Complexation of Be(II) Ion with 1-(2,4-Dihydroxy-1-phenylazo)-8-hydroxy-3,6-naphthalenedisulfonate as the Chemical Basis of the Selective Detection of Ultratrace Be by Reversed-Phase High-Performance Liquid Chromatography

The complexation reactions of beryllium(II) ion with 1-(2,4-dihydroxy-1-phenylazo)-8-hydroxy-3,6-naphthalenedisulfonate (H-resorcinol) are studied. The acid dissociation constants of H-resorcinol, H(3)L(2-), at 293 K and I = 0.10 [K(OH, NO(3))] are pK(a)((1)) = 5.67, pK(a)((2)) = 8.57, and pK(a)((3)) > 13. The formation constant at 293 K and I = 0.10 [(K,H)NO(3)] is estimated to be log[{[Be(HL)(2-)][H(+)](2)}/{[Be][H(3)L(2-)]}] = -4.58, and pK(a)' = 6.39 for [Be(HL)](2-), which give the basis for the optimization of the precolumn chelation reactions and the masking system with EDTA. The kinetic data for ligand substitution reactions with sulfosalicylate ion are also reported to demonstrate the remarkable inertness of the Be chelate, which is suitable for HPLC separation. Reported is an accurate method for determining traces of Be(II) ion at nanomolar levels with photometric detection coupled with ion-pair reversed-phase HPLC. The chelate, [Be(II)L](3-), is efficiently separated on an Asahipak ODP-50 column using tetrabutylammonium bromide as an ion-pairing agent in a methanol (35 wt %)-water eluent. Only Al and Fe give peaks under the conditions used. The large molar absorptivity of the H-resorcinol chelate, 3.99 × 10(4) M(-1) cm(-1) at 500 nm, and the short retention time with excellent peak resolution ensure the ultralow detection limit (3σ blank) down to 7.2 ppt (0.8 nM) with no preconcentration procedures. The excellent toughness toward the matrix influence was demonstrated using the model solution for an air-dust sample. The HPLC separation, coupled with the EDTA masking procedure, enables one to detect Be(II) ion at 20 nM in the presence of metals at the natural abundance levels in air samples, such as Al, Fe, Ca, Mg, Zn, and Pb at 240, 140, 300, 66, 16, and 6.2 μM, respectively, in the final solution.     

On-line HPLC/ESI-MS separation and characterization of hyaluronan oligosaccharides from 2-mers to 40-mers

A new method for the separation and identification of oligosaccharides obtained by enzymatic digestion of hyaluronic acid (HA) with hyaluronidase (EC 3.2.1.35) using on-line high-performance liquid chromatography/electrospray mass spectrometry (HPLC/ESI-MS) is presented. Reversed-phase ion pairing-HPLC, based on tributylamine salts and a volatile mobile phase, provided excellent chromatographic resolution and separation was achieved for HA oligosaccharides containing 2-40 monomers (from 2- to 40-mers). Using the on-line ion trap mass analyzer, complete identification and structural information for each HA oligomer species was obtained. In particular, a series of negatively charged species of different m/z ratios are seen for each oligosaccharide. Smaller HA species, from 2- to 4-mers, exhibit mainly [M-H](-1) anions, whereas the 6-10-mers exist predominantly as the charge state of -2. The HA oligomers from 12- to 18-mers are mainly represented by [M-3H](-3) anions while species from 20- to 28/30-mers are characterized by a charge state of -4. HA oligosaccharides from 32- to 40-mers exist as [M-5H](-5) anions. Furthermore, for smaller HA species, from 4/6- to 18/20-mers, ESI-MS revealed, generally in low relative abundance, anions related to the loss of one/two monosaccharide unit(s) from the oligomers, and no odd-numbered anions were produced for HA species greater than 20-mers.     

Matrix interference-free method for the analysis of small molecules by using negative ion laser desorption/ionization on graphene flakes

This work presents a new approach for the analysis of small molecules with direct negative ion laser desorption/ionization (LDI) on graphene flakes. A series of matrix interference-free mass spectra were obtained for the analysis of a wide range of small molecules including peptides, amino acids, fatty acids, as well as nucleosides and nucleotides. The mixture of analytes and graphene flakes suspension were directly pipetted onto a sample plate for LDI-time-of-flight mass spectrometry (TOFMS) analysis. Deprotonated monomeric species [M-H](-) ions were homogeneously obtained on uniform graphene flakes film when negative ion mode was applied. In positive ion mode, the analytes were detected in form of multiple adduct ions such as sodium adduct [M+Na](+), potassium adduct [M+K](+), double sodium adduct [M+2Na-H](+), double potassium adduct [M+2K-H](+), as well as sodium and potassium mixed adduct [M+Na+K-H](+). Better sensitivity and reproducibility were achieved in negative ion mode compared to positive ion mode. It is believed that the new method of matrix interference-free negative ion LDI on graphene flakes may be expanded for LDI-MS analysis of various small molecules.     

Electrochemical degradation of aromatic amines on BDD electrodes

The electrochemical oxidation of four aromatic amines, with different substituent groups, 3-amino-4-hydroxy-5-nitrobenzenesulfonic acid (A1), 5-amino-2-methoxybenzenesulfonic acid (A2), 2,4-dihydroxyaniline hydrochloride (A3) and benzene-1,4-diamine (A4), was performed using as anode a boron-doped diamond electrode, commercially available at Adamant Technologies. Tests were run at room temperature with model solutions of the different amines, with concentrations of 200 ppm, using as electrolyte 0.035 M Na(2)SO(4) aqueous solutions, in a batch cell with recirculation, at different current densities (200 and 300 A m(-2)). The following analyses were performed with the samples collected during the assays: UV-Vis spectrophotometry, chemical oxygen demand (COD), total organic carbon (TOC), total Kjeldahl nitrogen, ammonia nitrogen, nitrates and HPLC. Results have shown a good electrodegradation of all the amines tested, with COD removals, after 6 h assays, higher than 90% and TOC removals between 60 and 80%. Combustion efficiency (η(C)), which measures the tendency to convert organic carbon to CO(2), was also determined for all the amines, being η(CA1)<η(CA2)<η(CA3)<η(CA4)=0.99.     

Electrospray ionization mass spectrometry of tetracycline, oxytetracycline, chlorotetracycline, minocycline, and methacycline

The effects of mobile-phase additives and analyte concentration on electrospray ionization mass spectra of a series of tetracyclines were investigated in both positive and negative ion modes. Only [M + H](+) and [M - H](-) ions were observed. The greatest sensitivity as [M + H](+) ions was obtained with 1% acetic acid and the greatest sensitivity as [M - H](-) ions was obtained using 50 mM ammonium hydroxide. Sensitivities in the positive ion mode were greater than those in the negative ion mode. The sensitivity as [M + H](+) showed no systematic variation with pH; however, the sensitivity as [M - H](-) did increase with increasing pH. A larger linear range was observed for [M - H](-) than for [M + H](+) ions. Both [M + Na](+) and [M + H](+) ions were observed with 0.5 mM sodium acetate and sodium iodide, but no adduct ions were observed with ammonium acetate. Some M(2)H(+) ions were observed at higher concentrations. Cluster ions, Na(NaOAc)(n)(+) or Na(NaI)(n)(+), but no sample ions were observed using 5 mM salts. The data suggest that mechanisms in addition to solution ionization are involved in the formation of the ESI sample ions. The utility of mobile phases containing 1% HOAc or 50 mM NH(4)OH was demonstrated for chromatographic separations.     

离子对色谱法测定Roxarsone的含量

本文提出一种用于测定对氨基苯胂酸硝化反应产物中4-羟基-3-硝基苯胂酸(Roxarsone)及对氨基苯胂酸含量的离子对色谱法,选择甲醇:水=25:75(v/v)作为流动相,0.005mol/L的四丁基氢氧化铵为离子对试剂,用磷酸调至pH=4.0,定量测定重现性良好,对Roxarsone中的杂质对氨基苯胂酸(ASA)的最低检出浓度为0.05μg/mL,结果令人满意。     

Phosphate group-driven fragmentation of multiply charged phosphopeptide anions. Improved recognition of peptides phosphorylated at serine, threonine, or tyrosine by negative ion electrospray tandem mass spectrometry

The nanoelectrospray product ion spectra of multiply charged phosphopeptide anions reveal the occurrence of phosphate-specific high-mass fragment ions of the type [M - nH - 79](n-1)-. These so far unrecognized fragments, which are observed for phosphoserine-, phosphothreonine-, and phosphotyrosine-containing peptides, are the counterparts of the established inorganic phosphopeptide marker ion found at m/z 79 = [PO3]-. The high-mass marker ions are formed with high efficiency at moderate collision offset values and are particularly useful for sensitive recognition of pSer-, pThr-, and pTyr-peptides due to the low background level in MS/MS spectra at m/z values above those of the precursor ions. By virtue of this feature, the detection of the new phosphorylation-specific fragment ions appears to be more sensitive than the detection of the low-mass phosphate marker ion at m/z 79, where a higher interference by nonspecific background signals is generally observed. The number of phosphate groups within a phosphopeptide can also be estimated on the basis of the [M - nH - 79](n-1)- ions, since these exhibit an effective, sequential neutral loss of H3PO4 of the residing phosphate groups. A mechanistic explanation for the formation of the [M - nH - 79](n-1)- ions from multiply charged phosphopeptides is given. The high-mass marker ions are proposed to originate from phosphopeptide anions, which carry two negative charges located at the phosphate group. A new search tool denominated "variable m/z gain analysis", which utilizes these newly recognized high-mass fragments for spotting of phosphopeptides in a negative ion parent scan, is proposed. The findings strengthen the value of negative ion ESI-MS/MS for analysis of protein phosphorylation.     

Desorption and ionization mechanisms in desorption atmospheric pressure photoionization

The factors influencing desorption and ionization in newly developed desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS) were studied. Redirecting the DAPPI spray was observed to further improve the versatility of the technique: for dilute samples, parallel spray with increased analyte signal was found to be the best suited, while for more concentrated samples, the orthogonal spray with less risk for contamination is recommended. The suitability of various spray solvents and sampling surface materials was tested for a variety of analytes with different polarities and molecular weights. As in atmospheric pressure photoionization, the analytes formed [M + H](+), [M - H](-), M(+*), M(-*), [M - H + O](-), or [M - 2H + 2O](-) ions depending on the analyte, spray solvent, and ionization mode. In positive ion mode, anisole and toluene as spray solvents promoted the formation of M(+*) ions and were therefore best suited for the analysis of nonpolar compounds (anthracene, benzo[a]pyrene, and tetracyclone). Acetone and hexane were optimal spray solvents for polar compounds (MDMA, testosterone, and verapamil) since they produced intensive [M + H](+) ion peaks of the analytes. In negative ion mode, the type of spray solvent affected the signal intensity, but not the ion composition. M(-*) ions were formed from 1,4-dinitrobenzene, and [M - H + O](-) and [M - 2H + 2O](-) ions from 1,4-naphthoquinone, whereas acidic compounds (naphthoic acid and paracetamol) formed [M - H](-) ions. The tested sampling surfaces included various materials with different thermal conductivities. The materials with low thermal conductivity, i.e., polymers like poly(methyl methacrylate) and poly(tetrafluoroethylene) (Teflon) were found to be the best, since they enable localized heating of the sampling surface, which was found to be essential for efficient analyte desorption. Nevertheless, the sampling surface material did not affect the ionization mechanisms.     

Interfacing an ion mobility spectrometry based explosive trace detector to a triple quadrupole mass spectrometer

Hardware from a commercial-off-the-shelf (COTS) ion mobility spectrometry (IMS) based explosive trace detector (ETD) has been interfaced to an AB/SCIEX API 2000 triple quadrupole mass spectrometer. To interface the COTS IMS based ETD to the API 2000, the faraday plate of the IMS instrument and the curtain plate of the mass spectrometer were removed from their respective systems and replaced by a custom faraday plate, which was fabricated with a hole for passing the ion beam to the mass spectrometer, and a custom interface flange, which was designed to attach the IMS instrument onto the mass spectrometer. Additionally, the mass spectrometer was modified to increase the electric field strength and decrease the pressure in the differentially pumped interface, causing a decrease in the effect of collisional focusing and permitting a mobility spectrum to be measured using the mass spectrometer. The utility of the COTS-ETD/API 2000 configuration for the characterization of the gas phase ion chemistry of COTS-ETD equipment was established by obtaining mass and tandem mass spectra in the continuous ion flow and selected mobility monitoring operating modes and by obtaining mass-selected ion mobility spectra for the explosive standard 2,4,6 trinitrotoluene (TNT). This analysis confirmed that the product ion for TNT is [TNT - H](-), the predominant collision-induced dissociation pathway for [TNT- H](-) is the loss of NO and NO(2), and the reduced mobility value for [TNT - H](-) is 1.54 cm(2)V(-1) s(-1). Moreover, this analysis was attained for sample amounts of 1 ng and with a resolving power of 37. The objective of the research is to advance the operational effectiveness of COTS IMS based ETD equipment by developing a platform that can facilitate the understanding of the ion chemistry intrinsic to the equipment.     

Analysis of a retan agent used in the tanning process and its determination in tannery wastewater

The chemical structure and composition of a retan agent, CNSF (condensation product of naphthalenesulfonic acid (NSA) and formaldehyde), and related components contained in tannery wastewaters were analyzed by ion-pair liquid chromatography coupled to electrospray ionization mass spectrometry (IPC-HPLC/ESI-MS) in negative ion mode. This method allows high-resolution separation of polymers. CNSF contained linear NSA oligomers (n = 1-11) that were eluted in order of increasing degree of polymerization. The area under the peaks was correlated to the concentration. The theoretical correlation between retention time and the molecular mass of CNSF oligomers can be used to predict the actual distribution of molecular mass or degree of polymerization. The CNSF consisted of 34.3% monomers, 14.8% dimers, 15.3% trimers and 12.1% tetramers. Other oligomers (n = 5-11) accounted for the remaining 23.5%. Using solid-phase extraction techniques and HPLC/MS, sulfonated monomers, dimers, and trimers were detected in three tannery wastewaters (A-C). Monomers (NSA and naphthalenedisulfonic acid) were one of the major components and ranged from 1.2- (C) to 22.0% (B). Concentrations of 2-naphthalenesulfonic acid were 4.9 mg/L (A), 30.1 mg/L (B), and 0.6 mg/L (C). A high proportion of dimers (18.5%) and trimers (14.5%) were detected in wastewater C, as compared with A (6.4 and 0.7%) and B (3.92 and 0.2%). The method presented allows the analysis of aromatic sulfonates in syntan and tannery wastewater.     

Extraction and isolation of linear alkylbenzenesulfonate and its sulfophenylcarboxylic acid metabolites from fish samples

Linear alkylbenzenesulfonate (LAS) is the most widely used synthetic surfactant. In fish, assessment of the environmental risk and investigation of the biotransformation behavior of LAS require compound-specific methods for extraction and isolation of LAS and its biotransformation products, sulfophenylcarboxylic acids (SPC). Matrix solid-phase dispersion (MSPD) extraction with subsequent ion-pair liquid-liquid (IP-LL) partitioning of the extract was a time-efficient sample preparation method for analysis of LAS. The recovery of parent LAS from spiked fish exceeded 70%, and the limit of quantitation ranged around 0.2 mg.kg-1 corresponding to 0.6 mumol.kg-1. In a simultaneous determination of LAS and SPC in fish, the analytes were MSPD extracted in different fractions. The target compounds were separated from the sample matrix by protein precipitation and subsequent isolation of (a) SPC by graphitized carbon black solid-phase extraction of the supernatant and (b) parent LAS by IP-LL partitioning of the pellet obtained after protein precipitation. The recoveries of the model compounds C12-2-LAS and C4-3-SPC were 84 +/- 6 and 65 +/- 11%, respectively. The use of C3-3-SPC as an internal standard corrected for the loss of the biotransformation product during sample workup. The suitability of both methods was demonstrated by analyzing fish containing LAS and SPC incurred during aqueous exposure.     

Identification of polar toxicants in industrial wastewaters using toxicity-based fractionation with liquid chromatography/mass spectrometry.

An efficient and novel method for the identification of toxic compounds in industrial wastewater was developed. In the first step, the samples collected were tested for toxicity using the recently developed ToxAlert 10 system based upon luminescence inhibition of freeze-dried Vibrio fischeri. In the second step, sequential solid-phase extraction (SSPE) and liquid chromatography/mass spectrometry (LC/MS) for compound identification were employed to isolate and identify compounds in the waters. Average recoveries ranging from 72 to 95% were obtained using the SSPE methodology for ubiquitous analytes such as poly(ethylene glycol)s, nonylphenol and alcohol polyethoxylates, phenols, linear alkylbenzenesulfonates, and benzene- and naphthalenesulfonates. In the third step, all the extracts obtained after SSPE followed by LC/MS identification were tested again with the ToxAlert system. The procedure was applied to influent and effluent samples of a sewage treatment plant (STP) and to a raw tannery effluent that constitutes the main type of influent in the receiving waters of the STP. This method has shown that, despite the complexity of the untreated tannery wastewaters with an average total organic carbon (TOC) value of 1960 mg of C/L, the biological treatment of the STP eliminates compounds that inhibit luminiscence of V. fischeri. In the final step, the chemical toxicity of the tentatively identified chemicals was tested to identify the toxicants in the waters. Comparison of the toxicities of the sample, the extracts, and individual components has shown that diverse classes of pollutants were responsible for toxicity, as all fractions of toxic samples gave significant bioluminescence inhibition values. Toxicity of the two intermediate-polarity SSPE fractions was attributed to alcohol ethoxylates, nonylphenol ethoxylates, bis(2-ethylhexyl)phthalate, and linear alkylbenzenesulfonates. In the most nonpolar and most polar fractions, identification of the compounds responsible for toxicity was unclear. By the toxicity-based fractionation, followed by LC/MS methodology, it was feasible to identify between 1.4 and 7.5% of the TOC, thus expanding the number of toxicants identified in these complex wastewaters as compared to those identified by conventional gas chromatography/mass spectrometric (GC/MS) methods. When artificial water samples were reconstituted using similar concentrations of the chemicals detected in the wastewaters, nonsynergetic toxicity effects were observed for all analytes with the exception of 2,6-naphthalenedisulfonate (2,6-NPS), which promoted the bioluminescence inhibition. The toxicity-directed identification was successful for the STP's samples and showed 1400 times higher toxicity for the raw tannery wastewaters as compared to the mixed industrial and domestic wastewaters by applying the Weibull model.     

Identification and quantification of flavonoids in human urine samples by column-switching liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry

A rapid and sensitive high-performance liquid chromatographic mass spectrometric (HPLC-MS) method is described for the determination and quantification of 12 dietary flavonoid glycosides and aglycons in human urine samples. Chromatographic separation of the analytes of interest was achieved by column-switching, using the first column (a Zorbax 300SB C-3 column) for sample cleanup and eluting the heart-cut flavonoid fraction onto the second column (a Zorbax SB C-18 column) for separation and detection by ultraviolet and atmospheric pressure chemical ionization MS using single ion monitoring in negative mode. The fragmentor voltage was optimized with regard to maximum abundance of the molecular ion and qualifier ions of the analytes. Calibration graphs were prepared for urine, and good linearity was achieved over a dynamic range of 2.5-1000 ng/mL. The inter- and intraassay coefficients of variation for the analysis of the 12 different flavonoids in quality control urine samples were 12.3% on average (range 11.0-13.7%, n = 24, reproducibility) and the repeatability of the assay were 5.0% (mean, range 0.1-14.8%, n = 12). A subset of 10 urine samples from a human dietary intervention study with high and low flavonoid content was analyzed, and the results are reported.     

Characterisation of two chemical compounds formed between hydrated portland cement and benzene-1,2-diol (pyrocatechol)

Exposure to benzene-1,2-diol (pyrocatechol), a common soil contaminant, has been shown to cause loss of strength in concrete. Synthesis and characterisation of two compounds formed when Portland cement comes in contact with benzene-1,2-diol has been conducted. These compounds are (benzene-1,2-diolato(1-))hydroxidocalcium(II) (formula: [Ca(C₆O₂H₅)OH]) and triaqua(benzene-1,2-diol)(benzene-1,2-diolato(1-))hydroxidocalcium(II) (formula: [Ca(C₆O₂H₅)(C₆O₂H₆)(H₂O)₃(OH)]). The compounds may play a role in the deterioration process. Characterisation was conducted in terms of thermal decomposition behaviour, infra-red spectra and crystal structure (using powder X-ray diffraction). The likely thermal decomposition reactions of both compounds have been determined, and features in the infra-red spectra assigned to molecular vibrations. Both structures have been solved, with the exception of the location of some hydrogen atoms, and the structures refined using Rietveld refinement methods. It is anticipated that both the thermal analysis data obtained, and crystal structures deduced, in this article can now be used to quantify these phases in cement and concrete exposed to benzene-1,2-diol.     

Injection port derivatization following ion-pair hollow fiber-protected liquid-phase microextraction for determining acidic herbicides by gas chromatography/mass spectrometry

Injection port derivatization following ion-pair hollow fiber-protected liquid-phase microextraction (LPME) for the trace determination of acidic herbicides (2,4-dichlorobenzoic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 3,5-dichlorobenzoic acid, 2-(2,4,5-trichlorophenoxy)propionic acid) in aqueous samples by gas chromatography/mass spectrometry (GC/MS) was developed. Prior to GC injection port derivatization, acidic herbicides were converted into their ion-pair complexes with tetrabutylammonium chloride in aqueous samples and then extracted by 1-octanol impregnated in the hollow fiber. Upon injection, ion pairs of acidic herbicides were quantitatively derivatized to their butyl esters in the GC injection port. Thus, several parameters related to the derivatization process (i.e., injection temperature, purge-off time) were evaluated, and main parameters affecting the hollow fiber-protected LPME procedure such as extraction organic solvent, ion-pair reagent type, pH of aqueous medium, concentration of ion-pair reagent, sodium chloride concentration added to the aqueous medium, stirring speed, and extraction time profile, optimized. At the selected extraction and derivatization conditions, no matrix effects were observed. This method proved good repeatability (RSDs <12.3%, n = 6) and good linearity (r2 > or = 0.9939) for spiked deionized water samples for five analytes. The limits of detection were in the range of 0.51-13.7 ng x L(-1) (S/N =3) under GC/MS selected ion monitoring mode. The results demonstrated that injection port derivatization following ion-pair hollow fiber-protected LPME was a simple, rapid, and accurate method for the determination of trace acidic herbicides from aqueous samples. In addition, this method proved to be environmentally friendly since it completely avoided open derivatization with potentially hazardous reagents.     

Quantitative analysis of 39 polybrominated diphenyl ethers by isotope dilution GC/low-resolution MS

A GC/low-resolution MS method for the quantitative isotope dilution analysis of 39 mono- to heptabrominated diphenyl ethers was developed. The effects of two different ionization sources, electron impact (EI) and electron capture negative ionization (ECNI), and the effects of their parameters on production of high-mass fragment ions [M - xH - yBr](-) specific to PBDEs were investigated. Electron energy, emission current, source temperature, ECNI system pressure, and choice of ECNI reagent gases were optimized. Previously unidentified enhancement of PBDE high-mass fragment ion [M - xH - yBr](-) abundance was achieved. Electron energy had the largest impact on PBDE high-mass fragment ion abundance for both the ECNI and EI sources. By monitoring high-mass fragment ions of PBDEs under optimized ECNI source conditions, quantitative isotope dilution analysis of 39 PBDEs was conducted using nine (13)C(12) labeled PBDEs on a low-resolution MS with low picogram to femtogram instrument detection limits.     

Achievement of near-reversible behavior for the

Voltammetric studies in the absence of added supporting electrolyte are presently dominated by the use of near-steady-state microelectrode techniques and millimolar or lower depolarizer concentrations. However, with this methodology, large departures from conventional migration-diffusion theory have been reported for the [Fe(CN)6](3-/4-) process at both carbon fiber and platinum microdisk electrodes. In contrast, data obtained in the present study reveal that use of the transient cyclic voltammetric technique at glassy carbon, gold, or platinum macrodisk electrodes and K4[Fe(CN)6] or K3[Fe(CN)6] concentrations of 50 mM or greater provides an approximately reversible response in the absence of added electrolyte. It is suggested that the use of very high [Fe(CN)6](3-) and [Fe(CN)6](4-) concentrations overcomes problems associated with a diffuse double layer and that large electrode surface areas and faster potential sweep rates minimize electrode blockage and passivating phenomena that can plague voltammetric studies at microelectrodes. The cyclic voltammetry of the [Fe(CN)6](3-/4-) couple at a range of concentrations at macroelectrodes in the absence of added inert electrolyte is compared with that obtained in the presence of 1 M KCl. The enhanced influences of uncompensated resistance, migration, and natural convection arising from density gradients under transient conditions at macrodisk electrodes also are considered.     

Electromechanical properties and anisotropy of single- and multi-domain 0.72Pb(Mg(1∕3)Nb(2∕3))O(3)-0.28PbTiO(3) single crystals

Complete sets of elastic, piezoelectric, and dielectric constants of 0.72Pb(Mg(1∕3)Nb(2∕3))O(3)-0.28PbTiO(3) single crystal poled along [111](c) (single domain) as well as non-polar axes [001](c) and [011](c) (multidomain) have been measured under natural conditions. These data allowed us to evaluate accurately the extrinsic contributions to the superior piezoelectric properties. Very large extrinsic contributions to the unusual anisotropies in multidomain crystals are confirmed. We found that the instability of domain structures is the origin of the low mechanical quality factor Q for the multidomain relaxor-based ferroelectric single crystals. Our results can provide useful guidance in future design of domain engineered materials.     

Detection of explosives and related compounds by low-temperature plasma ambient ionization mass spectrometry

Detection of explosives is important for public safety. A recently developed low-temperature plasma (LTP) probe for desorption and ionization of samples in the ambient environment ( Anal. Chem. 2008 , 80 , 9097 ) is applied in a comprehensive evaluation of analytical performance for rapid detection of 13 explosives and explosives-related compounds. The selected chemicals [pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), cyclo-1,3,5-trimethylenetrinitramine (RDX), tetryl, cyclo-1,3,5,7-tetramethylenetetranitrate (HMX), hexamethylene triperoxide diamine (HMTD), 2,4-dinitrotoluene, 1,3-dinitrobenzene, 1,3,5-trinitrobenzene, 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,6-dinitrotoluene, and 4-nitrotoluene) were tested at levels in the range 1 pg-10 ng. Most showed remarkable sensitivity in the negative-ion mode, yielding limits of detection in the low picogram range, particularly when analyzed from a glass substrate heated to 120 °C. Ions typically formed from these molecules (M) by LTP include [M + NO(2)](-), [M](-), and [M - NO(2)](-). The LTP-mass spectrometry methodology displayed a linear signal response over three orders of magnitude of analyte amount for the studied explosives. In addition, the effects of synthetic matrices and different types of surfaces were evaluated. The data obtained demonstrate that LTP-MS allows detection of ultratrace amounts of explosives and confirmation of their identity. Tandem mass spectrometry (MS/MS) was used to confirm the presence of selected explosives at low levels; for example, TNT was confirmed at absolute levels as low as 0.6 pg. Linearity and intra- and interday precision were also evaluated, yielding results that demonstrate the potential usefulness and ruggedness of LTP-MS for the detection of explosives of different classes. The use of ion/molecule reactions to form adducts with particular explosives such as RDX and HMX was shown to enhance the selectivity and specificity. This was accomplished by merging the discharge gas with an appropriate reagent headspace vapor (e.g., from a 0.2% trifluoracetic acid solution).     

Pure low-frequency flexural mode of [011](c) poled relaxor-PbTiO(3) single crystals excited by k(32) mode

Rhombohedral phase relaxor-PbTiO(3) solid solution single crystals poled along [011](c) exhibits superior lateral extensional piezoelectric response, which enables the excitation of a pure low frequency flexural mode with a bridge-type electrode configuration. For the ternary 0.24Pb(In(1/2)Nb(1/2)) O(3)-0.46Pb(Mg(1/3)Nb(2/3))O(3)-0.30PbTiO(3) single crystal poled along [011](c), the electromechanical coupling factor of the flexural mode reached as high as 0.66, and the resonance frequency of this mode can be easily made in kHz range, making it possible to fabricate very small size low frequency sensors and actuators. We have delineated theoretically the coupling between flexural mode and other modes and realized a strong pure flexure mode.