True detection limit of rare earth elements in atomic emission analysis with an arc two-jet plasmatron

The “true detection limit” C_L,true was measured by a method proposed by Boumans et al. for 10 prominent lines of La, Ce, Pr, Nd and Sm, the most abundant rare earth elements (REEs) in geological samples. It is demonstrated how spectral interferences can increase of C_L,true. The spectra were excited in an argon arc plasma jet with evaporation powders of five complex natural samples. The data show that there is a significant increase of C_L,true in real samples containing large concentrations of such elements as Ti, Zr, Cr, Nb, Ta and REEs emitting complex spectra.     

Monosegmented flow-analysis of slow enzymatic reactions: Determination of triglycerides in serum

 A monosegmented flow system (MCFA) is proposed to achieve slow enzymatic spectrophotometric determinations, here applied to the determination of triglycerides in blood serum. The sample (4.5 μL), enzymatic reagent (150 μL) and an air plug (100 μL) are simultaneously inserted into a carrier stream buffered to pH 7.9 (Tris ⋅ HCl). In order to avoid the cumbersome step of air removal, a relocating detector was used. This system handles about 60 samples/h, yielding precise results (r.s.d. usually<2.5%). Sensitivity is 56 mAU ⋅ L/mmol up to 6 mmol/L triglycerides. Accuracy was assessed by running 50 samples already analysed by a conventional procedure yielding the equation C_MCFA(mmol/L)=1.00(±0.04) C_Ref(mmol/L)−0.03(±0.08); r=0.990. Received: 22 January 1997/Revised: 12 March 1997/Accepted: 28 March 1997     

Study of the preconcentration and determination of ultratrace rare earth elements in environmental samples with an ion exchange micro-column

A study was carried out on the preconcentration of ultratrace rare earth elements (REEs) in environmental samples with a micro ion-exchange column and determination by inductively coupled plasma mass spectrometry (ICP-MS). The preconcentration parameters were optimized and the REE recovery was ca. 100% in the pH range 4 to 6 with an ionic strength (μ) less than 0.18. The ion-exchange column capacity with respect to REEs was estimated as 0.96 mmol/g. The linear response coefficients ranged from 0.995 to 0.997 at the pg mL^–1 level. The concentration in the blank could be minimized (0.09 to 3.1 pg mL^–1) if the buffer solution and the water were purified. The detection limits ranged from 0.03 to 0.40 pg mL^–1, for a preconcentration factor of 100. The precision and accuracy of the method was evaluated with a synthetic standard solution and real samples. Results indicated that the REE recovery ranged from 88.1% to 100.2%, and the RSD ranged from 2.7% to 6.7%. Satisfactory results were achieved when this method was applied for the determination of REEs in raw water, purified water and tap water, as well as in environmental aquatic samples. Meanwhile, the method is simple and flexible. Received: 17 January 1997 / Revised: 23 April 1997 / Accepted: 29 April 1997     

Voltammetric behavior of C60-p-tert-butylcalix[8]arene inclusion complex film

The C₆₀-p-tert-butylcalix[8]arene inclusion complex film has been directly formed on the surface of a glassy carbon electrode, and its electrochemical behavior in acetonitrile containing tetra-n-butylammonium hexafluorophosphate as the supporting electrolyte studied. The film has a two-electron reduction wave at −1.0 V (vs Ag/AgCl), but limits to the first cathodic potential scan. Received: 16 September 1997 / Accepted: 27 October 1997     

Determination of rare earth and other elements in algae by ICP-MS and neutron activation analysis

Several rare earth elements (REEs) and other elements in algae were investigated by ICP-MS and INAA. Algae materials were supplied from an IAEA Intercomparison Study:Chlorella vulg. grown under reduced levels of toxic elements (IAEA-391) and IAEA-393 algae was grown in a medium to which certain toxic elements were added. 34–691 mg of algae samples were dissolved in conc, nitric acid using a microwave sampleppreparation system. REEs could be detected in the order of magnitude of 10⁻³ ng/g by ICP-MS. Activation analysis failed to detect any REEs because of a strong interference due mainly to²⁴Na and³²P. The distriubtion patterns of these REEs in algae slightly differed from those ofCarya sp. and tobacco leaves, and differed significantly from that of fern leaves. The distribution pattern was rather similar to that found in the North American shale composite (NASC).     

Preparation and properties of highly dispersed copper oxide in a zeolite matrix

Highly dispersed CuO clusters inserted into a zeolite matrix were prepared by oxidative degradation of the (μ₄-O)L₄Cu₄Cl₆ tetranuclear complex (L isN,N-diethylnicotinamide) preadsorbed on a dehydrated NaX zeolite from a solution in anhydrous dichloromethane. The catalytic activity of the CuO/NaX catalyst thus obtained in the oxidation of CO is an order of magnitude higher than that of massive CuO. Presented at the First Moscow Workshop on Highly Organized Catalytic Systems (June 19, 1997). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1761–1764, October, 1997.     

Colorimetric determination of iron in infant fortified formulas by sequential injection analysis

 A procedure is described for the colorimetric determination of iron in infant fortified formulas based on sequential injection analysis (SIA). Iron(III) complexation with thiocyanate is used as colour developing reaction. The system enables the determination of iron in the samples (after digestion by dry ashing and treatment with 0.2 mol/L nitric acid in the range of 0.50–20.0 mg/L, consuming 140 μL of the sample and 8 mg thiocyanate per determination. The reactor geometry and the adjustment of the ionic content of the calibration solutions is important for the accuracy of the results. A regression line according to the equation [Fe(III) (mg/L)]_SIA=−0.3(±0.4)+1.03(±0.04) [Fe(III) (mg/L)]_FAAS was obtained after comparative analysis of a set of 12 samples. The measurement rate was 34 s, thus allowing to analyze 100 samples per hour with a relative standard deviation lower than 2%. Received: 30 July 1996/Revised: 1 October 1996/Accepted: 4 October 1996     

An amperometric biosensor using toluidine blue as an electron transfer mediator intercalated in α-zirconium phosphate-modified horseradish peroxidase immobilization matrix

A novel H₂O₂ biosensor was constructed employing α-zirconium phosphate as a new support substrate to hold an electron shuttle toluidine blue between a glassy carbon electrode and horseradish peroxidase. Toluidine blue was intercalated into α-zirconium phosphate-modified horseradish peroxidase immobilization matrix cross-linked on a glassy carbon electrode surface via bovine serum albumin-glutaraldehyde. This co-immobilization matrix of the mediator and the enzyme was formed from the α-zirconium phosphate (α-ZrP)-toluidine blue (TB) inclusion colloid in which horseradish peroxidase (HRP) was dissolved. Intercalation of TB in layered α-ZrP was investigated by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and electrochemical measurements. TB immobilized in this way underwent a quasi-reversible electrochemical redox reaction at the electrode. Cyclic voltammetry and amperometric measurements demonstrated good stability and efficiently-shuttled electrons between HRP and the electrode. The sensor responded rapidly to H₂O₂ with a detection limit of 3.0 × 10^–7 mol/L. Received: 1 July 1997 / Revised: 13 October 1997 / Accepted: 21 October 1997     

Development of the FTIR properties of nano-structure silica gel doped with different rare earth elements,prepared by sol-gel route

Structural characteristics of pure silica gel (silica-xerogel, SiO₂) and silica gel doped with some rare earth elements (REEs) such as, praseodymium Pr³⁺, and Europium Eu³⁺, Erbium Er³⁺ and Holmium Ho³⁺ ions, with different concentrations ranging from 1 up to 6%, in the form of monolith materials were prepared by sol-gel technique, Using tetra-ethoxysilane as precursor materials, which are of particular interest for sol-gel integrated optics applications. Some structural features of sol-gel derived monolith are analyzed, namely the structure of nano-particle momolith samples, based on X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR). We show that the XRD spectra of α-crystobalite are obtained for the pure samples at 1100°C and even by doping with the four REEs ions.     

Simultaneous determination of Co(II), Cr(VI), Ni(II) and Pb(II) in water by solvent extraction and high-field 1H NMR Spectrometry

A novel analytical approach is described that combines the preconcentration power of solvent extraction with the resolution and sensitivity of a 500 MHz ¹H NMR spectroscopic detection method for the quantitative determination of metals. Co(II), Cr(VI), Ni(II) and Pb(II) in water are extracted into chloroform as dithiocarbamate complexes. By decoupling the protons and employing a solvent-induced shift method, the ¹H NMR spectrum containing the dithiocarbamate complexes of Co(II), Cr(VI), Ni(II) and Pb(II) is fully resolved at CDCl₃/ C₆D₆ below 40%/60%. The detection limits for Co(II), Cr(VI), Ni(II) and Pb(II) are estimated to be 0.12, 0.073, 0.11 and 0.27 μg/mL, respectively, in the sample solution. Received: 31 July 1997 / Revised: 24 October 1997 / Accepted: 31 October 1997     

Combining TXRF,FT-IR and GC–MS information for identification of inorganic and organic components in black pigments of rock art from Alero Hornillos 2 (Jujuy,Argentina)

Archaeological samples are complex in composition since they generally comprise a mixture of materials submitted to deterioration factors largely dependent on the environmental conditions. Therefore, the integration of analytical tools such as TXRF, FT-IR and GC–MS can maximize the amount of information provided by the sample. Recently, two black rock art samples of camelid figures at Alero Hornillos 2, an archaeological site located near the town of Susques (Jujuy Province, Argentina), were investigated. TXRF, selected for inorganic information, showed the presence of manganese and iron among other elements, consistent with an iron and manganese oxide as the black pigment. Aiming at the detection of any residual organic compounds, the samples were extracted with a chloroform–methanol mixture and the extracts were analyzed by FT-IR, showing the presence of bands attributable to lipids. Analysis by GC–MS of the carboxylic acid methyl esters prepared from the sample extracts, indicated that the main organic constituents were saturated (C_16:0 and C_18:0) fatty acids in relative abundance characteristic of degraded animal fat. The presence of minor C_15:0 and C_17:0 fatty acids and branched-chain iso-C_16:0 pointed to a ruminant animal source. Figure Rock art painting at Hornillos 2 Cave, Susques, Argentina     

In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states

Niobium oxide (Nb₂O₅) films and powders have been obtained via the sol-gel route from an NbCl₅ precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500  °C and 800  °C, respectively, while at 300  °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb₂O₅ in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb₃-O stretching modes and the appearance of polaron absorption were noted with Li⁺ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail. Received: 21 August 1997 / Accepted: 9 October 1997     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Performance comparison between packed column supercritical fluid chromatography (SFC) and HPLC using cyclandelate as the model analyte

A reproducible and fast method has been developed for the assay of cyclandelate in bulk and drug forms using packed column supercritical fluid chromatography using dicyclohexyl phthalate (DCHP) as internal standard. The drug and the internal standard were resolved by elution with supercritical fluid carbon dioxide doped with 14.29% (v/v) methanol on an RP-C₁₈ column and detected spectrophotometrically at 228 nm. Chromatographic figures of merit using C₈, C₁₈, cyano and phenyl columns have been assessed. Parallel experiments have been performed by HPLC and the data have been compared. Supercritical fluid extraction using CO₂ modified with a small amount of methanol was found to give quantitative analytical recoveries of cyclandelate from a dosage form. SFC has been shown to be a viable, faster alternative technique to HPLC generating less disposable waste. Received: 20 June 1997 / Revised: 20 October 1997 / Accepted: 26 October 1997     

Determination of trace amounts of Galaxolide? (HHCB) by HPLC

An analytical method for the determination of trace amounts of Galaxolide^? (HHCB) by HPLC is presented. It is based on the separation of HHCB in different samples by a C18-column and a gradient elution by water and acetonitrile, both containing some acetic acid. The detection is carried out with a combination of a fast scanning UV detector and a fast scanning fluorescence detector. The fluorescence detection limit is 5 μg/L HHCB without sample pretreatment. HHCB adsorbed on solids or suspended solids can be extracted by ethanol. Received: 17 October 1997 / Revised: 24 November 1997 / Accepted: 24 November 1997     

Cyclic voltammetric studies of certain industrially potential iron chelate catalysts

 For the analysis of infrared spectroscopic bands and complex patterns partial cross correlation functions of a sample spectrum with reference spectra are calculated. The chosen ranges of the spectra are based on empirical knowledge of infrared spectrum structure correlations. The normalised maxima of the partial cross correlation functions are interpreted as fuzzy truth values and are combined by fuzzy logical operators. By application of that procedure larger common substructures will be derived from the reference spectra than by a maximum common substructure search based on the complete spectra. Received: 30 October 1996/Revised: 24 February 1997/Accepted: 26 February 1997     

Endohedral chemical shifts in higher fullerenes with 72–86 carbon atoms

For all isolated pentagon isomers of the fullerenes C₆₀–C₈₆ with nonzero HOMO–LUMO gap and for one nonclassical C₇₂ isomer (C_{2 v} ), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The experimental ³He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C₆₀, C₇₀ and C₇₆). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental ³He chemical shifts, the assignments of the observed ³He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C₈₂ and one C₈₆ isomer (C₈₂:3 and C₈₆:17). The calculated helium chemical shifts also suggest the reassignment of the δ(³He) resonances of two C₇₈ isomers. Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001     

Two-step surfactant binding of solvated and cross-linked poly(N-isopropylacrylamide-co- (2-acrylamido-2-methyl propane sulfonic acid))

 A solvated and cross-linked copolymer of N-isopropylacrylamide (IPAAm) and 2-(acrylamido)-2-methyl propane sulfonic acid (AMPS) was synthesized and its interaction with cationic surfactant lauryl-pyridinium chloride (C₁₂PyCl) was investigated. The solvated copolymer exhibited a lower critical solution temperature (LCST) in water, which was extensively shifted to a higher temperature due to the increase of hydrophilicity introduced by AMPS. In C₁₂PyCl solution, LCST of the copolymer was dramatically decreased due to the binding of C₁₂PyCl to AMPS unit, forming a stoichiometric complex. However, in the concentrated C₁₂PyCl solution, its LCST increased due to the non-stoichiometric complex formation. This phenomenon was further examined in the cross-linked copolymer, analyzed by binding isotherms. Two-step binding of surfactant was demonstrated followed by gel shrinking and re-swelling. This binding mechanism was further discussed regarding the effect of charge density and the hydro-phobicity of the main-chain backbone in terms of electrostatic and hydrophobic interactions. Received: 13 May 1997 Accepted: 13 August 1997     

Elimination of the spectral interference from polyatomic ions with rare earth elements in inductively coupled plasma mass spectrometry by combining algebraic correction with chromatographic separation

A simple and effective procedure is developed to avoid the spectral interference from light rare earth elements (REEs) and barium polyatomic ions on some rare earth elements in inductively coupled plasma mass spectrometry (ICP-MS) by combining algebraic correction with AG50W-×8 cation exchangeable chromatography. Algebraic correction is made to reduce the spectroscopic overlap interference of ¹⁴¹Pr¹⁶O and ¹⁴³Nd¹⁶O on ¹⁵⁷Gd and ¹⁵⁹Tb. The spectroscopic overlap interference of BaO⁺ and BaOH⁺ on some middle REEs are overcome by separation of REEs from barium with AG50W-×8 cation exchangeable chromatography. Prior to the determination, REEs are separated from complicated matrix samples using AG50W-×8 cation exchangeable resin. Ba is eluted with 2 mol/l HNO₃ solution. REEs are retained and could then be eluted with 5 mol/l HNO₃ solution. Recoveries for REEs are from 96 to 110%. More than 99.5% of Ba in the sample is removed, ensuring that the spectral interference from barium polyatomic ions on some middle REEs such as Nd, Sm, Eu and Gd are eliminated. The potential of the proposed method is evaluated by analysis of Certified Reference Materials (CRMs). Results show that experimental data are in good agreement with the certified values. The new technique has been successfully employed for the determination of REEs in practical soil and plant samples.