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Determination of cadmium in biodiesel using microemulsion and electrothermal atomization atomic absorption spectrometry.

Environmental monitoring and assessment (2014-11-10)
Adriana S Lima, Deise G Silva, Leonardo S G Teixeira
ABSTRACT

This work aimed to prepare biodiesel microemulsions for the subsequent quantification of cadmium via graphite furnace atomic absorption spectrometry (GFAAS). The biodiesel samples were prepared using n-propanol as an emulsifier, 10% (v/v) nitric acid as the aqueous phase, and biodiesel. Pseudoternary phase diagrams were constructed to determine the microemulsion region with the specified components. The optimized conditions for microemulsion formation were 57.6% (v/v) n-propanol, 21.2% (v/v) biodiesel, and 21.2% (v/v) nitric acid solution. The stability of the microemulsified system was investigated using aqueous and organic standards, and the system was found to be stable for at least 240 min. The applied pyrolysis and atomization temperatures were 800 and 2000 °C, respectively, and 5 μg of aluminum was used as the chemical modifier. The obtained limits of detection and quantification were 0.2 and 0.5 μg kg(-1), respectively, and the characteristic mass was 1.6 pg. The precision, expressed as the relative standard deviation (% R.S.D., n = 10), was 2.5% for a sample with a cadmium concentration of 6.5 μg kg(-1). The accuracy was determined from addition and recovery experiments, with results varying from 93 to 108% recovery. This study demonstrates that the proposed method based on the use of a microemulsion formation in sample preparation can be applied as an efficient alternative for the determination of cadmium in biodiesel by GFAAS. Cadmium determination in biodiesel samples of different origins (soybean, corn, cotton, and sunflower) was evaluated after acid digestion using the inductively coupled plasma-mass spectrometry (ICP-MS) technique, and the obtained results were compared to the results obtained using the proposed method. The paired t test (95% confidence level) did not show significant differences. The concentrations of cadmium found ranged from 5.3 to 8.0 μg kg(-1).

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Nitric acid, ACS reagent, 70%
Sigma-Aldrich
Nitric acid, 70%, purified by redistillation, ≥99.999% trace metals basis
Sigma-Aldrich
Nitric acid, puriss. p.a., 65.0-67.0%
Sigma-Aldrich
Nitric acid, puriss. p.a., reag. ISO, reag. Ph. Eur., for determinations with dithizone, ≥65%
Sigma-Aldrich
Nitric acid, ACS reagent, ≥90.0%
Supelco
Nitric acid concentrate, 0.1 M HNO3 in water (0.1N), eluent concentrate for IC
Sigma-Aldrich
Cadmium, powder, −100 mesh, 99.5% trace metals basis
Sigma-Aldrich
Nitric acid, puriss. p.a., ≥65% (T)
Sigma-Aldrich
Cadmium, granular, 30-80 mesh, ≥99%
Sigma-Aldrich
Cadmium, granular, ≥99%, 5-20 mesh
Cadmium, foil, 100x100mm, thickness 1.0mm, as rolled, 99.99%
Cadmium, wire reel, 0.1m, diameter 0.70mm, as drawn, 99.99+%
Cadmium, wire reel, 0.1m, diameter 1.2mm, as drawn, 99.99+%
Cadmium, wire reel, 0.1m, diameter 2.0mm, hard, 99.99+%
Cadmium, wire reel, 0.1m, diameter 1.0mm, hard, 99.999%
Cadmium, wire reel, 0.2m, diameter 0.5mm, hard, 99.99+%
Cadmium, wire reel, 0.2m, diameter 0.70mm, as drawn, 99.99+%
Cadmium, wire reel, 0.2m, diameter 1.2mm, as drawn, 99.99+%
Cadmium, wire reel, 0.2m, diameter 2.0mm, hard, 99.99+%
Cadmium, wire reel, 0.2m, diameter 0.125mm, as drawn, 99.9%
Cadmium, wire reel, 0.2m, diameter 1.0mm, hard, 99.999%
Cadmium, wire reel, 0.5m, diameter 0.25mm, hard, 99.99+%
Cadmium, wire reel, 0.5m, diameter 0.5mm, hard, 99.95+%
Cadmium, wire reel, 0.5m, diameter 0.5mm, hard, 99.99+%
Cadmium, wire reel, 0.5m, diameter 1.2mm, as drawn, 99.99+%
Cadmium, wire reel, 0.5m, diameter 2.0mm, hard, 99.99+%
Cadmium, wire reel, 0.5m, diameter 1.0mm, hard, 99.999%
Cadmium, wire reel, 10m, diameter 0.25mm, hard, 99.99+%
Cadmium, wire reel, 1m, diameter 0.25mm, hard, 99.99+%
Cadmium, foil, 100x100mm, thickness 0.125mm, as rolled, 99.95%