Search

A quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was developed and combined with liquid chromatography-tandem mass spectrometry to analyze 12 acidic pesticides in cabbage and spinach. The extraction solvents, phase partition salts and sorbents effect was studied to optimize the method followed by dilution before sample injection. The extraction involved 5% formic acid in acetonitrile, and the liquid-liquid partition was salt-induced. Carbopack Z, a high surface area graphitized carbon black, was a new sorbent used in the clean-up. The results show that Carbopack Z effectively removes interferences with little loss of acidic pesticides. All tested pesticide recoveries were satisfactory when Carbopack Z was combined with C18 in the clean-up at optimized condition. After clean-up, the extract was subjected to 10-fold dilution to sufficiently reduce the matrix effect (20%). The limit of quantification (LOQ) was 1-5 ng/g, and the mean recovery was between 95 and 110% with a relative standard deviation20% (between 2% and 10%) for the spiking of three concentrations: 5, 50, and 500 ng/g. The extract was less pigmented in the modified QuEChERS method than its original version. Thus, the modified method is a useful alternative for investigating the acidic pesticide residues in cabbage and spinach.

This article describes the comparison of different versions of an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits and vegetables by concurrent use of gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) for detection. The sample preparation approach is known as QuEChERS, which stands for "quick, easy, cheap, effective, rugged and safe". The three compared versions were based on the original unbuffered method, which was first published in 2003, and two interlaboratory validated versions: AOAC Official Method 2007.01, which uses acetate buffering, and European Committee for Standardization (CEN) Standard Method EN 15662, which calls for citrate buffering. LC-MS/MS and GC-MS analyses using each method were tested from 50 to 1000ng/g in apple-blueberry sauce, peas and limes spiked with 32 representative pesticides. As expected, the results were excellent (overall average of 98% recoveries with 10% RSD) using all 3 versions, except the unbuffered method gave somewhat lower recoveries for the few pH-dependent pesticides. The different methods worked equally well for all matrices tested with equivalent amounts of matrix co-extractives measured, matrix effects on quantification and chemical noise from matrix in the chromatographic backgrounds. The acetate-buffered version gave higher and more consistent recoveries for pymetrozine than the other versions in all 3 matrices and for thiabendazole in limes. None of the versions consistently worked well for chlorothalonil, folpet or tolylfluanid in peas, but the acetate-buffered method gave better results for screening of those pesticides. Also, due to the recent shortage in acetonitrile (MeCN), ethyl acetate (EtOAc) was evaluated as a substitute solvent in the acetate-buffered QuEChERS version, but it generally led to less clean extracts and lower recoveries of pymetrozine, thiabendazole, acephate, methamidophos, omethoate and dimethoate. In summary, the acetate-buffered version of QuEChERS using MeCN exhibited advantages compared to the other tested methods in the study.

A new polymeric Fe(II) chloride complex, [FeCl2(OPMe3)]∞ (1), has been synthesized from the reaction of stoichiometric quantities of FeCl3, Fe and OPMe3 (2:1:3) in THF. Use of a 2:1:6 ratio in the above reaction gives instead the mononuclear complex FeCl2(OPMe3)2 (2). The structure of the polymer consists of infinite chains of FeCl2(OPMe3) units, where each Fe atom is linked by four bridging chlorine atoms to two other Fe atoms. The arrangement of the four chlorine atoms and one OPMe3 molecule around the iron atom results in a trigonal bipyramidal coordination geometry. Complex 2 has tetrahedral geometry. The magnitudes of the magnetic moments for 1 and 2 at room temperature are 4.90 and 5.51 BM, respectively, indicative of high spin Fe2+. In 1, two different Fe…Fe distances 3.560(0) and 3.688(0) A alternate along the chain, the FeCl bond distances are in the range 2.35–2.60 A, the FeO distance is 1.954(2) A and the PO distance is 1.513(2) A. In 2, the FeCl distances average to 2.291(4) A, the average FeO and PO distances are 1.994(2) and 1.504(1) A, respectively. Crystallographic data: 1, monoclinic, space group P21/n, a=6.810(2), b=12.943(5), c=9.645(2) A, β=100.224(2)°, V=836.6(11) A3, Z=4, R=O.041 (Rw=0.058) for 101 parameters and 1665 unique data having Fo2>3σ(Fo2). 2, orthorhombic, space group P212121, a=11.270(3), b=12.011(2), c=10.811(2) A, V=1463.5(5) A3, Z=4, R=0.052 (Rw=0.064) for 142 parameters and 1356 unique data having Fo2>3σ(Fo2).

A new polynuclear compound of Fe(II) chloride with oxygen donor ligands has been isolated as a colorless crystalline solid, Fe4Cl8(THF)6 (1), by the reaction of FeCl3 and Fe in THF. 1 consists of centrosymmetric, tetranuclear molecules with two different types of Fe atoms, two (Fe(1) and Fe(1)′) in trigonal bipyramidal environments and the others (Fe(2) and Fe(2)′) in octahedral environments. Each trigonal bipyramidally coordinated iron atom is linked through doubly- and triply-shared chlorine atoms to an iron atom in an octahedral environment. The magnetic moment of 1, per iron atom, at room temperature is 5.40 BM, which is a reasonable value for high spin Fe2+. The Fe…Fe distances are 3.656(1) and 3.750(1) A for Fe(1)…Fe(2) and Fe(2)…Fe(2)′, respectively. The order of FeCl distances, Fe(μ3-Cl)>Fe(μ2-Cl)>FeClt is as expected. The FeClt distance is 2.244(1) ]A, the Fe(μ2-Cl) distances are 2.355(1)–2.488(2) A and the Fe(μ3-Cl) distances are 2.506(1)–2.737(1) A. The average FeO distance is 2.135(9) A. Crystallographic data: 1, triclinic, space group P 1 , a = 10.607(2), b = 10.993(3), c = 10.038(2) A, α = 111.84(3)°, β = 98.28(3)°, γ = 63.18(3) °, V = 969.2(6) A3, Z = 1, R = 0.048 (Rw = 0.069) for 188 parameters and 2616 unique data having Fo2>3σ(Fo2).