Analytical and Bioanalytical Chemistry (v.373, #3)

Analytical equilibrium gradient methods by Qinggang Wang; Dennis H. Tolley; David A. LeFebre; Milton L. Lee (125-135).
Analytical equilibrium gradient methods are non-linear separation methods in which the separation mechanism involves a force gradient along the separation channel. These methods can be classified into two categories: those in which the gradient is a field gradient applied along the separation channel (i.e., field gradient), and those in which the channel is subjected to a constant field with a gradient formed in some other property (i.e., constant field). Standard deviation of peak width, resolution and peak capacity are important parameters in characterizing equilibrium gradient methods, and general expressions can be obtained from considering both the point of force acting on the analyte and the basic flux equation. Several successful examples, such as density gradient sedimentation, isoelectric focusing and electromobility focusing are discussed. Based on equilibrium gradient methods in the field gradient category, a method to dynamically improve peak capacity is described. An example of such an approach is given using electromobility focusing.
Keywords: Equilibrium gradient method Electromobility focusing Filed gradient Electric field gradient Capillary electrophoresis Proteins

Electronic tongues and their analytical application by Yuri Vlasov; Andrey Legin; Alisa Rudnitskaya (136-146).
Electronic tongues for liquid analysis, based on the organizational principles of biological sensory systems, developed rapidly during the last decade. A brief historical overview of the research and development in the field of electronic tongue systems is presented. Current achievements of scientific groups working in this field are outlined and critically reviewed. The performance of electronic tongues in quantitative analysis and in classification of multicomponent media is considered. The exciting possibility of establishing a correlation between the output from an electronic tongue and human sensory assessment of food flavour, thereby enabling quantification of taste and flavour, is described. Application areas of electronic tongue systems including foodstuffs, clinical, industrial, and environmental analysis are discussed in depth. Prospective research and development in the field of electronic tongues is discussed.
Keywords: Electronic tongue Multi-sensor systems Classification Multicomponent analysis Taste quantification

Headspace solid phase micro-extraction (HS-SPME) has been applied as a sampling technique for the determination of petroleum contamination in shellfish using capillary gas chromatography-mass spectrometry (GC-MS). A poly(dimethylsiloxane) fused silica fibre (100 µm thickness) was found to be satisfactory for the extraction of a range of aliphatic hydrocarbons (HCs) from homogenised shellfish tissues. The SPME conditions, including temperature, salt content, extraction time and desorption temperature, were optimised for a range of aliphatic HCs (C9–C20). A methyl silicone column GC (12 m×0.20 mm, 0.33 µm layer thickness) was used with a temperature programme from 40 to 260 °C and the HCs were determined within a mass range of m/z=50–550 in electron impact mode. Calibration range was from 10 to 5000 ng/g with linear correlation coefficients (r 2) of 0.982 for nonane to 0.997 for octadecane. Detection limits for aliphatic HCs, spiked into shellfish (mussel) tissues, varied from 3.6 ng/g (tetradecane) to 51 ng/g (eicosane) and relative standard deviation (% RSD) values ranged from 1.4% (hexadecane) to 24.3%(eicosane).
Keywords: Solid phase micro-extraction Mussels Aliphatic hydrocarbons Headspace

An open focused microwave-assisted digestion procedure has been developed to decompose and dissolve vegetal matrices for subsequent macro- and micronutrients analysis. The parameters of the microwave oven were evaluated using an experimental design. Sulfuric acid (5 mL) and hydrogen peroxide (3 mL) were found to be suitable for quantitative determination of Ca, Cu, Fe, K, Mg, Mn, N, P, and Zn in 0.100–0.500 g of vegetal sample. The precision was better than 6% for all elements at different concentrations. Results for reference and laboratory control materials are in agreement with certified and indicative values. In addition, the sample digest could be used for ICP-OES of all the elements mentioned. The proposed microwave-assisted digestion procedure offers the ability to determine the most important essential plant nutrients in one unique solution by means of analytical techniques usually found in most laboratories.
Keywords: Vegetal material Focused microwave-assisted digestion Spectroscopy analysis Mineral elements ICP

The competitive interaction with DNA of daunorubicin (DR), being present in the clinical anti-tumor drug daunoblastina, and the fluorescence probe ethidium bromide (EB) has been studied by parallel-factor analysis (PARAFAC) and full-rank parallel-factor analysis (FRA-PARAFAC) of a fluorescence excitation–emission three-way data array. The PARAFAC algorithm can furnish stable resolution results for the data array studied, if the estimated number of chemical components is consistent with the real number. The FRA-PARAFAC algorithm is not sensitive to the estimated number of components of the fluorescence data array if the estimated number is not less than the real number. Both algorithms gave identical resolution for the three components concerned DR, EB, and the complex EB–DNA. Variations of the equilibrium concentrations of free DR, EB, and the complex EB–DNA were resolved by both algorithms. Experimental observation confirms the hypothesis that DR is an intercalator of DNA and that the binding interactions of DR and EB with DNA are a pair of parallel competitive intercalation reactions on same base sites of DNA. The method exemplified by this study provides a useful approach for studying competitive interactions of different drugs with DNA in the presence of interferents.
Keywords: Competitive interaction Daunorubicin Ethidium bromide DNA Trilinear resolution.

Spectral studies of the binding of lucigenin, a bisacridinium derivative, with double-helix DNA by Hui-Ling Wu; Wen-You Li; Xi-Wen He; Kun Miao; Hong Liang (163-168).
The non-covalent binding of the cationic reagent lucigenin to DNA has been investigated by spectroscopic methods. Results from absorption, circular dichroism, and fluorescence studies revealed that lucigenin could intercalate into the helix of DNA. Polarization and melting studies provided further evidence of the intercalation binding of lucigenin with DNA. The binding constant was obtained by varying the DNA concentration while keeping the concentration of lucigenin constant. It was of the order of 104 mol–1 L in DNA base pairs. The experiment also showed that electrostatic interaction played a significant role in the intercalation of lucigenin with DNA. It is suggested that lucigenin can be intercalated into the interior of the DNA double helix because it is initially attracted by the anionic DNA. This research offers a new intercalation functional group for DNA-targeted drug design.
Keywords: Lucigenin DNA Intercalation binding Electrostatic interaction Spectroscopic method

A method based on capillary electrophoresis with electrochemical detection (CE–ED) has been developed for the determination of hesperidin (HP) and synephrine (SP) in the Chinese traditional herbal drug, Pericarpium Citri Reticulatae, the dried rind of the ripe fruits of Citrus reticulata Blanco (mandarin orange). The effects of some important factors such as the acidity and concentration of running buffer, separation voltage, and detection potential were investigated to determine the optimum conditions. The working electrode was a 300 µm diameter carbon disc electrode positioned opposite the outlet of the capillary. Both analytes could be well separated within 5 min in a 40 cm long capillary at a separation voltage of 12 kV in 50 mmol L–1 borate buffer (pH 9.0). Excellent linearity was observed for the dependence of peak current on analyte concentration in the range from 2.5×10–6 to 1.0×10–3 mol L–1 for SP and from 5.0×10–6 to 1.0×10–3 mol L–1 for HP. The detection limits (S/N=3) for SP and HP were 4.96×10–7 mol L–1 and 6.54×10–7 mol L–1, respectively. This method has been successfully applied for the analysis of real samples, with satisfactory results.
Keywords: Pericarpium Citri Reticulatae Hesperidin Synephrine Capillary electrophoresis Electrochemical detection

The acid–base properties of a lignocellulosic substrate extracted from wheat bran have been investigated. The lignocellulosic substrate was first studied by use of FTIR, XPS, and solid-state 13C NMR to characterize the surface-active groups. Major contributions arise from the presence of carboxylic and phenolic sites. The former are associated with long-chain fatty acids and the latter are constituent units of lignin. All ionizable sites were quantified by use of the Ca-acetate method and by potentiometric titrations in non-aqueous media. Results were compared with those from conductimetric titrations in water and in the presence of barium ions. Protometric titration curves for the lignocellulosic substrate were obtained at several ionic strengths. Data were also treated with the NICA–Donnan model to determine the intrinsic ionization parameters.
Keywords: Wheat bran Characterization Acid–base properties NICA–Donnan model Affinity distribution

Determination of Cd and Pb in food slurries by GFAAS using cryogenic grinding for sample preparation by D. Santos; F. Barbosa; A. Tomazelli; F. Krug; J. Nóbrega; M. Arruda (183-189).
A simple method combining slurry sampling after cryogenic grinding and the use of a permanent modification of the integrated platform inside the transversely heated graphite atomizer (THGA) was proposed for the determination of Cd and Pb in foods. Potentialities of the cryogenic grinding were evaluated for grinding different materials of difficult homogenization such as high fat and high fiber tissues. Animal and vegetal samples were cut into small pieces and ground in liquid nitrogen for 2 min. Slurries were prepared directly in the autosampler cup after cryogenic grinding by transferring an exact amount of homogeneous powdered material (5–20 mg) to the cup, followed by 1.00 mL of 0.2% (v/v) HNO3 containing 0.04% (v/v) Triton X-100 and sonication for 30 s, before transferring into the platform previously coated with 250 µg W and 200 µg Rh. Use of a tungsten carbide-rhodium permanent modifier combined with NH4H2PO4 conventional modifier improves tube lifetime and increases the pyrolysis temperature for Cd. Homogeneity tests, carried out by comparing the between- and within-batch precision for each kind of sample, showed no significant differences at the 95% confidence level, indicating good homogeneity for 5–20 mg masses. Detection limits were 3.3 ng g–1 Cd and 75 ng g–1 Pb for 1% m/v slurries. Results for determination of Cd and Pb in foods slurries were in agreement with those obtained with digested samples, since no statistical differences were found by the paired t-test at the 95% level.
Keywords: Cryogenic grinding Sample preparation Food slurry GFAAS Cadmium Lead

A four-stage sequential leaching procedure was applied to assess the bioavailability and environmental mobility of heavy metals (Cr, Fe, Cu, Ni and Cd) in total suspended particulate (TSP) material emitted from an opencast chrome mine complex (Kemi, Northern Finland). TSP material was collected on glass fibre filters by a high-volume sampler, and a sequential leaching procedure was used to determine the distribution of heavy metals between the water-soluble fraction (H2O), environmentally mobile fraction (CH3COONH4), the fraction bound to carbonate and oxides (HONH3Cl + CH3COOH), and the fraction bound to silicates and organic matter, that is the environmentally immobile fraction (HNO3 + HF + HCl). The sequential leaching procedure was also applied to the certified reference materials VKI (QC Loam Soil A) and PACS-2 (Marine Sediment) to evaluate the accuracy and reproducibility of the leaching procedure. The heavy metals were determined by graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS). The concentrations of metals in the water-soluble fraction (H2O) decreased in the order Fe >Cu >Cr >Ni >Cd, and in the environmentally mobile fraction (CH3COONH4) in the order Cu >Fe >Ni >Cr >Cd.
Keywords: Total suspended particulate matter Heavy metals Bioavailability Leaching

Quality control materials for the determination of trace elements in airborne particulate matter by J. Sysalová; J. Kučera; B. Kotlík; V. Havránek (195-199).
The development of quality control materials for the determination of selected trace elements in air pollution studies is described. Three types of test samples were prepared for proficiency testing: (1) filters loaded with PM10 fraction of urban air particulate matter (APM) using high-volume air samplers, which were subsequently divided into smaller sections, (2) a bulk sample of APM collected in an automobile tunnel in Prague, and (3) simulated air filters loaded with APM using a wet deposition process. Homogeneity of the test samples was studied using instrumental neutron activation analysis, proton induced X-ray emission and atomic absorption spectrometry, and inductively coupled plasma optical emission spectrometry and mass spectrometry. Sufficiently homogeneous samples were prepared by all three procedures. The simulated air filters appeared to be the most suitable test samples for proficiency testing.
Keywords: Quality control Air particulate matter Air filters Sample homogeneity Proficiency testing

Chromium, cadmium and lead were determined in different fractions of the winemaking process such as in grape, pressed pomace, must deposit, deposit of lees, must and wine. Grape, pressed pomace, must deposit and deposit of lees were digested by a high-pressure microwave-assisted digestion system with a mixture of nitric acid and hydrogen peroxide, while for must and wine no special treatment was required. The temperature programs of the graphite furnace were optimised and different matrix modifiers were applied: Mg(NO3)2, NaVO3 for Cr and NH4H2PO4, Pd(NO3)2 for Pb and Cd determinations. Mg(NO3)2 and NaVO3 thermally stabilized Cr and enabled the increase of pyrolysis temperatures up to 1500 °C. NH4H2PO4 and Pd(NO3)2 are suitable modifiers for Pb and allowed pyrolysis temperatures up to 800 °C in grape, pressed pomace and wine samples, 1100 °C in must samples and 1200 °C in deposit of lees. The non-specific background absorption of NH4H2PO4 was 1.5–2 orders of magnitude higher than that of the Pd(NO3)2.
Keywords: Lead Cadmium Chromium ETAAS Wine

An ultrasonic slurry-sampling electrothermal atomic absorption spectrometry with a molybdenum tube atomizer has been developed for the determination of manganese in herbal medicine samples. Ten percent glycerol solution was used as the slurry medium. The optimum pyrolysis temperature was 400 °C. The detection limit was 69 fg (3×S/N). Matrix element interference was checked and it was found that glycerol as a chemical modifier eliminated the interference. The amounts of manganese in herbal medicines determined by the proposed method are in good accordance with those measured in dissolved acid-digested samples. The method enables rapid calibration, and simple and rapid analysis of manganese in herbal medicine samples at low cost.
Keywords: Manganese Slurry-sampling Herbal medicine samples Atomic absorption spectrometry Metal tube atomizer