Analytical Detectors Based on Microplasma Spectrometry

Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry. Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas for utilisation in analytical instruments.     

Study by liquid secondary ion and electrospray mass spectrometry of synthesized and formed-in-source metallocorroles

Liquid secondary ion and electrospray mass spectrometry were used to study the complexation in-source of 5,10,15-tris(pentafluorophenyl)corrole with several divalent transition-metal ions. The metallocorrole ions formed in-source were identified by comparing their product ion mass spectra with the spectra of the same ions formed from metallocorroles obtained from classical procedures. Positive metallocorrole ion formation is accompanied by oxidation of the metal centre. Mechanisms were proposed for the oxidation processes, and data from negative-ion spectra reinforced these mechanisms.     

Chemiluminometric determination of the pesticide 3-indolyl acetic acid by a flow injection analysis assembly

A new method is proposed for the chemiluminescent determination of the pesticide 3-indolyl acetic acid by means of an flow injection analysis system. The chemiluminescence emission is obtained by oxidation of the analyte with Ce (IV) in nitric acid and presence of β-cyclodextrine.The continuous-flow method allows the determination of 159 samples h⁻¹ of 3-indolyl acetic acid in an interval of concentrations over the range 0.5-15.0 mg l⁻¹. The limit of detection was 0.1 μg l⁻¹ and the R.S.D. (n, 17) at 2.0 mg l⁻¹ of the pesticide level was 2.7%. The method was applied to water samples.     

A simplified approach to the determination of N-nitroso glyphosate in technical glyphosate using HPLC with post-derivatization and colorimetric detection

A simple and sensitive HPLC post-derivatization method with colorimetric detection has been developed for the determination of N-nitroso glyphosate in samples of technical glyphosate. Separation of the analyte was accomplished using an anionic exchange resin (2.50 mm × 4.00 mm i.d., 15 μm particle size, functional group: quaternary ammonium salt) with Na₂SO₄ 0.0075 M (pH 11.5) (flow rate: 1.0 mL min⁻¹) as mobile phase. After separation, the eluate was derivatized with a colorimetric reagent containing sulfanilamide 0.3% (w/v), [N-(1-naphtil)ethilendiamine] 0.03% (w/v) and HCl 4.5 M in a thermostatized bath at 95 °C. Detection was performed at 546 nm. All stages of the analytical procedure were optimized taking into account the concept of analytical minimalism: less operation times and costs; lower sample, reagents and energy consumption and minimal waste. The limit of detection (k = 3) calculated for 10 blank replicates was 0.04 mg L⁻¹ (0.8 mg kg⁻¹) in the solid sample which is lower than the maximum tolerable accepted by the Food and Agriculture Organization of the United Nations.     

Determination of aflatoxins in olive oil by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometric with electrospray ionization (LC/ESI-MS/MS) method for determining the four naturally occurring aflatoxins (AFs) B1, B2, G1, and G2 in olive oil is proposed. AFs were extracted from oil sample by means of matrix solid phase dispersion (MSPDE), utilizing C18 as dispersing material. No further purification step, such as lipid removal, was performed. Aflatoxin M1, the hepatic metabolite of AFB1, was employed as internal standard. Olive oil extract was analyzed by LC/ESI-MS/MS in positive ionization mode, with multireaction monitoring acquisition. Due to a signal suppression ranging between 4 and 23%, quantitation was performed by matrix-matched calibration curves. The regression line coefficients of determination were above 0.9991. Sample recoveries ranged from 92 to 107%, with relative standard deviations below 13% for spiking levels between 0.5 and 5 ng g⁻¹; method quantification limits ranged between 0.04 and 0.12 ng g⁻¹. The developed LC/ESI-MS/MS method, although not as sensitive as LC coupled to fluorescence detection, is rapid, selective, accurate and precise, thus it can be used as confirmatory assay. The MSPDE appears suitable for application to other oleaginous matrices and for multiresidue investigation.     

Computational study of the thermal decomposition of 2-methylbutyraldehyde and 2-pentanone through retro-ene reactions

In this work, a theoretical study at the MP2/6-31G(d) level of the thermal decomposition retro-ene reaction of 2-methylbutyraldehyde was carried out at a pressure of 1.5 atm. and temperatures ranging from 1110 to 1190 K. The progress of the reaction has been followed by means of the Wiberg bond indices which in turn allowed the calculation of the reaction synchronicity. Transition state theory was used to calculate the theoretical rate constant at 1150 K which was compared with the previously reported experimental value at the same conditions. We found that both values show a close agreement. The obtained computational evidence allowed us to support a reaction mechanism which proceeds in two steps: the first one with the formation of ethylene and 1-propenol via a six-membered cyclic transition state and the second one involving keto-enol equilibrium of 1-propenol to propionaldehyde via a four-membered cyclic transition state. It was found that the reaction is a highly synchronous and concerted process. The results obtained for the thermolysis of 2-methylbutyraldehyde were compared with those obtained for the thermolysis of 2-pentanone. A comparison of our results with those reported for their corresponding β-hydroxy counterparts, 3-hydroxy-2-methylpropionaldehyde and 4-hydroxy-2-butanone has also been made. A study of the thermochemistry of the compounds involved in the reactions studied has been carried out at the G3 level.     

First report of the nutritional profile and antioxidant potential of Holothuria arguinensis,a new resource for aquaculture in Europe

This work reports for the first time the nutritional profile and antioxidant potential of the edible sea cucumber Holothuria arguinensis from the North-eastern Atlantic. H. arguinensis has high levels of protein, with the amino acids profile dominated by alanine, glycine and proline and low lysine/arginine ratios. Its carbohydrate and energetic contents are also low as well as the total lipid levels, although its lipid profile is rich in polyunsaturated fatty acids (PUFA), especially arachidonic, eicosapentaenoic and docosahexaenoic acids. In addition, H. arguinensis has high levels of calcium. The water and ethanol extracts show ability to scavenge free radicals and to chelate copper and iron ions. Our results indicate that H. arguinensis has a balanced nutritional quality suitable for human consumption. In addition, it contains compounds with antioxidant potential; thus its intake can contribute for a healthy and well-balanced diet.