porous graphitic carbon sorbent.

An HPLC separation of alkyl phosphonic acids on porous graphitic carbon adsorbent Hypercarb, based upon a step gradient of formic acid concentration in an aqueous mobile phase, was evaluated in this study. Analytes were detected by single quadrupole and triple quadrupole MS. Good separation was achieved for methyl phosphonic acid, ethylphosphonic acid, n-propylphosphonic acid, isopropylphosphonic acid, ethyl methylphosphonic acid, isopropyl methylphosphonic acid, isobutyl methylphosphonic acid, pinacolyl methylphosphonic acid. Solid-phase extraction of these analytes on Hypercarb was also proposed, desorption was carried out with aqueous ammonium formate and water-methanol mixtures. LODs were 0.1-0.2 ng mL-1 for these analytes without SPE; solid-phase extraction resulted in the decrease of LODs at least 100-fold. Accuracy was proven by analyses of spiked samples of river water and snow meltwater.

Effect of amines on formation of gold/polyurethane foam nanocomposites and its sensing opportunities.

Effect of amines on formation of gold nanoparticles (AuNPs)/polymer nanocomposites has been observed and studied. Nanocomposites based on polyurethane foam and AuNPs were synthesized by interaction between the polymer modified with sodium borohydride and aqueous solution of tetrachloroauric acid. It has been shown that some amines cause a remarkable decrease of the surface plasmon resonance band of AuNPs in the nanocomposite material. Both aliphatic and aromatic amines as well as amines containing several amino groups were studied. A possible mechanism of the effect is discussed. It is probably based on stabilization of AuNPs with an amine that entails a decrease in the degree of their adsorption on PUF and appearance of the stabilized AuNPs in solution. The decrease of the nanocomposite surface plasmon resonance band is proportional to the concentration of amine in the solution. Based on this effect, a method for the determination of cetylamine, ß-naphthylamine and neomycin in water and medical formulations using a monitor calibrator as a portable household tool is proposed. Under the selected conditions, the detection limits for amines were in the range of 0.7-1.5 µM, the determination ranges were approximately an order of magnitude. The observed color change of the nanocomposite samples also provides a good basis for semiquantitative determinations.

Potentialities of differently-stabilized silver nanoparticles for spectrophotometric determination of peroxides.

One of the possible ways for using silver nanoparticles (AgNPs) in spectrophotometry is their application for the determination of oxidizing agents, based on oxidative destruction of these nanoobjects. This process depends on the structure of AgNPs surface layer, which is essentially affected by the chosen stabilizer. To assess influence of the nanoparticle stabilizer and the nature of the analyte, possibilities of AgNPs covered with stabilizers of three types (citrate, polyvinylpyrrolidone, and polyhexamethylene guanidinium) for the spectrophotometric determination of hydrogen peroxide and differently substituted organic peroxides were studied. The approach is based on AgNPs oxidation leading to discoloration of the solution monitored spectrophotometrically. Different selectivity of the oxidation depending on the stabilizer was shown. Effects of various factors (time of interaction, pH, concentration of AgNPs) on the oxidation and analytical performance of the procedure were investigated. The method allows for the determination of hydrogen peroxide, peracetic acid, m-chloroperbenzoic acid, and t-butylhydroperoxide in the range of 0.3-1.5, 0.1-0.8, 1.0-7.5, and 1-7 µg mL-1 and with the limits of detection of 0.1, 0.04, 0.3, and 0.3 µg mL-1, respectively. The analysis can be performed using either spectrophotometry or naked-eye detection.

Determination of pyrophosphate and sulfate using polyhexamethylene guanidine hydrochloride-stabilized silver nanoparticles.

Positively charged polyhexamethylene guanidine hydrochloride-stabilized silver nanoparticles (PHMG-AgNPs) were prepared and applied as a colorimetric probe for single-step determination of pyrophosphate and sulfate. The approach is based on the nanoparticles aggregation leading to change in their absorption spectra and color of the solution. Due to both electrostatic and steric stabilization these nanoparticles show decreased sensitivity relatively to many common anions, which allows for simple and rapid direct single-step determination of pyrophosphate and sulfate. Effects of different factors (time of interaction, pH, concentrations of anions and the nanoparticles) on aggregation of PHMG-AgNPs and analytical performance of the procedure were investigated. The method allows for the determination of pyrophosphate and sulfate in the range of 0.16-2µgmL-1 and 20-80µgmL-1 with RSD of 2-5%, respectively. The analysis can be performed using either spectrophotometry or naked-eye detection. Practical application of the method was shown by the example of pyrophosphate determination in baking powder sample.

Formation of plasmonic silver nanoparticles by flavonoid reduction: A comparative study and application for determination of these substances.

Formation of plasmonic silver nanoparticles by flavonoid reduction was studied. Effects of the nature and the concentration of a flavonoid and a stabilizer, composition of the solution and the interaction time were revealed. It was found that quercetin, dihydroquercetin, rutin and morin produced an intense surface plasmon resonance band of silver nanoparticles at 415 nm which was linearly related to the concentration of a flavonoid, while chrysin, naringenin and naringin did not produce any remarkable changes. It was used for the spectrophotometric determination of the former four flavonoids with the detection limits of 0.03; 0.06; 0.09 and 0.1 µg mL(-1), respectively. The developed method was applied for the determination of flavonoids in biologically active food additives.

X-ray fluorescence determination of As, Bi, Co, Cu, Fe, Ni, Pb, Se, V and Zn in natural water and soil extracts after preconcentration of their pyrrolidinedithiocarbamates on cellulose filters.

A simple method for the elements preconcentration on thin-layer paraffin-treated cellulose filters was proposed. It was found that pyrrolydinedithiocarbamates of As(III), Bi, Cd, Co, Cu, Fe(III), Ni, Pb, Se(IV), V(V) and Zn obtained after mixing of sample (3-5 ml min(-1)) and reagent (0.7-1.0 ml min(-1)) streams were quantitatively recovered from 100 ml sample. The sample acidity was adjusted to pH 4.8-5.2 for preconcentration of Cd, Co, Cu, Fe(III), Ni, Pb, V(V) and Zn, and to 2 M HCl for preconcentration of As, Bi and Se. The optimum reagent concentration was found to be 0.1%. The elements were determined on the filters by X-ray fluorescence spectrometry. The detection limits achieved were 0.1-4.0 mug of element on the filter. Relative standard deviation (R.S.D.) was not higher than 0.08 while determining 5-50 mug of elements on filter. Accuracy and precision of the technique proposed were evaluated by the analysis of spiked natural samples.