2 research outputs found
Studies of a microporous membrane for analyte preconcentration and separation
A dual phase gas diffusion-FIA system containing a tubular PTFE-membrane
was studied as a mean of producing gas samples for routine
15N/14N isotopic ratio mass spectrometry. The method is based on
Rittenberg's reaction; the ammonium sample is injected into a liquid alkaline
stream containing hypobromite and the N2 gas produced in the reaction
diffuses across a PTFE-membrane into a helium carrier stream which carries it
to the detector.
Initially here, the use of a tubular microporous PTFE-membrane as a device
for the preconcentration of samples in aqueous solutions was investigated.
The performance of such a membrane was studied under a variety of
operating conditions. A qualitative model of the membrane mechanism was
developed based on the diffusion transport of vapour away from the
contained liquid surface through the connected pore space. The dispersion
undergone by the sample in the GD-FIA system containing this
preconcentration unit was also studied and this FIA system was applied as a
practical device for the determination and speciation of aluminium in a river
water sample.
The procedure for generating nitrogen gas involved optimisation of the
system parameters including the oxidation reaction step and the production
on-line of the chemicals used. The nitrogen gas was generated easily and
rapidly, allowing a sample throughput capability of the order of 20 h-1. The
system was applied to the determination of total nitrogen content in
agricultural sample prepared by the Kjeldahl digestion. The method offered
precision and accuracy comparable to those of the standard distillationtitration
procedure. Isotope ratios were determined with good precision and
means for obtaining accuracy comparable with established techniques were
developed.
It was also shown that the DPGD-FIA system can be readily adapted to enable different forms of nitrogen e. g. N02-, N03- and NH4+ to be determined
Arsenic, cadmium and lead concentrations in Yerba mate commercialized in Southern Brazil by inductively coupled plasma mass spectrometry
<div><p>ABSTRACT: “Mate” or “Yerba Mate” (Ilex paraguariensis) is a native South American plant, commonly consumed in Argentina, Paraguay, Uruguay and southern Brazil. Recent research has detected the presence of many vitamins and metals in this plant. Theses metals are also part of yerba mate’s mineral composition, due to soil and water contamination by pesticides and fertilizers, coal and oil combustion, vehicle emissions, mining, smelting, refining and the incineration of urban and industrial waste. Regardless of their origin, some inorganic elements, such as arsenic, cadmium and lead, are considered toxic, since they accumulate in all plant tissues and are, thus, introduced into the food chain. In this context, the aim of the present study was to determine and compare arsenic, cadmium, lead concentrations in 104 samples of yerba mate (Ilex paraguariensis) marketed, and consumed in three southern Brazilian States, namely Paraná (PR), Santa Catarina (SC) and Rio Grande do Sul (RS). Each element was determined by inductively coupled plasma mass spectrometry (ICP-MS), on a Nexion 300D equipment (Perkin Elmer). As, Cd and Pb concentrations in yerba mate leaves ranged from 0.015 to 0.15mg kg-1, 0.18 to 1.25mg kg-1 and 0.1 to 1.20mg kg-1, respectively. Regarding Cd, 84% of the samples from RS, 63% from PR and 75% from SC showed higher concentrations than the maximum permissible limit of 0.4mg kg-1 established by the Brazilian National Sanitary Surveillance Agency (ANVISA), while 7% of the samples from RS and 5% from PR were unsatisfactory for Pb. Concentrations were below the established ANVISA limit of 0.6mg kg-1 for all samples.</p></div