Use of different stationary phases for separation of isoniazid, its metabolites and vitamin B6 forms

The ability of different stationary phases developed for the analysis of polar compounds (ZIC-HILIC, ZIC-pHILIC and Zorbax SB-Aq) to separate isoniazid, its metabolites (acetylisonazid, pyridoxal isonicotinoyl hydrazone, pyridoxal isonicotinoyl hydrazone 5-phosphate), pyridoxine, pyridoxal and pyridoxal 5-phosphate under MS compatible conditions was systematically investigated using HPLC-UV. The mobile phase strength, pH and buffer concentration were modified to assess their impact on the retention of these compounds. The best available separation of the compounds was achieved using 1 mM ammonium formate (pH≈6) and ACN (20:80, v/v) on ZIC-HILIC and employing 5 mM ammonium formate (pH 3.0) and ACN (40:60, v/v) on ZIC-pHILIC. A gradient profile using 0.5 mM ammonium formate (pH≈6) and MeOH (0-12 min: 10% MeOH, 12-15 min: 10-50% MeOH, 15-35 min: 50% MeOH, 35.0-35.2 min: 50-10% MeOH, 35.2-45.0 min: 10% MeOH) provided the best separation of the compounds on Zorbax SB-Aq. Subsequent LC-MS analysis demonstrated that ZIC-HILIC is useful for the analysis of pyridoxine, pyridoxal and pyridoxal isonicotinoyl hydrazone. However, the chromatographic conditions developed for the analysis of the compounds on Zorbax SB-Aq are capable of achieving the best separation of all compounds in this study with the higher sensitivity for most of the analytes.     

Determination of fumonisins B1 and B2 in corn-based foods for infants and young children by LC with immunoaffinity column cleanup: interlaboratory validation study

A liquid chromatographic method for the determination of fumonisins B1 (FB1) and B2 (FB2) in corn-based foods for infants and young children was subjected to an interlaboratory validation study involving 11 laboratories. Five blind duplicate sample pairs of each matrix were analyzed to establish the accuracy, repeatability, and reproducibility of the method. Mass fractions in the baby food samples ranged from 89.1 to 384.4 microg/kg FB1 and from 22.5 to 73.6 microg/kg FB2. The method involved a warm extraction with citrate phosphate buffer-methanol-acetonitrile (50 + 25 + 25, v/v/v), a cleanup through an immunoaffinity column, and an end-determination of fumonisins by LC after automated precolumn derivatization with o-phthaldialdehyde reagent. RSDs for within-laboratory repeatability (RSDr) ranged from 6.8 to 23.5% for FB1 and 7.6 to 22.9% for FB2. RSDs for between-laboratory reproducibility (RSDR) ranged from 15.4 to 26.2% for FB1 and 21.6 to 36.3% for FB2. Mean FB1 recoveries from baby foods spiked at 100.0 and 250.0 microg/kg were 89 and 96%, respectively; for FB2 spiked foods at 25.0 and 62.5 microg/kg recoveries were 90 and 85%, respectively. HorRat values ranged from 0.8 to 1.2 for FB1, whereas for FB2 they ranged from 0.9 to 1.4 when calculated according to Horwitz, and from 1.0 to 1.7 when calculated according to Thompson, indicating an acceptable among-laboratory precision for all matrixes (HorRat values <2).     

Nonaqueous and aqueous-organic media for the enantiomeric separations of neutral organophosphorus pesticides by CE

The enantiomeric separation of some poorly water-soluble organophosphorus pesticides (OPs) has been investigated using nonaqueous solvent and aqueous-organic solvent systems. In this work, sodium cholate (SC) either with SDS or gamma-CD was used to achieve enantiomeric separations of four neutral and poorly water-soluble OPs, i.e., profenofos, prothiofos, sulprofos, and pyraclofos. Electrophoretic medium consisted of a mixture of methanol (MeOH) with ACN (4:1 v/v) or a mixture of MeOH with H(2)O and ACN (5:4:1 v/v/v). On one hand, NACE was applied for enantiomeric separation of pyraclofos using a large amount of chiral and achiral surfactants (SC and SDS). On the other hand, H(2)O was added to act as a solvent additive to increase the solubility of gamma-CD in the organic solvents such as MeOH and ACN, in which the solubility of gamma-CD was very low. The presence of H(2)O was found to be particularly useful for the enantiomeric separation of profenofos, prothiofos, and sulprofos. In this way, the range of application of the neutral CDs in CE has been extended. In addition, SC was used as the only electrolyte. The proposed method has been applied for the analysis of soil samples.     

Determination of type B fumonisin mycotoxins in maize and maize-based products by liquid chromatography/tandem mass spectrometry using a QqQlinear ion trap mass spectrometer

A sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for determining the type B fumonisin mycotoxins in corn-based foodstuffs is described. Fumonisins FB1 and FB2 were extracted from a 1 g sample by homogenization with acetonitrile/water (75:25, v/v, 50 mmol/L formic acid, 25 mL final volume) and the extract was defatted on C18 phase. Volumes of 5 mL of crude extracts were cleaned up on Carbograph-4 cartridges. The final solution was analyzed by HPLC with electrospray ionization mass spectrometry in positive ion mode using multiple reaction monitoring with a QqQ linear ion trap mass spectrometer. Recoveries for spiked corn-based foodstuffs ranged from 91-105% (RSD% < or =8%), and method detection limits were < or =2 ng/g for FB1 and < or =1 ng/g for FB2. Two different spiking levels were tested (5000 and 100 ng/g for FB1, 1000 and 20 ng/g for FB2). Quantitation was achieved by an external calibration procedure using matrix-matched standards, with diclofenac added post-cleanup as internal standard for the LC/MS/MS analyses. Calibration curves showed linearity in the concentration range 0.005-5 ng/microL of final extract (0.992 < or = R2< or =0.995). Two other fumonisins, FB3 and FB4, were identified in naturally contaminated samples of corn meal using an information-dependent acquisition protocol that looped three experiments, including neutral loss scan, enhanced resolution scan, and enhanced product ion scan. FB3 and FB4 quantitation was estimated as peak area ratios relative to the FB2 response in view of the lack of both standards. This work also includes an application of the present LC/MS/MS method to some maize and maize-based product samples (corn meal, cornflakes and popcorn) collected from Italian stores. FB1 and FB2 contamination levels exceeding the European Union recommendation were found in 8 out of 15 corn meal samples.     

Analysis of fumonisins B(1), B(2) and B(3) in corn-based baby food by pressurized liquid extraction and liquid chromatography/tandem mass spectrometry

A sensitive and reliable method using pressurized liquid extraction (PLE) and liquid chromatography (LC)/electrospray ionization (ESI) tandem mass spectrometry with a triple quadrupole (QqQ) analyzer has been developed for the analysis of fumonisin B(1) (FB(1)), fumonisin B(2) (FB(2)) and fumonisin B(3) (FB(3)) in corn-based baby foods. Influence of several extraction parameters that affect PLE efficiency such as temperature, pressure, solvent extraction, number of cycles and dispersant/clean-up agents were studied. The selected PLE operating method was: 3g of sample was packed into 11 ml stainless-steel cell and fumonisins were extracted with methanol at 40 degrees C, 34 atm in one cycle of 5 min at 60% flush. The analytes were ionized in ESI operating with positive ion mode and identified by selecting two monitoring transitions, permitting quantification and confirmation in a single injection. Recoveries ranged from 68% to 83% at fortification levels of 200 microg kg(-1) with relative standard deviation (RSD) from 4% to 12%. The limits of quantification were from 2 microg kg(-1) for FB(1) and FB(2), and 5 microg kg(-1) for FB(3), which are below the maximum residue level established by the European Union legislation in infant formulas. The proposed method was successfully applied to the analysis of twenty seven samples of baby food products collected from different markets, and one positive sample with a content of 15.9 microg kg(-1) for FB(1), 9.2 microg kg(-1)for FB(2) and 5.8 microg kg(-1) for FB(3) was obtained. Given the simplicity and potential of the proposed procedure, its application for safety control is recommended.     

Determination of fumonisins B1 and B2 in corn by liquid chromatography/mass spectrometry with immunoaffinity column cleanup: single-laboratory method validation

A single-laboratory method validation was conducted to establish the effectiveness of an immunoaffinity column cleanup procedure followed by liquid chromatography/mass spectrometry (LCIMS) for the determination of fumonisins B1 and B2 (FBI + FB2) in corn. The test portion is extracted with acetonitrile-methanol-water (25 + 25 + 50). The extract is filtered, diluted with phosphate-buffered saline solution, and applied to an immunoaffinity column. FB1 + FB2 are removed with methanol and directly determined by reversed-phase LC with MS detection using selected-ion monitoring of 2 characteristic ions in each case. Test portions of blank corn samples were spiked with a mixture of FB1 + FB2 to give total levels of 200 and 500 ng/g, respectively. Recoveries of both FB1 and FB2 from spiked samples averaged 90.4-101%. Based on results for spiked raw corn (triplicates at 2 levels), the relative standard deviation for repeatability ranged from 2.8 to 7.1%. The accuracy of the method was demonstrated by analysis of Food Analysis Performance Assessment Scheme (FAPAS) test material. The method was also applied to a small survey of processed corn products such as corn chips, cornflakes, and popcorn.     

Determination of fumonisins B1 and B2 in corn and corn flakes by liquid chromatography with immunoaffinity column cleanup: collaborative study.

A liquid chromatographic (LC) method for the determination of fumonisins B1 (FB1) and B2 (FB2) in corn and corn flakes was collaboratively studied by 23 laboratories, which analyzed 5 blind duplicate pairs of each matrix to establish the accuracy, repeatability, and reproducibility characteristics of the method. Fumonisin levels in the corn ranged from <0.05 (blank) to 1.41 microg/g for FB1 and from <0.05 to 0.56 microg/g for FB2, whereas in the corn flakes they ranged from <0.05 to 1.05 microg/g for FB1 and from <0.05 to 0.46 microg/g for FB2. The method involved double extraction with acetonitrile-methanol-water (25 + 25 + 50), cleanup through an immunoaffinity column, and LC determination of the fumonisins after derivatization with o-phthaldialdehyde. Relative standard deviations for the within-laboratory repeatability (RSDr) of the corn analyses ranged from 19 to 24% for FB1 and from 19 to 27% for FB2; for the corn flakes analyses, RSDr ranged from 9 to 21 % for FB1 and from 8 to 22% for FB2. Relative standard deviations for the between-laboratories reproducibility (RSDR) of the corn analyses ranged from 22 to 28% for FB1 and from 22 to 30% for the FB2; for corn flakes analyses, RSDR ranged from 27 to 32% for FB1 and from 26 to 35% for FB2. Mean recoveries of FB1 and FB2 from corn spiked with FB1 at 0.80 microg/g and with FB2 at 0.40 microg/g were 76 and 72%, respectively; for corn flakes spiked at the same levels recoveries were 110 and 97% for FB1 and FB2, respectively. HORRAT ratios for the analyses of corn ranged from 1.44 to 1.53 for FB1 and from 0.96 to 1.48 for FB2, whereas for corn flakes they ranged from 1.60 to 1.82 for FB1 and from 1.39 to 1.68 for FB2.     

Combined column–mobile phase mixture statistical design optimization of high-performance liquid chromatographic analysis of multicomponent systems

A statistical approach for the simultaneous optimization of the mobile and stationary phases used in reversed-phase liquid chromatography is presented. Mixture designs using aqueous mixtures of acetonitrile (ACN), methanol (MeOH) and tetrahydrofuran (THF) organic modifiers were performed simultaneously with column type optimization, according to a split-plot design, to achieve the best separation of compounds in two sample sets: one containing 10 neutral compounds with similar retention factors and another containing 11 pesticides. Combined models were obtained by multiplying a linear model for column type, C8 or C18, by quadratic or special cubic mixture models. Instead of using an objective response function, combined models were built for elementary chromatographic criteria (retention factors, resolution and relative retention) of each solute or pair of solutes and, after their validation, the global separation was accomplished by means of Derringer's desirability functions. For neutral compounds a 37:12:8:43 (v/v/v/v) percentage mixture of ACN:MeOH:THF:H₂O with the C18 column and for pesticides a 15:15:70 (v/v/v) ACN:THF:H₂O mixture with the C8 column provide excellent resolution of all peaks.     

Pharmaceutical analysis by supercritical fluid chromatography: Optimization of the mobile phase composition on a 2-ethylpyridine column

The separation of neutral, acidic, and basic pharmaceuticals with diverse physicochemical properties by packed column supercritical fluid chromatography (pSFC) on a 2-ethylpyridine column (25 cmx4.6 mm id, 3 mum particles) is presented. The optimization strategy involved separations at 100% methanol (MeOH) and at 50% MeOH/50% ACN while keeping the peak symmetry additives formic acid (FA) and isopropylamine (IPA) at constant levels of 0.25% v/v. By plotting the adjusted retention times as a function of the MeOH/ACN ratio, an optimal modifier ratio composition of 65% MeOH/35% ACN was found. The total set of 26 neutral, acidic, and basic pharmaceuticals was analyzed and the optimal composition experimentally verified. This mobile phase composition is currently used in pharmaceutical method development and open-access generic screening environments.     

Single-molecule magnets: a Mn25 complex with a record S = 51/2 spin for a molecular species

The reaction of MnCl2.4H2O (3 equiv), pyridine-2,6-dimethanol (pdmH2) (10 equiv), and NaN3 (10 equiv) in MeOH/MeCN (1:2 v/v) with NMe4OH (1 equiv) gave [Mn25O18(OH)2(N3)12(pdm)6(pdmH)6](Cl)2.12MeCN (1.12MeCN) in approximately 30% yield. The cation of complex 1 comprises five Mnx layers of three types in an ABCBA arrangement. Fitting of variable-temperature and -field magnetization data establishes that 1 has an S = 51/2 ground state, the largest value for a molecular species. The complex also displays hysteresis loops below 0.6 K in magnetization vs applied field sweeps, establishing it as the largest spin single-molecule magnet to date.     

Validated LC Method for Determination of Enantiomeric Purity of Apremilast Using Polysaccharide-Type Stationary Phases in Polar Organic Mode

Enantioseparation of an anti-psoriatic agent, apremilast (APR), was performed by HPLC using polysaccharide-type chiral stationary phases in polar organic mode for the first time. The separation capability of six different chiral columns (Chiralpak AD, Chiralpak IA, Chiralpak AS, Lux Amylose-2, Chiralcel OD and Chiralcel OJ-H) was investigated using neat MeOH and ACN. During the preliminary experiments the best results were obtained on Chiralpak IA column with ACN (R_s?=?5.4). The effects of binary mobile phases on the resolutions and retention factors were also investigated containing different percentages of MeOH:ACN. U-shaped retention pattern was obtained when plotting the retention factors of the APR enantiomers versus the MeOH content of the binary mobile phases on Chiralpak IA column. For further method optimizations an L25 orthogonal array table was employed altering the concentration of MeOH in ACN, column temperature, and flow rate. The best result was achieved on Chiralpak IA column with 80/20 (v/v%) MeOH/ACN with 0.7 mL min^?1 flow rate at 25 °C (R_s?=?5.4, t₂?=?7.45 min). Thermodynamic analysis revealed an enthalpy-driven enantioseparation. The developed HPLC method was validated according to the ICH guideline Q2(R1) and proved to be reliable, linear, precise and accurate for the determination of 0.1% R-enantiomer as chiral impurity in S-APR as well as quantification of the S-enantiomer.

Graphical Abstract

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CE hydrogen deuterium exchange-MS in peptide analysis

CE and hydrogen-deuterium (H/D) exchange MS are useful tools in the analysis and characterisation of peptides. This study reports the facile coupling of these tools in the H/D exchange CE-MS analysis of model and pharmaceutically important peptides, using a sheath flow interface. The peptides varied in mass from 556 (leucine enkephalin) to 1620 Da (bombesin), and in charge state from 0.33 (leucine enkephalin) to 3.0 (substance P). The application of a BGE composed of ammonium formate buffer (25 mM, pD 3.5 in D(2)O (>98% D atom)), a sheath liquid composed of formic acid (0.25% v/v in D(2)O) and ACN (30:70 v/v), and dissolving the samples in a mixture of ACN/D(2)O (50:50 v/v) facilitates complete H/D exchange. Because of complete H/D exchange the ESI mass spectra produced are easy to interpret and comparable to those obtained from LC-MS analysis. The CE-H/D-MS approach has the advantage of requiring lower volumes of deuterated solvents. The b- and y-series fragments produced by using in-source decomposition correspond to those predicted. With the peptides studied, the complete exchange H/D exchange observed with both the molecular and fragment ions helps to confirm both amino acid composition and sequence.     

Molecularly imprinted polymers applied to the clean-up of zearalenone and α-zearalenol from cereal and swine feed sample extracts

A molecularly imprinted polymer prepared using 1-allylpiperazine (1-ALPP) as the functional monomer, trimethyltrimethacrylate (TRIM) as the crosslinker and the zearalenone (ZON)-mimicking template cyclododecanyl-2,4-dihydroxybenzoate (CDHB) has been applied to the clean-up and preconcentration of this mycotoxin (zearalenone) and a related metabolite, alpha-zearalenol (alpha-ZOL), from cereal and swine feed sample extracts. The extraction of ZON and alpha-ZOL from the food samples was accomplished using pressurized liquid extraction (PLE) with MeOH/ACN (50:50, v/v) as the extraction solvent, at 50 degrees C and 1500 psi. The extracted samples were cleaned up and preconcentrated through the MIP cartridge and analyzed using HPLC with fluorescence detection (lambda (exc)=271/ lambda (em)=452 nm). The stationary phase was a polar endcapped C18 column, and ACN/MeOH/water 10/55/35 (v/v/v, 15 mM ammonium acetate) at a flow rate of 1.0 mL min(-1) was used as the mobile phase. The method was applied to the analysis of ZON and alpha-ZOL in wheat, corn, barley, rye, rice and swine feed samples fortified with 50, 100 and 400 ng g(-1) of both mycotoxins, and it gave recoveries of between 85 and 97% (RSD 2.1-6.7%, n=3) and 87-97% (RSD 2.3-5.6%, n=3) for alpha-ZOL and ZON, respectively. The method was validated using a corn reference material for ZON.     

Chiral capillary electrophoretic determination of the enantiomeric purity of homocamptothecin derivatives, promising antitumor topoisomerase I inhibitors, using highly sulfated CDs and fluorescence detection

EKC methods for the enantiomeric resolution of homocamptothecin derivatives, potent anticancer agents targeting DNA topoisomerase I selected for clinical trials, were developed using highly sulfated beta-CD as chiral selectors at acidic pH. Optimal electrophoretic conditions, with migration times under 15 min, were as follows: for the neutral homocamptothecin analog 1, a BGE of 75 mM phosphate buffer pH 2.5 (H(3)PO(4) + triethanolamine)/ACN - 95/5 v/v, with 7.5% w/v highly S-beta-CD, an applied field of 0.2 kV/cm and a fused capillary temperature control of 30 +/- 0.1 degrees C (typical current approximately 175 microA); for the cationic homocamptothecin 2, a BGE of 25 mM phosphate buffer pH 2.5 (H(3)PO(4) + TEA)/ACN - 90/10 v/v, with 2.5% w/v highly S-beta-CD, an applied field of 0.15 kV/cm and a fused capillary temperature control of 25 +/- 0.1 degrees C (typical current approximately 45 muA), and both are validated. The best results in terms of LOQ were obtained by EC with fluorescence detection: 10 ng/mL and 20 ng/mL for 1 and 2, respectively (LOQ divided by 150 for 1 and 5 for 2 with respect to UV), thus making this method particularly convenient for enantiomeric purity determination of galenic forms. UV detection appears to be an alternative to fluorescence for the analysis of the main component either for the control of galenic forms or for therapeutic adaptation. Moreover, this method exhibits better performances than HPLC.     

Development and validation of an HPLC method for the determination of penicillin antibiotics residues in bovine muscle according to the European Union Decision 2002/657/EC

A high-performance liquid chromatographic method was developed for the determination of five penicillins: penicillin G (PENG), penicillin V (PENV), oxacillin (OX), cloxacillin (CLO), and dicloxacillin (DICLO), in bovine muscle. Samples were macerated with a mixture of H(2)O/CH(3)CN (1:1) and purified using RP-8 Adsorbex SPE cartridges after centrifugation, with mean recovery from spiked samples higher than 89%. The separation of the examined penicillins was achieved on an analytical column, an Inertsil C8 5 microm, 250x4 mm(2), at ambient temperature. The mobile phase consisted of 0.1% TFA/ACN 50:50 v/v delivered isocratically at a flow rate of 1.1 mL/min. Analytes were monitored at 240 nm. The procedure was validated according to the European Union Decision 2002/657/EC by means of selectivity, stability, decision limit, detection capability, accuracy, and precision. Method's LOQ values achieved were 54 microg/kg for PENG and DICLO, 46 microg/kg for PENV, 16 microg/kg for OX, and 43 microg/kg for DICLO. The detection capabilities (CC(beta)) were 73.6 microg/kg for PENG, 29.1 microg/kg for PENV, 350.6 microg/kg for OX, 379.9 microg/kg for CLO, and 355.8 microg/kg for DICLO. The method was applied to various samples from the local market. Two penicillins were identified by photodiode array (PDA) detection and quantified.     

Preparative isolation of alkaloids from Corydalis bungeana Turcz. by high-speed counter-current chromatography using stepwise elution

High‐speed counter‐current chromatography (HSCCC) was successfully applied for the preparative separation and purification of alkaloids from Corydalis bungeana Turcz. (Kudiding in Chinese) for the first time. After the measurement of partition coefficient of seven target alkaloids in the nine two‐phase solvent systems composed of CHCl₃–MeOH–(0.1 M; 0.2 M; 0.3 M) HCl (4:1.5:2; 4:2:2; 4:3:2, v/v), CHCl₃–MeOH–0.2 M HCl (4:2:2, v/v) and CHCl₃–MeOH–0.3 M HCl (4:3:2, v/v) were finally selected for the HSCCC separation using the first upper phase as the stationary phase and the stepwise elution of the two lower mobile phases. Consequently, sanguinarine (10 mg), corynoline (25 mg), protopine (20 mg), corynoloxine (18 mg), and 12‐hydroxycorynoline (8 mg) were obtained from 200 mg of crude alkaloid extracts with purities of 94–99% as determined by HPLC. Their chemical structures were characterized on the basis of ¹H‐NMR, ¹³C‐NMR, and LC‐ESI‐Q‐TOF‐MS/MS analyses.     

Very strong C-H...O, N-H...O, and O-H...O hydrogen bonds involving a cyclic phosphate.

Very short C-H...O, N-H...O, and O-H...O hydrogen bonds have been generated utilizing the cyclic phosphate [CH2(6-t-Bu-4-Me-C6H2O)2]P(O)OH (1). X-ray structures of (i) 1 (unsolvated, two polymorphs), 1...EtOH, and 1...MeOH, (ii) [imidazolium](+)[CH2(6-t-Bu-4-Me-C6H2O)2PO2](-)...MeOH [2], (iii) [HNC5H4-N=N-C5H4NH](2+)[(CH2(6-t-Bu-4-Me-C6H2O)2PO2)2](2-)...4CH3CN...H2O [3], (v) [K, 18-crown-6](+)[(CH2(6-t-Bu-4-Me-C6H2O)2P(O)OH)(CH2(6-t-Bu-4-Me-C6H2O)2PO2)](-)...2THF [4], (vi) 1...cytosine...MeOH [5], (vii) 1...adenine...1/2MeOH [6], and (viii) 1...S-(-)-proline [7] have been determined. The phosphate 1 in both its forms is a hydrogen-bonded dimer with a short O-H...O distance of 2.481(2) [triclinic form] or 2.507(3) A [monoclinic form]. Compound 2 has a helical structure with a very short C-H...O hydrogen bond involving an imidazolyl C-H and methanol in addition to N-H...O hydrogen bonds. A helical motif is also seen in 5. In 3, an extremely short N-H...O hydrogen bond [N...O 2.558(4) A] is observed. Compounds 6 and 7 also exhibit short N-H...O hydrogen bonds. In 1...EtOH, a 12-membered hydrogen-bonded ring motif, with one of the shortest known O-H...O hydrogen bonds [O...O 2.368(4) A], is present. 1...MeOH is a similar dimer with a very short O(-H)...O bond [2.429(3) A]. In 4, the deprotonated phosphate (anion) and the parent acid are held together by a hydrogen bond on one side and a coordinate/covalent bond to potassium on the other; the O-H...O bond is symmetrical and very strong [O...O 2.397(3) A].     

Simultaneous determination of seven pesticides in waters using multi-walled carbon nanotube SPE and NACE

In this work, NACE with UV detection is combined with SPE using multi-walled carbon nanotubes (MWCNT) as stationary phase to determine a group of seven pesticides (pirimicarb, pyrifenox, penconazol, carbendazim, cyromazine, pyrimethanil and cyprodinil) in mineral water samples using ametryn as internal standard. The optimized BGE, consisting of a mixture of MeOH and ACN (1:2 v/v) with 90 mM SDS and 20.5 mM HClO(4), was satisfactory to get a good resolution of the seven compounds in less than 13 min. On-line preconcentration was carried out by electrokinetic injection of the sample dissolved in 78:22 v/v MeOH/ACN, 1.11 mM HClO(4). Repeatability was studied for the same day (n=4), for nine different days (n=36) and for four different capillaries. RSD values were appropriate in all cases, i.e. in the range 4.3-9.4% between different capillaries. MWCNT of 10-15 nm od, 2-6 nm id and 0.1-10 mum length were used as SPE materials for the preconcentration of these pesticides from water samples. SPE parameters influencing the enrichment were optimized and the most favorable conditions were as follows: the amount of stationary phase, eluent, sample pH and sample volume were 40 mg MWCNT, 10 mL ACN and 10 mL dichloromethane containing 5% v/v formic acid, pH 8.0, and 750 mL, respectively. Mean recovery values ranged between 53 and 94% for Milli-Q water and between 47 and 93% for mineral waters (RSD values were in the range 2-16%). The method allowed the determination of these pesticides at concentrations below the maximum residue limits established by the European Union legislation (LOD in the range 27-58 ng/L). When the cost, amount and type of the carbon nanotubes used in this work are compared with those carbon nanotubes previously used in the literature it is clear that the proposed materials can be used as economical stationary phases, even cheaper than conventional SPE cartridges.     

From pseudo to true C(3) symmetry: magnetic anisotropy enhanced by site-specific ligand substitution in two Mn(15)-carboxylate clusters

Two new mixed-valence manganese-carboxylate clusters, [MnIII9MnIV6(O2CPh)12(micro3-O)13(micro-O)4(micro-OMe)5(MeOH)4(H2O)5]2.1.5PhCO2H.MeOH.6H2O (1, PhCO2H = benzoic acid) and [MnIII9MnIV6(O2CCh)12(micro3-O)13(micro-O)4(micro-OMe)5(MeOH)3(H2O)6].0.5MeOH.2.5H2O (2, ChCO2H= cyclohexanecarboxylic acid) contain new disklike Mn15 cores. Both 1 and 2 can be synthesized by the conventional manganese redox reaction (MnO4- oxidizing Mn2+) in methanol solution. 2 can be also synthesized via the site-specific ligand substitution reaction from 1. 1 crystallizes in the triclinic space group P, whereas 2 crystallizes in the trigonal space group P. Magnetic study shows that both 1 and 2 have the same ground spin states ST = 2. Compared to the silence of the out-of-phase ac susceptibility of 1, 2 shows clearly slow magnetic relaxation behavior above 1.8 K due to the dramatically enhanced axial magnetic anisotropy (D = -0.89 and -1.58 cm-1 for 1 and 2, respectively, which was obtained by fitting the plots of M vs H/T with the program ANISOFIT 2.0).     

Development of a NACE method for simultaneous measurement of three adenosine monophosphate isomers in biomimicking prebiotic synthesis without sample pretreatment

A practical NACE method was developed for simultaneous determination of three adenosine monophosphate (AMP) isomers. Separation of three AMP isomers was achieved using 200 mM Tris/H(3)BO(3) in acetontrile/water (2:1 v/v) at pH* 10.0 as the running buffer and +25 kV as the applied voltage over a bare fused-silica capillary of 50 microm id x 375 microm od x 54.5 cm (46 cm to the detector window). At 260 nm, the calibration curves were linear in the range of 1-100 microg/mL. The detection limits were less than 0.70 microg/mL. The recovery ranged from 94.5 to 106.4%. The intraday RSDs of the migration times were between 2.1 and 3.0%. The developed NACE method has been successfully applied for the determination of three AMP isomers in the real samples of biomimicking prebiotic synthesis reaction between N-(O,O-diisopropyl) phosphoryl amino acid and adenosine.