The experience of accreditation of an analytical laboratory at the Argentine Atomic Energy Commission

The implementation of a quality system based on the ISO/IEC 17025:1999 standard is a growing necessity for analytical laboratories to demonstrate their technical competence. In 2001, the Nuclear Analytical Techniques Group of the Argentine Atomic Energy Commission obtained the recognition of the International Atomic Energy Agency in the application of neutron activation analysis and the accreditation by the national accreditation body. The importance of the participation of the group in the Agency's Regional Programme for Latin America, ARCAL XXVI on Quality Assurance in Analytical laboratories is discussed, as well as the activities performed to attain these objectives. Some improvements worth mentioning resulted from the implementation of the quality system and, following the premise of continuous improvement, changes were introduced aiming at the laboratory re-accreditation.     

Determination of triclosan in foodstuffs

A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese).     

Application of ultrasound-assisted acid leaching procedures for major and trace elements determination in edible seaweed by inductively coupled plasma-optical emission spectrometry

A new method using diluted reagents (nitric and hydrochloric acids and oxygen peroxide) and ultrasound energy to assist metals acid leaching with from edible seaweed was optimized. The method uses a first sonication at high temperature with hydrochloric acid as a previous stage to an ultrasound-assisted acid leaching with 7 ml of an acid solution containing nitric acid, hydrochloric acid and hydrogen peroxide at concentrations of 3.7, 3.0 and 3.0 M, respectively. Optimum conditions for the first sonication step were ultrasound energy at 17 kHz, sonication temperature at 65 °C, an acid volume of 2 ml, an hydrochloric acid concentration of 6.0 M and a sonication time of 10 min. It has been found that the first sonication stage at high temperature with hydrochloric acid is necessary to obtain quantitative recoveries for As, Ba, Fe and V. Otherwise quantitative recoveries were reached for the other elements investigated (Ca, K, Na, Mg, Cd, Cr, Cu, Mn, Ni, Pb and Zn). The repeatability of the ultrasound-assisted acid leaching method was around 10% for all elements. Adequate limit of detection and limit of quantification were reached by using inductively coupled plasma-optical emission spectrometry (ICP-OES) for measurements. The method resulted accurate after analysing several seaweed certified reference materials (IAEA-140/TM, NIES-03 and NIES-09). The method was finally applied to the multi-element determination in edible seaweed samples.     

An ultrasensitive method for the determination of thiouracil and phenylthiouracil using capillary zone electrophoresis and laser-induced fluorescence detection

This paper reports the development of a method based on capillary electrophoresis with laser-induced fluorescence detection for the simultaneous determination of thiouracil (TU) and phenylthiouracil (PhTU) with high sensitivity (nanomolar range, i.e., attomoles detected). After derivatization with 5-iodoacetamidofluorescein, the analytes were separated by capillary zone electrophoresis using 20 mM phosphate buffer (pH 10.0) and quantified by fluorescence detection. The linearity range, precision, recovery, and detection limits were determined, and the method was shown to be applicable for the determination of TU and PhTU in spiked feed samples and urine.     

Protein adsorption in fused-silica and polyacrylamide-coated capillaries

The model proteins cytochrome c, myoglobin, ovalbumin, and beta-lactoglobulin were investigated with regard to their adsorption properties on capillaries for electrophoresis. The model compounds were selected to cover a wide range of properties. Cytochrome c is a basic protein (isoelectric point (pI): 9.6; M(r): 11.7 kDa), beta-lactoglobulin is rather acidic (pI: 5.4, M(r): 18.4 kDa), myoglobin was chosen as a neutral reference protein (pI: 6.8-7.4, M(r): 17.8 kDa), and ovalbumin (pI: 5.1, M(r): 45.0 kDa) was selected as a relatively larger analyte. First, the pH dependence of adsorption was investigated for the bare fused silica. A clear correlation to the respective pIs was noted. For myoglobin and ovalbumin, none or negligible adsorption was found above the pI, whereas strong adsorption was noted just below this parameter. Cytochrome c and beta-lactoglobulin already showed distinct adsorption above their pIs. However, none of the proteins showed any significant adsorption more than one pH unit above the pIs. For linear polyacrylamide-coated capillaries, a decreased but not a complete lack of adsorption was observed. Here, pH-dependent adsorption was noted as well. Regeneration of the capillaries by rinsing with buffers containing 200 mM SDS was also investigated. This method was completely successful for myoglobin, but that too for only freshly-adsorbed protein. After a storage time of 24 h and due to the aging of the adsorbate, a sufficient regeneration was no longer possible.     

Alternative high-performance liquid chromatographic peptide separation and purification concept using a new mixed-mode reversed-phase/weak anion-exchange type stationary phase

This article describes a new complementary peptide separation and purification concept that makes use of a novel mixed-mode reversed-phase/weak anion-exchange (RP/WAX) type stationary phase. The RP/WAX is based on N-(10-undecenoyl)-3-aminoquinuclidine selector, which is covalently immobilized on thiol-modified silica particles (5 microm, 100 A pore diameter) by radical addition reaction. Remaining thiol groups are capped by radical addition with 1-hexene. This newly developed separation material contains two distinct binding domains in a single chromatographic interactive ligand: a lipophilic alkyl chain for hydrophobic interactions with lipophilic moieties of the solute, such as in the reversed-phase chromatography, and a cationic site for anion-exchange chromatography with oppositely charged solutes, which also enables repulsive ionic interactions with positively charged functional groups, leading to ion-exclusion phenomena. The beneficial effect that may result from the combination of the two chromatographic modes is exemplified by the application of this new separation material for the chromatographic separation of the N- and C-terminally protected tetrapeptide N-acetyl-Ile-Glu-Gly-Arg-p-nitroanilide from its side products. Mobile phase variables have been thoroughly investigated to optimize the separation and to get a deeper insight into the retention and separation mechanism, which turned out to be more complex than any of the individual chromatography modes alone. A significant anion-exchange retention contribution at optimal pH of 4.5 was found only for acetate but not for formate as counter-ion. In loadability studies using acetate, peptide masses up to 200 mg could be injected onto an analytical 250 mm x 4 mm i.d. RP/WAX column (5 microm) still without touching bands of major impurity and target peptide peaks. The corresponding loadability tests with formate allowed the injection of only 25% of this amount. The analysis of the purified peptide by capillary high-performance liquid chromatography (HPLC)-UV and HPLC-ESI-MS employing RP-18 columns revealed that the known major impurities have all been removed by a single chromatographic step employing the RP/WAX stationary phase. The better selectivity and enhanced sample loading capacity in comparison to RP-HPLC resulted in an improved productivity of the new purification protocol. For example, the yield of pure peptide per chromatographic run on RP/WAX phase was by a factor of about 15 higher compared to the standard gradient elution RP-purification protocol.     

Determination of organophosphorus and triazine pesticides in olive oil by on-line coupling reversed-phase liquid chromatography/gas chromatography with nitrogen-phosphorus detection and an automated through-oven transfer adsorption-desorption interface

A method is described for the simultaneous determination of organophosphorus and triazine pesticides in olive oil, whereby reversed-phase liquid chromatography (LC) is coupled to gas chromatography by means of an automated through-oven transfer adsorption-desorption (TOTAD) interface. The olive oil needs to be filtered only before it is loaded into the liquid chromatograph, where preseparation of the pesticide residues from the other olive oil components is carried out by using methanol-water as the eluant. The LC fraction containing the pesticides is automatically transferred to the gas chromatograph by using the TOTAD interface, which almost totally eliminates the solvent, so that water-sensitive detectors such as the nitrogen-phosphorus detector can be used. Detection limits range from 0.07 to 0.38 microg/L for organophosphorus pesticides and from 6.0 to 7.0 microg/L for triazines. The results were compared with those obtained by flame ionization detection.     

Photodegradation of the pharmaceuticals amoxicillin, bezafibrate and paracetamol by the photo-Fenton process—Application to sewage treatment plant effluent

Photodegradation of the pharmaceuticals amoxicillin (AMX), bezafibrate (BZF) and paracetamol (PCT) in aqueous solutions via the photo-Fenton process was investigated under black-light and solar irradiation. The influences of iron source, initial H₂O₂ concentration and matrix (distilled water and sewage treatment plant effluent) on degradation efficiency were discussed in detail. The results showed that (i) the degradation of the drugs was favored in the presence of potassium ferrioxalate (FeOx) in comparison to Fe(NO₃)₃; (ii) the increase of the H₂O₂ concentration improved the efficiency of AMX and BZF oxidation; however, the same was not observed for PCT; (iii) the influence of the matrix was observed for the degradation of BZF and PCT; (iv) under solar irradiation, the oxidation of the BZF and PCT is faster than under black-light irradiation. All these pharmaceuticals can be efficiently degraded employing the process evaluated.     

Exact wave functions for generalized harmonic oscillators

We transform the time-dependent Schrödinger equation for the most general variable quadratic Hamiltonians into a standard autonomous form. As a result, the time evolution of exact wave functions of generalized harmonic oscillators is determined in terms of the solutions of certain Ermakov and Riccatitype systems. In addition, we show that the classical Arnold transform is naturally connected with Ehrenfest’s theorem for generalized harmonic oscillators.     

Realization of 2D convolutional codes of rate \frac{1}{n} by separable Roesser models

In this paper, two-dimensional convolutional codes constituted by sequences in $(\mathbb F ^n)^{\mathbb{Z }^{2}}$ where $\mathbb F $ is a finite field, are considered. In particular, we restrict to codes with rate $\frac{1}{n}$ and we investigate the problem of minimal dimension for realizations of such codes by separable Roesser models. The encoders which allow to obtain such minimal realizations, called R-minimal encoders, are characterized.