New subcritical fluid nebulizer (ScFN) for improving the determination of inorganic tin in gunshot residues by flame furnace-atomic absorption spectrometry

The determination of tin by FAAS is widely recognized as a difficult task in atomic spectrometry because of low sensitivity, poor detection limits and important interferences. In this work a new sample introduction system, the subcritical fluid nebulizer (ScFN) combined with the flame furnace-atomic absorption spectrometry (FF-AAS) was applied for improving the determination of inorganic tin in aqueous solutions. Online preconcentration of tin as Sn-PDC complex was carried out in a HPLC-guard cartridge (5 mm length, 2 mm diameter) filled with C-18 coated monolithic silica having an absorption capacity of 2.5 μg of tin. For preconcentration optimized conditions were achieved at 0.015% (m/v) of APDC and pH 5 obtaining a preconcentration factor of 17 using 2.5 mL of sample volume. The elution was done by means of subcritical liquid carbon dioxide and methanol with a flow rate of 1.5 L min− 1 which was directly introduced as a dry aerosol into the flame furnace where tin complexes are vaporized and atomized. Applying ScFN-FF-AAS the detection and quantification limits for tin in water were 0.008 mg L− 1 and 0.024 mg L− 1, respectively, increasing the power of detection in 325 times compared to the conventional detection limits obtained by flame atomic absorption spectrometry. The precision at 1 mg L− 1 was 1.5% expressed as RSD (N = 10). Tin was determined in samples of gunshot residues generated by firing four ammunition brands. The concentrations fluctuated between 52 and 151 μg L− 1.