Simultaneous determination of Cl, Br and I by aerosol-assisted PVG-ICP-MS†

Abstract

Simultaneous determination of Cl, Br and I by aerosol-assisted photochemical vapor generation (PVG) with detection by inductively coupled plasma mass spectrometry (ICP-MS) was investigated. The photoreactor comprised a modified cyclonic spray chamber fitted with a central UV source for irradiation of pneumatically generated sample aerosol. A systematic evaluation of variables was conducted, focusing on achieving compromise optimal PVG conditions suitable for simultaneous Cl, Br and I generation. By using a sample medium comprising 1% v/v acetic acid containing 20 mg L⁻¹ Cu²⁺ as mediator, the signal intensities for Cl, Br and I were enhanced by 3-, 40- and 30-fold, respectively, compared to those obtained by conventional pneumatic nebulization (PN). LODs of 4.2 ng mL⁻¹, 6.3 pg mL⁻¹ and 1.9 pg mL⁻¹ were achieved for Cl, Br and I, respectively, with corresponding estimated overall PVG efficiencies of 10, 99 and 90%. In addition to the halides, halate species, i.e., ClO₃⁻, BrO₃⁻ and IO₃⁻, were also examined, but poor PVG efficiencies (lower than 5%) were encountered. However, addition of 20 mg L⁻¹ SO₃²⁻ to the generation medium enhanced response for BrO₃⁻ and IO₃⁻, achieving similar values to those obtained from Br⁻ and I⁻. The impact of NO₃⁻ (as both HNO₃ and KNO₃) and NH₄OH on generation efficiencies was also investigated. The method was tested by the successful simultaneous determination of total Cl, Br and I in a variety of certified reference materials (CRMs) digested by microwave-induced combustion (MIC), including NRCC DORM-5 – Fish Protein, NIST SRM 1632c – Coal, NIST SRM 1515 – Apple Leaves and NIST SRM 1549 – Non-fat Milk Powder.