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Analytical and Bioanalytical Chemistry (v.385, #2)
Application of LIBS to the in-line process control of liquid high-alloy steel under pressure by Gerhard Hubmer; Reinhard Kitzberger; Karl Mörwald (pp. 219-224).
A process optimization and control system called VAI-CON Chem has been developed that uses laser-induced breakdown spectroscopy (LIBS) to quasi-continuously chemically analyze liquid high-alloy steel under pressure. The beam from a Nd:YAG laser, located on safe ground and operating at its fundamental wavelength, is guided by a mirror system to a process tuyere below bath level. Passing through the ∼1.5 m long tuyere, the beam is then focused onto the steel bath. Light emitted from the induced plasma passes back through the tuyere, which is coupled to a fiber optic cable that carries the information over a distance of approximately 10 m back to an Echelle spectrometer located beside the laser. Calibrations were performed using the complete system, located in a laboratory, during system testing. An induction furnace was used to simulate the AOD converter, wherein the samples were molten and superheated to a temperature of ∼1600 °C and kept at a pressure of ∼1.7 bar under an argon atmosphere. Twelve different high alloyed reference samples taken from normal AOD production with Fe concentrations of >48 wt.% and non-Fe element concentrations of up to 25 wt.% were available for calibration. The mean residual deviations (defined as the square root of the variance of the concentration ratios determined by LIBS and the reference element concentration ratios) obtained were close to those reported for other comparable high-alloy samples that were investigated at room temperature under normal atmospheric pressure.
Keywords: LIBS; High-alloy steel; Stainless steelmaking AOD converter; Process control
New approach to online monitoring of the Al depth profile of the hot-dip galvanised sheet steel using LIBS by Herbert Balzer; Manuela Hoehne; Reinhard Noll; Volker Sturm (pp. 225-233).
In this study a new approach to the online monitoring of the Al depth profile of hot-dip galvanised sheet steel is presented, based on laser-induced breakdown spectroscopy (LIBS). The coating composition is measured by irradiating the traversing sheet steel with a series of single laser bursts, each at a different sheet steel position. An ablation depth in the same range as the coating thickness (about 10 μm) is achieved by applying a Nd:YAG laser at 1064 nm in collinear double-pulse and triple-pulse mode. The ablation depth is controlled by adjusting the burst energy with an external electro-optical attenuator. A fingerprint of the depth profile is gained by measuring the LIBS signals from zinc, aluminium and iron as a function of the burst energy, and by post-processing the data obtained. Up to three depths can be sampled simultaneously with a single laser burst by measuring the LIBS signals after each pulse within the laser burst. A concept for continuously monitoring the Al depth profile during the galvanising process is presented and applied to different hot-dip galvanised coatings. The method was tested on rotating sheet steel disks moving at a speed of up to 1 m/s. The potential and limitations of the new method are discussed.
Keywords: Laser-induced breakdown spectroscopy; Depth profile; Galvanized coating; Zn; Online analysis; Collinear double pulses; Triple pulses
Systematic line selection for online coating thickness measurements of galvanised sheet steel using LIBS by Herbert Balzer; Stefan Hölters; Volker Sturm; Reinhard Noll (pp. 234-239).
LIBS can be used as an online method of characterizing galvanized coatings on sheet steel moving through a production line. The traversing sheet steel is irradiated with a series of single laser bursts, each at a different position on the sheet steel. An ablation depth in the same range as the coating thickness (about 10 μm) is achieved by using a Nd:YAG laser at 1064 nm in collinear double-pulse mode. The coating thickness is determined from the ratio of the intensities of an iron line and a zinc line measured at a burst energy high enough to penetrate the coating with a single burst. Experiments at different burst energies were carried out to optimize the thickness resolution, and a method of systematically selecting iron and zinc lines was deduced, which is based on multivariate data analysis (MVDA) of the intensity ratios calculated for a set of 6 zinc lines and 21 iron lines. A temperature correction was applied, because the parameters of the plasma change with burst energy, and the influence of this on the thickness resolution is discussed. The ambient atmosphere present (air, Ar, N2) as well as self-absorption of spectral lines both have an influence on the thickness resolution. At optimum conditions, a thickness measurement accuracy of better than 150 nm was obtained for a set of electrolytic galvanized sheet steels with coating thicknesses in the range 4.1–11.2 μm.
Keywords: Laser-induced breakdown spectroscopy; Coating thickness measurement; Galvanized coating; Zn; Online analysis; Multivariate data analysis
Modì: a new mobile instrument for in situ double-pulse LIBS analysis by A. Bertolini; G. Carelli; F. Francesconi; M. Francesconi; L. Marchesini; P. Marsili; F. Sorrentino; G. Cristoforetti; S. Legnaioli; V. Palleschi; L. Pardini; A. Salvetti (pp. 240-247).
Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ elemental analysis. A new mobile instrument for LIBS analysis, developed in a collaboration between Marwan Technology s.r.l. and the Applied Laser Spectroscopy Laboratory in Pisa, is presented, and some applications of it and results from it are outlined. The innovative experimental set-up, based on the use of two suitably retarded laser pulses and a standardless analysis procedure, which overcomes problems related to matrix effects, greatly improves the potential of this technique for accurate quantitative analysis.
Keywords: LIBS; Elemental analysis; Cultural heritage; Environmental diagnostics
Effect of heterogeneity on the quantitative determination of trace elements in concrete by Friederike Weritz; Dieter Schaurich; Alexander Taffe; Gerd Wilsch (pp. 248-255).
Laser-induced breakdown spectroscopy has been used for quantitative measurement of trace elements, e.g. sulfur and chlorine, in concrete. Chloride and sulfate ions have a large effect on the durability of concrete structures, and quantitative measurement is important for condition assessment and quality assurance. Concrete is a highly heterogeneous material in composition and grain-size distribution, i.e. the spatial distribution of elements. Calibration plots were determined by use of laboratory-made reference samples consisting of pressings of cement powder, hydrated cement, cement mortar, and concrete, in which the heterogeneity of the material is increasing because of the aggregates. Coarse aggregate and cement paste are distinguishable by the intensity of the Ca spectral lines. More advanced evaluation is necessary to account for the effect of the fine aggregate. The three series of reference samples enable systematic study of the effects of heterogeneity on spectral intensity, signal fluctuation, uncertainty, and limits of detection. Spatially resolved measurements and many spectra enable statistical evaluation of the data. The heterogeneity has an effect on measurement of the sulfur and chlorine content, because both occur mainly in the cement matrix. Critical chloride concentrations are approximately 0.04% (m/m). The chlorine spectral line at 837.6 nm is evaluated. The natural sulfur content of concrete is approximately 0.1% (m/m). The spectral line at 921.3 nm is evaluated. One future application may be simultaneous determination of the amount of damaging trace elements and the cement content of the concrete.
Keywords: LIBS; Heterogeneity; Concrete; Chlorine; Sulfur
Qualitative and quantitative investigation of chromium-polluted soils by laser-induced breakdown spectroscopy combined with neural networks analysis by J.-B. Sirven; B. Bousquet; L. Canioni; L. Sarger; S. Tellier; M. Potin-Gautier; I. Le Hecho (pp. 256-262).
Laser-induced breakdown spectroscopy (LIBS) has been applied to the analysis of three chromium-doped soils. Two chemometric techniques, principal components analysis (PCA) and neural networks analysis (NNA), were used to discriminate the soils on the basis of their LIBS spectra. An excellent rate of correct classification was achieved and a better ability of neural networks to cope with real-world, noisy spectra was demonstrated. Neural networks were then used for measuring chromium concentration in one of the soils. We performed a detailed optimization of the inputs of the network so as to improve its predictive performances and we studied the effect of the presence of matrix-specific information in the inputs examined. Finally the inputs of the network—the spectral intensities—were replaced by the line areas. This provided the best results with a prediction accuracy and precision of about 5% in the determination of chromium concentration and a significant reduction of the data, too.
Keywords: Laser-induced breakdown spectroscopy (LIBS); Soils; Neural networks analysis (NNA); Principal components analysis (PCA); Classification; Quantitative measurement
Laser-induced breakdown spectroscopy analysis of complex silicate minerals—beryl by Nancy J. McMillan; Catherine E. McManus; Russell S. Harmon; Frank C. De Lucia Jr; Andrzej W. Miziolek (pp. 263-271).
Beryl (Be3Al2Si6O18) is a chemically complex and highly compositionally variable gem-forming mineral found in a variety of geologic settings worldwide. A methodology and analytical protocol were developed for the analysis of beryl by laser-induced breakdown spectroscopy (LIBS) that minimizes the coefficient of variance for multiple analyses of the same specimen. The parameters considered were laser energy/pulse, time delay and crystallographic orientation. Optimal analytical conditions are a laser energy/pulse of 102 mJ and a time delay of 2 μs. Beryl compositions measured parallel and perpendicular to the c axis were identical within analytical error. LIBS analysis of 96 beryls from 16 countries (Afghanistan, Brazil, Canada, China, Colombia, India, Ireland, Italy, Madagascar, Mexico, Mozambique, Namibia, Norway, Russia, Tanzania and United States), Antarctica, and ten US states (AZ, CA, CO, CT, ID, ME, NC, NH, NM and UT) were undertaken to determine whether or not LIBS analysis can be used to determine the provenance of gem beryl.
Keywords: Laser-induced breakdown spectroscopy; LIBS; Beryl; Gem
Influence of laser wavelength on LIBS diagnostics applied to the analysis of ancient bronzes by L. Fornarini; V. Spizzichino; F. Colao; R. Fantoni; V. Lazic (pp. 272-280).
In this work the influence of laser wavelength upon the analytical results obtained from applying LIBS diagnostics to bronzes was investigated theoretically and experimentally at 1,064 nm and 355 nm. The laser ablation process was modeled for a set of reference samples of quaternary Cu/Sn/Pb/Zn alloys and the difference between plume composition and known target stoichiometry was estimated for both of the wavelengths considered. LIBS measurements were performed on the same set of reference samples and under the same experimental conditions to validate the model at different wavelengths. Results from the application of the model to calculate sample optical properties during laser irradiation, absorption in the plasma and plasma temperature are also presented.
Keywords: LIBS; Laser ablation; Copper alloys; Bronze; Modeling
Laser-induced breakdown spectroscopy (LIBS) for carbon single shot analysis of micrometer-sized particles by E. Vors; L. Salmon (pp. 281-286).
The purpose of this work is to study the ability of the laser-induced breakdown spectroscopy (LIBS) technique to perform in situ (without sample preparation) detection of graphite particles circulating in a gas loop used to simulate the cooling gas circuit of a helium-cooled nuclear reactor. Results obtained with a laboratory scale set up are presented. The experiments were performed in nitrogen with micrometer-sized particles containing carbon (glucose particles and sodium hydrogenocarbonate particles). Statistical shot to shot analysis was used to determine the concentration of the analyte. The variation of LIBS signal as a function of glucose particle diameter showed an underestimation of the signal of particles of diameters larger than 5 μm. This phenomenon is likely to be correlated to an incomplete vaporization in the laser-induced plasma of particles of sizes above 5 μm. Analytical measurements were performed with glucose particles and sodium hydrogenocarbonate particles, and the concentration-based limit of detection of carbon was evaluated to be about 60 μg m−3.
Keywords: Laser-induced breakdown spectroscopy; Aerosols/particulates; Carbon analysis
Evaluation of femtosecond LIBS for spectrochemical microanalysis of aluminium alloys by Igor V. Cravetchi; Mike T. Taschuk; Ying Y. Tsui; Robert Fedosejevs (pp. 287-294).
The analytical performance of femtosecond laser-induced breakdown spectroscopy (LIBS) for elemental microanalysis of aluminium alloys and for mapping precipitate distribution on the sample surface has been studied in detail. A Ti–sapphire laser system producing pulses of 130 fs at 800 nm was used to generate the laser-induced plasma. Multi-element microanalysis of commercially available aluminium alloys was performed in air at atmospheric pressure. Crater characteristics such as diameter and crater morphology were characterized by optical and scanning-electron microscopy. Scaling of plasma emission and limit of detection as a function of laser pulse energy was also investigated. Current experimental results are presented and are compared with previous nanosecond microLIBS measurements.
Keywords: Laser-induced breakdown spectroscopy (LIBS); Aluminium alloy; Precipitates; Spectrochemical microanalysis; Solid sampling; Emission scaling
Spatial distributions of the number densities of neutral atoms and ions for the different elements in a laser induced plasma generated with a Ni-Fe-Al alloy by C. Aragón; F. Peñalba; J. A. Aguilera (pp. 295-302).
Spatially-resolved emission spectroscopy, including spatial devonvolution of the spectra, has been used to determine the three-dimensional distributions of the relative number densities of neutral atoms and ions of the elements present in a laser-induced plasma generated with a Ni-Fe-Al alloy. The method is based on the precise measurement of the local electronic temperature from Saha–Boltzmann plots constructed with Fe I and Fe II lines. The plasma was generated in air at atmospheric pressure using a 1064-nm Nd:YAG laser, and the emission was detected in the time window 3.0–3.5 μs. The ionization fraction was very high (above 0.9) for the three elements in the sample, only decreasing behind the expanding plasma front. The relative number densities were obtained from the emissivities of selected elemental lines as well as the temperature. The error in this procedure was estimated, and it was found that it is largely due to the uncertainties in the transition probability values used. The spatial distributions of the total relative number densities of the three elements were shown to coincide within the error, a result which is relevant to the development of models of plasma emission used in analytical applications. The ratios of the total number densities of the elements in the plasma were compared to their concentration ratios in the sample; however, the relatively high errors in the relative number densities did not permit any definitive conclusions to be drawn about the stoichiometry of the laser ablation process.
Keywords: Laser-induced plasma spectroscopy; LIBS; Laser ablation; Plasma characterization; Number density
Elemental chemical analysis of submerged targets by double-pulse laser-induced breakdown spectroscopy by A. De Giacomo; M. Dell’Aglio; A. Casavola; G. Colonna; O. De Pascale; M. Capitelli (pp. 303-311).
Double-pulse laser-induced plasma spectroscopy (DP-LIPS) is applied to submerged targets to investigate its feasibility for elemental analysis. The role of experimental parameters, such as inter-pulse delay and detection time, has been discussed in terms of the dynamics of the laser-induced bubble produced by the first pulse and its confinement effect on the plasma produced by the second laser pulse. The analytical performance of this technique applied to targets in a water environment are discussed. The elemental analysis of submerged copper alloys by DP-LIPS has been compared with conventional (single-pulse) LIBS in air. Theoretical investigation of the plasma dynamics in water bubbles and open air has been performed.
Keywords: Laser-induced plasma spectroscopy; Copper alloys; Elemental analysis
Resonance fluorescence spectroscopy in laser-induced cavitation bubbles by Sandra Koch; Walter Garen; Walter Neu; Rainer Reuter (pp. 312-315).
Laser-induced breakdown spectroscopy (LIBS) in liquids using a double-pulse Q-switched Nd:YAG laser system has provided reliable results that give trace detection limits in water. Resonant laser excitation has been added to enhance detection sensitivity. A primary laser pulse (at 532 nm), transmitted via an optical fiber, induces a cavitation bubble and shockwave at a target immersed in a 10 mg l−1–100 mg l−1 indium (In) water suspension. The low-pressure rear of the shockwave induces bubble expansion and a resulting reduction in cavity pressure as it extends away from the target. Shortly before the maximum diameter is expected, a secondary laser pulse (also at 532 nm) is fed into the bubble in order to reduce quenching processes. The plasma field generated is then resonantly excited by a fiber-guided dye laser beam to increase detection selectivity. The resulting resonance fluorescence emission is optically detected and processed by an intensified optical multichannel analyzer system.
Keywords: Resonance fluorescence spectroscopy; Cavitation bubble; LIBS; Indium
Comparison of detection limits, for two metallic matrices, of laser-induced breakdown spectroscopy in the single and double-pulse configurations by Marwa A. Ismail; Gabriele Cristoforetti; Stefano Legnaioli; Lorenzo Pardini; Vincenzo Palleschi; Azenio Salvetti; Elisabetta Tognoni; Mohamed A. Harith (pp. 316-325).
Limits of detection have been studied for several elements in aluminium and steel alloys, at atmospheric pressure in air, by use of the single and collinear double-pulse configurations of laser-induced breakdown spectroscopy. For this purpose, calibration plots were constructed for Mg, Al, Si, Ti, Cr, Mn, Fe, Ni, and Cu using a set of certified aluminium alloy samples and a set of certified steel samples. The investigation included optimization of the experimental conditions to furnish the best signal-to-noise ratio. Inter-pulse delay, gate width, and acquisition delay were studied. The detection limits for the elements of interest were calculated under the optimum conditions for the double-pulse configuration and compared with those obtained under the optimum conditions for single-pulse configuration. Significantly improved detection limits were achieved, for all the elements investigated, and in both aluminium and steel, by use of the double-pulse configuration. The experimental findings are discussed in terms of the measured plasma conditions (particle and electron density, and temperature).
Keywords: Laser-induced breakdown spectroscopy; Double-pulse; AES; UV–visible; Metals/Heavy Metals
Laser-induced ablation of a steel sample in different ambient gases by use of collinear multiple laser pulses by Andrea Löbe; Jens Vrenegor; Rüdiger Fleige; Volker Sturm; Reinhard Noll (pp. 326-332).
The sensitivity of laser-induced breakdown spectroscopy of solid samples depends on the number of ablated and excited analytes. Laser ablation of solid samples can be enhanced by using collinear multiple laser pulses, for example double or triple pulses, rather than single laser pulses with the same total laser pulse energy. The ablation rates and the plasma conditions are affected by the ambient gas. In this study laser ablation was examined by varying the interpulse separation of the multiple pulses, within double and triple-pulse bursts, and the gas mass density at constant gas pressure. Different ambient gases and gas mixtures consisting of argon, oxygen, and nitrogen were used to study their effect on ablation rates. In a pure argon atmosphere (99.999% v/v Ar) the ablation burst number required to penetrate a steel plate of thickness 100 μm is reduced by a factor of approximately six by use of triple-pulse bursts with a symmetric interpulse separation of 15 μs rather than single pulses with the same total burst energy of 105 mJ. For double and single pulses the factors are 1.6 for Ar and 2.8 for synthetic air. Analyte lines are 4 to 8 times more intense if an argon atmosphere, rather than air, is used.
Keywords: LIBS; Ablation; Single pulse; Double pulse; Triple pulse; Ambient gas; Mixture of gases; Argon; Oxygen; Nitrogen
New near-infrared LIBS detection technique for sulfur by George Asimellis; Aggelos Giannoudakos; Michael Kompitsas (pp. 333-337).
Sulfur has been detected in a spectral window (around 868 nm) previously unexplored by laser-induced breakdown spectrometry (LIBS), using an ablation laser with an ultraviolet wavelength, a gated detector, and inert ambient gas at a low, controlled pressure. This spectral window enables new-generation gated iCCD cameras to be used, which have adequate quantum efficiencies up to 900 nm. Application of our technique can substantially improve signal strength and thus extends the ability of LIBS to detect many nonmetallic elements.
Keywords: Halogens; Ambient gas; Plasma; Sulfur
Comparisons between LIBS and ICP/OES by P. Fichet; M. Tabarant; B. Salle; C. Gautier (pp. 338-344).
In the framework of the development of new techniques, the ability of laser-induced breakdown spectroscopy (LIBS) to analyse remotely complex aqueous solutions was investigated. The jet configuration with a collimated gas stream was chosen because it appeared to be the most promising method for the LIBS probe, particularly in terms of sensitivity and repeatability. For emission collection, the echelle spectrometer offers a simultaneously recorded wavelength range from the UV to the near IR and is interesting for multielemental analysis for LIBS and also for inductively coupled plasma (ICP) optical emission spectroscopy (OES). The importance of parameters influencing the quantitative results of LIBS such as multispecies analysis, sheath gas, use of an internal standard and temporal parameters for analysis is described. LIBS quantitative data have been directly compared with results from the more standard ICP/OES technique.
Keywords: Laser; Laser-induced breakdown spectroscopy; Inductively coupled plasma optical emission spectroscopy; Echelle spectrometer
Validation and use of three complementary analytical methods (LC–FLS, LC–MS/MS and ICP–MS) to evaluate the pharmacokinetics, biodistribution and stability of motexafin gadolinium in plasma and tissues by Dale R. Miles; Mimi Mesfin; Tarak D. Mody; Mark Stiles; Jean Lee; John Fiene; Bernie Denis; Garry W. Boswell (pp. 345-356).
Liquid chromatography–fluorescence (LC–FLS), liquid chromatography–tandem mass spectrometry (LC–MS/MS) and inductively coupled plasma–mass spectrometry (ICP-MS) methods were developed and validated for the evaluation of motexafin gadolinium (MGd, Xcytrin) pharmacokinetics and biodistribution in plasma and tissues. The LC–FLS method exhibited the greatest sensitivity (0.0057 μg mL−1), and was used for pharmacokinetic, biodistribution, and protein binding studies with small sample sizes or low MGd concentrations. The LC–MS/MS method, which exhibited a short run time and excellent selectivity, was used for routine clinical plasma sample analysis. The ICP–MS method, which measured total Gd, was used in conjunction with LC methods to assess MGd stability in plasma. All three methods were validated using human plasma. The LC–FLS method was also validated using plasma, liver and kidneys from mice and rats. All three methods were shown to be accurate, precise and robust for each matrix validated. For three mice, the mean (standard deviation) concentration of MGd in plasma/tissues taken 5 hr after dosing with 23 mg kg−1 MGd was determined by LC–FLS as follows: plasma (0.025±0.002 μg mL−1), liver (2.89±0.45 μg g−1), and kidney (6.09±1.05 μg g−1). Plasma samples from a subset of patients with brain metastases from extracranial tumors were analyzed using both LC–MS/MS and ICP–MS methods. For a representative patient, ≥90% of the total Gd in plasma was accounted for as MGd over the first hour post dosing. By 24 hr post dosing, 63% of total Gd was accounted for as MGd, indicating some metabolism of MGd.
Keywords: Motexafin gadolinium; Bioanalytical method; Liquid chromatography; Mass spectrometry
Rapid screening of dioxin-contaminated soil by accelerated solvent extraction/purification followed by immunochemical detection by Malin Nording; Mikaela Nichkova; Erik Spinnel; Ylva Persson; Shirley J. Gee; Bruce D. Hammock; Peter Haglund (pp. 357-366).
Since soils at industrial sites might be heavily contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), there is a need for large-scale soil pollution surveys and, thus, for cost-efficient, high-throughput dioxin analyses. However, trace analysis of dioxins in complex matrices requires exhaustive extraction, extensive cleanup, and very sensitive detection methods. Traditionally, this has involved the use of Soxhlet extraction and multistep column cleanup, followed by gas chromatography—high-resolution mass spectrometry (GC/HRMS), but bioanalytical techniques may allow much more rapid, cost-effective screening. The study presented here explores the possibility of replacing the conventional method with a novel approach based on simultaneous accelerated solvent extraction (ASE) and purification, followed by an enzyme-linked immunosorbent assay (ELISA). Both the traditional and the novel cleanup and detection approaches were applied to contaminated soil samples, and the results were compared. ELISA and GC/HRMS results for Soxhlet-extracted samples were linearly correlated, although the ELISA method slightly underestimated the dioxin levels. To avoid an unacceptable rate of false-negative results, the use of a safety factor is recommended. It was also noted that the relative abundance of the PCDDs/PCDFs, evaluated by principal component analysis, had an impact on the ELISA performance. To minimize this effect, the results may be corrected for differences between the ELISA cross-reactivities and the corresponding toxic equivalency factor values. Finally, the GC/HRMS and ELISA results obtained following the two sample preparation methods agreed well; and the ELISA and GC/HRMS results for ASE extracts were strongly correlated (correlation coefficient, 0.90). Hence, the ASE procedure combined with ELISA analysis appears to be an efficient approach for high-throughput screening of PCDD-/PCDF-contaminated soil samples.
Keywords: Immunoassay; ELISA; Soil; Dioxin; Accelerated solvent extraction
Human metabolism of arsenolipids present in cod liver by Ernst Schmeisser; Walter Goessler; Kevin A. Francesconi (pp. 367-376).
We report results from the first investigation of the human metabolism of arsenic-containing lipids (arsenolipids), significant arsenic constituents of some seafood products. Two male volunteers ingested canned cod liver and the arsenic metabolites in their urine were monitored by high-performance liquid chromatography inductively coupled plasma mass spectrometry over a 66-h period. Volunteer A consumed 85 g (wet mass) of cod liver containing a total of approximately 120 μg arsenic, 77% of which was present as arsenolipids, and volunteer B consumed 85 g (wet mass) of cod liver, 25% of which was present as arsenolipids, together with 20 g of cod liver oil, containing a total of about 180 μg arsenic. The structures of the arsenolipids are currently unknown, whereas the majority of the non-lipid arsenic in the cod liver was identified as arsenobetaine, which was excreted unchanged. The arsenolipids were rapidly metabolised to water-soluble compounds and excreted in the urine; peak arsenic concentrations were recorded between 7 and 15 h (volunteer A) and between 6.5 and 15 h (volunteer B), and by the end of the experiment about 90% of the ingested arsenic had been accounted for in the urine for both volunteers. The major arsenolipid metabolite was dimethylarsinate (DMA), constituting 73% (volunteer A) or 41% (volunteer B) of the total urinary arsenic, and most of the remaining arsenolipid-derived arsenic, constituting about 10% (volunteer A) and 5% (volunteer B), comprised four novel arsenic-containing fatty acids, namely oxo-dimethylarsenopropanoic acid, thio-dimethylarsenopropanoic acid, oxo-dimethylarsenobutanoic acid, and thio-dimethylarsenobutanoic acid. Unchanged arsenobetaine (15% for volunteer A and 51% for volunteer B) made up the remaining urinary arsenic together with trace quantities of other, mostly unknown, arsenicals. In a second experiment (volunteer A only), performed with pure cod liver oil, which contains only arsenolipids, DMA and the same four arsenic fatty acids were excreted in the urine. The study shows that arsenolipids in cod liver are bioavailable, and that they are quickly biotransformed to several water-soluble arsenicals, the structures of which suggest that the native arsenolipids contain a dimethylarsine oxide moiety.
Keywords: Arsenolipids; Biotransformation; Arsenic speciation; Urine metabolites
Quantitative plasma determination of a novel antiretroviral derivative of zidovudine by solid-phase extraction and high-performance liquid chromatography by Mario A. Quevedo; Silvina A. Teijeiro; Margarita C. Briñón (pp. 377-384).
A solid-phase extraction methodology, followed by high-performance liquid chromatography (HPLC) quantification with UV absorbance detection (λ=267 nm), was developed in order to study the stability of 3′-azido-3′-deoxy-5′-O-isonicotinoylthymidine (AZT-Iso), a novel derivative of the antiretroviral AZT, in different matrixes. The half-lives (t 1/2) for AZT-Iso were 1.19, 1.13 and 0.30 h for human, rat and rabbit plasma, respectively, and 14.91 and 25.49 h for potassium phosphate buffer (pH 7.4) and human serum albumin solution, respectively. The HPLC method proved to be selective, sensitive and accurate. Good recovery, linearity and precision were achieved using p-fluorophenol as an internal standard. The validity of this method was tested using synthetic mixtures of the intact drug with its decomposition products. In conclusion, the method presented is applicable to in vivo pharmacokinetics studies of AZT-Iso in rats.
Keywords: Solid-phase extraction; High-performance liquid chromatography; Plasma stability; Zidovudine derivatives
Resolution of an intense sweetener mixture by use of a flow injection sensor with on-line solid-phase extraction by L. F. Capitán-Vallvey; M. C. Valencia; E. Arana Nicolás; J. F. García-Jiménez (pp. 385-391).
An integrated solid-phase spectrophotometry–FIA method is proposed for simultaneous determination of the mixture of saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide; E-954) (SA) and aspartame (N-l-α-aspartyl-l-phenylalanine-1-methyl ester; E-951) (AS). The procedure is based on on-line preconcentration of AS on a C18 silica gel minicolumn and separation from SA, followed by measurement, at λ=210 nm, of the absorbance of SA which is transiently retained on the adsorbent Sephadex G-25 placed in the flow-through cell of a monochannel FIA setup using pH 3.0 orthophosphoric acid–dihydrogen phosphate buffer, 3.75×10–3 mol L−1, as carrier. Subsequent desorption of AS with methanol enables its determination at λ=205 nm. With a sampling frequency of 10 h−1, the applicable concentration range, the detection limit, and the relative standard deviation were from 1.0 to 200.0 μg mL−1, 0.30 μg mL−1, and 1.0% (80 μg mL−1, n=10), respectively, for SA and from 10.0 to 200.0 μg mL−1, 1.4 μg mL−1, and 1.6% (100 μg mL−1, n=10) for AS. The method was used to determine the amounts of aspartame and saccharin in sweets and drinks. Recovery was always between 99 and 101%. The method enabled satisfactory determination of blends of SA and AS in low-calorie and dietary products and the results were compared with those from an HPLC reference method.
Keywords: Biparameter sensor; Aspartame and saccharin mixture analysis; Flow-through optical sensor; On-line solid phase extraction; Sweets and drink products
Orthogonal projection (OP) technique applied to pattern recognition of fingerprints of the herbal medicine houttuynia cordata Thunb. and its final injection products by Zhong-Da Zeng; Yi-Zeng Liang; Ting Zhang; Foo-Tim Chau; Ya-Li Wang (pp. 392-400).
It is a crucial issue to determine the origins of herbal medicinal materials and identify the quality grades and fakes of their final products collected from different pharmaceutical corporations. Pattern recognition technique may assist the manufacturers to achieve this purpose and effectively control the quality of their products. In this work, a widely used method in chemometrics, orthogonal projection (OP) technique, was applied to discrimination analysis and identification of fingerprints of the herbal medicine houttuynia cordata Thunb. (HCT) and its final injection products. The advantages of the OP technique are clearly shown after comparing with the conventional methods such as principal component analysis (PCA), Mahalanobis distance (MD), and similarity comparison method (SCM). Three different sources of medicinal material HCT and its final injection products from six different manufacturers were studied under ‘sixfold’, ‘threefold’ and ‘threefold-bis’ cross-validation procedures. The good performance of the proposed method in determination and identification of unknown samples shows it could be a powerful tool for quality control in herbal medicine production and other related research fields.
Keywords: Orthogonal projection; Pattern recognition; Fingerprints; Herbal medicines; Houttuynia cordata Thunb.