Check out our New Publishers' Select for Free Articles

Analytical and Bioanalytical Chemistry (v.380, #2)

2004 Winter Conference on Plasma Spectrochemistry, 5–10 January 2004, Fort Lauderdale, Florida by Ramon Barnes (pp. 183-184).

Some trends in the development of microplasmas for spectrochemical analysis by José A. C. Broekaert; Volker Siemens (pp. 185-189).

The development of microplasmas for spectrochemical analysis by optical methods is discussed. Recent achievements in miniaturization are highlighted, especially for three types of plasmas, namely high-frequency plasmas, dc-discharges and microwave plasmas. The potentials of each of these groups of plasmas as sources for atomic emission spectrometry are discussed. Literature citations and experiments indicate that the plasmas are also very useful as atom reservoirs for atomic absorption spectrometry. Methods of sampling, including feeding with gas chromatography effluents, the use of electrothermal vaporization, and the evolution of gaseous species (as shown for the case of Hg vapor), are discussed as prominent interfaces to make use of these sources for elemental analysis.

Keywords: Atomic spectrometry; Microplasma; Plasma-on-the-chip; Plasma spectrometry

Accurate determination of sulfur in gasoline and related fuel samples using isotope dilution ICP–MS with direct sample injection and microwave-assisted digestion by Jens Heilmann; Sergei F. Boulyga; Klaus G. Heumann (pp. 190-197).

Inductively coupled plasma isotope-dilution mass spectrometry (ICP–IDMS) with direct injection of isotope-diluted samples into the plasma, using a direct injection high-efficiency nebulizer (DIHEN), was applied for accurate sulfur determinations in sulfur-free premium gasoline, gas oil, diesel fuel, and heating oil. For direct injection a micro-emulsion consisting of the corresponding organic sample and an aqueous ³⁴S-enriched spike solution with additions of tetrahydronaphthalene and Triton X-100, was prepared. The ICP–MS parameters were optimized with respect to high sulfur ion intensities, low mass-bias values, and high precision of ³²S/³⁴S ratio measurements. For validation of the DIHEN–ICP–IDMS method two certified gas oil reference materials (BCR 107 and BCR 672) were analyzed. For comparison a wet-chemical ICP–IDMS method was applied with microwave-assisted digestion using decomposition of samples in a closed quartz vessel inserted into a normal microwave system. The results from both ICP–IDMS methods agree well with the certified values of the reference materials and also with each other for analyses of other samples. However, the standard deviation of DIHEN–ICP–IDMS was about a factor of two higher (5–6% RSD at concentration levels above 100 μg g⁻¹) compared with those of wet-chemical ICP–IDMS, mainly due to inhomogeneities of the micro-emulsion, which causes additional plasma instabilities. Detection limits of 4 and 18 μg g⁻¹ were obtained for ICP–IDMS in connection with microwave-assisted digestion and DIHEN–ICP–IDMS, respectively, with a sulfur background of the used Milli-Q water as the main limiting factor for both methods.

Keywords: Gasoline; Sulfur; Inductively coupled plasma mass spectrometry; Isotope dilution technique; Direct injection high-efficiency nebulizer; Microwave-assisted digestion

Application of SEC-ICP-MS for comparative analyses of metal-containing species in cancerous and healthy human thyroid samples by Sergei F. Boulyga; Valeria Loreti; Jörg Bettmer; Klaus G. Heumann (pp. 198-203).

Size exclusion chromatography (SEC) was coupled on-line to inductively coupled plasma mass spectrometry (ICP-MS) for speciation study of trace metals in cancerous thyroid tissues in comparison to healthy thyroids aimed to estimation of changes in metalloprotein speciation in pathological tissue. The study showed a presence of species binding Cu, Zn, Cd and Pb in healthy thyroid tissue with a good reproducibility of chromatographic results, whereas the same species could not be detected in cancerous tissues. Thus, remarkable differences with respect to metal-binding species were revealed between healthy and pathological thyroid samples, pointing out a completely different distribution of trace metals in cancerous tissues. The metal-binding species could not be identified in the frame of this work because of a lack of appropriate standards. Nevertheless, the results obtained confirm the suitability of SEC-ICP-MS for monitoring of changes in trace metal distribution in cancerous tissue and will help to better understand the role of metal-containing species in thyroid pathology.

Keywords: Thyroid cancer; Metal speciation; Metalloprotein; Size exclusion chromatography; Inductively coupled plasma mass spectrometry

Total protein determinations by particle beam/hollow cathode optical emission spectroscopy (PB/HC-OES) system III: Investigation of carrier salts for enhanced particle transport by Fuxia Jin; James J. Hickman; Keith Lenghaus; R. Kenneth Marcus (pp. 204-211).

Particle beam hollow cathode optical emission spectroscopy (PB/HC-OES) is evaluated as a generic tool for total protein determinations by monitoring the carbon atomic emission (C (I) 193.0 nm) resultant from dissociated analyte species. Previous studies demonstrated the capability of the PB/HC-OES system for total protein determinations with limits of detection for bovine serum albumin (BSA) samples being at the single-nanogram level for 200 μl injections. Non-linear behavior across the concentration range in the calibration curve was observed due to the poor transport of small particles (owing to low analyte concentrations) through the PB interface. The potential use of non-volatile salts as carrier agents is investigated in the determination of protein samples by PB/HC-OES. A range of chloride salts (different cations), potassium salts (different anions), and an organic modifier (ammonium acetate) is investigated here for possible use as carriers upon addition as sample injection matrices for protein samples. The analyte response curves of BSA samples with KCl added as the sample injection matrix show higher sensitivity, better linearity (R²) and subsequently lower detection limits in comparison to those obtained with water, HCl, KNO₃ or ammonium acetate as carrier matrices.

Keywords: Protein; Particle beam; Hollow cathode glow discharge; Atomic emission; Total protein determination; Carrier effect

Simultaneous determination of the Cd and Zn total body burden of individual, nearly microscopic, nanoliter-volume aquatic organisms (Hyalella azteca) by rhenium-cup in-torch vaporization (ITV) sample introduction and axially viewed ICP-AES by Andrea T Smith; Hamid R Badiei; J. Catherine Evans; Vassili Karanassios (pp. 212-217).

The Cd and Zn total body burden of individual, up to 7-day-old aquatic organisms (Hyalella azteca benthic amphipod) with an average volume of approximately 100 nL was determined simultaneously by using rhenium-cup (Re-cup) in-torch vaporization (ITV) sample introduction and an axially viewed inductively coupled plasma atomic emission spectrometry (ICP-AES) system. The direct elemental analysis capabilities of this system (i.e., no sample digestion) reduced sample preparation time, eliminated contamination concerns from the digestion reagent and, owing to its detection limits (e.g., in the low pg range for Cd and Zn), vit enabled simultaneous determinations of Cd and Zn in individual, neonate and young juvenile specimens barely visible to the unaided eye (e.g., nearly microscopic). As for calibration, liquid standards and the standard additions method were tested. Both methods gave comparable results, thus indicating that in this case liquid standards can be employed for calibration, and in the process making use of the standard additions method unnecessary. Overall, the ITV-ICP-AES approach by-passed the time-consuming acid digestions, eliminated the potential for contamination from the digestion reagents, improved considerably the speed of acquisition of analytical information and enabled simultaneous determinations of two elements using individual biological specimens.

Keywords: ICP; In-torch vaporization (ITV); Micro-samples; Hyalella azteca

Depth profile studies of ZrTiN coatings by laser ablation inductively coupled plasma mass spectrometry by Viktor Kanický; Hans-Rudolf Kuhn; Detlef Guenther (pp. 218-226).

The feasibility of depth profiling was studied by using a 193-nm ArF* excimer laser ablation system (GeoLas, MicroLas, Goettingen, Germany) with a lens array-based beam homogenizer in combination with an ICP-QMS Agilent 7500. Two ablation cells (20 and 1.5 cm³) were compared at the laser repetition rate of 1 Hz, laser beam energy of 135 mJ and the carrier gas flow rate 1.5 L min⁻¹ He + 0.78 L min⁻¹ Ar. The ablation cell dimensions are important parameters for signal tailing; however, very small cell volumes (e.g. 1.5 cm³) may cause memory effects, which can be probably explained by dominant inertial losses of aerosol on cell walls with its delayed mobilization. The 20-cm³ ablation cell seems to be appropriate for depth profiling by continuous single-hole drilling. The study of the influence of the pit diameter magnitude on the waning and emerging signals under small crater depth/diameter aspect ratios, which range between 0.75 and 0.0375 for the 3-μm-thick coatings and pit diameters 4–80 μm, revealed that the steady-state signals of pure coating and pure substrate (out of interface) were obtained at crater diameters between 20 and 40 μm. Depth resolution defined by means of slopes of tangents in the layer interface region depend on the pit diameter and has an optimum value between 20 and 40 μm and gives 0.6 μm for the 20-μm pit. In-depth variation of concentration of coating constituent (Ti) was proved to be almost identical with two different laser/ICP systems.

Keywords: Laser ablation; Inductively coupled plasma mass spectrometry; Excimer laser; Beam homogenizer; ZrTiN; Coating; Depth profiling; Depth resolution; Aspect ratio

Simultaneous multichannel mass-specific detection for high-performance liquid chromatography using an array detector sector-field mass spectrometer by James H. Barnes IV; Gregory D. Schilling; Steven F. Stone; Roger P. Sperline; M. Bonner Denton; Erick T. Young; Charles J. Barinaga; David W. Koppenaal; Gary M. Hieftje (pp. 227-234).

The use of a separation step, such as liquid chromatography, prior to inductively coupled plasma mass spectrometry (ICP–MS) has become a common tool for highly selective and sensitive analyses. This type of coupling has several benefits including the ability to perform speciation analysis or to remove isobaric interferences. Several limitations of conventional instruments result from the necessity to scan or pulse the mass spectrometer to obtain a complete mass spectrum. When the instrument is operated in such a non-continuous manner, duty cycle is reduced, resulting in poorer absolute limits of detection. Additionally, with scanning instruments, spectral skew can be introduced into the measurement, limiting quantitation accuracy. To address these shortcomings, a high-performance liquid chromatograph has been coupled to an ICP–MS capable of continuous sample introduction and simultaneous multimass detection. These features have been realized with a novel detector array, the focal plane camera. Instrument performance has been tested for both speciation analysis and for the elimination of isobaric interferences. Absolute limits of detection in the sub picogram to tens of picograms regime are obtainable, while the added mass dimension introduced by simultaneous detection dramatically increases chromatographic peak capacity.

Keywords: Array Detector; Inductively coupled plasma mass spectrometry; Sector field mass spectrometry; Liquid chromatography; Simultaneous detection; Focal plane camera

Separation of plutonium from uranium using reactive chemistry in a bandpass reaction cell of an inductively coupled plasma mass spectrometer by Vladimir Vais; Chunsheng Li; Jack Cornett (pp. 235-239).

Oxygen and ammonia were evaluated as reaction gases for the chemical separation between uranium and plutonium in the bandpass reaction cell or dynamic reaction cell (DRC) of the ELAN DRC II mass spectrometer. Both uranium and plutonium demonstrated similar reactivity with oxygen giving rise to corresponding oxides. At the same time, remarkable selectivity in the reaction with ammonia was observed. While uranium was rapidly converted into UNH ₂ ⁺ and UN₂H ₄ ⁺ , plutonium remained unreactive in the DRC pressurized with ammonia. This difference in the reactivity allowed the determination of plutonium isotopes in urine and water samples containing excess uranium without preceding separation procedure. Detection limits of 0.245, 0.092, 0.270 and 0.237 ng L⁻¹ were obtained for ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu and ²⁴²Pu, respectively, in urine spiked with 10 μg L⁻¹ of U.

Keywords: Plutonium; Uranium; Dynamic reaction cell; Condensation reactions; Chemical separation; ICP-MS

Regional distribution of manganese, iron, copper, and zinc in the rat brain during development by Tohru Tarohda; Masayoshi Yamamoto; Ryohei Amamo (pp. 240-246).

Manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn) concentrations were determined in the brain regions of normal 1-, 3-, 5-, 7-, 14-, 21-, 42-, 77-, and 147-day-old Wistar rats using inductively coupled plasma mass spectrometry (ICP-MS), and their maps were illustrated in color to visually compare the distribution of the elements at various stages of the growth process. Sagittal slices (1-mm thickness) sectioned at the level of the substantia nigra were divided into 18 regions, and the small slice samples were digested in microwave-assisted closed vessels for ICP-MS measurement. Mn, Fe, Cu, and Zn concentrations increased region-specifically with age, and their distributional maps showed some characteristics. These findings are discussed in terms of needs for these trace elements in the normal brain. Among new findings about their brain distribution, it is especially noteworthy that higher concentrations of Mn, Fe, and Zn were observed in the substantia nigra compared with those in neighboring regions. The mapping method in this work is expected to open up possibilities for screening of the in vivo element–element interrelationships among these essential elements.

Keywords: Manganese; Iron; Copper; Zinc; Brain; ICP-MS

Determination of low-abundance elements at ultra-trace levels in urine and serum by inductively coupled plasma–sector field mass spectrometry by Ilia Rodushkin; Emma Engström; Anna Stenberg; Douglas C. Baxter (pp. 247-257).

A procedure is described for the determination of Y, Zr, Nb, Ru, Rh, Pd, Ag, Sb, Te, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Bi, and U in human urine and serum at concentrations relevant to the occupationally unexposed population. Sample preparation was limited to tenfold dilution with 2% HCl. A combination of a sample-introduction system designed to provide enhanced sensitivity and the use of water and acids of high-purity has resulted in limits of quantification (LOQ) in the sub-nanogram per liter range for 13 analytes. Instrumental background caused by release of analytes (Y, Zr, Ag, Sb, Au, Tl, Bi, U) from different parts of the sample-introduction system was found to be the major limitation in obtaining even better LOQ. Nevertheless, detection capabilities of the proposed procedure were adequate for all elements except Ru, Pd, and Rh. Despite of the use of high-resolution mode for these analytes some unresolved spectral interferences might still be present. For 13 elements an external accuracy assessment was accomplished by participation in proficiency testing and inter-comparison programs. Results obtained for pooled urine and serum were compared with concentrations reported for occupationally unexposed populations in recent publications.

Keywords: Low-abundance elements; Inductively coupled plasma–sector field mass spectrometry; Urine; Serum; Environmental monitoring; Clinical samples

Trace element determination in seawater by ICP-SFMS coupled with a microflow nebulization/desolvation system by Clara Turetta; Giulio Cozzi; Carlo Barbante; Gabriele Capodaglio; Paolo Cescon (pp. 258-268).

Direct and simultaneous determination of Al, Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Sb, U, V and Zn in diluted (1:10 v:v) seawater from the Antarctic Ocean and the Venice Lagoon at the ng mL⁻¹ and pg mL⁻¹ level has been performed by using an inductively coupled plasma sector field mass spectrometer (ICP-SFMS). Samples were analysed by using a PFA microflow nebulizer coupled with a desolvation system or a PFA microflow nebulizer coupled with a Teflon spray chamber, respectively. Measurements were carried out at low (LR, m/Δm=300), medium (MR, m/Δm=3,000) and high (HR, m/Δm=7,500) resolutions depending on the studied isotope. To avoid contamination, sample pre-treatment was carried out in a clean laboratory equipped with a Class 100 vertical laminar flow hood. Concentration ranges (minimum–maximum in ng mL⁻¹) found in the Antarctic seawater samples (in depth profiles) were: Ag 0.0004–0.0018, As 0.69–1.32, Cd 0.031–0.096, Co 0.018–0.065, Cr 0.18–0.46, Cu 0.04–1.58, Fe 0.13–1.63, Mn 0.02–0.12, Mo 5.97–12.46, Pb 0.007–0.074, Sb 0.033–0.088, U 0.5–1.9, V 0.6–2.5 and Zn 0.16–0.80. Concentration ranges (min–max in ng mL⁻¹) found in the Venice Lagoon water samples (temporal profile from a benthic chamber experiment) were: Al 0.24–0.61, Ag 0.007–0.031, As 1.42–2.27, Cd 0.050–0.182, Co 0.440–1.461, Cr 0.15–0.34, Cu 0.81–2.46, Fe 0.25–1.66, Mn 11.6–31.7, Mo 6.50–10.6, Pb 0.047–0.225, Sb 0.240–0.492, U 1.7–3.3, V 1.3–2.8 and Zn 5.20–21.5. The detection limits range between 0.06 pg mL⁻¹ for Ag and U to 15 pg mL⁻¹ for Fe. In order to check the accuracy of the analytical procedure, measurements of the trace elements in a certified reference material (coastal Atlantic seawater, CASS-4-NRCC) were compared with the certified values. In addition, the results from the Antarctic and Venice Lagoon samples were compared with those obtained by using different analytical techniques.

Keywords: Trace elements; Seawater; ICP-SFMS; Desolvation system

Development of a fluorescent microplate assay for determining cyanovirin-N levels in plasma by Scott D. Bringans; Barry R. O’Keefe; Michael Bray; Chris A. Whitehouse; Michael R. Boyd (pp. 269-274).

A sensitive immunosorbent competition assay was developed for quantitation of the anti-HIV protein cyanovirin-N (CV-N) in plasma using a 96-well plate format and a fluorescent endpoint. The assay is based on the binding of CV-N in plasma to plate-bound anti-CV-N antibodies, followed by removal of the plasma and addition of europium-labeled CV-N (Eu³⁺-CV-N) to compete for the remaining antibody sites. Detection by addition of a dissociative fluorescence enhancement solution and time-resolved fluorescence measurements allowed correlation to the concentration of the native CV-N in plasma. A linear detection range of 1–100 nM (r²>0.99) was obtained for CV-N in mouse plasma. This assay was then utilized for analysis of plasma levels of CV-N samples following subcutaneous injection of CV-N into mice. The results of these studies confirmed the reliability and sensitivity of this assay and the feasibility of its use for pharmacokinetic studies in a variety of species.

Keywords: Cyanovirin-N (CV-N); HIV; Plasma; Analysis

High-throughput analysis of phthalate esters in human serum by direct immersion SPME followed by isotope dilution–fast GC/MS by Ivelisse Colón; Jean-Marie D. Dimandja (pp. 275-283).

Solid-phase microextraction (SPME) coupled to gas chromatography/mass spectrometry (GC/MS) was applied to the determination of phthalate esters in human serum. The present method decreased the sample preparation time by a factor of 50 by using direct immersion SPME with an 85-μm polyacrylate fiber to extract phthalate esters from the matrix. The use of fast GC/MS further improves total analysis time when compared to other techniques. Isotope dilution was successfully applied to improve the precision, reproducibility, and repeatability of the SPME method. The linear dynamic range spans several orders of magnitude from low ppb to ppm levels, and the LOD for the method is 15 pg μL⁻¹ on average with RSDs less than 4% for the six phthalate esters included in this study.

Keywords: Solid-phase microextraction; SPME; Phthalate esters; Isotope dilution; Serum analysis

Urease–glutamic dehydrogenase biosensor for screening heavy metals in water and soil samples by Belen Bello Rodriguez; John A Bolbot; Ibtisam E Tothill (pp. 284-292).

A screen-printed three-electrode amperometric biosensor based on urease and the nicotinamide adenine dinucleotide hydrogen (NADH)–glutamic dehydrogenase system was developed and applied to the screening of heavy metals in environmental samples. The development of an amperometric sensor for the monitoring of urease activity was feasible by coupling the urea breakdown reaction catalysed by urease to the reductive ammination of ketoglutarate catalysed by glutamic dehydrogenase (GLDH). The ammonia provided by the urea conversion is required for the conversion of ketoglutarate to glutamate with the concomitant oxidation of the NADH cofactor. NADH oxidation is monitored amperometrically at 0.3 V (vs. Ag/AgCl) after urease immobilization onto the screen-printed three-electrode configuration. Immobilization of urease on the surface of screen-printed electrodes was performed by entrapment in alginate gel and adsorption on the electrode in a nafion film. Low sensitivity to inactivation by metals was recorded after urease entrapment in alginate gel with detection limits of 2.9 and 29.8 mg L⁻¹ for Hg(II) and Cu(II), respectively. The use of the negatively charged nafion film created a more concentrated environment of cations in proximity to the enzyme, thus enhancing the urease inhibition when compared to gel entrapment. The calculated detection limits were 63.6 and 55.3 μg L⁻¹ for Hg(II) and Cu(II), respectively, and 4.3 mg L⁻¹ for Cd(II). A significant urease inactivation was recorded in the presence of trace amounts of metals (μg L⁻¹) when the enzyme was used free in solution. Analysis of water and soil samples with the developed nafion-based sensor produced inhibition on urease activity according to their metal contents. The obtained results were in agreement with the standard methods employed for sample analysis. Nevertheless, the use of the amperometric assay (with free urease) proved more feasible for the screening of trace amounts of metals in polluted samples.

Keywords: Metal ion biosensor; NADH; Urease inhibition; Glutamic dehydrogenase; Screen-printed electrodes; Water and soil samples; Gel entrapment; Nafion

Influence of cetyltrimethylammonium bromide on phosphatidylcholine-coated capillaries by Ruth Kuldvee; Maria V. Lindén; Susanne K. Wiedmer; Marja-Liisa Riekkola (pp. 293-302).

Large unilamellar vesicles of egg-phosphatidylcholine (eggPC), a naturally occurring phospholipid, were used in capillary electrophoresis (CE) for semi-permanent coating of fused silica capillaries. The stability of the phospholipid coating was tested at different cetyltrimethylammonium bromide (CTAB) concentrations with and without CaCl₂ present in the coating solution. The effect of physical factors influencing the coating stability (e.g. duration of the coating time, storage temperature of the coating solution) were also studied. Standing overnight in background electrolyte (BGE) solution did not alter the eggPC phospholipid coating noticeably. The performance of the coating was tested with a mixture of basic proteins (lysozyme, ribonuclease A and α-chymotrypsinogen A). Highest efficiencies (over 200,000 plates m⁻¹) were achieved when the capillary was filled for 15 h with a liposome solution containing both CTAB and CaCl₂.

Keywords: Capillary electrophoresis; Liposomes; Phospholipids; Semi-permanent coating; CTAB; Protein separation

Development of an acetylene black–dihexadecyl hydrogen phosphate composite-modified glassy-carbon electrode, and its application in the determination of lovastatin in dosage drug forms by Huajie Zhang; Chengguo Hu; Wei Lan; Shengshui Hu (pp. 303-309).

An electrochemical method has been established for the determination of lovastatin (LV). It is based on the enhanced oxidation of lovastatin at a novel acetylene black–dihexadecyl hydrogen phosphate composite-modified glassy-carbon electrode (AB–DHP/GCE) in the presence of Triton X-100. This electrode was prepared by dispersion of acetylene black particles in an aqueous suspension of DHP and the formation of a stable film of the resulting AB–DHP composite on the surface of a glassy carbon electrode (GCE). As a result of modification of the AB–DHP composite, the electrochemical response of lovastatin at GCE was apparently enhanced; this was apparent as amplification of the oxidation current and the negative shift of the oxidation potential. The oxidation current can be further increased in the presence of a trace amount of Triton X-100. The enhanced oxidation of lovastatin at AB–DHP/GCE was due to enlargement of the effective electrode area, catalysis of lovastatin oxidation by AB, and accumulation of lovastatin at the hydrophobic surface of the DHP layer, which would be enhanced by the coherence with Triton X-100. The effects of some working conditions on the oxidation current of lovastatin were tested and the calibration plot was examined. The result showed that the oxidation current was a linear function of lovastatin concentration in the range 2.5×10⁻⁸–1.0×10⁻⁶ mol L⁻¹ and a low detection limit of 4.0×10⁻⁹ mol L⁻¹ was obtained under optimum conditions. This electrode system was applied to the determination of lovastatin in dosage drug forms and the results were in accordance with the ultraviolet–visible spectroscopy method.

Keywords: Acetylene black; Dihexadecyl hydrogen phosphate; Lovastatin; Determination; Drug

Study of the disulfide reduction of denatured proteins by liquid chromatography coupled with on-line cold-vapor-generation atomic-fluorescence spectrometry (LC–CVGAFS) by Emilia Bramanti; Cristina Lomonte; Massimo Onor; Roberto Zamboni; Giorgio Raspi; Alessandro D’Ulivo (pp. 310-318).

Hydrophobic-interaction chromatography coupled on-line with chemical-vapor-generation atomic-fluorescence spectrometry (HIC–CVGAFS), optimized recently for the analysis of thiol-containing proteins under denaturing conditions, has been used to study the chemical reduction of denatured proteins. Four proteins chosen as models (human serum albumin (HSA), bovine serum albumin (BSA), α-lactalbumin (α-Lac) from bovine milk, and lysozyme from chicken egg (Lys)) were denatured with urea and reduced with dithiothreitol (DTT), with selenol as catalyst. The method is based on derivatization of the –SH groups of proteins with p-hydroxymercurybenzoate (PHMB), followed by HIC separation and post-column on-line reaction of the derivatized reduced, denatured proteins with bromine generated in situ. Hg^II, derived from rapid conversion of uncomplexed and protein-complexed PHMB, is selectively detected by AFS in an Ar/H₂ miniaturized flame after sodium borohydride (NaBH₄) reduction to Hg°. The yield of the reduction was studied as a function of reductant concentration, reduction time (t_red), and urea concentration. Results showed that the optimum values for DTT and selenol concentrations and for t_red were between 1 and 100 mmol L⁻¹ and between 1 and 20 min, respectively, depending on the protein studied. The percentage disulfide bond reduction increases as the urea concentration used for protein denaturation increases, giving a single-step sigmoid increment for single-domain, low-MW proteins (α-Lac and Lys), and a two-step sigmoid increment for multi-domain, high MW proteins (HSA and BSA). The shapes of plots of percentage reduced disulfide against urea concentration are characteristic of each protein and are correlated with the location of S–S in the protein. Under the adopted conditions complete protein denaturation is the conditio sine qua non for obtaining 100% S–S reduction. The detection limit for denatured, reduced proteins examined under the optimized conditions was found to be in the range 1–5×10⁻¹² mol L⁻¹ (10–30 pg), depending on the protein considered.

Keywords: Disulfide reduction; Thiol-containing proteins; Atomic-fluorescence spectrometry; Chromatographyp-Hydroxymercurybenzoate; Hyphenated technique

Evaluation of solid-phase microextraction with PDMS for air sampling of gaseous organophosphate flame-retardants and plasticizers by Sindra Isetun; Ulrika Nilsson; Anders Colmsjö (pp. 319-324).

As an inexpensive, simple, and low-solvent consuming extraction technique, the suitability of solid-phase microextraction (SPME) with polydimethylsiloxane (PDMS) sorbent was investigated as a quantitative method for sampling gaseous organophosphate triesters in air. These compounds have become ubiquitous in indoor air, because of their widespread use as additive flame retardants/plasticizers in various indoor materials. Results obtained by sampling these compounds at controlled air concentrations using SPME and active sampling on glass fibre filters were compared to evaluate the method. A constant linear airflow of 10 cm s⁻¹ over the fibres was applied to increase the extraction rate. For extraction of triethyl phosphate with a 100-μm PDMS fibre, equilibrium was achieved after 8 h. The limit of detection was determined to be less than 10 pg m⁻³. The PDMS–air partition coefficients, K_fs, for the individual organophosphate triesters were determined to be in the range 5–60×10⁶ at room temperature (22–23°C). Air measurements were performed utilising the determined coefficients for quantification. In samples taken from a lecture room four different airborne organophosphate esters were identified, the most abundant of which was tris(chloropropyl) phosphate, at the comparatively high level of 1.1 μg m⁻³. The results from SPME and active sampling had comparable repeatability (RSD less than 17%), and the determined concentrations were also similar. The results suggest that the investigated compounds were almost entirely associated with the gaseous phase at the time and place sampled.

Keywords: Organophosphate triesters; Flame retardants; Plasticizers; Air sampling; SPME; PDMS

Determination of diethanolamine or N-methyldiethanolamine in high ammonium concentration matrices by capillary electrophoresis with indirect UV detection: application to the analysis of refinery process waters by N. Bord; G. Crétier; J.-L. Rocca; C. Bailly; J.-P. Souchez (pp. 325-332).

Alkanolamines such as diethanolamine (DEA) and N-methyldiethanolamine (MDEA) are used in desulfurization processes in crude oil refineries. These compounds may be found in process waters following an accidental contamination. The analysis of alkanolamines in refinery process waters is very difficult due to the high ammonium concentration of the samples. This paper describes a method for the determination of DEA in high ammonium concentration refinery process waters by using capillary electrophoresis (CE) with indirect UV detection. The same method can be used for the determination of MDEA. Best results were achieved with a background electrolyte (BGE) comprising 10 mM histidine adjusted to pH 5.0 with acetic acid. The development of this electrolyte and the analytical performances are discussed. The quantification was performed by using internal standardization, by which triethanolamine (TEA) was used as internal standard. A matrix effect due to the high ammonium content has been highlighted and standard addition was therefore used. The developed method was characterized in terms of repeatability of migration times and corrected peak areas, linearity, and accuracy. Limits of detection (LODs) and quantification (LOQs) obtained were 0.2 and 0.7 ppm, respectively. The CE method was applied to the determination of DEA or MDEA in refinery process waters spiked with known amounts of analytes and it gave excellent results, since uncertainties obtained were 8 and 5%, respectively.

Keywords: Capillary electrophoresis; Indirect UV detection; Alkanolamines; High ammonium sample content; Refinery process waters; Standard addition

A highly sensitive PVC membrane iodide electrode based on complexes of mercury(II) as neutral carrier by Y. -Q. Chai; R. Yuan; L. Xu; W. -J. Xu; J. -Y. Dai; F. Jiang (pp. 333-338).

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO₃)₄], has a Nernstian potentiometric response from 2.0×10⁻⁸ to 2.0×10⁻² mol L⁻¹ with a detection limit of 8.0×10⁻⁹ mol L⁻¹ and a slope of −59.0±0.5 mV/decade in 0.01 mol L⁻¹ phosphate buffer solution (pH 3.0, 20°C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV–Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results.

Keywords: 1,4-Bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II); Neutral carrier; Iodide; Ion-selective electrode

Detection of enzymatic activity by means of a diffraction-based biosensor by Patrick T. Fiori; Matthew F. Paige (pp. 339-342).

We demonstrate here, for the first time, the capability of a diffraction-based sensor to detect enzyme activity and provide a simple measure of enzyme kinetics. Patterned samples of mouse IgG were exposed to the enzyme trypsin and the progress of enzymatic degradation of IgG was followed by measuring the decrease in diffraction signal intensity as a function of time. The diffraction signal intensity decreased exponentially as a function of time over a range of trypsin concentrations from 2–100 μg mL⁻¹. Atomic-force microscope images of the samples before and after exposure to trypsin show that the thickness of patterned protein is greatly reduced by the enzyme action, providing useful insight into the mechanism of signal change for the diffraction sensor.

Keywords: Biosensor; Enzyme; Kinetics; Diffraction; Microcontact printing

Chromatographic molecular recognition for catechol-related compounds using thiacalix[4]arene as an effective selector by Ken Hosoya; Natsuki Hira; Yoshiyuki Watabe; Nobuo Tanaka; Takuya Kubo; Kunimitsu Kaya (pp. 343-345).

Thiacalix[4]arene (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrahydroxy-2,8,14,20-tetrathiacalix[4]arene) is an amphiphilic molecule comprising four p-tert-butylphenol-like groups ortho-linked by single sulfur atoms. This molecule has a high electron density area owing to the close proximity of the hydroxyl groups and sulfur atoms. We studied the applicability of this interesting compound as a selector for high-performance liquid chromatography (HPLC) thereby presumably exploiting this feature. Firstly, uniformly sized polymer particles were prepared by using a multi-step swelling and polymerization method with ethylene glycol dimethacrylate (EDMA) as a cross-linker. Methacrylic acid (MAA) was introduced onto the surface of the resulting polymer particles through a new modification method. Thiacalix[4]arene was chemically bonded through the MAA group by using 1,4-dibromobutane as a spacer to reduce steric hindrance around the MAA and the polymer particle itself. The performance of the prepared polymer-based thiacalix[4]arene-modified stationary phase was evaluated with HPLC. Specific chromatographic retention behavior was observed for catechol relative to positional isomers of xylene, cresol, and benzene-diol. Catecholamine and catechol showed specific chromatographic retention behavior.

Keywords: HPLC; Molecular recognition; Catechol; Thiacalix[4]arene

Sampling procedure and a radio-indicator study of mercury determination in whole blood by using an AMA 254 atomic absorption spectrometer by Věra Spěváčková; Vlasta Korunová; Mája Čejchanová; Miloslav Vobecký (pp. 346-350).

A sampling procedure appropriate for the determination of mercury in whole blood was tested by using both inactive controls and a ¹⁹⁷Hg mercury radio-indicator. To exclude the influence of the instrumental device (an AMA 254 single-purpose mercury atomic absorption spectrometer) on the determination of mercury in whole blood, the function of the instrument was checked by using rat blood with metabolised ¹⁹⁷Hg. The measurement procedure was found to be free of errors. However, the study showed that the material used for the sampling vessels is a crucial parameter for obtaining accurate analytical results. The stability of solutions and samples was tested towards polyethylene (PE) and polypropylene (PP) vessels. PE displayed a time-dependent increase in the mercury content both in the samples and in the blood control material. The probable cause of this increase was direct contamination from the material of the vessel and/or diffusion of mercury from the environment through the vessel walls related to a strong complexing affinity of the sample matrix. This assumption was confirmed by supplying the vessels with the complexing agent Na₂EDTA (0.05 mol L⁻¹). Commercial PP vessels for blood sampling (Sarstedt S-Monovette Metall Analytik) did not give rise to statistically significant variations in mercury content in the samples and blood control material over a 30-day period.

Keywords: Mercury; Blood sample stability; Radio-indicator ¹⁹⁷Hg; AAS–AMA 254

Preconcentration technique for nonylphenol using cellulose cotton with homogenous liquid–liquid extraction for liquid chromatographic analysis by Yoshitaka Takagai; Toshio Kubota; Ryoutaro Akiyama; Eiji Aoyama; Shukuro Igarashi (pp. 351-354).

A powerful preconcentration method for nonylphenol (NP) has been developed for liquid-chromatography by combining the use of cellulose cotton (solid-phase extraction) with homogeneous liquid–liquid extraction. A 100 ml of sample solution was preconcentrated using cotton, and the eluate obtained (acetonitrile; 5 ml) was further preconcentrated to 50 μl within 10 min using a homogeneous liquid–liquid extraction method (volume ratio, 2,000-fold; 100 ml→ 50 μl). The sample concentration increases from preconcentration was 1,599-fold, and NP was extracted into the sedimented phase at 80%. The proposed method was applied to high performance liquid chromatography with fluorescence detection (FL/HPLC); the lowest determination limit obtained was 1.0×10⁻⁹ mol l⁻¹.

Keywords: Nonylphenol; Alkylphenol; Preconcentration; Cellulose; Homogeneous liquid–liquid extraction; Chromatography

European Winter Conference on Plasma Spectrochemistry, Budapest, Hungary, 30 January–3 February 2005 (pp. 355-355).

Liquid chromatography coordination ion-spray mass spectrometry (LC–CIS–MS) of docosahexaenoate ester hydroperoxides by Jennifer R. Seal; Ned A. Porter (pp. 356-356).

Sections

Personal tools

Analytical and Bioanalytical Chemistry (v.380, #2)

Sections

Personal tools

Local resources

Analytical and Bioanalytical Chemistry (v.380, #2)