Determination of several pesticides in water by solid-phase extraction, liquid chromatography and electrospray tandem mass spectrometry

The analysis of pesticides in water samples is a problem of primary concern for quality control laboratories due to the toxicity level of these compounds and their public health risk. In order to evaluate the impact of pesticides in the Lisbon drinking water supply system, following the requirements of the European Union Directive 98/83/EC, we developed and validated an analytical method based on the combination of solid-phase extraction with liquid chromatography and tandem mass spectrometry. In this work, several pesticides were studied: imidacloprid, dimethoate, cymoxanil, carbendazime, phosmet, carbofuran, isoproturon, diuron, methidathion, linuron, pyrimethanil, methiocarbe, tebuconazole and chlorpyrifos. Several parameters of the electrospray source were optimized in order to get the best formation conditions of the precursor ion for each pesticide, namely capillary and extractor voltage, cone voltage, cone gas flow rate and desolvation gas flow rate. After optimization of the collision cell energy of the triple quadrupole, two different precursor ion-product ion transitions were selected for each pesticide, one for quantification and one for qualification, and these ions were monitored under time-scheduled multiple reaction monitoring (MRM) conditions. The selection of specific fragment ions for each pesticide guarantees a high degree of selectivity as well as additional sensitivity to quantify trace levels of these pesticides in water samples. This method showed excellent linearity ranges for all pesticides, with correlation coefficients greater than 0.9989. Determination limits (between 0.0041 and 0.0480 microg/L), precision (RSD <9.18%), accuracy and recovery studies in several water samples using solid-phase extraction were also performed.     

Bionanoconjugates of tyrosinase and peptide-derivatised gold nanoparticles for biosensing of phenolic compounds

Bionanoconjugates of the enzyme tyrosinase (TYR) and gold nanoparticles (AuNPs) functionalised with a peptide (CALNN) were produced in solution and characterised. The formation of stable TYR–AuNP:CALNN bionanoconjugates (BNCs) was supported by a decrease of the surface charge of the BNCs as determined by ζ-potential and an increase in hydrodynamic diameter as determined by Dynamic Light Scattering (DLS). UV/Vis studies of pH-induced aggregation revealed distinct protonation patterns for the BNCs when compared with AuNP:CALNN alone, further substantiating BNC formation. Activity studies of the BNCs for the reduction of di-phenols in solution indicated that TYR not only remains active after conjugation, but interestingly its activity in the BNCs is higher than for the free enzyme. In conclusion, AuNP:CALNN can provide a suitable platform for the immobilisation of TYR, leading to BNCs with increased enzyme activity and a wider pH working range, with promising uses in electrochemical biosensors for the detection of mono- and di-phenolic compounds.     

Structural analysis of three methyl N-phosphorylated 5,6-dihydroxy-2-azabicyclo[2.2.1]heptane-3-carboxylates

Both exo and endo isomers of (±)-methyl N-diphenylphosphoryl-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate and (±)-methyl N-diphenylphosphoryloxy-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate were dihydroxylated with OsO₄. The unexpected formation of (±)-methyl 5,6-dihydroxy-N-diphenylphosphoryl-2-azabicyclo[2.2.1]heptane-3-endo-carboxylate from (±)-methyl N-diphenylphosphoryloxy-2-azabicyclo[2.2.1]hept-5-ene-3-endo-carboxylate is discussed based on NMR analyses and experimental observations. The two N-diphenylphosphoryl dihydroxybicycles are analyzed in terms of their crystalline structure by X-ray crystallography.     

New heavy charged leptons at future high energy electron-positron colliders

New heavy charged lepton production and decay signatures at future electron-positron colliders are investigated at GeV. The consequences of model dependence for vector singlets and vector doublets are studied. Distributions are calculated including hadronization effects and experimental cuts that suppress the standard model background. The final state leptonic energy distributions are shown to give a very clear signature for heavy charged leptons.Received: 28 May 2003, Revised: 3 July 2003, Published online: 5 September 2003     

Pseudorapidity distribution of charged particles in d+Au collisions at sqrt[sNN]=200 GeV

The measured pseudorapidity distribution of primary charged particles in minimum-bias d+Au collisions at sqrt[s(NN)]=200 GeV is presented for the first time. This distribution falls off less rapidly in the gold direction as compared to the deuteron direction. The average value of the charged particle pseudorapidity density at midrapidity is |eta|< or =0.6)=9.4+/-0.7(syst) and the integrated primary charged particle multiplicity in the measured region is 82+/-6(syst). Estimates of the total charged particle production, based on extrapolations outside the measured pseudorapidity region, are also presented. The pseudorapidity distribution, normalized to the number of participants in d+Au collisions, is compared to those of Au+Au and p+(-)p systems at the same energy. The d+Au distribution is also compared to the predictions of the parton saturation model, as well as microscopic models.     

High-resolution continuum source electrothermal atomic absorption spectrometry — An analytical and diagnostic tool for trace analysis

The literature about applications of high-resolution continuum source atomic absorption spectrometry (HR-CS AAS) with electrothermal atomization is reviewed. The historic development of HR-CS AAS is briefly summarized and the main advantages of this technique, mainly the ‘visibility’ of the spectral environment around the analytical line at high resolution and the unequaled simultaneous background correction are discussed. Simultaneous multielement CS AAS has been realized only in a very limited number of cases. The direct analysis of solid samples appears to have gained a lot from the special features of HR-CS AAS, and the examples from the literature suggest that calibration can be carried out against aqueous standards. Low-temperature losses of nickel and vanadyl porphyrins could be detected and avoided in the analysis of crude oil due to the superior background correction system. The visibility of the spectral environment around the analytical line revealed that the absorbance signal measured for phosphorus at the 213.6 nm non-resonance line without a modifier is mostly due to the PO molecule, and not to atomic phosphorus. The future possibility to apply high-resolution continuum source molecular absorption for the determination of non-metals is discussed.     

Feasibility of employing permanent chemical modifiers for the determination of cadmium in coal using slurry sampling electrothermal atomic absorption spectrometry

Iridium and ruthenium, alone and in combination with tungsten, thermally deposited on the platform of a transversely heated graphite tube, were investigated for their suitability as permanent chemical modifiers for the determination of cadmium in coal slurries by electrothermal atomic absorption spectrometry (ET AAS). The conventional mixed palladium and magnesium nitrates (Pd–Mg) modifiers, added in solution, were also investigated for comparison. The latter one showed the best performance for aqueous solutions, and the mixed W–Ir and W–Ru permanent modifiers had the lowest stabilizing power. All of the investigated modifiers lost some of their stabilizing power when coal slurries were investigated. The Pd–Mg modifier, pure Ir and Ru, and a mixture of 300 μg W + 200 μg Ir could stabilize Cd at least to a pyrolysis temperature of 600 °C, whereas all the other combinations already failed at temperatures above 500–550 °C. Additional investigations of the supernatant liquid of the slurries supported the assumption that the high acid concentration of the slurries and/or a concomitant leaching out of the coal might be responsible for the reduced stabilizing power of the modifiers. The maximum applicable pyrolysis temperature of 600 °C was not sufficient to reduce the background absorption to a manageable level in the majority of the coal samples. High-resolution continuum source ET AAS revealed that the continuous background absorption was exceeding values of A = 2, and was overlapping with the analyte signal. Although the latter technique could correct for this background absorption, some analyte was apparently lost with the rapidly vaporizing matrix so that the method could not be considered to be rugged. A characteristic mass of 1.0 pg and a detection limit of 0.6 ng g^− 1 could be obtained under these conditions.     

Synthesis of imidazolidin-4-one and 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-dione derivatives of primaquine: scope and limitations

The synthesis of imidazolidin-4-one derivatives of primaquine as potential antimalarial agents is described. The target compounds were synthesized in three steps: (i) condensation of (±)-primaquine with N^α-protected amino acids, (ii) removal of the N^α-protecting group, and (iii) reaction of the N-acylprimaquine with a carbonyl compound: acetone, three cyclic ketones and veratraldehyde. Using 2-formylbenzoic acid in the third step afforded 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-diones. All products were isolated in good to excellent yields. Whereas imidazolidin-4-ones were formed as mixtures of all possible diastereomers in equal amounts, 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-diones were produced in a stereoselective fashion. The compounds hydrolyse very slowly (t_1/2 5-30 d) in pH 7.4 buffer to release primaquine. These primaquine derivatives are being submitted to biological assays, and preliminary results of their antimalarial activity are quite encouraging.     

Stereoselective synthesis of polyhydroxylated pyrrolidines: a route to novel 3,5-bis(hydroxymethyl)pyrrolidines from 2-azabicyclo[2.2.1]hept-5-enes

An efficient preparation of racemic and chiral 2-functionalized-3,5-bis(hydroxymethyl)pyrrolidines is described. The method uses 2-azabicyclo[2.2.1]hept-5-enes, readily obtained from glyoxylates of aliphatic amines and cyclopentadiene, as starting material. The hydroxylation of the double bond followed by the oxidative cleavage of the six-membered ring and in situ reduction of the dialdehyde intermediate gives the title pyrrolidines.