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Analytica Chimica Acta (v.566, #2)

Editorial Board (pp. co1).

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n3).

Improvements in protein identification confidence and proteome coverage for human liver proteome study by coupling a parallel mass spectrometry/mass spectrometry analysis with multi-dimensional chromatography separation by Jie Zhang; Mingxia Gao; Jia Tang; Pengyuan Yang; Yinkun Liu; Xiangmin Zhang (pp. 147-156).

Recently, matrix-assisted laser desorption ionization (MALDI) technique has been shown to be complementary to electrospray ionization (ESI) with respect to the population of peptides and proteins that can be detected. In this study, we tried to hyphenate MALDI–TOF–TOF–MS and ESI–QUADRUPOLE–TOF–MS with a single 2D liquid chromatography for complicated protein sample analysis. The effluents of RPLC were split into two parts for the parallel MS/MS detection. After optimizing the operation conditions in LC separation and MS identification, a total of 1149 proteins were identified from the global lysate of normal human liver (NHL) tissue. Compared to the single MS/MS detection, the combined analysis increased the number of proteins identified (more than 25%) and enhanced the protein identification confidence. Proteins identified were categorized and analyzed based upon their cellular location, biological process and molecular function. The identification results demonstrated the application potential of a parallel MS/MS analysis coupled with multi-dimensional LC separation for complicated protein sample identification, especially for proteome analysis, such as human tissues or cells extracts.

Keywords: 2D LC; Parallel MS/MS analysis; Human liver proteome

Investigation of Symphytum cordatum alkaloids by liquid–liquid partitioning, thin-layer chromatography and liquid chromatography–ion-trap mass spectrometry by Tomasz Mroczek; Karine Ndjoko-Ioset; Kazimierz Głowniak; Agnieszka Miętkiewicz-Capała; Kurt Hostettmann (pp. 157-166).

From the alkalised crude extract of Symphytum cordatum (L.) W.K. roots, pyrrolizidine alkaloids (PAs) were extracted as free tertiary bases and polar N-oxides in a merely one-step liquid–liquid partitioning (LLP) in separation funnel and subsequently pre-fractionated by preparative multiple-development (MD) thin-layer chromatography (TLC) on silica gel plates. In this way three alkaloid fractions of different polarities and retention on silica gel plates were obtained as: the most polar N-oxides of the highest retention, the tertiary bases of medium retention, and diesterified N-oxides of the lowest retention. The former fraction was reduced into free bases by sodium hydrosulfite and purified by LLP on Extrelut-NT3 cartridge. It was further analysed together with the two other fractions by high-performance liquid chromatography (HPLC)–ion-trap mass spectrometry with atmospheric pressure chemical ionization (APCI) interface on XTerra C₁₈ column using a gradient elution. Based on MSⁿ spectra, 18 various alkaloids have been tentatively determined for the first time in this plant as the following types of structure: echimidine- N-oxide (three diasteroisomers), 7-sarracinyl-9-viridiflorylretronecine (two diasteroisomers), echimidine (two diasteroisomers), lycopsamine (two diasteroisomers), dihydroechinatine- N-oxide, dihydroheliospathuline- N-oxide, lycopsamine- N-oxide (three diasteroisomers), 7-acetyllycopsamine- N-oxide, symphytine- N-oxide (two diasteroisomers) and 2″,3″-epoxyechiumine- N-oxide.

Keywords: Pyrrolizidine alkaloids; Symphytum cordatum; (L.) W.K.; Preparative thin-layer chromatography; Liquid–liquid partitioning; High-performance liquid chromatography; Ion-trap mass spectrometry

Simultaneous determination of urinary hippuric acid, o-, m- and p-methylhippuric acids, mandelic acid and phenylglyoxylic acid for biomonitoring of volatile organic compounds by gas chromatography–mass spectrometry by Yasuhiro Ohashi; Tomoko Mamiya; Kurie Mitani; Bingling Wang; Tomoko Takigawa; Shohei Kira; Hiroyuki Kataoka (pp. 167-171).

A sensitive and precise method for the simultaneous determination of hippuric acid, o-, m- and p-methylhippuric acids, mandelic acid and phenylglyoxylic acid, which are major urinary metabolites of toluene, o-, m- and p-xylenes, styrene and ethylbenzene, respectively, was developed. These metabolites were converted into their methyl ester derivatives with methanol in hydrochloric acid, and then quantitated by gas chromatography–mass spectrometry (GC–MS) with selected ion monitoring using a DB-1 capillary column. The injected compounds were quantitatively and reproducibly resolved within 19min with a detection limit of 8–27pg. The calibration curves were linear in the range of 0.05–25μg for each compound, with correlation coefficients above 0.9999. This method was successfully used to analyze small amounts of both rat and human urine samples without any interference from coexisting substances. Overall recoveries of these compounds spiked in urine samples were 92–104%. The analytical results of the contents of these metabolites in the rat and human urine samples are presented.

Keywords: Hippuric acid; Methylhippuric acid; Mandelic acid; Phenylglyoxylic acid; Gas chromatography–mass spectrometry; Urine samples

Comparison of direct thermal desorption with water distillation and superheated water extraction for the analysis of volatile components of Rosa damascena Mill. using GCxGC-TOF/MS by M.Z. Özel; F. Göğüş; A.C. Lewis (pp. 172-177).

The composition of the volatile components from Rosa damascena Mill. was investigated using comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (TOF/MS). The samples were collected from Turkey and were extracted by water distillation (WD), superheated water extraction (SWE) and direct thermal desorption (DTD). It was found that superheated water extraction gave a slightly higher oil yield than water distillation. The major compounds found in volatiles of R. damascena Mill. were linalool, phenylethylalcohol, citronellol, nerol and geraniol. Phenylethylalcohol content was significantly higher using the DTD (36.52%) and SWE (38.14%) techniques compared to the WD (1.92%) technique. A lower content of monoterpene alcohols was found in volatiles extracted using the DTD method (73.69%) compared to the SWE (86.51%) and WD (86.56%) techniques reflecting the main finding that DTD extracts showed a greater total number of different components than either of the other two methods. The number of volatile components identified with a percentage higher than 0.05% were 54, 37, and 34 for the DTD, SWE and WD techniques, respectively. This highlighted DTD as a promising method for qualitative analysis of rose oil which can yield comprehensive results without the traditional obligation for costly and time consuming extraction techniques.

Keywords: R. damascena; Mill.; Direct thermal desorption; Superheated water extraction; Water distillation; Comprehensive GC–TOF/MS

Quantification of 5′-monophosphate cytosine arabinoside (Ara-CMP) in cell extracts using liquid chromatography–electrospray mass spectrometry by Marie-Hélène Gouy; Huguette Fabre; Marie Dominique Blanchin; Suzanne Peyrottes; Christian Périgaud; Isabelle Lefebvre (pp. 178-184).

A LC/MS/ESI method is described to monitor 5′-monophosphate cytosine arabinoside (Ara-CMP) formed after incubation of an Ara-C prodrug in cell extracts. After addition of an internal standard and off-line treatment with perchloric acid, Ara-CMP is separated from Ara-C and endogeneous matrix components on a porous graphitic carbon stationary phase using gradient elution with a water/acetonitrile mobile phase containing formic acid. The results of method performances (accuracy, linearity, limit of quantification and repeatability) show that the method is acceptable for its intended use.

Keywords: Ara-CMP; Quantification; Liquid chromatography–mass spectrometry; Cell extracts

Chiral separation of glycidol enantiomers by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry by Sonia Morante-Zarcero; Isabel del Hierro; Mariano Fajardo; Isabel Sierra (pp. 185-192).

A chiral separation method for glycidol enantiomers determination by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry was developed. Two chiral stationary phases, amylose tris–(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) and ( S)-indoline-2-carboxylic acid and ( R)-1-(α-naphthyl) ethylamine (SUMICHIRAL OA-4900) have been investigated. The effects of the mobile phase composition, elution program and column temperature were also studied. Under the best conditions: Chiralpak AD-H column, mobile phase composition n-hexane:ethanol (70:30, v/v), flow rate of 0.8mL/min and 40°C column temperature, a good resolution (Rs=1.6) for both enantiomers has been achieved with an analysis time of 16min. The method was found to be linear in the range from 100 to 500ppm for both glycidol enantiomers with a good determination coefficient ( r² higher than 0.99) and good precision. Limits of detection of 31 and 50ppm for ( R)-(+)-glycidol and ( S)-(−)-glycidol, respectively, were obtained. The method was applied to the determination of the enantiomeric excess and yield obtained in a asymmetric epoxidation process of allyl alcohol with a chiral titanium–tartrate complex as catalyst.

Keywords: Chiral separation; Validation; Glycidol enantiomers; Normal-phase; HPLC/MS; APCI; Chiralpak AD-H

Simultaneous determination of nine trace mono- and di-chlorophenols in water by ion chromatography atmospheric pressure chemical ionization mass spectrometry by Micong Jin; Yiwen Yang (pp. 193-199).

A novel analytical method was proposed for the rapidly simultaneous determination of nine mono-chlorophenols (MCPs) and di-chlorophenols (DCPs) in water samples using eluent generator ion chromatography (IC) coupled with an atmospheric pressure chemical ionization mass spectrometry (APCI-MS) in the negative mode. The IC separation was carried out on an IonPac^® AS11 analytical column (250mm×4.0mm) using gradient KOH containing 15% acetonitrile as organic modifier at a constant flow rate of 1.0mL/min. The molecular ions m/ z [ M− H]⁻ 127 and 161 were selected for the quantification in selected ion monitoring (SIM) mode for MCPs and DCPs, respectively. The average recoveries were between 80.6% and 92.6%. Within-day and day-to-day relative standard deviations were less than 12.1% and 13.3%, respectively. The method allowed the nine objective compounds in water samples to be determined at μg/L levels. It was confirmed that this method could be used in routine analysis.

Keywords: IC-MS; APCI; Mono-chlorophenol; Di-chlorophenol; Water

Development of a liquid chromatographic–tandem mass spectrometric method with precolumn derivatization for the determination of dencichine in rat plasma by Yong Zhang; Xiaoyan Chen; Xiaoyan Li; Dafang Zhong (pp. 200-206).

Dencichine is a nonprotein amino acid used for hemostasis. A very sensitive method was developed for the determination of dencichine concentration in rat plasma using a derivatization step to enhance signal intensity. The method consisted of a protein precipitation extraction followed by derivatization with 10M hydrochloric acid–methanol (10:90, v/v) and analysis by liquid chromatography coupled with tandem mass spectrometry (LC–MS–MS) via atmospheric pressure chemical ionization (APCI) source. The separation was achieved using a XDB C₈ analytical column with an isocratic mobile phase composed of methanol–water–formic acid in the ratio of 35:65:0.5(v/v/v). Signal intensity of the dencichine derivative was increased up to 50-fold as compared to the underivatized dencichine in positive APCI mode. The matrix effect was also investigated. The method has a lower limit of quantification of 20ng/ml for a 100μl plasma aliquot. The intra- and inter-day precision (R.S.D.), calculated from quality control (QC) samples, was less than 6.3%. The accuracy (R.E.), determined using QC samples, ranged from −0.2 to 3.9%. The method offered increased sensitivity, selectivity and speed of analysis over existing method. The method was utilized to support clinical pharmacokinetic studies of dencichine in rat following intravenous administration. It indicated that this LC–MS–MS method is useful for pharmacokinetic studies of dencichine in animals, because it enabled the serial determination of plasma concentration of dencichine in rats.

Keywords: Liquid chromatography–tandem mass spectrometry; Dencichine; Rat plasma

Discriminant Analysis of Volatile Organic Compounds data related to a new location method of entrapped people in collapsed buildings of an earthquake by M. Statheropoulos; K. Mikedi; A. Agapiou; A. Georgiadou; S. Karma (pp. 207-216).

Discriminant Analysis is used as a part of a research, which aims at using expired air analysis for the early location of entrapped people under the ruins of collapsed buildings in an earthquake. This work focuses on the possibility of distinguishing Volatile Organic Compounds (VOCs) in the entrapment area which originate from different sources. Five categories of samples were analyzed by Thermal Desorption-Gas Chromatography–Mass Spectrometry (TD-GC–MS). Expired air samples from healthy humans (Category 1) and fasting people (Category 2) were analyzed for studying the VOCs attributed to entrapped people. Headspace air of urban waste disposal bins (Category 3), headspace air of bags with decaying human bodies (Category 4) and urban air samples (Category 5) were analyzed for studying the VOCs attributed to background sources. Discriminant Rotation, a specific type of Discriminant Analysis was applied on the VOCs concentration matrix of the five categories. Combinations of VOCs that best discriminated each category were determined. Cluster Analysis was used to validate the results of Discriminant Analysis. The advantages and limitations of the method are presented and discussed.

Keywords: Discriminant Analysis; Expired air analysis; Entrapped people; Collapsed buildings; Earthquakes; Search-and-rescue; VOCs

Analysis of palytoxin-like in Ostreopsis cultures by liquid chromatography with precolumn derivatization and fluorescence detection by P. Riobó; B. Paz; J.M. Franco (pp. 217-223).

A rapid liquid-chromatography (LC) method is presented which uses fluorescence detection (FLD) for palytoxin analogues analysis in benthic dinoflagellates of the genus Ostreopsis. The amino-acidic reagent 6-aminoquinolyl- N-hydroxisuccinimidyl carbamate (AccQ) was used for fluorescence labelling followed by LC–FLD.The efficacy of the method is exemplified by comparison of the results of the quantification obtained by LC–FLD and the hemolytic assay performed for palytoxins for which a highly significant linear correlation was achieved ( r²=0.9118). The derivatized palytoxin analogues were determined in the range of 0.75–25ng.The proposed method was successfully applied to the determination and quantification of palytoxin analogues in 14 samples from different strains of Ostreopsis from different locations (Western Mediterranean Sea, Canary Islands, Madeira Islands and Southern coasts of Brazil). To confirm the chemical structure of the toxins, samples were also analyzed by liquid chromatography coupled with mass spectrometry (LC–MS) with a system that has a poorer sensitivity when compared with LC–FLD detection and the hemolytic assay. The successful use of this method with dinoflagellates is a good indicator of suitability for other types of marine samples.

Keywords: Palytoxin; Ostreopsis; AccQ derivatization; Liquid chromatography fluorescence detection (LC–FLD); Mass spectrometry (MS); Hemolysis

Separation and characterization of alkyl phenol formaldehyde resins demulsifier by adsorption chromatography, gel permeation chromatography, infrared spectrometry and nuclear magnetic resonance spectroscopy by Jinxin Li; Jinjun Zhang; Haijun Yang; Yongcheng Ning (pp. 224-237).

This paper deals with the separation and characterization of alkyl phenol formaldehyde resins demulsifier by infrared spectrometry and nuclear magnetic resonance spectroscopy after separation of the different surfactants and low molecular additives by adsorption chromatography. Firstly, the types of surfactants are identified by methylene blue chloride–chloroform test method and the elemental analysis such as Ca, K, Mg, Na, P, S and N. Then, the different surfactants and low molecular components are separated by adsorption chromatography after parts of low molecular components are dried in an oven, and the molecular weight distribution is measured by gel permeation chromatography also. Finally, the separated surfactants are determined by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance (NMR) spectroscopy. The distortionless enhancement by polarization transfer (DEPT), H, C correlated spectroscopy (H, C–COSY), H, H correlated spectroscopy (H, H–COSY) and heteronuclear multiple-bond correlation (HMBC) spectroscopy are applied to determine the molecular structures.

Keywords: Nuclear magnetic resonance spectroscopy; Demulsifier

Low volume sampling device for mass spectrometry analysis of gas formation in nickel–metalhydride (NiMH) batteries by P.V.E. Krüsemann; A.J.G. Mank; A. Belfadhel-Ayeb; P.H.L. Notten (pp. 238-245).

Rechargeable nickel–metalhydride (NiMH) batteries have major advantages with respect to environmental friendliness and energy density compared to other battery systems. Research on thermodynamics and reaction kinetics is required to study the behaviour of these batteries, especially under severe operating conditions such as overcharging and (over)discharging. During these processes several reactions take place resulting in the formation of oxygen and hydrogen gas. Hence, the recombination processes should be well controlled to guarantee that the partial oxygen and hydrogen pressure inside the battery are kept low.Mass spectrometry is one of the analytical techniques capable of measuring the composition of gases released inside the battery during the charge and discharge processes. However, the sample gas needs to be withdrawn from the battery during the experiment. The gas consumption must be kept to a minimum otherwise the equilibrium inside the battery will be disturbed. A bench-top quadrupole mass spectrometer with a standard capillary by-pass inlet cannot be used for this purpose as its gas consumption is in the 1–10ml/min range. In this paper, a new gas inlet device is presented that reduces gas consumption to a value <50μl/h. The use of a capillary by-pass splitter and a discontinuous sampling procedure allow mass spectrometry to be used as a gas analysis tool in many applications in which small amounts of sample gas are involved.Experiments with standard AA-size NiMH batteries show that hydrogen release dominates during (over)charging at increased charging rates. Beside mass spectrometry, evolved gases are also analysed using Raman spectroscopy. Although some differences are observed, the results of similar experiments show a good agreement.

Keywords: Mass spectrometry; Battery; Gas analysis; Hydrogen; Oxygen

Development of high-performance liquid chromatography and nonaqueous capillary electrophoresis methods for the separation of calixarene derivatives by Chenghua Ding; Po Han; Juanmei Song; Hongxia Liu; Shusheng Zhang; Baoxian Ye; Yangjie Wu (pp. 246-252).

In the present work, the separations of calixarene derivatives have been investigated using both high-performance liquid chromatography (HPLC) and nonaqueous capillary electrophoresis (NACE) techniques. HPLC-1 method with LC-318 (pore size=300Å) column and MeCN mobile phase was optimized for the separation of calixarenes. At the flow-rate of 1ml/min p-nitrocalix[6]arene, calix[4]arene and calix[6]arene could be well baseline and symmetrically separated within 5min. For the separation of p- tert-butylcalix[n]arenes ( n=4, 6, 8), HPLC-2 and NACE methods have been optimized. The optimal conditions in HPLC-2 method included NH₂ column and MeCN mobile phase, and p- tert-butylcalix[n]arenes ( n=4, 6, 8) were baseline separated within 10min at 0.8min/min. The optimal conditions for NACE method employed MeCN–H₂O (8:2, v/v) as the nonaqueous medium and 120mM Tris/HCl (pH 9.0) as the buffer, and p- tert-butylcalix[n]arenes ( n=4, 6, 8) were successfully baseline resolved within 16min. With the detection at 280nm, the calibration lines were linear in the ranges of 1–200μg/ml for calixarene derivatives by HPLC-1 and HPLC-2 methods, and of 2.5–200μg/ml for p- tert-butylcalix[n]arenes ( n=4, 6, 8) by NACE method, respectively. The detection limits (S/N=3) and recoveries ranged from 0.5 to 1.4μg/ml and from 98.1 to 102.4% by both HPLC-1 and HPLC-2 methods, and from 1.3 to 2.0μg/ml and from 97.9 to 105.1% by NACE method, respectively. The intra-day reproducibility of the methods was determined with satisfactory results. The proposed HPLC and NACE methods were accurate and reproducible, and could be utilized to separate and determine calixarene derivatives.

Keywords: Calixarene derivatives; High-performance liquid chromatography; Nonaqueous capillary electrophoresis

A simple and rapid method for identification and determination of cordycepin in Cordyceps militaris by capillary electrophoresis by Yerra Koteswara Rao; Chia-Hsien Chou; Yew-Min Tzeng (pp. 253-258).

Cordycepin is the main active metabolite of Cordyceps militaris extracts; according to recent studies it has interesting therapeutic activities. A new capillary electrophoresis (CE) procedure with UV detection at 254nm for determination of cordycepin was developed and optimized. Optimal conditions found were 20mM sodium borate buffer with 28.6% methanol, pH 9.5, separation voltage 20kV, hydrodynamic injection time 10s and temperature 25°C. Linearity was found over the 20–100μg/mL concentration ranges of cordycepin. The developed method has been applied for determination of cordycepin in various pharmaceutical products. A comparison was made between CE and a high performance liquid chromatography (HPLC) method. Both of these methods gave comparable results. The shorter analysis time and low running cost are the main advantages of CE method.

Keywords: Cordyceps militaris; Cordycepin; Capillary electrophoresis; Separation method

Directly suspended droplet microextraction by Lu Yangcheng; Lin Quan; Luo Guangsheng; Dai Youyuan (pp. 259-264).

This work describes a new sampling method termed directly suspended droplet microextraction (DSDME) was developed. In this technique a free microdroplet of solvent is delivered to the surface of an immiscible aqueous sample while being agitated by a stirring bar placed on the bottom of the sample cell. After some time, the microdroplet of solvent is withdrawn by a syringe and analyzed. Under the proper stirring conditions, the suspended droplet can remain in a top-center position of the aqueous sample. The droplet can become partly engulfed within the sample while maintaining a stable shape with mechanical equilibrium and the mass transfer could be effectively intensified. Using 1,8-dioxyanthraquinone as a model compound and 1-octanol as the solvent, the extraction performance was investigated using HPLC. Since DSDME is based on a self-stable single microdroplet system, there are no requirements for special equipment or other supporting material like hollow fibers. Other advantages include ease of operation, free from cross contamination, quick to reach extraction equilibrium, and the ability to be combined with various analysis instruments. In our experiments, good linearity ( r²=0.9992) and precision (R.S.D.<1%, n=5) were achieved. DSDME is a promising pre-treatment method for the fast analysis of trace components in complicated matrices.

Keywords: Liquid-phase microextraction; Directly suspended droplet microextraction; Aqueous sample; Pre-treatment

Hepatobiliary excretion and brain distribution of caffeine in rats using microdialysis by Ming-Hwang Shyr; Lie-Chwen Lin; Chun-Hao Chang; Yu-Tse Wu; Yen-Ju Hsieh; Tung-Hu Tsai (pp. 265-270).

To investigate the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine, this study uses a method based on microdialysis technique and liquid chromatography that allows continuous and concurrent in vivo monitoring of extracellular caffeine in the blood, brain and bile of anesthetized rats following the administration of caffeine (3 or 10mg/kg, i.v.) through the femoral vein. Dialysates of the blood, brain and bile were directly injected onto the liquid chromatographic system and no further clean-up procedures were required. The study design consisted of two groups of six rats in parallel: the rats of the control group received caffeine (3 or 10mg/kg, i.v.) alone and those of the cyclosporine treated-group were injected cyclosporine (10mg/kg, i.v.) 10min prior to caffeine administration (3 or 10mg/kg, i.v.). The decline of caffeine in the blood, brain striatum and bile suggested that caffeine had rapid exchange and equilibration between the peripheral compartment and the central nervous system. In addition, the results indicated that caffeine underwent hepatobiliary excretion and was distributed into brain. When cyclosporine was co-administered, the pharmacokinetic parameters were not significantly altered. The results of this study reveal that the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine might not relate to P-glycoprotein.

Keywords: Abbreviations; AUC; area under the concentration versus time curve; BBB; blood–brain barrier; Cl; clearance; C; _max; peak concentration; t; _1/2; elimination half-life; T; _max; time to reach peak concentration; V; _ss; volume of distribution at steady-stateCaffeine; Hepatobiliary excretion; Microdialysis; P-glycoprotein; Pharmacokinetics

Novel nanostructured materials to develop oxygen-sensitive films for optical sensors by Jorge F. Fernández-Sánchez; Rita Cannas; Stefan Spichiger; Rolf Steiger; Ursula E. Spichiger-Keller (pp. 271-282).

Novel nanostructured materials, such as aluminum oxide (AlOOH), silicon oxide (SiO₂) or zirconium oxide (ZrO₂) embedded into PVA, were investigated as potential matrices to incorporate organometallic compounds (OMCs) for the development of optical oxygen-sensitive sensors which make use of the principle of luminescence quenching.In order to assess the benefits and drawbacks of the nanoporous material, the luminescence quantum yield and the Stern–Volmer constants were investigated and compared with the values shown for the same OMCs solubilized in polymer films (polystyrene). Referred to polymer films, the incorporation of the dyes into nanoporous membranes increased the Stern–Volmer constant by more than a factor of 100. Their response time was less than 1s and the optode membranes were stable at room temperature for at least 9 months. Sterilization by autoclavation and gamma irradiation resulted in a marginal loss in activity. The photostability and sterilizability of the oxygen-sensitive membranes and the performance of the optodes with respect to of different types of metal oxides are discussed in the paper, as well as the influence of the total pore volume (TPV), the pore diameter (PD), the transparency of the film and the geometry of the pores. The OMCs used in this work were: ETH^T-3003 (tris(4,7-bis(4-octylphenyl)-1,10-phenanthroline) ruthenium(II)), N-926 (bis(2-phenylpyridinyl)- N⁴, N⁴, N⁴′, N⁴′-tetramethyl-(4,4′-diamine-2,2′-bipyridine) iridium(III) chlorate), N-833 (tetrabutylammonium bis(isothiocyanate) bis(2-phenylpyridinyl)-iridium(III)) and N-837 (tetrabutylammonium bis(cyanate) bis(2-phenylpyridinyl)-iridium(III)).

Keywords: Luminescence oxygen sensor; FRET; Gamma-ray sterilization; Iridium(III) and ruthenium(II) complexes; Nanostructured material; Transparent nanoporous films

Development of a heavy metals enzymatic-based assay using papain by Yunus Shukor; Nor Azlan Baharom; Fadhil Abd. Rahman; Mohd. Puad Abdullah; Nor Aripin Shamaan; Mohd. Arif Syed (pp. 283-289).

A heavy metals enzymatic-based assay using papain was developed. Papain was assayed using the Casein-coomassie-dye-binding assay. The assay is sensitive to several heavy metals. The IC₅₀ (concentration of toxicant giving 50% inhibition) of Hg²⁺, Ag²⁺, Pb², Zn²⁺ is 0.39, 0.40, 2.16, 2.11mgl⁻¹, respectively. For Cu²⁺ and Cd²⁺ the LOQ (limits of quantitation) is 0.004 and 0.1mgl⁻¹, respectively. The IC₅₀ and LOQ values were found to be generally comparable to several other enzymatic and bioassays tests such as: immobilized urease, 15-min Microtox™, 48h Daphnia magna, and 96h Rainbow trout. The papain assay is xenobiotics tolerant, has a wide pH for optimum activity, is temperature stable, and has a relatively quick assay time. The papain assay was used to identify polluted water samples from industrial sources in Penang, Malaysia. We found one site where the assay gave a positive toxic response. The toxicity of the site was confirmed using Atomic Emission Spectrometry analysis.

Keywords: Assay; Papain; Heavy metal ions; Interference from xenobiotics; Environmental samples; Penang

Uncertainty estimation in measurement of p K_a values in nonaqueous media: A case study on basicity scale in acetonitrile medium by Lilli Sooväli; Ivari Kaljurand; Agnes Kütt; Ivo Leito (pp. 290-303).

The difficulties in estimating uncertainty of p K_a values determined in nonaqueous media are reviewed and two different uncertainty estimation approaches are presented and applied to the p K_a values of the compounds on a previously established self-consistent spectrophotometric basicity scale in acetonitrile. One approach is based on the ISO GUM methodology (the “ISO GUM�? approach) and involves careful analysis of the uncertainty sources and quantifying the respective uncertainty components. The second approach is based on the standard-deviation-like statistical parameter that has been used for characterization of the consistency of the scale (the “statistical�? approach). It is demonstrated that the ISO GUM approach somewhat overestimates the uncertainty. The statistical approach is based on long-term within-laboratory statistical data and it is demonstrated that it underestimates the uncertainty. In particular it neglects the laboratory bias effects that are taken into account at least to some extent by the ISO GUM approach. Thus, together these two approaches allow to “bracket�? the uncertainties of the p K_a values on the scale. The uncertainties of the p K_a values are defined in two different ways. Definition (a) includes the uncertainty of the p K_a of the reference base (anchor base of the scale) pyridine. Definition (b) excludes it. It is demonstrated that both definitions have their virtues. Definition (a) leads to the uncertainty ranges of 0.12–0.22 and 0.12–0.14 p K_a units at standard uncertainty level for different bases using the ISO GUM and statistical approach, respectively. Definition (b) leads to the uncertainty ranges of 0.04–0.19 and 0.02–0.08 p K_a units, respectively. The uncertainty of the p K_a of a given base is dependent on the quality of the measurements involved and on the distance from the reference base on the scale. The importance of the correlation between the p K_a values of bases belonging to the same scale is stressed.

Keywords: p; K; _a; values; Measurement uncertainty; Acetonitrile; Nonaqueous solutions; ISO GUM

Author Index (pp. 304-306).

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Analytica Chimica Acta (v.566, #2)