A definitive method for the determination of small amounts of copper in biological materials by neutron activation analysis

A highly accurate and precise procedure deserving the name of definitive method has been devised for the determination of copper in biological materials. The method is based on combination of neutron activation and very selective and quantitative post-irradiation separation of copper from other radionuclides by extraction chromatography, using columns with LIX 70 on Bio-Beads SM-1, followed by gamma-ray spectrometric measurement. All potential sources of errors were carefully examined and eliminated or appropriate corrections were introduced into the procedure. The method contains several warning mechanisms safeguarding against making gross errors. Limit of detection for rather short irradiation time (t_ir1 h) (which enables radiochemical work without sophisticated shielding) amounts to 15 g/kg. Results for copper concentration in several NBS, IAEA and other certified reference materials are presented and a new recommended value for IAEA's Milk Powder (A-11) is proposed.     

Electrothermal AAS determination of bismuth, antimony and tin in high-purity WO3

Summary Four methods for the bulk trace determination of Bi, Sb and Sn in WO₃ were developed and tested. In all cases, the final determination is carried out by graphite furnace atomic absorption spectrophotometry. The limits of detection range from 1 g/g for a very fast and simple method to 50 ng/g for a method comprising a trace-matrix separation by sorption and complexation on activated carbon powder loaded with TMDTC. A way of preparation of standard reference WO₃-samples doped with varying amounts of Bi, Sb and Sn traces is also described.     

A Comparative Study of Homemade C18 and Commercial C18 Sorbents for Preconcentration of Lead by Minicolumn Solid Phase Extraction

A comparative study of commercial C₁₈ chemically immobilized on silica and homemade C₁₈, as sorbents for Pb complexed with O,O-diethyl-dithiophosphate (DDTP) in a flow injection preconcentration system is reported. The homemade C₁₈ sorbent was obtained by sorption of poly(methyloctadecylsiloxane) (PMODS) on the silica support followed by immobilization using thermal treatment. The method follows the concept of green chemistry, since there are no toxic residues after synthesis. The complexed Pb was formed in 1.0molL^–1 HCl medium and retained on the minicolumn filled with the sorbents. The elution was carried out using ethanol, and the richest 210µL fraction was collected and analyzed by flame atomic absorption spectrometry. Chemical and flow variables were optimized for each sorbent. The results demonstrated that the performance of the proposed homemade C₁₈ sorbent for preconcentration of Pb complexed with DDTP is very similar to commercial C₁₈ chemically bonded on silica. By processing 25mL, the enrichment factors were 129 and 125 for commercial C₁₈ and homemade C₁₈, respectively. The limit of detection for commercial and homemade C₁₈ was 0.2µgL^–1 and 0.6µgL^–1, respectively. The relative standard deviation (RSD) was lower than 1.2% for both sorbents for a Pb concentration of 100µgL^–1. The method was also applied successfully to the analysis of water samples, and the accuracy was tested by recovery measurements on spiked samples and biological reference material.     

Investigation for the determination of ultra trace amounts of Co2+ complexed with 1,10-phenanthroline by adsorptive voltammetry

Summary The spontaneous adsorption of the Co²⁺ complex with 1,10-phenanthroline on HMDE was utilized for the development of a voltammetric analytical method employing phase selective alternating current, with first harmonic AC₁ in phase, =0°, voltammetry. The dependence of the analytical voltammetric response on physical and chemical parameters in various supporting electrolytes was investigated in detail. Optimum conditions for Co²⁺ determination were established. The method is very sensitive and selective. The determination limit is 205 ng/l Co²⁺ (adsorption time, t_ads=20 min). The precision and accuracy were evaluated: 1.84 g/l Co²⁺, RSD=3.24%, RE=–0.54%; for 205 ng/l Co²⁺, RSD=4.85%, RE=–3.90%. The results showed good reproducibility and reliabiality. The method was applied to natural waters, wines, mussel tissue and aquatic algae certified reference material.     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

A monitor for atmospheric sulphur dioxide,based on enrichment of SO2 by a polydispersive water aerosol

A monitor for continuous analysis of sulphur dioxide in the atmosphere at the ppb v/v level (1 ppb v/v = 2.62 g/m³ SO₂) is described. The apparatus operates on the principle of equilibrium accumulation of sulphur dioxide from the air by a polydispersive water aerosol which continuously transfers SO₂ from an air-flow of l/min into microlitre volumes of water condensate. High sensitivity (1 ppb v/v), low relative error (± 5% at 4 ppb v/v SO₂), high selectivity (CO₂ does not interfere at a concentration of 2 × 10³ ppm v/v, interference by NO _x and H₂S is acceptably low), and low response delay (10 s) are provided by a compact coupling of the enrichment procedure with conductivity detection of SO₂ in the film of water aerosol condensate formed directly on the wire-gauze sensor. The reliability of the method has been studied under simulated conditions, with spectrophotometric method as reference. The analyser is computer-controlled, and the detector response is processed on-line and displayed (as g/m³) in real-time on a screen or is transmitted telemetrically to a control centre. It is portable and suitable for use in both stationary and moving locations.The paper is dedicated to the 65th anniversary of the birthday of Prof. Josef F. K. Huber     

Development of mycotoxin reference materials

Summary The analytical difficulties in mycotoxin determination have given rise to the development of mycotoxin reference materials by the European Community Bureau of Reference (BCR) in cooperation with several European Laboratories, among them the National Institute of Public Health and Environmental Protection. The first project undertaken concerned four milk powders certified for their aflatoxin M₁ content (concentrations 0, 0.1, 0.3 and 0.8 g/ kg). Projects that are well-advanced include two peanut meals (aflatoxin B₁ contents 0 and ca. 200 g/kg) and two compounded animal feedingstuffs (aflatoxin B₁ contents 0 and 10 g/kg). Mycotoxin reference materials are also under development for zearalenone in wheat and maize, and for ochratoxin A in wheat.The general approach followed in the development and certification of mycotoxin reference materials (preparation, testing for homogeneity and stability, intercomparisons of methods and certification exercise) will be discussed and exemplified with the help of the completed project on aflatoxin M₁ in milk powder.

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Entwicklung von Mycotoxin-Referenzmaterialien

     

Radiochemical neutron activation analysis of chromium in biological materials using ion chromatography with “on-line” yield determination

The use of ion chromatography with continuous UV detection for radiochemical separation of Cr with simultaneous yield determination is presented. The RNAA method consists of sample destruction in HNO₃+HClO₄, extraction of Cr(VI) with tribenzylamine in CHCl₃, backextraction in NaOH and chromatography of chromate. From radiotracer experiments, the ratio of signals for⁵¹Cr and Cr spike was found to be constant for a chromium mass range of 15 to 100 g. Application of the RNAA method to Cr determination in biological reference materials showed a reasonable agreement with the reference values. A relative standard deviation of 3% on the 100 g/kg level for homogeneous material was achieved.IAEA-fellow, on leave from the Philippine Nuclear Research Institute Philippine     

A normal phase HPTLC method for the quantitative determination of fumonisin B1 in rice

Summary A normal phase HPTLC method has been validated by spiking, in quadruplet, uncontaminated extract of rice with fumonisin B₁ over the range 0 to 16g/g. The method utilises solid phase extraction using strong anionic exchange (SAX) cartridges, uni-directional normal phase high performance thin layer chromatography (HPTLC), novel visualisation by dipping into a 0.16% acidic solution ofp-anisaldehyde and quantification by scanning fluoro-densitometry. Response was linear only over the range 0 to 5 g/g (0 to 125 ng/spot) where recoveries averaged 81% for rice. Weighted linear regression yielded a limit of detection of 0.25 g/g for rice. Coefficients of variance were 15.4, 5.3, 2.8, 3.5, and 0.9% at fumonisin B₁ levels of 0.20, 0.5, 1.0, 2.0 and 5 g/g respectively, demonstrating good precision. This method claims to be the first fully quantitative HPTLC method for determining fumonisin B₁ in rice.     

Negative thermal ionization mass spectrometry of selenium part 4. Selenium trace determination in sediments and related samples

Summary Selenium traces have been determined in different sediments (estuarine, river, lake), sandy soil and sewage sludge with isotope dilution mass spectrometry (IDMS). Negative selenium atomic ions are formed in a double-filament thermal ion source. The use of a silica gel technique for ionization improves the mass spectrometric sensitivity by a factor of 40 compared with the technique previously applied. An enriched⁸²Se spike is used for the isotope dilution process. The samples are decomposed with a mixture of conc. HNO₃ and conc. HE After decomposition selenium is separated by the formation of SeH₂ in a hydride generation system which is normally applied for atomic absorption spectrometry. The IDMS results for three standard reference sediments agree well with the certified values. In the case of three other standard reference materials, which are not certified for selenium up to now, the IDMS analyses were able to improve the selenium data given for information or as indicative values. The precision of the IDMS method in the concentration range of 0.2–3.5 g/g lies between 0.8 % and 4.1 %. The detection limit is 6 ng/g. A comparison with several other methods shows that IDMS is one of the very few analytical methods which produces accurate selenium results even at concentration levels of 0.2 g/g and less in sediments and related samples of environmental interest.

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Negative Thermionen-Massenspektrometrie von Selen Teil 4. Selenspurenbestimmung in Sedimenten und vergleichbaren Proben

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Dedicated to Prof. Dr. G. Tblg on the occasion of his 60th birthday     

Measurement uncertainty of iodine determination in radiochemical neutron activation analysis

The measurement uncertainty of iodine determination in NIST standard reference material (SRM) 1549 using radiochemical neutron activation analysis (RNAA) was studied. This method is based on ignition of the irradiated sample [¹²⁷I(n,)¹²⁸I, t_1/2=25 min, E=422.9 keV] in an oxygen atmosphere, followed by absorption of iodine in a reducing acid solution and its purification by a selective extraction–stripping–reextraction cycle. The purified solution of iodine in CHCl₃ was transferred to a well-type HPGe detector for -ray measurement of the induced radionuclide ¹²⁸I. The detection limit of the method employed under the conditions described was 1 ng/g. The reproducibility of iodine determination in the SRM was 3.6% (12 determinations within 1 month), calculated by the analysis of variance procedure. Using the commercially available software program GUM Workbench and the recommendations of the Eurachem/CITAC Guide, we evaluated the uncertainty budget for this RNAA method and the relative uncertainty obtained was 3.6%. The largest uncertainty contributions were due to the repeatability of the chemical yield determination, the count rate of the induced nuclide in the standard and sample, the mass of the carrier and the mass of the irradiation standard.     

A new internal reference method for activation analysis and its application

A new internal reference method for activation analysis has been developed. The method can be used effectively for special samples in which suitable elements as internal standards are absent and the self-shielding effect can be neglected. In this method, W_b g of element B as an internal reference is added to the sample which contains W_a g of element A to be determined, whereas the comparative standard is prepared by mixing only the element A and B in a known concentration ratio of W _a ^* /W_b. When the sample and comparative standard are irradiated by particles with the same energy distribution, even though both are irradiated separately by particles with different flux, W_a can be determined easily by the following equation. $$W_a = \left( {{{A_R } \mathord{\left/ {\vphantom {{A_R } {A_R^* }}} \right. \kern-\nulldelimiterspace} {A_R^* }}} \right)W_a^* $$ where A_g and A_R are count ratios between gamma-rays emitted by two radioactive nuclides produced from elements A and B in the sample and comparative standard, respectively. The usefulness of the present method was examined through the determination of Ti, Cr, Ni and Zr in several commercial aluminium alloys by means of photon activation, and the accuracy and precision of the method were verified.     

Spectrophotometric method for phosphine residue determination in coriander

Spectrophotometric method for the determination of phosphine (PH₃) residues in coriander has been developed based on the reaction of phosphine with silver nitrate in 2% aqueous isopropanol. The yellow chromophore formed has an absorption maximum at 430 nm and the linear relation between the absorbances at 430 nm and the concentration of PH₃ is obeyed in the range of 0.02 to 0.17 g. The method is sensitive with a detection limit of 0.008 g and can be applied for determination of 0.02 g/g residue in coriander. Recovery of added PH₃ from a closed system ranges from 96 to 101%.     

Preparation,thermal decomposition process and kinetics for terbium<Emphasis Type="Italic">p</Emphasis>-methoxybenzoate ternary complex with 1,10-phenanthroline

The complex of [Tb₂(p-MOBA)₆(PHEN)₂] (p-MOBA=C₈H₇O₃,p-methoxybenzoate; PHEN=C₁₂H₈N₂, 1,10-phenanthroline) was prepared and characterized by elemental analysis and IR spectroscopy. The thermal behavior of Tb₂(p-MOBA)₆(PHEN)₂ in a static air atmosphere was investigated by TG-DTG, DTA, SEM and IR techniques. By the kinetic method of processing thermal analysis data put forward by Malek et al., it is defined that the kinetic model for the first-step thermal decomposition is SB(m,n). The activation energy E for this step reaction is 140.92 kJ mol^-1, the enthalpy of activation H is 136.06 kJ mol^-1, the Gibbs free energy of activation G is 145.16 kJ mol^-1, the entropy of activation S is -15.53 J mol^-1, and the pre-exponential factor lnA is 29.26. The lifetime equation at mass loss of 10% was deduced as ln =-28.72+1.943·10⁴/T by isothermal thermogravimetric analysis.     

Determination of Cd,Mo, Cr and Co in biological materials by RNAA

A method for the determination of trace amounts of Mo, Cd, Co and Cr in biological materials by neutron activation analysis with radiochemical separation is presented. The method is based on the ion-exchange scheme developed by SAMSAHL, where Co and Cr are trapped on BioRad Chelex-100 and Cd and Mo on BioRad AG2X8. The elements Mo, Cd and Co can be determined without systematic errors. For the element chromium the situation is less clear, partially due to lack of sufficient certified reference materials for Cr. The method has been used in the characterization of candidate reference materials. Detection limits in these materials range from 1.5 g/kg for Co to 10 g/kg for Cr. Actual levels as low as 8 g/kg for Cd and 7 g/kg for Co were measured.     

Time-based on-line preconcentration cold vapour generation procedure for ultra-trace mercury determination with inductively coupled plasma atomic emission spectrometry

A time-based sequential dispensing on-line column preconcentration procedure for mercury determination at trace levels by cold vapour generation inductively coupled plasma atomic emission spectrometry (CV-ICP-AES), by means of a unified module of a preconcentration column and a gas–liquid separator (PCGLS) is described. The complex of mercury formed on-line with ammonium pyrrolidine dithiocarbamate (APDC) is retained on the surface of the hydrophobic poly(tetrafluoroethylene) (PTFE) turnings, which are packed into the lower compartment of the PCGLS. Subsequently, mercury vapour is generated directly on the PTFE turnings by reductant SnCl₂ and separated from the liquid mixture via the PCGLS by argon purge gas. The outlet of the PCGLS is connected directly to the torch adapter of the plasma without the normal spray chamber and nebulizer. With 60-s preconcentration time and 12.0 mL min^–1 sample flow rate, the sampling frequency is 30 h^–1. The calibration curve is linear over the concentration range 0.02–5.0 g L^–1, the detection limit (c_L) is 0.01 g L^–1 and the relative standard deviation (s_r) is 3.1% at the 1.0 g L^–1 level. The proposed method was evaluated by analysis of BCR CRM 278 (Mytilus Edulis) reference material and applied to the determination of total mercury in digested urine, blood and hair samples.     

Two-Temperature Transport Coefficients in Argon–Hydrogen Plasmas—II: Inelastic Processes and Influence of Composition

Recently, a two-temperature transport properties theory has been proposed that retains the coupling between electrons and heavy species in thermal plasmas where the kinetic temperature of electrons Te can be different from that of heavy species Th. This paper is devoted to the application of this approach to an argon–hydrogen mixture at atmospheric pressure, taking into account inelastic processes and considering chemical equilibrium. In this second part are studied: the development of a new method to calculate the reaction thermal conductivity (inelastic collisions) in a non-equilibrium (two-temperature) plasma taking into account the coupling between electrons and heavy species; the influence of the composition calculation methods comparing the modified equilibrium constant method used in part 1 to the stationary kinetic calculation one; the influence on the transport properties (, , ) of the composition calculation method and non-equilibrium parameter =T_e/T_h.The different plasma compositions obtained either through an equilibrium constant or a stationary kinetic method are first compared and, for example, for =1.6, a discontinuity at T_e=11,000 K and an ionization delay are observed in stationary kinetic calculation, relative to the equilibrium constant method. Electrical conductivity, viscosity as well as thermal conductivity, including the translational, internal and reactional contributions, are calculated up to 25,000 K. It is shown that the plasma composition has a strong influence on transport coefficients, inducing shifts or discontinuities in the curves of transport coefficients, depending on the chosen method of calculation.     

Binding/antibinding analyses for diatomic interactions. The effect of nuclear charge on one-electron chemical bonding

For a one-electron homonuclear diatomic system with arbitrary nuclear charge Z, the change in the nature of diatomic interaction and its density origin are quantitatively examined as a function of Z by the method of binding/antibinding analyses based on the Hellmann-Feynman theorem. In the Is_g ground state, two energy extrema, potential barrier at a large internuclear distance and potential minimum at a smaller distance, appear for 1<Z<1.44. The binding part of the partitioned Hellmann-Feynman forces suffers little effect of Z, and these two extrema are attributed respectively to the increase in the nuclear repulsion and to the decrease in the antibinding part of the partitioned forces. In the antibonding 2p_u state, a stable molecule is formed for Z<1. This appearance of the bonding nature is shown to have its origin in the binding part which is almost unchanged by the decrease of Z.     

A comparative study of phenyl bonded-phase,CB and romer clean-up procedures for determining aflatoxin levels in maize by bi-directional HPTLC

Summary A modified phenyl non-polar bonded-phase clean-up procedure for determining aflatoxin concentrations in aqueous acetone extracts of maize by bi-directional HPTLC was assessed. The accuracy and precision of the method was evaluated for a range of aflatoxin concentrations between 3.4 and 901 g/kg. The coefficients of variation varied between 1.7 and 10.8% with mean recoveries of 92–99%. Application of regression analysis revealed systematic errors for aflatoxins B₂ (–0.36 to –1.19%) and G₂ (–0.03 to –0.57), and small relative errors for all four toxins. The limits of detection were 1.7 g/kg (B₁), 1.2 g/kg (B₂), 0.9 g/kg (G₁) and 0.8 g/kg (G₂).The method was compared with the first action AOAC CB and Romer methods and a previously described PH bonded-phase procedure. It was found to recover significantly more aflatoxin from a sample of naturally contaminated maize, and to have accuracy better than and precision equivalent to the other methods. In addition, it was shown to be more rapid and cost effective than the AOAC methods.     

β-Naphthoquinone sulfonate as electrochemical labelling reagent for high-sensitivity LC analysis of drugs in biological fluids

Summary A new sensitive, high-performance liquid chromatography (HPLC) method using electrochemical detection (ECD) is reported for the determination of 21 amphetamine-like compounds such as amphetamine, methamphetamine, methoxyphenamine, phentermine, ephedrine, mescaline, STP and methylenedioxyamphetamine, in biological fluids. Primary and secondary amines in biological specimens were easily labelled with -naphtho-quinone-4-sulfonate (BNQS) at 60°C for 30 min. Hydrodynamic voltamograms of BNQ-derivatives showed a maximum response at an applied potential of around zero V (against Ag/AgCl) in reducing model. BNQ derivatives of amines were analyzed by HPLC using a reducing ECD at zero V (Ag/AgCl). Separation was on a Bondasphere C18 with mobile phase: acetonitrile-methanol-0.01 M H₂SO₄. Good separations of twenty one amphetamine-analogs were obtained. Only 50 l of biological fluid containing those drugs at a concentration of over 1 g ml^–1 were needed direct for determination with good accuracy. When extraction was carried out prior to the labelling reaction, the detection limits were much improved to less than 10 ng ml^–1.This method was successfully applied to determination of methamphetamine in hair.