Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.534, #2)

Calendar of forthcoming meeings (pp. n5-n7).

Outside front cover - Editorial Board (pp. co1).

Contents (pp. iii-iv).

Screening method for organic aciduria by spectrofluorometric measurement of total dicarboxylic acids in human urine based on intramolecular excimer-forming fluorescence derivatization by Hideyuki Yoshida; Junya Araki; Junichiro Sonoda; Hitoshi Nohta; Junichi Ishida; Shinichi Hirose; Masatoshi Yamaguchi (pp. 177-183).

A simple screening method of organic aciduria by spectrofluorometric measurement of total dicarboxylic acids in human urine is described. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butanoic acid hydrazide (PBH). Dicarboxylic acids in urine were converted to the corresponding dipyrene-labeled derivatives by reaction with PBH in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and pyridine, and the derivatives afforded intramolecular excimer fluorescence (420–540nm) which can clearly be discriminated from the normal fluorescence (360–420nm) emitted from reagent blanks. The technique is so selective that it permits spectrofluorometric measurement of total amount of dicarboxylic acids by the direct derivatization of diluted urine samples. The same reaction mixture has also served as a liquid chromatographic (LC) sample for the separative determination of individual dicarboxylic acids. The spectrofluorometric data did not contradict with the LC data. These methods were usefully applied to preliminary screening test of glutaric aciduria. In conclusion, the present derivatization method allows rapid and direct determination of total amount of dicarboxylic acids in human urine samples.

Keywords: Spectrofluorometric measurement; Dicarboxylic acids; Urine; Screening; Excimer fluorescence

Fluorimetric determination ofd-lactate in urine of normal and diabetic rats by column-switching high-performance liquid chromatography by Jen-Ai Lee; Yih-Chiao Tsai; Hsiang-Yin Chen; Chih-Chun Wang; Shih-Ming Chen; Takeshi Fukushima; Kazuhiro Imai (pp. 185-191).

A highly sensitive method for the fluorimetric determination ofd-lactate in urine of normal and diabetic rats was developed using column-switching high-performance liquid chromatography (HPLC) with an octadecylsilica (ODS) column connected to a chiral column, an amylose tris(3,5-dimethylphenylcarbamate) coated on silica gel (Chiralpak AD-RH). During the separation step on the ODS column, the peak fraction of the (d+l)-lactate derivative with a fluorescence reagent, 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ), was introduced directly to the chiral column by changing the flow of the eluent via a six-port valve. Thed-lactate derivative was separated enantiomerically from thel-lactate derivative, and the enantiomeric ratio was determined from the chromatogram. The accuracy values for the determination ofd-lactate in 20μL of rat urine were 96.93–104.85%, and the intra- and inter-day precision values were within 0.80 and 14.44%, respectively. The detection limit ford-lactate was approximately 10nM (with a signal-to-noise ratio of 3).The proposed HPLC method was applied to the urine of normal and diabetic rats induced by intraperitoneal administration of streptozotocin, and significant increases ind-lactate excreted into the urine were observed in diabetic rats compared to normal rats. In diabetic rats,d-lactate concentrations showed a rising tendency from the seventh day and then remained stable from the 28th day after induction, suggesting that urinaryd-lactate may be used as an indicator to determine the diabetic stage and the level of kidney damage.

Keywords: Abbreviations; NBD-PZ; 4-nitro-7-piperazino-2,1,3-benzoxadiazole; DBD-PZ; 4-(N,N-dimethylaminosulfonyl)-7-piperazino-2,1,3-benzoxadiazole; TPP; triphenylphosphine; DPDS; 2,2′-dipyridyl disulfide; TFA; trifluoroacetic acidd-; Lactate; Column-switching HPLC; Enantiomeric separation; NBD-PZ; Fluorescence derivatization; Chiralpak AD-RH

Direct resolution of chiral ‘pineno’ fused terpyridyl ligands on amylose based chiral stationary phase using long chain alcohol modifiers by Radhakrishna Tatini; Omowunmi Sadik; Stefan Bernhard; Hector Abru�a (pp. 193-198).

Chiral separation of novel pineno fused terpyridyl ligands have been investigated on a silica-based amylose tris(3,5-dimethylphenyl carbamate) stationary phase (Chiralpak AD), using normal phase conditions. The chromatographic parameters investigated include retention factor ( k), separation factor ( α), column efficiency ( N) and resolution ( R_S) of the analytes. In addition, the effect of alcohol modifiers on the enantioselectivity of the column has been discussed. The chiral resolution of the ligands was significantly improved by using 1-pentanol as alcohol modifier in the mobile phase. The reversal of the elution order achieved in this study allows a lower detection limit (<0.1%) of the minor enantiomer and the chromatographic system described is suitable for assessing the enantiomeric excess (ee) of the ctpy≥99.9%. The method is selective and sensitive with a limit of detection (LOD) and quantification (LOQ) of 0.2μg/ml and 0.6μg/ml for ctpy, 0.6μg/ml and 1.2μg/ml for ctpy– x–ctpy, respectively. This study suggests that superior enantioseparation may be obtained for certain analytes using the same column by simply changing the type of alcohol modifier in the mobile phase instead of choosing another expensive chiral stationary phase for the same purpose.

Keywords: Chiral separation; Novel pineno fused terpyridyl ligands; Alcohol modifiers and optimization

A method for the simultaneous determination of β-ODAP, α-ODAP, homoarginine and polyamines in Lathyrus sativus by liquid chromatography using a new extraction procedure by Ze yi Yan; Cheng jin Jiao; Yang peng Wang; Feng min Li; Yong min Liang; Zhi xiao Li (pp. 199-205).

The paper proposes a new method to extract β- N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP), α- N-oxalyl-l-α,β-diaminopropionic acid (α-ODAP), homoarginine and polyamines using 0.2M HClO₄ for only 1h at 0–4°C. Based on the proposed extraction, an assay is presented for simultaneously determining polyamines, the neurotoxin β-ODAP, its non-neurotoxic isomer α-ODAP and homoarginine in Lathyrus sativus extracts using a liquid chromatography (LC) system after derivatization with para-nitrobenzyloxycarbonyl chloride (PNZ-Cl). The method exhibits some prominent advantages, which include: shorter extraction-time, simultaneous extraction of non-protein amino acids and polyamines and inhibition of the isomerization of β-ODAP to α-ODAP. The assay proved satisfactory for the quantitative determination of L. sativus extracts of seeds and seedlings.

Keywords: PNZ-Cl; ODAP; Homoarginine; LC; Polyamines; New extraction

Separation and determination of aminophenols and phenylenediamines by liquid chromatography and micellar electrokinetic capillary chromatography by Shu-Ping Wang; Tuen-Hwei Huang (pp. 207-214).

The separation and determination of aminophenols and phenylenediamines were investigated by liquid chromatography (LC) and micellar electrokinetic chromatography (MEKC) in this study. Aminophenols and phenylenediamines are commonly used components in commercial hair colorants. The problem of tailing peaks in LC was improved by the technique of using mobile phase containing 15mM triethylamine at pH 8.0. The analysis of o-aminophenol was not succeeded with LC even though the modifier of triethylamine was added. But it could be quantitative successfully by MEKC. The optimum separation condition of MEKC was achieved by employing 55mM cetyltrimethyl ammonium chloride in 50mM borate buffer (pH 9.2) with electric field strength of −145Vcm⁻¹. Finally, the commercial hair dyes were analyzed by developing methods of LC and MEKC. From both the results, there is no significant difference presence at 99.5% confidence level. These two methods could give the complementary results.

Keywords: Liquid chromatography; Micellar electrokinetic chromatography; Aminophenols; Phenylenediamines; Triethylamine

High-performance liquid chromatography determination of triptolide in vitro permeation studies by Xue-Ling Chang; Hua-Bing Chen; Xiao-Zhi Zhao; Zhong-Hong Gao; Hui-Bi Xu; Xiang-Liang Yang (pp. 215-221).

A simple, rapid and sensitive high-performance liquid chromatography (HPLC) method has been developed for the determination of triptolide. Triptolide was separated from skin endogenous and blank matrices on a 5μm LiChrospher RP-C₁₈ column by a mobile phase of methanol–water (65:35, v/v). The permeation samples were injected directly without pretreatment. The limit of quantitation (LOQ) and detection (LOD) for triptolide in permeation samples were far below (0.01 and 0.005μg/mL, respectively). The method was linear over the range of 0.1–104.2μg/mL with r²=0.9999. This HPLC assay is promising for measuring in vitro percutaneous penetration of triptolide through mice skins and also can be performed in the triptolide-loaded microemulsions formulation screening.

Keywords: Triptolide; Permeation study; HPLC

A novel amperometric immunosensor based on three-dimensional sol–gel network and nanoparticle self-assemble technique by Ruping Liang; Jianding Qiu; Peixiang Cai (pp. 223-229).

A novel hepatitis B surface antigen (HBsAg) immunosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol–gel network. A cleaned gold electrode was first immersed in a hydrolyzed mercaptopropyltrimethoxysilane (MPS) sol–gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol–gel network. Finally, hepatitis B surface antibody (HBsAb) was adsorbed onto the surface of the gold nanoparticles. Thus, an interfacial design of bare gold electrode (BGE)/MPS/Au/HBsAb was prepared to detect HBsAg in human serum based on the specific reaction of HBsAb and HBsAg. The electrochemistry of ferricyanide redox reaction was used as a marker to probe the interface and as a redox probe to determinate HBsAg. The main conditions of the assembly of MPS sol–gel, gold nanoparticles, the immobilization of HBsAb, and incubation time were investigated in detail. Compared with the glutaraldehyde binding approach, the antibodies immobilized by this method present larger amount and higher immunoactivity. The linearity of HBsAg in the range of 2–360ng/mL with the correlation coefficient of 0.998 was obtained. This immunosensor system was evaluated on several clinical sample, the analytical results obtained by this method were in agreement with those detected by the enzyme-linked immunosorbent assay (ELISA) method, indicating a promising alternative tool for clinical diagnosis. Moreover, the studied immunosensor exhibited good reproducibility, long-term stability, high sensitivity and specificity.

Keywords: Sol–gel; Nanoparticle; Self-assemble; Immunosensor

Detection of leucoindigo in alkaline phosphatase and peroxidase based assays using 3-indoxyl phosphate as substrate by Pablo Fanjul-Bolado; Mar�a Bego�a Gonz�lez-Garc�a; Agust�n Costa-Garc�a (pp. 231-238).

3-Indoxyl phosphate (3-IP) is the first common electrochemical substrate of the two most important label enzymes in immunoassays: alkaline phosphatase (AP) and horseradish peroxidase (HRP). The product of the enzymatic reactions is indigo blue, an aromatic heterocycle compound insoluble in aqueous solutions. Through the reduction of water insoluble indigo in an alkaline media and in presence of a dithionite salt (Na₂S₂O₄), a water-soluble compound, called leucoindigo, is obtained. This solubilisation methodology, widely used in the textile dyeing industry, is applied in this work for the measurement of AP and HRP activity. Leucoindigo is electroactive and also develops a rich yellow color in solution with a maximum absorbance at 415nm, so 3-IP is shown also as the first common chromogenic substrate for HRP and AP. Through an electrochemical (alternating current adsorptive stripping voltammetry) and a spectrophotometric detection of leucoindigo, picomolar levels of AP and HRP in solution can be measured. Using this approach, two ELISA assays to quantify pneumolysin (PLY) and osteocalcin (BGP) were carried out using AP and HRP, respectively as enzymatic label. Therefore, the suitability of the detection of leucoindigo in ELISAs that employ 3-IP as substrate is demonstrated. This approach can unify solutions and procedures to develop AP and HRP based affinity devices.

Keywords: Leucoindigo; 3-Indoxyl phosphate; Alkaline phosphatase; Horseradish peroxidase; ELISA

Maximising metal ions flux across a microdialysis membrane by incorporating poly-l-aspartic acid, poly-l-histidine, 8-hydroxyquinoline and ethylenediaminetetraacetic acid in the perfusion liquid by Dikabo Mogopodi; Nelson Torto (pp. 239-246).

This paper presents a study of quiescent microdialysis sampling of Cr³⁺, Cu²⁺, Ni²⁺ and Pb²⁺ involving the incorporation of poly-l-aspartic acid, poly-l-histidine, 8-hydroxyquinoline (8-HQ) and ethylenediaminetetraacetic acid (EDTA), in the perfusion liquid as an approach to maximise metal analyte flux across the microdialysis membrane. These chelating agents were individually optimised with respect to microdialysis recovery and subsequently combined in the perfusion liquid. A combination of 20% (w/v) poly-l-histidine, 0.032% (w/v) poly-l-aspartic acid and 1mM 8-HQ achieved microdialysis recovery up to 90%. Since 1mM EDTA achieved recoveries greater than 80% for all metals understudy, EDTA was not combined with any of the chelating agents. Under the optimal conditions of maximum metal ion flux across the microdialysis membrane, metal ions from natural and wastewater were sampled and analysed with an electrothermal atomic absorption spectrometer equipped with a Zeeman background corrector. Results showed higher concentrations of detected metal ions after microdialysis sampling compared to direct detection without sample clean-up. Incorporation of chelating agents in the microdialysis perfusion liquid enhanced metal ions recovery in real samples and achieved enrichment factors of up to 42. The study demonstrated that combining chelating agents is a good approach towards maximising metal flux across the dialysis membrane. Given that recoveries between 80 and 90% were achieved under quiescent microdialysis sampling conditions, these findings are an important development for in vivo diagnostic sampling of metal ions.

Keywords: Microdialysis; Chelating agents; Poly-; l; -aspartic acid; Poly-; l; -histidine; 8-Hydroxyquinoline; Ethylenediaminetetraacetic acid; Relative recovery; Metal ions

Optimisation of microwave-assisted extraction for the determination of nonylphenols and phthalate esters in sediment samples and comparison with pressurised solvent extraction by E. Cortazar; L. Bartolom�; A. Delgado; N. Etxebarria; L.A. Fern�ndez; A. Usobiaga; O. Zuloaga (pp. 247-254).

Microwave-assisted extraction (MAE) of nonylphenols (NP), nonylphenol mono- and diethoxylates (NP1EO and NP2EO, respectively) and phthalate esters was optimised using an experimental design approach. A D-optimal mixture design was used to optimise the pressure inside the extraction vessel (110–207kPa), the extraction time (5–25min) and the extraction solvent (methanol, acetone or n-hexane) or the solvent mixture for the microwave-assisted extraction. Percentage of microwave power (80%) and solvent volume (15ml) were fixed in all the experiments. As a consequence, the optimum extraction of these compounds was carried out at an intermediate pressure (159kPa) with pure methanol and during 15min. Moreover, solid phase extraction was also optimised for the clean-up of the extracts and C-18, LiChrolut^® and Oasis^® cartridges were studied in order to obtain the best recoveries of the compounds of interest. The highest recoveries were obtained with LiChrolut^® cartridges after the elution with ethyl acetate. The cleaned extracts were analysed in a gas chromatograph with mass spectrometric detection and in a liquid chromatograph with diode array and fluorescence detection (HPLC–DAD-UV–FLD). The same sediment was also extracted twice in order to check that an exhaustive extraction of the analytes had occurred. Finally, the optimised extraction method was compared with pressurised solvent extraction (PSE), using an estuarine sediment sample.

Keywords: Microwave-assisted extraction; Pressurised solvent extraction; Sediment samples; Nonylphenols; Nonylphenol ethoxylates; Phthalates and experimental design approach

Improved determination of selenium in plant and peat samples using hydride generation-atomic fluorescence spectrometry (HG-AFS) by Julia Barciela Garc�a; Michael Krachler; Bin Chen; William Shotyk (pp. 255-261).

A robust, accurate and sensitive analytical procedure for the determination of Se in plant and peat samples by hydride generation-atomic fluorescence spectrometry (HG-AFS) was developed. Aliquots (200mg) of dried samples were digested with 3mL nitric acid and 0.5mL hydrogen peroxide in closed, pressurized PTFE vessels in a microwave oven at 220°C. Addition of HBF₄ or HF to the digestion mixture was not required because experiments demonstrated that Se was not hosted in the silicate fraction of the investigated sample matrices. Selenium(VI) was directly reduced to Se(IV) in the undiluted digestion solutions after addition of 3.8mL of 4M HCl in a microwave oven at 103°C for 3min. Other reduction reagents, such as hydroxylamine hydrochloride or urea, were not necessary to cope with potential interferences from nitrogen oxides that could hamper the reliable determination of Se by HG-AFS. Optimum hydride generation of Se was achieved by using 0.9% NaBH₄ and 4.5M HCl. A solution detection limit of 11ngL⁻¹ was obtained under the optimized experimental conditions which corresponds to a method detection limit of 2.8ngg⁻¹ in solid peat and plant materials. The precision of replicate measurements was better than 3% at Se concentrations of 50ngL⁻¹. The analytical procedure was critically evaluated by analysing two certified plant reference materials (SRM 1515 Apple Leaves and SRM 1547 Peach Leaves) as well as three peat reference materials. Excellent agreement between the experimental values ranging from 50ngg⁻¹ to ∼2μgg⁻¹ and the certified concentrations was obtained.

Keywords: Selenium; HG-AFS; Peat; Plants; Microwave digestion

Determination of airborne isocyanates as di- n-butylamine derivatives using liquid chromatography and tandem mass spectrometry by Daniel Karlsson; Jakob Dahlin; �sa Marand; Gunnar Skarping; Marianne Dalene (pp. 263-269).

A method for the determination of isocyanates as di- n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d₉-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1μgml⁻¹ of the studied derivatives was <2%. Performing MRM of the product ion [DBA+H]⁺ ( m/ z=130) from the protonated molecular ion resulted in the lowest detection limits, down to 10amol (for TDI). Quantification of concentrations below 10⁻⁶ of the occupational exposure limit (OEL) for TDI during 10min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M+Li]⁺ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d₄-HDI, d₃-2,4-TDI, d₃-2,6-TDI and d₂-MDI), (2) d₉-DBA derivatives of the corresponding isocyanates and (3) d₁₈-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series.

Keywords: Isocyanates; LC–MS/MS; Di-; n; -butylamine; Air sampling; Thermal degradation

Determination of radioactive strontium in seawater by Željko Grahek; Martina Rožmarić Ma�?efat (pp. 271-279).

This paper describes the procedures of isolating strontium and yttrium from seawater that enable the determination of^89,90Sr. In one procedure, strontium is directly isolated from seawater on the column filled with Sr resin by binding of strontium to the resin from 3M HNO₃ in a seawater, and successive elution with HNO₃. In others, strontium is precipitated from seawater with (NH₄)₂CO₃, followed by isolation on a Sr column or an anion exchange column. It is shown that strontium precipitation is optimal with concentration of 0.3M (NH₄)₂CO₃ at pH=11. In these conditions, 100% Y, 78% Sr, 80% Ca and 50% Mg are precipitated. Strontium is bound on to Sr column from 5 to 8M HNO₃, separated from other elements by elution with 3M HNO₃ and 0.05M HNO₃. Strontium and yttrium are bound on to anion exchange column from alcoholic solutions of nitric acid. The optimum mixture of alcohols for sample binding is a mixture of ethanol and methanol with the volume ratio 1:3. Strontium and yttrium are separated from Mg, Ca, K, and other elements by elution with 0.25M HNO₃ in the mixture of ethanol and methanol. After the separation, yttrium and strontium are eluted from the column with water or methanol.In the procedure of direct isolation from 1l of the sample, the average recovery of 50% was obtained. In the remaining two procedures, the strontium recovery was about 60% for the Sr column and 65% for anion exchange column. Recovery of yttrium is about 70% for the anion exchange column. It turned out that the procedure with the Sr resin (direct isolation and isolation after precipitation) is simpler and faster in the phase of the isolation on the column in comparison with the procedure with the anion exchanger. The procedure with the anion exchanger, however, enables the simultaneous isolation of yttrium and strontium and rapid determination of^89,90Sr. These procedures were tested by determination of^89,90Sr on liquid scintillation counter and Cherenkov counting in 5M HNO₃. Obtained results showed that activity of 50mBql⁻¹ of^89,90Sr and higher can be simultaneously determined.

Keywords: Seawater; Yttrium; Strontium; Isolation; Radiostrontium; Determination

Evaluation of the stability and analysis of halogenated furanones in disinfected drinking waters by Gretchen D. Onstad; Howard S. Weinberg (pp. 281-292).

A refined method for the sub-nanomolar analysis of 13 halogenated furanones in chlorinated drinking water is proposed which uses liquid–liquid extraction, methylation where necessary, gas chromatographic separation, and either micro-electron capture or ion trap mass spectrometric detection. Liquid–liquid extraction with methyl tert-butyl ether was demonstrated to be effective for recovery of halogenated furanones. Confirmation of the halogenated furanones identity and reduction of natural organic matter interference were achieved by ion trap tandem mass spectrometry. Compound stabilities and procedural efficiencies were evaluated to permit optimization of the method for reasonable sample volumes and a 1000:1 pre-concentration factor that would permit feasible sample collection in the field. Both chlorinated and brominated analogues of MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H)-furanone) were included in a suite of compounds targeted in a national occurrence study of disinfection by-products.

Keywords: Disinfection by-products; MX; BMX; 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5; H; )-furanone; MS/MS; GC-μECD

Separation of trace antimony and arsenic prior to hydride generation atomic absorption spectrometric determination by Müşerref Yersel; Aslı Erdem; Ahmet E. Eroğlu; Talal Shahwan (pp. 293-300).

A separation method utilizing a synthetic zeolite (mordenite) was developed in order to eliminate the gas phase interference of Sb(III) on As(III) during quartz furnace hydride generation atomic absorption spectrometric (HGAAS) determination. The efficiency of the proposed separation method in the reduction of suppression effects of transition metal ions on As(III) signal was also investigated. Among the volatile hydride-forming elements and their different oxidation states tested (Sb(III), Sb(V), Se(IV), Se(VI), Te(IV), and Te(VI)), only Sb(III) was found to have a signal depression effect even at low (μgl⁻¹) concentrations under the experimental conditions employed. It has been shown that mordenite adsorbs Sb(III) quantitatively, even at a concentration of 1000μgl⁻¹, at pHs greater than two, and also, it reduces the initial concentrations of the transition metal ions to lower levels which can be tolerated in many studies. The adsorption of Sb(III) on mordenite follows the Freundlich isotherm and is endothermic in nature.

Keywords: Hydride generation atomic absorption spectrometry; Arsenic; Antimony; Interference; Mordenite

Optical sensing of HCl with phenol red doped sol–gels by Enju Wang; Kwok-Fan Chow; Wenqun Wang; Crystal Wong; Cynthia Yee; Alvin Persad; Jonathan Mann; Andrew Bocarsly (pp. 301-306).

A dye doped sol–gel for the sensing of hydrochloric acid in solution and/or gaseous phase is described. The sol–gel is obtained by acidic hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (Ph-TriEOS) in the presence of phenol red (PR) and further spin-coating onto glass slides. The sensitive response is based on an increase of the absorption band at 510nm of phenol red entrapped in the sol–gel casting when exposed to HCl solution or gas, due to protonation of the dye. The detection limit of the sol–gel response to moisturized gaseous HCl is below 12ppm, and its response to HCl in solution falls in the range of 0.01–6M. The sol–gel coating has a response time of less than 40s in steady-state, and life-time of more than a year. Weak acids such as acetic acid, benzoic acid, salicylate acid, citrate acid, and carbonic acid do not interfere the response. The responses in acid solutions are completely reversible. In the gaseous phase, response of HCl appears to be moisture sensitive.

Keywords: Sol–gel; HCl; Phenol red; Optical sensing

Selective spectrophotometric determination of TNT in soil and water with dicyclohexylamine extraction by Ayşem Üzer; Erol Erçağ; Reşat Apak (pp. 307-317).

Contaminated land and groundwater remediation in military waste dumping sites often necessitates the use of simple, cost-effective, and rapid tests for detecting trinitrotoluene (TNT) residues in the field along with their dinitro-analogues. A simple, rapid, low-cost, and field-adaptable (on-site) colorimetric method was developed for quantifying TNT in the presence of RDX, PETN, picric acid, 2,4-DNT (dinitrotoluene), dinitrophenol, and dinitroaniline. Most commercialized methods for TNT assay-with the exception of Cold Regions Research and Engineering Laboratory of the U.S. Army (CRREL) method-use proprietary chemicals, and the color stability and intensity are highly dependent on the composition of the organic solution comprised of acetone or methanol. The developed colorimetric method is based on the extraction of TNT from water–acetone solution into an organic solvent mixture of dicyclohexylamine (DCHA)–isobutyl methyl ketone (IBMK) (10:1, v/v), filtration through a filter paper into a stoppered optical cell containing anhydrous sodium sulfate, and measurement of the absorbance of the organic extract at 531nm after 5min. The red-violet color of the extract was due to intermolecular charge-transfer (CT) between the electron attracting TNT and electron-donating DCHA, and the molar absorptivity for TNT in final organic solution was (1.16±0.02)×10⁴Lmol⁻¹cm⁻¹.The R.S.D. of the slope of calibration line was 0.7%. The LOD of the method in the final organic phase was 0.38μM TNT, and LOD values expressed on the basis of original soil TNT content were 0.5, 1.3, and 1.5ppm (μgg⁻¹) for clay, loamy clay, and sandy soils, respectively. Unlike other spectrophotometric methods, the developed assay was basically tolerant to common cations and anions found in soil and water at 100-fold weight ratios, and to soil humic acids. Among a number of compounds that may be encountered in polynitro-explosive storage and waste reclaimation sites such as picric acid, dinitrophenol, 2,4-dinitrotoluene, dinitroaniline, RDX, PETN, and tetryl, only tetryl interfered with the developed TNT assay. Water tolerance and exploitability over a wide pH range were other superiorities over the CRREL method. The CT-complex was relatively stable, as the absorbance of the organic extract was not significantly influenced from the dilution of the water–acetone phase. Aside from the extractive-photometric procedure established for aqueous solutions, a simulated field colorimetric assay for TNT directly applicable to soil was also devised, based on direct color development in a 4:1 (v/v) acetone–dicyclohexylamine organic extract of soil at a liquid-to-solid ratio of 5mLg⁻¹.

Keywords: TNT determination; Dicyclohexylamine; Charge-transfer; Extraction; Polynitroaromatic explosives; Spectrophotometry; Field colorimetry

Chemical speciation of chromium(III,VI) employing extractive spectrophotometry and tetraphenylarsonium chloride or tetraphenylphosphonium bromide as ion-pair reagent by M.S. El-Shahawi; S.S.M. Hassan; A.M. Othman; M.A. Zyada; M.A. El-Sonbati (pp. 319-326).

A simple and accurate extractive spectrophotometric procedure for the chemical speciation of chromium(III,VI) species in aqueous media has been developed. The method is based upon the extraction of the complex ion-associate formed between the chloro chromate (CrO₃Cl⁻) anion and the ion-pair reagent tetraphenylarsonium chloride (TPAs⁺Cl⁻) or tetraphenylphosphonium bromide (TPP⁺Br⁻) at pH≤0 in chloroform followed by direct spectrophotometric measurement at 355nm. The optimum concentration range evaluated by Beer–Lambert's law, Ringbom's plot, the molar absorptivity, the Sandell's sensitivity, the extraction and stability constants ( K_D, K_ex and β), the stoichiometry and the extraction equilibria of the produced complex ion-associates have been determined and gave a convenient applications of the investigated system for analytical purposes. Chromium(III) was also determined by the proposed procedure after prior oxidation to chromate with H₂O₂ in alkaline solution. The method has been applied successfully for the analysis of chromium(VI) and total chromium(III,VI) in industrial wastewater of electroplating plant.

Keywords: Chemical speciation; Chromium(III,VI); Ion-pairs; Extraction equilibria and spectrophotometry

Improved detection limit for ammonium/ammonia achieved by Berthelot's reaction by use of solid-phase extraction coupled to diffuse reflectance spectroscopy by Y. Moliner-Mart�nez; R. Herr�ez-Hern�ndez; P. Camp�ns-Falc� (pp. 327-334).

The proposed procedure is based on the extraction of the indothylmol blue into C₁₈ solid-phase extraction (SPE) membranes and direct quantification on the membrane surface by diffuse reflectance spectroscopy. The analytical performance of the proposed method has been evaluated for standard solutions of ammonium using reflectance values, R, as well as the Kubelka–Munk function, F( R). The results have been compared with those obtained by the conventional method, which uses UV–vis absorption spectroscopy with a sensor-based method. The described methodology provided satisfactory linearity and reproducibility within the ammonium concentration intervals 25–250μgL⁻¹ and 25–500μgL⁻¹ when using R and F( R), respectively. The limit of detection was around 10μgL⁻¹, which is markedly lower than that of the classical procedure and than those provided by Nessler and OPA/thiol fluorimetric methods. For air samples the linear interval expressed as μg of ammonia is 0.24–2.4 or 0.24–4.7 employing R or F( R), respectively. The effect of potential interferences such as metals and aliphatic amines has also been evaluated. Finally, the proposed methodology has been adapted to the determination of ammonia in air and water samples. The method can be also used as a detector support for visual estimation.

Keywords: Solid-phase extraction (SPE); Reflectance spectroscopy; Ammonia; Ammonium

Electrocatalytic properties of [Ru(bpy)(tpy)Cl]PF₆ at carbon ceramic electrode modified with nafion sol–gel composite: application to amperometric detection ofl-cysteine by Abdollah Salimi; Rahman Hallaj; Mohammad Kazem Amini (pp. 335-342).

A two-step sol–gel technique was used here to prepare a carbon ceramic electrode modified with nafion and [Ru(bpy)(tpy)Cl]PF₆. This involves two steps: first, forming a bulk-modified carbon ceramic electrode with nafion, and then immersing the electrode into a Ru-complex solution (electroless deposition) for a short period of time (5–25s). Cyclic voltammograms of the resulting surface-modified carbon ceramic electrode show stable and a well-defined redox couple due to Ru(II)/Ru(III) system with surface-confined characteristic.l-Cysteine (CySH) has been chosen as a model to elucidate the electrocatalytic ability of Ru-complex nafion sol–gel composite electrode. Not only the modified electrode shows excellent catalytic activity towardl-cysteine electrooxidation in pH range 3–9, but the antifouling effect of nafion film also increases the reproducibility of results in comparison with CCE modified with homogeneous mixing of graphite powder and Ru-complex (one step sol–gel method). Under the optimized conditions in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.1–100μM, 20nM and 50nA/μM, respectively. The advantages of this modified electrode are good reproducibility, excellent catalytic activity, simplicity of preparation and especially its antifouling properties towardsl-cysteine and its oxidation products. Additionally, it is promising as a detector in flow system or chromatography systems.

Keywords: Two step sol–gel technique; Carbon composite electrode; Nafion; Ru-complex; l; -Cysteine

Electrochemical behavior and assembly of tetranuclear Dawson-derived sandwich compound [Cd₄(H₂O)₂(As₂W₁₅O₅₆)₂]¹⁶⁻ on 4-aminobenzoic acid modified glassy carbon electrode by Lihua Bi; Yan Shen; Junguang Jiang; Erkang Wang; Shaojun Dong (pp. 343-351).

The transition metal-substituted heteropolyoxoanion, Cd₄(H₂O)₂(As₂W₁₅O₅₆)₂¹²⁻ (As₄W₃₀Cd₄), is one of the trivacant Dawson derivatives. Its redox electrochemistry has been studied in acid buffer solutions using cyclic voltammetry. It exhibited three steps of four-electron redox waves attributed to redox processes of the tungsten-oxo framework. Through layer-by-layer assembly, the compound was first successfully immobilized on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)₂Cl]^2+/+ (denoted as QPVP-Os). Thus, prepared multilayer films have been characterized by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and UV–vis spectroscopy (UV–vis). The electrocatalytic activities of the multilayer films containing As₄W₃₀Cd₄ have been investigated on the reduction of three substrates of important analytical interests, NO₂⁻, BrO₃⁻ and IO₃⁻. And with the increase of the number of As₄W₃₀Cd₄ layers, the catalytic current towards the reduction of BrO₃⁻ was enhanced and the catalytic potential shifted positively.

Keywords: Self-assembly; 4-Aminobenzoic acid; Modified glassy carbon electrode; Electrocatalytical; Polyoxometalate

Author Index (pp. 353-355).

Sections

Personal tools

Analytica Chimica Acta (v.534, #2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.534, #2)