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Analytical and Bioanalytical Chemistry (v.382, #6)

Crime Scene to Court: The Essentials of Forensic Science, P.C. White (ed.) by Richard Turle (pp. 1343-1343).

Eamonn Mullins: Statistics for the Quality Control Chemistry Laboratory by Stefan Leigh (pp. 1344-1345).

Thermostability of landscape phage probes by Jennifer R. Brigati; Valery A. Petrenko (pp. 1346-1350).

Immunoassays have traditionally relied on antibodies as diagnostic probes. Their use outside of a laboratory, however, may be problematic because antibodies are often unstable in severe environmental conditions. Environmental monitoring requires thermostable probes, such as landscape phage, that carry thousands of foreign peptides on their surfaces, are superior to antibodies, and can operate in non-controlled conditions. While parent wild-type phage are known to be extremely stable in various media at high temperatures, no work has been done to demonstrate the stability of landscape phage probes. We examined the thermostability of a landscape phage probe and a monoclonal antibody specific for β-galactosidase in parallel in an enzyme-linked immunosorbent assay (ELISA) format. They were both stable for greater than six months at room temperature, but at higher temperatures the antibody degraded more rapidly than the phage probe. Phage retained detectable binding ability for more than six weeks at 63 °C, and three days at 76 °C. The activation energy of phage degradation was determined to be 1.34×10⁵ J/mol. These results confirm that phage probes are highly thermostable and can function even after exposure to high temperatures during shipping, storage and operation.

Keywords: Landscape phage; Diagnostic probes; Thermostability; β-Galactosidase; Enzyme-linked immunosorbent assay (ELISA)

Rapid screening of selective serotonin re-uptake inhibitors in urine samples using solid-phase microextraction gas chromatography–mass spectrometry by Carmen Salgado-Petinal; J. Pablo Lamas; Carmen Garcia-Jares; Maria Llompart; Rafael Cela (pp. 1351-1359).

In this paper a solid-phase microextraction–gas chromatography–mass spectrometry (SPME–GC–MS) method is proposed for a rapid analysis of some frequently prescribed selective serotonin re-uptake inhibitors (SSRI)—venlafaxine, fluvoxamine, mirtazapine, fluoxetine, citalopram, and sertraline—in urine samples. The SPME-based method enables simultaneous determination of the target SSRI after simple in-situ derivatization of some of the target compounds. Calibration curves in water and in urine were validated and statistically compared. This revealed the absence of matrix effect and, in consequence, the possibility of quantifying SSRI in urine samples by external water calibration. Intra-day and inter-day precision was satisfactory for all the target compounds (relative standard deviation, RSD, <14%) and the detection limits achieved were <0.4 ng mL⁻¹ urine. The time required for the SPME step and for GC analysis (30 min each) enables high throughput. The method was applied to real urine samples from different patients being treated with some of these pharmaceuticals. Some SSRI metabolites were also detected and tentatively identified.

Keywords: Solid-phase microextraction; Gas chromatography–mass spectrometry; Derivatization; Selective serotonin re-uptake inhibitors; Urine

A dynamic continuous-flow dialysis system with on-line electrothermal atomic-absorption spectrometric and pH measurements for in-vitro determination of iron bioavailability by simulated gastrointestinal digestion by Jeerawan Promchan; Juwadee Shiowatana (pp. 1360-1367).

A dynamic continuous-flow dialysis (CFD) method with on-line electrothermal atomic absorption spectrometric (ETAAS) and pH measurements for study of simulated gastrointestinal digestion has been developed for prediction of iron bioavailability. The method used to estimate mineral bioavailability was based on gastric digestion in a batch system then dynamic continuous-flow intestinal digestion. The intestinal digestion was performed in a dialysis bag placed inside a chamber containing a flowing stream of dialyzing solution. Mineral concentration and dialysate pH were monitored by ETAAS and use of a pH meter, respectively. The amount of dialyzed minerals in the intestinal digestion stage was used to evaluate the dialyzability. The dialysis profile and pH change can be used to understand or examine differences between the dialyzability of different food samples. To test the proposed system it was used to estimate the iron dialyzability of different kinds of milk. Iron dialyzability for powdered cow milk, cereal milk, and two brands of soymilk was found to be 1.7, 20.4, 24.9, and 37.7%, respectively. The developed CFD–ETAAS–pH system is a simple, rapid, and inexpensive tool for bioavailability studies, especially for minerals at ultratrace levels.

Keywords: Continuous-flow; Dialysis; Gastrointestinal digestion

Assay for uric acid level in rat striatum by a reagentless biosensor based on functionalized multi-wall carbon nanotubes with tin oxide by Fen-Fen Zhang; Xiao-Li Wang; Chen-Xin Li; Xiao-Hua Li; Qiao Wan; Yue-Zhong Xian; Li-Tong Jin; Katsunobu Yamamoto (pp. 1368-1373).

A novel reagentless amperometric uric acid biosensor based on functionalized multi-wall carbon nanotubes (MWCNTs) with tin oxide (SnO₂) nanoparticles has been developed. This was successfully applied to assay uric acid levels from an in vivo microdialysis sampling. Compared with unfunctionalized or traditional carboxylic acid (–COOH)-functionalized MWCNTs, the MWCNTs–SnO₂ electrode exhibited higher electrocatalytic oxidation to uric acid. Here, MWCNTs–SnO₂ may act as an efficient promoter, and the system exhibited a linear dependence on the uric acid concentration over the range from 1.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹. In addition, there was little ascorbic acid interference. The high sensitivity of the MWCNTs–SnO₂ modified enzyme electrode enabled the monitoring of trace levels of uric acid in dialysate samples in rat striatum.

Keywords: Multi-wall carbon nanotubes; Tin oxide; Uricase; Uric acid biosensor; Microdialysis

Horseradish peroxidase-based organic-phase enzyme electrode by Nina Dimcheva; Elena Horozova (pp. 1374-1379).

An organic-phase enzyme electrode (OPEE) based on horseradish peroxidase (HRP) immobilized within Nafion on spectroscopic graphite was investigated in acetonitrile. The amperometric electrode response to hydrogen peroxide and cumene hydroperoxide present was found to be the result of the reduction of oxygen, produced upon enzymatic decomposition of both hydroperoxides (i.e., by the catalase-like activity of HRP). The electrode response was found to depend linearly on the hydroperoxide concentration up to 700 μM within the range of potentials from −200 to −400 mV (versus Ag|AgCl). Detection limits of approximately 45 μM for H₂O₂ and 100 μM for cumene hydroperoxide were determined under the selected experimental conditions. Nernstian dependence (the open circuit voltage of HRP-based electrode versus logarithm of H₂O₂ concentration) was obtained between 0.2 and 2.0 mM, with a slope of approximately 23 mV per logarithmic unit, suggesting a catalase-like, two-electron disproportionation of the substrate in acetonitrile.

Keywords: Horseradish peroxidase; Organic-phase enzyme electrode; Hydroperoxides; Catalase-like activity

Three-way partial least-squares regression for the simultaneous kinetic-enzymatic determination of xanthine and hypoxanthine in human urine by José Manuel Amigo; Jordi Coello; Santiago Maspoch (pp. 1380-1388).

The performance of three-way principal component analysis and three-way partial least-squares regression when applied to a complex kinetic-enzymatic system is studied, in order to investigate the analytical potential of the combined use of these chemometric technologies for non-selective enzymatic systems. A enzymatic-kinetic procedure for the simultaneous determination of hypoxanthine and xanthine in spiked samples of human urine is proposed. The chemical system involves two consecutive reactions catalyzed by xanthine oxidase (EC 1.17.3.2). This enzyme catalyzes the oxidation of hypoxanthine, first to xanthine and then to uric acid, a competitive inhibitor of the reactions. The influence of uric acid during quantitative determination was considered in the design of the calibration set. The sample and enzyme solution were mixed in a stopped-flow module and the reaction was monitored using a diode array spectrophotometer. The recorded data have an intrinsical three-component structure (samples, time and wavelength). This data array was studied via three-way principal component analysis and was modeled for quantitative purposes using a three-way partial least-squares calibration procedure. Results are compared with those obtained by applying classical bilinear PLS to the previously unfolded data matrix.

Keywords: Oxipurines; Urine analysis; Three-way principal component analysis; Three-way partial least-squares regression; Simultaneous kinetic determination

Determining PAHs and PCBs in aqueous samples: finding and evaluating sources of error by Lidia Wolska; Magdalena Rawa-Adkonis; Jacek Namieśnik (pp. 1389-1397).

This work describes the problems that occur during routine multi-step determinations of polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), which can be present at trace levels in water, and identifies sources of analyte losses at particular steps during the analytical procedure. PAH and PCB adsorption onto the walls of the container ranged from 0 to 70%. PAH and PCB recoveries of >70% were achieved during the LLE and SPE extraction steps. During the process of enriching the dichloromethane extract with PAHs and PCBs, based on the gentle evaporation of solvent, losses were <24% and <19%, respectively. Model experiments show that neither isolation of PAHs and PCBs (performed using either LLE or SPE) nor extract enrichment reduce the reliability of PAH and PCB determination. The steps that lead to the greatest loss of analyte are the ones that involve sampling, transport and storage of the water samples.

Keywords: PAHs; PCBs; Analyte losses; Water analysis

Diagnostic Raman spectroscopy for the forensic detection of biomaterials and the preservation of cultural heritage by Howell G. M. Edwards; Tasnim Munshi (pp. 1398-1406).

This paper reviews the contributions of analytical Raman spectroscopy to the non-destructive characterisation of biological materials of relevance to forensic science investigations, including the sourcing of resins and the identification of the biodegradation of art and archaeological artefacts. The advantages of Raman spectroscopy for non-destructive analysis are well-appreciated; however, the ability to record molecular information about organic and inorganic species present in a heterogeneous specimen at the same time, the insensitivity of the Raman scattering process to water and hydroxyl groups, which removes the necessity for sample desiccation, and the ease of illumination for samples of very small and very large sizes and unusual shapes are also apparent. Several examples are used to illustrate the application of Raman spectroscopic techniques to the characterisation of forensic biomaterials and for the preservation of cultural heritage through case studies in the following areas: wall-paintings and rock art, human and animal tissues and skeletal remains, fabrics, resins and ivories.

Keywords: Raman spectroscopy; Biomaterials; Art history; Archaeology

Rapid screening for ethyl carbamate in stone-fruit spirits using FTIR spectroscopy and chemometrics by Dirk W. Lachenmeier (pp. 1407-1412).

Ethyl carbamate (EC, urethane, C₂H₅OCONH₂) is a known genotoxic carcinogen of widespread occurrence in fermented food and beverages with the highest concentrations being found in stone-fruit spirits. Time-consuming procedures requiring extraction and gas chromatographic–mass spectrometric determination are regarded as reference procedures for the analysis of EC in alcoholic beverages. In this study, the rapid method of Fourier transform infrared (FTIR) spectroscopy in combination with partial least-squares (PLS) regression using selected wavelength bands is applied for the first time to the screening analysis of EC in stone fruit spirits (analysis time only 2 min). Apart from the actual content of EC in the sample, additional information was available from the FTIR spectra. This included data concerning the EC precursor hydrocyanic acid (HCN) and the maximum EC concentration which could be formed during storage. The PLS procedure was validated using an independent set of samples (Q² = 0.71–0.76, SEP = 0.42–0.67). The method was found to lack the accuracy required for a quantitative determination; it could only be used semi-quantitatively in the context of a screening analysis. If a rejection level of 0.8 mg L⁻¹ is applied as cut-off, overall correct classification rates of 85–91% for the calibration set and 77–85% for the validation set were achieved. False negative results can be avoided by lowering the cut-off to 0.6 mg L⁻¹. Through use of FTIR screening, 60–70% of all samples can be classified as negative and removed, leaving only conspicuous analysis results exceeding cut-off to be confirmed by complex and labour-intensive reference analyses.

Keywords: Ethyl carbamate; Hydrocyanic acid; Stone-fruit spiritsPrunus ss. (L.); PLS

Preconcentration and fluorimetric determination of polycyclic aromatic hydrocarbons based on the acid-induced cloud-point extraction with sodium dodecylsulfate by Irina Yu. Goryacheva; Sergei N. Shtykov; Alexander S. Loginov; Irina V. Panteleeva (pp. 1413-1418).

The acid-induced cloud-point extraction (CPE) technique based on sodium dodecylsulfate (SDS) micelles has been used for preconcentration of ten representatives of polycyclic aromatic hydrocarbons (PAHs) for the following fluorescence determination. The effect of the acidity of solution, SDS and electrolyte concentrations, centrifugation time and rate on the two-phase separation process and extraction percentages of PAHs have systematically been examined. Extraction percentages have been obtained for all PAHs after CPE ranged from 67 to 93%. Pyrene was used as a fluorescent probe to monitor the micropolarity of the surfactant-rich phase compared with SDS micelles and this allows one to conclude that water content in micellar phase after CPE is reduced. The spectral, metrological and analytical characteristics of PAH fluorimetric determination after acid-based CPE with sodium dodecylsulfate are presented. Advantages provided by using CPE in combination with fluorimetric determination of PAHs are discussed. The determination of benz[a]pyrene in tap water is presented as an example.

Keywords: Cloud-point extraction; PAHs determination; Fluorimetry

Performance of a new nebulizer system for simultaneous determination of Sb, Sn (hydride generation), V, and Zn by ICP–OES by T. Zoltan; Z. Benzo; M. Murillo; E. Marcano; C. Gómez; J. Salas; M. Quintal (pp. 1419-1430).

A new nebulizer system is described that extends the analytical capability of the inductively coupled plasma technique to include the simultaneous determination of two elements Sb and Sn (hydride-forming), with two conventional elements, V and Zn. The main advantage of this system is its simultaneous determination of elements that form volatile hydrides and elements that do not, without any instrumental changes. Optimization of reaction and instrumental conditions was performed to characterize the new system. The performance of the new nebulizer system was evaluated by studying the effect of some transition metals (Ni, Cu, Co, and Fe, 1–1000 mg L⁻¹) on the Sb, Sn, V, and Zn emission signals (1 mg L⁻¹). Interferences from transition metal ions were found to be insignificant for determination of the four elements in presence of L-cysteine. Long-term and short-term stability was also evaluated. The precision, expressed as RSD for 15 replicate measurements was 0.7% for Sb, 1.7% for Sn, 2.5% for V, and 2.3% for Zn at 200 μg L⁻¹ of each analyte. The detection limits obtained were 0.52, 1.3, 3.2, and 4.7 μg L⁻¹ for Sb, Sn, V, and Zn, respectively. Spike and recovery experiments were performed on the NIST 1643c trace metals in water standard reference material and results were in agreement with the certified values.

Keywords: Simultaneous determination; New nebulizer system; Sb; Sn; V; Zn; ICP–OES

Investigation of 2-[(E)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3H-indolium as a new highly sensitive reagent for the spectrophotometric determination of nitrophenols by Roman Shkumbatiuk; Yaroslav R. Bazel; Vasil Andruch; Marcel Török (pp. 1431-1437).

A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of nitrophenols [picric acid (PA); dinitrophenols (DNP)] in wastewater samples. The method is based on the reaction of nitrophenols with 2-[(E)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3 H-indolium chloride reagent to form the colored ion associates, which are extracted by organic solvents. The molar absorptivity of the ion associates of PA with the investigated reagent ranges from 8.3×10⁴ to 11.3×10⁴ L mol⁻¹ cm⁻¹, depending on the extractant. Because only PA is extracted in an acidic medium with the investigated reagent, but both PA and DNP are extracted in an alkaline medium, it is possible to determine both substances in a mixture. Appropriate reaction conditions have been established. The absorbance of the colored extracts obeys Beer’s law in the range of 0.04–4.58 mg L⁻¹ PA, 1.0–18.4 mg L⁻¹ 2,4-DNP and 1.2–14.7 mg L⁻¹ 2,6-DNP, respectively. The limit of detections, calculated from a blank test (n=10; P=0.95), are 0.05 mg L⁻¹ PA, 0.9 mg L⁻¹ (2,4-DNP), and 1.1 mg L⁻¹ (2,6-DNP), respectively.

Keywords: 2-[(E)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3H-indolium; Nitrophenol; Determination; Spectrophotometry

Fluorescence spectroscopy for monitoring deterioration of extra virgin olive oil during heating by Rana Cheikhousman; Manuela Zude; Delphine Jouan-Rimbaud Bouveresse; Claude L. Léger; Douglas N. Rutledge; Inés Birlouez-Aragon (pp. 1438-1443).

The potential of fluorescence spectroscopy for characterizing the deterioration of extra virgin olive oil (EVOO) during heating was investigated. Two commercial EVOO were analysed by HPLC to determine changes in EVOO vitamin E and polyphenols as a result of heating at 170°C for 3 h. This thermal oxidation of EVOO caused an exponential decrease in hydroxytyrosol and vitamin E (R²=0.90 and 0.93, respectively) whereas the tyrosol content was relatively stable. At the same time, amounts of preformed hydroperoxides (ROOH), analysed by an indirect colorimetric method, decreased exponentially during the heating process (R²=0.94), as a result of their degradation into secondary peroxidation products. Fluorescence excitation spectra with emission at 330 and 450 nm were recorded to monitor polyphenols and vitamin E evolution and ROOH degradation, respectively. Partial least-squares calibration models were built to predict these indicators of EVOO quality from oil fluorescence spectra. A global approach was then proposed to monitor the heat charge from the overall fluorescence fingerprint. Different data pretreatment methods were tested. This study indicates that fluorescence spectroscopy is a promising, rapid, and cost-effective approach for evaluating the quality of heat-treated EVOO, and is an alternative to time-consuming conventional analyses. In future work, calibration models will be developed using a wide range of EVOO samples.

Keywords: Olive oil; Fluorescence; EVOO; Polyphenols; Vitamin E; PLS

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Analytical and Bioanalytical Chemistry (v.382, #6)