A highly flexible technology for constructing plasma sources based on the rotating field concept and the digitally controlled modulation of plasma heating is presented with the plasma source ...operating at audio and ultrasonic frequency adjustable in the 6-100 kHz range and powered in the 50-250 W range. The device allows for the production of non-stationary plasma discharge sustained by a rotating electric field produced within 5 electrodes positioned in the plane around the axis, while the plasma is temporarily stretched between at least two electrodes. A stable symmetrical low-flow helium discharge is formed at atmospheric pressure operating at total gas consumption of 100-1500 mL min
1
and it is self-igniting. The plasma fundamental parameters can be easily controlled in the wide range including He excitation temperature, OH rotational temperature and electron number density between 2200 and 3300 K, 850 and 1600 K, and 0.6 and 2.0 × 10
14
cm
3
, respectively. Therefore, the excitation power of the source may be controlled by variations of the pulse width, frequency, commutation mode and gas flow rate. The device is shown to be useful for atomic emission spectrometric determination of hydride forming elements and mercury at the ng mL
1
level. The excess of hydrogen produced in the hydride generation process can be tolerated by the helium plasma. Also, the plasma can be stably operated with argon, air and nitrogen.
A digitally controlled pulse-operated rotating field helium plasma source operating at atmospheric pressure has been proposed for atomic spectrometry.
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► Se is easily determined in dietary supplements by OES. ► Alkaline solubilization with TMAH may be used for sample preparation. ► The excess iron and copper do not interfere. ► ...HSSPME is useful for separation of Se in the form of SeH2 from alkaline medium.
Headspace solid phase microextraction (HSSPME) of chemically generated selenium hydride from alkaline solution followed by thermal desorption (TD) coupled directly to a microwave plasma (MWP) source has been examined for the optical emission spectrometric (OES) determination of Se. Various chemical and operating parameters including the NaBH4 and HCl concentrations as well as the fiber exposure time and desorption temperature have been optimized. Alternatively, continuous hydride generation (HG) from alkaline medium and inductively coupled plasma (ICP) may be used for Se determination by OES. With the procedure developed, the determination of Se in dietary supplements at the tens of μgg−1 level and an accuracy of 3–6% could be performed even in the presence of the 1000-fold excess of Fe and Cu. Additionally, Se was determined in the NIST 8418 material (Wheat gluten) with a certified concentration of Se of 2.58±0.19μgg−1, and a value of 2.45±0.25μgg−1 was found using HG-HSSPME-MWP-OES. The detection limit for Se (3.2ngml−1) with the proposed procedure was comparable to those obtained with HG-ICP-OES and the calibration curve was linear of about 2 orders of magnitude.
A hydride generation headspace solid phase microextraction technique has been developed in combination with optical emission spectrometry for determination of total arsenic and selenium. Hydrides ...were generated in a 10
mL volume septum-sealed vial and subsequently collected onto a polydimethylsiloxane/Carboxen solid phase microextraction fiber from the headspace of sample solution. After completion of the sorption, the fiber was transferred into a thermal desorption unit and the analytes were vaporized and directly introduced into argon inductively coupled plasma or helium microwave induced plasma radiation source. Experimental conditions of hydride formation reaction as well as sorption and desorption of analytes have been optimized showing the significant effect of the type of the solid phase microextraction fiber coating, the sorption time and hydrochloric acid concentration of the sample solution on analytical characteristics of the method developed. The limits of detection of arsenic and selenium were 0.1 and 0.8
ng mL
−
1
, respectively. The limit of detection of selenium could be improved further using biosorption with baker's yeast
Saccharomyces cerevisiae for analyte preconcentration. The technique was applied for the determination of total As and Se in real samples.
The analytical potential of living bacteria Lactobacillus plantarum for the preconcentration of selenium from mineral water and beer samples followed by the selenium determination by continuous ...powder introduction microwave induced plasma-optical emission spectrometry (CPI-MIP-OES) has been investigated. The use of the bacteria immobilized on silica permits on-column preconcentration of selenium with minimum sample pretreatment by the pH adjustment. Experimental conditions for the preconcentration were optimized and the mechanism of the biosorption was investigated. Results showed that the use of the preconcentration stage leads to the substantial lowering of the detection limit of selenium by OES. The detection limit of 52 ng g-1 by the CPI-MIP-OES was achieved which corresponds to 0.06 ng mL-1 in the sample solution regarding the preconcentration factor of 1000. Precision of 5 replicate measurements expressed as relative standard deviation was about 3%. The utility of the method was demonstrated in the determination of selenium in hard drinking water ERM-CA011a as well as in mineral water and beer samples.
The feasibility of the use of the NOVA-2 dual-flow ultrasonic nebulizer for the determination of selenium, antimony and arsenic in drinking and mineral waters by direct hydride generation inductively ...coupled plasma-optical emission spectrometry (HG-ICP-OES) has been investigated. The acidic sample and the borohydride solution are mixed directly on the surface of a quartz oscillating plate converting liquids into aerosol at the entrance of the spray chamber. The analytical figures of merit for the multielement determination of selenium, antimony and arsenic were evaluated. Results showed that the analytical performance of the new system was superior to that of conventional nebulization systems as well as conventional continuous HG with gas-liquid separation, regarding the susceptibility to non-spectroscopic interferences produced by transition metals. Detection limits between 0.7 and 2.1 ng mL-1 were achieved with ICP-OES detection. The precision of 10 replicate measurements at the 0.25 mg L-1 level was between 1.0 to 1.5% relative standard deviation. The utility of the system was demonstrated in the determination of selenium, antimony and arsenic in hard drinking water ERM-CA011a as well as selenium in mineral water samples. The advantages and limitations of this system, compared with existing techniques, are discussed.
A spectrometric determination of aqueous fluoride has been improved by coupling of continuous powder introduction microwave-induced plasma optical emission spectrometry with separation of the analyte ...onto powdered sorbents. A selective solid phase extraction method for preconcentrating trace fluoride from aqueous environmental samples on calcium hydrogenphosphate dihydrate in batch operation was employed while, for flow operation, the zirconium modified activated carbon method was adopted. The fluoride could be readily excited in helium plasma at 685.6 nm. Using a 1-L sample volume and a preconcentration factor of 1000, practical detection limit with respect to water sample is in the range 4.0-4.7 ng mL
−1
, depending on the sorbent used. External calibration was done using standards obtained by the dropping of standard fluoride solution on the powdered sorbent covering fluoride content from 50 to 5000 µg g
−1
. The procedure was applied to the determination of fluoride in mineral waters and certified reference material (CRM) drinking water.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Selective UV-spectrophotometric methods for determination of iron(III) in iron(II) samples have been developed. The methods are based on the interaction of Fe(III) with quercetin and morin, compounds ...of the flavonoid group. Redox reactions occurring between Fe(III) ions and the reagents used make the basis for the detection. Iron(II) does not react with quercetin and morin under the conditions applied aqueous-methanolic (3:2) soluions, 0.3 mol L-1 HCl, 1.2 x 10-4 mol L-1 quercetin (morin) and does not interfere with the determination of Fe(III). Iron(III) can be determined up to 15 μg mL-1 using both the examined systems. The detection limits are 0.06 and 0.38 μg mL-1 when using quercetin or morin, respectively. The method with quercetin was applied to the determination of Fe(III) (ca. 0.2%) in a Fe(II) pharmaceutical product.
U radu je opisan razvoj selektivnih UV-spektrofotometrijskih metoda za određivanje željeza(III) u uzorcima željeza(II). Metode se temelje na redoks reakciji Fe(III) sa spojevima iz skupine flavonoida -- kvercetinom i morinom u reakcijskim uvjetima u kojima željezo(II) ne reagira (vodeno/metanolna otopina 3:2, 0,3 mol L-1 HCl, 1,2 x 10-4 mol L-1 kvercetin ili morin). Najniža koncentracija željeza(III) koja se može odrediti u oba ispitivana sustava je 15 μg mL-1. Granice detekcije su 0,06 i 0,38 μg mL-1 ako se koristi kvercetin odnosno morfin. Metoda s kvercetinom primijenjena je za određivanje Fe(III (približno 0,2%) u farmaceutskom proizvodu Fe(II).
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