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Analytica Chimica Acta (v.545, #2)
A radiofrequency plasma in a polydimethylsiloxane (PDMS) microchip by H.B. Lim; Donghoon Kim; Taeyoon Jung; R.S. Houk; Yangsun Kim (pp. 119-121).
This is the first report of an analytical plasma in a polymer (polydimethylsiloxane, PDMS) microchip. The plasma channel has dimensions 2mm diameter×50mm long, is operated at atmospheric pressure in Ar, 27.12MHz and 70W, and is viewed axially through a purged fiber optic cable. CF4 gas at 0.1% in argon yields mainly C2 emission bands. This PDMS microchip is manufactured easily, inexpensive, and more tolerant to fluorocarbons than microchip plasmas in silica. Based on these initial results, this PDMS microchip plasma could become useful as a sensor for the fluorocarbon gases emitted in semiconductor process or as a gas chromatography (GC) detector for potential application.
Keywords: Microchip; RF plasma; Emission spectroscopy; Optical emission sensor
Construction of a novel molecularly imprinted sensor for the determination of O, O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate by Chunya Li; Changfa Wang; Chenghang Wang; Shengshui Hu (pp. 122-128).
A novel voltammetric sensor for O, O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate (Phi-NO2) based on molecularly imprinted polymer (MIP) film electrode is constructed by using sol–gel technology. The sensor responds linearly to Phi-NO2 over the concentration range of 2.0×10−5 to 1.0×10−8molL−1 and the detection limit is 1.0×10−9molL−1 (S/N=3). This sensor provides an efficient way for eliminating interferences from coexisting substances in the solution. The high sensitivity, selectivity and stability of the sensor demonstrates its practical application for a simple and rapid determination of Phi-NO2 in cabbage samples.
Keywords: Molecular imprinting; Sol–gel; O; ,; O; -Dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate; Voltammetric sensor
Chemiluminescence determination of indapamide using indapamide-imprinted polymer as recognition material by Nie Fei; Lu Jiuru; Niu Weifen (pp. 129-136).
A chemiluminescence reaction between soluble Mn(IV) and indapamide was found. An indapamide MIP was synthesized and its adsorption selectivity to indapamide in aqueous solution was evaluated. Using soluble Mn(IV)–formaldehyde–indapamide chemiluminesence system as detection system and the indapamide MIP as recognition material, a selective molecule imprinting-chemiluminesence method of determination of indapamide was established. The linearly response range of this method was from 2.0×10−8 to 5.0×10−6g/mL with a linear correlation coefficient of 0.995. The detection limit was 8×10−9g/mL. The relative standard deviation for 5.0×10−7g/mL of indapamide solution was 3.5% ( n=9).
Keywords: Indapamide; Soluble Mn(IV); Molecule imprinting-chemiluminescence method
Simultaneous determination of two active ingredients in Flos daturae by capillary electrophoresis with electrochemiluminescence detection by Ying Gao; Yiling Tian; Erkang Wang (pp. 137-141).
The coupling of Ru(bpy)32+ based electrochemiluminescence (ECL) detection with capillary electrophoresis (CE) was developed for the simultaneous determination of the two major active ingredients (atropine and scopolamine) in Flos daturae. Parameters related to the separation and detection were discussed and optimized. It was proved that 20mM phosphate buffer at pH 8.48 could achieve the most favorable resolution, and the high sensitivity of detection was obtained by maintaining the detection potential at 1.2V. Under the optimized conditions: ECL detection at 1.2V, 20mM phosphate buffer at pH 8.48, 5mM Ru(bpy)32+ and 50mM phosphate buffer at pH 7.48 in the detection reservoir, detection limits of 5×10−8mol/l for atropine and 1×10−6mol/l for scopolamine were obtained. Relative standard derivations of the ECL intensity and the migration time were 5.16 and 0.71% for atropine and 5.07 and 1.22% for scopolamine, respectively. Developed method was successfully applied to determine the amounts of both alkaloids in Flos daturae. A baseline separation for atropine and scopolamine was achieved within 11min.
Keywords: Electrochemiluminescence; Capillary electrophoresis; Atropine; Scopolamine
Application of photochemical reactions of Se in natural waters by hydride generation atomic fluorescence spectrometry by Yu-Wei Chen; Ming-Da Zhou; Jian Tong; Nelson Belzile (pp. 142-148).
A simple, sensitive and accurate method for selenium speciation in natural waters is proposed. The principle of this method is based on recently discovered photochemical reactions of Se(IV) and organic selenium in different aqueous solutions. The speciation of all selenium species was performed with hydride generation–atomic fluorescence spectrometry. Only one pre-reduction step is needed in this procedure, which can greatly reduce the risk of contamination, minimize the analytical work and improve the quality of selenium speciation. In this paper, a comparison is made between the proposed method and a previous method [A.G. Cutter, Anal. Chim. Acta 98 (1978) 59]. In this proposed protocol, Se(IV) was directly measured in 3.0M HCl. Se(IV)+org-Se was measured directly after a UV irradiation (300nm) for 2.5h in a 1.0% (v/v) HNO3–2.0% (v/v) HCl matrix. Total selenium was obtained in another aliquot sample after a UV irradiation in the 3.0M HCl. No pre-concentration, separation or more sophisticated instruments are required.
Keywords: Selenium speciation; UV oxidation; Photochemical reaction; Hydride generation; Atomic fluorescence spectrometry
Photochemical behavior of inorganic and organic selenium compounds in various aqueous solutions by Yu-Wei Chen; Xian-Liang Zhou; Jian Tong; Yen Truong; Nelson Belzile (pp. 149-157).
Selenium possesses interesting chemical, biochemical and geochemical behaviors. However, studies of its photochemical properties in aqueous systems are scarce. A better understanding of these phenomena is of great importance for further application of such properties to selenium speciation. In this work, the photochemical behavior of selenium and some of its organic compounds have been systematically studied in various aqueous matrices under UV irradiation at 300nm. It was observed that the photochemical oxidation rate of Se(IV) to Se(VI) was greatly enhanced in the presence of HN03 at ≥1×10−3M, but not by NaNO3. However this photo-oxidation could be inhibited by the presence of Cl−. Under UV irradiation, organoselenium compounds went through two successive photochemical reactions in pure water: a direct photolysis (photo-cleavage) followed by a photo-oxidation to form Se(VI). These two steps could also be greatly accelerated in presence of NO3− although the second step required an acidic condition. The photo cleavage rates varied from one organic compound to another and 10-fold differences were observed. Similarly to Se(IV), the further oxidation to Se(VI) could be prevented by Cl− for all studied organoselenium compounds. Detailed reaction mechanisms involving OH radicals are proposed to explain Se photochemical behaviors in different matrices.
Keywords: Selenium; Photo-oxidation; UV irradiation; Aqueous solutions
Carbon paste electrode modified with silver thimerosal for the potentiometric flow injection analysis of silver(I) by Hosny Ibrahim (pp. 158-165).
The utility of carbon paste electrode modified with silver ethylmercurythiosalicylate (silver thimerosal) in both static mode and flow injection analysis (FIA) is demonstrated. The electrode was fully characterized in terms of composition, response time, thermal stability, usable pH and ionic strength ranges. It has been shown that diisononyl phthalate (DINP) acts as more suitable solvent mediator for preparation of the electrode, which exhibits linear response range to Ag(I) extending from 5.0×10−7 to 1.0×10−3M with detection limit of 2.5×10−7M and Nernstian slope of 59.3±1.0mV/decade. The proposed chemically modified carbon paste electrode shows a very good selectivity for Ag(I) over a wide variety of metal ions and successfully used for the determination of the silver content of silver sulphadiazine (burning cream) and developed radiological films. The electrode was also used as an indicator electrode in the potentiometric titration of thiopental and thimerosal with AgNO3.
Keywords: Silver; Thimerosal; Chemically modified carbon paste electrode; FIA; Thiopental
Signal enhancement in adsorptive stripping voltammetry of Pt by forced convection during the measurement step by Günther Weber; Jürgen Messerschmidt (pp. 166-172).
Adsorptive stripping voltammetry (‘formazone-method’) is already known as one of the most sensitive methods for platinum analysis with a detection limit in the low picograms range. In this work, it is shown that the detection limit can be lowered even more by one order of magnitude to 0.2pg (=1fmol) Pt in 15mL electrolyte, corresponding to 68fmol/L, by applying forced convection during the stripping step of the voltammetric measurement. The sensitivity of the method (given in nA/pg Pt) is enhanced by a factor of 3–5 (in differential pulse mode and 15mL vial), up to a factor of 30 (using square-wave mode and 3mL vial). The maximum enhancement factor is limited by the maximum stirrer speed, which can be applied without negative effects on the hanging mercury drop electrode.To check for similar enhancement effects in other types of stripping methods, the behaviour of adsorptive stripping voltammetry for Pt is compared to conventional anodic stripping voltammetry (ASV) of lead, and to adsorptive stripping voltammetry of nickel and cobalt using their dimethylglyoxime (DMG) complexes. No enhancement effect is observed in ASV of lead upon stirring, and the nickel-DMG-system exhibits only a smaller enhancement factor of about 1.5. A reasonable explanation of the higher signal enhancement in the catalytic Pt–formazone-system is the mass transport of reaction products, namely hydrogen, away from the working electrode during the catalytic hydrogen evolution cycle.
Keywords: Platinum; Adsorptive stripping voltammetry; Catalytic hydrogen wave; Convection
Critical evaluation of potentiometric redox titrations in enology by H. Durliat; M. Comtat (pp. 173-181).
Measurements of the zero current potential of a platinum electrode immersed in solutions of tanins or in wines of various origins, were performed during the additions of a solution of Ti(III), or of a solution of dichlorophenolindophenol (DCPIP), in order to obtain a global indication for the resistance to oxidation of some wines. The steady state intensity–potential curves on a platinum electrode highlight the occurrence of mixed potentials between the oxidation of ethanol or catechin and the reduction of oxygen present at very low concentrations, as well as the irreversibility of the redox system Ti(IV)/Ti(III). The adsorption of various species on the platinum and the slowness of the oxidation reactions by DCPIP exclude use of potentiometric titration theory. The shape of the potential–reagent volume curves depends on the nature of the solution and on the rate of reagent introduction. Generally, due to the slowness of the oxidation reactions with DCPIP it is impossible to find a linear relationship between the volume of titrant solution necessary to reach the inflexion point of the curves and the solution composition.
Keywords: Catechin; Dichlorophenolindophenol; Potentiometric titration; Titanium(III); Wines
Simultaneous determination of total homocysteine, cysteine and methionine in hypothyroid patients’ plasma by liquid chromatography using platinum/poly(methyl violet) modified electrode by Haihong Xu; Wen Zhang; Wei Zhu; Dan Wang; Jun Ye; Katsunobu Yamamoto; Litong Jin (pp. 182-188).
The fabrication and application of a novel electrochemical detection (ED) system with the platinum/poly(methyl violet) (Pt/MV) chemically modified electrode (CME) for high performance liquid chromatography (HPLC) were described. The Pt particles deposited on the poly-MV film were characterized by atomic force microscope (AFM). It was found that the Pt/MV CME exhibited efficiently electrocatalytic effect on the current responses of cysteine (Cys), homocysteine (Hcy) and methionine (Met) with relatively high sensitivity, stability and long-life of activity. In HPLC-ED, these three amino acids had good and stable current responses at the CME and their linear ranges were over three orders of magnitude ( R≥0.9996) with the detection limits being 7.5×10−8molL−1 for Cys, 1.0×10−7molL−1 for Hcy, 5.0×10−7molL−1 for Met. The application of this method coupled with microdialysis sampling for the determination of Cys, Hcy and Met in plasma from patients with hypothyroidism was satisfactory.
Keywords: Pt particles/poly(methyl violet); Cysteine; Homocysteine; Methionine; Hypothyroid
A composite thin film optical sensor for dissolved oxygen in contaminated aqueous environments by R.N. Gillanders; M.C. Tedford; P.J. Crilly; R.T. Bailey (pp. 189-194).
A robust optical composite thin film dissolved oxygen sensor was fabricated by ionically trapping the dye ruthenium(II) tris(4,7-diphenyl-1,10-phenanthroline) dichloride in a blended fluoropolymer matrix consisting of Nafion® and Aflas®. Strong phosphorescence, which was strongly quenched by dissolved oxygen (DO), was observed when the sensor was immersed in water. The sensor was robust, optically transparent, with good mechanical properties. Fast response, of a few seconds, coupled with sensitivity of about 0.1mgL−1 (DO) over the range 0–30mgL−1 and resistance to leaching, were also exhibited by this system. The Stern–Volmer (SV) plot exhibited slight downward turning at all oxygen concentrations. A linear plot was obtained when the SV equation was modified to account for the varying sensitivity of dye molecules in the matrix to the quencher. Good long term stability was observed.
Keywords: Nafion; ®; Aflas; ®; Ruthenium(II) complex; Dissolved oxygen; Sensor; Phosphorescence
Optimisation of an electronic amplifier applied to electrolyte/insulator/semiconductor structure by J. Launay; M.L. Pourciel-Gouzy; W. Sant; A. Martinez; P. Temple-Boyer (pp. 195-199).
This paper reports on the final development of a MOSFET-based amplifier for the electrical characterisation of chemical field-effect capacitors (ChemFEC) based on electrolyte/insulator/semiconductor (EIS) capacitive structure. Experimental demonstration is performed through the study of SiO2/Si3N4 ion sensitive field-effect capacitor (ISFEC) sensors for pH measurement. This study deals with the amplification's properties according to the ISFEC and MOSFET electrical characteristics. Thus, the ISFEC transition from the accumulation to the inversion regime is shown to be responsible for a non-linear phenomenon. Nevertheless, thanks to a compromise between the ISFEC flat-band voltage and the MOSFET threshold voltage, linear responses are evidenced on the [2–12] pH range. Thus, the non-linear phenomenon observed in previous works is clarified. The detection structure evidences linear responses, which is an essential parameter for sensors. Finally, high detection sensitivities are obtained on a small pH range due to this non-linearity.
Keywords: ChemFEC microsensor; EIS; MOSFET amplifier; Improved detection properties
Sensitive and rapid method for the determination of urinary cotinine in non-smokers: an application for studies assessing exposures to second hand smoke (SHS) by Liguo Song; Warren Davis; Sara M. Abrams; Jeremy Hemiup; A. Latif Kazim; K. Michael Cummings; Martin C. Mahoney (pp. 200-208).
We describe a sensitive and rapid method to assay urinary cotinine levels among non-smokers using liquid chromatography-electrospray ionization tandem mass spectrometry (LC–ESI/MS/MS) and its application in studies assessing exposures to second hand smoke (SHS). Cotinine was initially extracted from 1ml of urine with methylene chloride by using a liquid–liquid extraction Chem Elut™ column. The extracted sample was further separated by using a BetaBasic C18 column (1mm×150mm, 3μm) with isocratic elution (60:40 acetonitrile and 5mM ammonium acetate at pH 5), and then examined using a triple quadrupole mass spectrometer with an electrospray ionization (ESI) source in multiple-reaction-monitoring (MRM) mode. The elution of cotinine from the LC column took approximately 2.3min and the detection of cotinine by ESI/MS/MS provided a limit of detection (LOD) of 0.3ng/ml. The ESI/MS/MS detection was able to easily distinguish between cotinine and nicotine. This method, validated using a cotinine concentration range from 0.8 to 102.4ng/ml, was successfully applied in a cross-sectional study examining differences in levels and sources of second hand smoke (SHS) exposure among non-smokers. Self-reported measures of SHS exposure were significantly associated with urinary cotinine levels. This urinary cotinine assay using LC–ESI/MS/MS provides a robust, high throughput and very sensitive method for the evaluation of SHS exposure for use in epidemiologic and clinical research studies.
Keywords: Second hand smoke; Cotinine; Liquid chromatography; Electrospray ionization; Tandem mass spectrometry
Comparison of dimethylformamide dialkylacetal derivatization reagents for the analysis of heterocyclic amines in meat extracts by gas chromatography–mass spectrometry by E. Barceló-Barrachina; F.J. Santos; L. Puignou; M.T. Galceran (pp. 209-217).
A simple and selective methodology for the analysis of heterocyclic amines (HAs) in a meat extract by gas chromatography–mass spectrometry (GC–MS) is proposed. A comparative study of several HAs derivatization procedures based on the formation of Schiff bases using N, N-dimethylformamide dialkylacetals reagents was performed. Optimization of the reaction conditions was carried out, such as reagent volume (2μl to derivatize 1ng of HAs) temperature (100°C) and time (10min). After that, the GC–MS working parameters for the analysis of HAs derivatives were also studied in order to achieve the best chromatographic separation with the maximum sensitivity. Among the derivatization reagents, N, N-dimethylformamide di- tert-butylacetal (DMF-DtBA) was selected because it provided the best yield in the derivatization process, and consequently the best sensitivity in the GC–MS method. Quality parameters such as limits of detection and repeatability were established using a meat extract sample. A complete validation of the methodology was achieved using a laboratory reference material previously analyzed in a European interlaboratory exercise.
Keywords: Heterocyclic amines; Gas chromatography; Derivatization
Determination of benzoic acid in soft drinks by gas chromatography with on-line pyrolytic methylation technique by Zaifa Pan; Lili Wang; Weimin Mo; Chen Wang; Wei Hu; Juanjuan Zhang (pp. 218-223).
A new application of pyrolytic methylation was developed to determine benzoic acid in soft drinks by gas chromatography (GC) without using any pretreatment procedures and special pyrolyzer. With the on-line pyrolytic methylation by tetramethylammonium hydroxide (TMAH), benzoic acid was converted into its corresponding methyl ester in the injector at 280°C. Thus, samples containing benzoic acid could be well determined by direct-injection in GC on the medium polar stationary phase column. To obtain optimum methylation conditions, important factors were investigated and then applied to the following experiments. The results were obtained as following: 280°C as reaction temperature, 2:1 as the proportion of TMAH to benzoic acid. The storage time of mixed solution had no obvious effect on the area of benzoic acid methyl ester peak. With the p-xylene as an inter-standard, GC behaviors were investigated under these optimum conditions. The linear range achieved for benzoic acid was 1–10,000mg/l with the correlation coefficient of 0.9985. The precision was quite high with the R.S.D. of 2.8% and the limit of detection reached 0.1mg/l. The potential of the proposed method was assessed by applying it to the determination of benzoic acid in soft drinks. The results obtained coincided with the statement on the labels and all of the detected data were below the maximum permitted concentration of the European Union Legislation. This on-line pyrolytic methylation technique was proved to be simple to implement, sensitive and selective.
Keywords: Pyrolytic methylation; TMAH; GC; Benzoic acid; Soft drinks
Comparison of comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry and gas chromatography–mass spectrometry for the analysis of tobacco essential oils by Shukui Zhu; Xin Lu; Jun Xing; Shaowen Zhang; Hongwei Kong; Guowang Xu; Caiying Wu (pp. 224-231).
A sample of tobacco essential oil was analyzed using gas chromatography–mass spectrometry (GC/MS) and comprehensive two-dimensional gas chromatography coupled to a time-of-flight mass spectrometry (GC×GC/TOFMS), respectively. In the GC/MS analysis, serially coupled columns were used. By comparing the GC/MS results with GC×GC/TOFMS results, many more components in the essential oil could be found within the two-dimensional separation space of GC×GC. The quantitative determination of components in the essential oil was performed by GC×GC with flame ionization detection (FID), using a method of multiple internal standards calibration.
Keywords: Gas chromatography–mass spectrometry; Comprehensive two-dimensional gas chromatography; GC; ×; GC; Time-of-flight mass spectrometry; Coupled columns; Essential oil
Development of a fiber-in-tube microextraction protocol for gas chromatography–electron capture detection of hexachlorocyclohexanes in water samples by Jun-Xia Wang; Dong-Qing Jiang; Xiu-Ping Yan (pp. 232-238).
A fiber-in-tube microextraction protocol was developed and coupled with gas chromatography–electron capture detector (GC–ECD) for determination of trace hexachlorocyclohexanes (HCHs) in water samples. The developed technique was performed by immersing a PTFE fiber-packed and organic solvent-filled PTFE tube in the stirred aqueous solution. Extraction took place between the solvent permeated fibers and sample solution. The extract was then analyzed by GC–ECD. The effects of fiber quantity, extraction time, agitation, addition of salt and pH of sample solution were investigated in detail. Extraction of the analytes in 8ml aqueous solution for 20min yielded enrichment factors of 221–538. The limits of detection (S/N=3) and the limits of quantitation (S/N=8) were 2–12ngl−1 and 6–32ngl−1, respectively. The precision (R.S.D.s, n=5) was 0.1% for retention time and 1.8–4.8% for peak height. The developed methodology was applied to the determination of trace HCHs in local river water samples.
Keywords: Hexachlorocyclohexanes; Water; Microextraction; Gas chromatography; PTFE fibers
The leaching of V(V) with PO43− in the speciation analysis of soil by Khakhathi L. Mandiwana; Nikolay Panichev; Ronny Molatlhegi (pp. 239-243).
The leaching of V(V) from soil by two phosphate reagents, viz. (NH4)2HPO4 and Na3PO4 has been studied. (NH4)2HPO4 (1M) and Na3PO4 (0.01M) were efficient enough to extract all V(V) species from samples. The results were compared with that extracted by Na2CO3. Statistical evaluations show that the proposed method is similar to the established method utilizing Na2CO3.The method was applied in the analysis of soil samples from contaminated area of the vanadium mine where many grazing cattle died.Validation of the method was also done by comparing the sum of V(IV) and V(V) and the total vanadium obtained from the samples by an independent method. It was found that the sum of V(V) and V(IV) is in good agreement with the total content of vanadium in all samples after HF–H2SO4–HClO4 digestion. From the results of the investigation, it follows that the use of phosphate fertilizers in V(V)-rich soil may enhance the mobility and availability of V(V) to plants. The plants, in turn, are consumed by animals that may die depending on the level of poisoning.
Keywords: Leaching; Soil; Speciation; (NH; 4; ); 2; HPO; 4
Evaluation of V, Ir, Ru, V–Ir, V–Ru, and W–V as permanent chemical modifiers for the determination of cadmium, lead, and zinc in botanic and biological slurries by electrothermal atomic absorption spectrometry by Orhan Acar (pp. 244-251).
Permanent modifiers (V, Ir, Ru, V–Ir, V–Ru, and W–V) thermally coated on to platforms of pyrolytic graphite tubes were employed for the determination of Cd, Pb, and Zn in botanic and biological slurries by electrothermal atomic absorption spectrometry (ETAAS). Conventional Pd+Mg(NO3)2 modifier mixture was also used for the determination of analytes in slurries and digested samples. Optimum masses and mass ratios of permanent modifiers for Cd, Pb, and Zn in slurry sample solutions were investigated. The 280μg of V, 280μg of V+200μg of Ir, 280μg of V+200μg of Ru or 240μg of W+280μg of V in 0.2% (v/v) Triton X-100 plus 0.5% (v/v) HNO3 mixture was found as efficient as 5μg of Pd+3μg of Mg(NO3)2 modifier mixture for obtaining thermal stabilization, and for obtaining best recoveries. Optimization conditions of analytes, such as pyrolysis and atomization temperature, characteristic masses and detection limits, and atomization and background peak profiles were studied with permanent and 5μg of Pd+3μg of Mg(NO3)2 conventional modifiers and compared with each other. The permanent V–Ir, V–Ru, and W–V modifiers remained stable for approximately 250–300 firings when 20μl of slurries and digested samples were delivered into the atomizer. In addition, the mixed permanent modifiers increase the tube lifetime by 50–95% when compared with untreated platforms. The characteristic masses and detection limits of analytes (dilution factor of 125mlg−1) obtained with V–Ir based on integrated absorbance as example for 0.8% (m/v) slurries were 1.0pg and 3ngg−1 for Cd, 18pg and 17ngg−1 for Pb, and 0.7 pg and 4ngg−1 for Zn, respectively. The results of analytes obtained by employing V–Ir, V–Ru, and W–V permanent modifier mixtures in botanic and biological certified and standard reference materials were in agreement with the certified values of reference materials.
Keywords: Permanent modifiers; ETAAS; Slurries; Cadmium; Lead; Zinc
Optimization of210Pb determination via spontaneous deposition of210Po on a silver disk by P. Vesterbacka; T.K. Ikäheimonen (pp. 252-261).
The accuracy of210Pb determination via spontaneous deposition of210Po on a silver disk and alpha spectrometric measurement was examined. The study focused on the storage conditions of the polonium-containing solutions, the tracer used in polonium analysis and the effect of storage time and acid concentration on210Po deposition. The intermediate precision and repeatability associated with the improved210Pb analysis of fresh groundwater samples was 5 and 14%, respectively. These improved values were achieved by using glass bottles as storage containers for the solution remaining from the first210Po deposition, by rinsing the sample container with concentrated hydrochloric acid after storage and by using different isotopes of polonium as the yield determinant tracer in the first and the second deposition. Less polonium adsorption onto the storage container walls occurred with HCl than with HNO3. The overall uncertainty in210Pb analysis was (11±7)% at the 95% confidence level. The minimum detectable activity concentration was 0.1mBql−1 calculated from blank samples and 0.05mBql−1 using the background counts of the alpha spectrometer.
Keywords: 210; Pb; Spontaneous deposition; Alpha spectrometry; Quality assurance
Multivariate data analysis for Raman imaging of a model pharmaceutical tablet by Lin Zhang; Mark J. Henson; S. Sonja Sekulic (pp. 262-278).
Spectroscopic imaging techniques provide spatial and spectral information about a sample simultaneously and are finding ever-increasing application in the pharmaceutical industry. Effective extraction of chemical information from imaging data sets is a crucial step during the application of imaging techniques. Multivariate imaging data analysis methods have been reported but few applications of these methods for pharmaceutical samples have been demonstrated. In this study, a bilayer model tablet consisting of avicel, lactose, sodium benzoate, magnesium stearate and red dye was prepared using custom press tooling, and Raman mapping data were collected from a 400μm×400μm area of the tablet surface. Several representative multivariate methods were selected and used in the analysis of the data. Multivariate data analysis methods investigated include principal component analysis (PCA), cluster analysis, direct classical least squares (DCLS) and multivariate curve resolution (MCR). The relative merits and drawbacks of each technique for this application were evaluated. In addition, some practical issues associated with the use of these methods were addressed including data preprocessing, determination of the optimal number of clusters in cluster analysis and the optimization of window size in second derivative calculation.
Keywords: Raman imaging; PCA; Cluster analysis; DCLS; Multivariate curve resolution; Pharmaceutical tablet