Indirect determination of iodide by tungsten coil atomic emission spectrometry

The spectroscopic determination of iodide is a difficult challenge, especially in small sample volumes. The strongest transition lines for this element lie in the vacuum ultraviolet region of the spectrum, so most conventional instruments produce very weak signals. This work describes a tungsten coil atomic emission procedure for the indirect determination of iodide. A 25 μl aliquot of a solution containing a known amount of indium is deposited on the tungsten coil and dried with a simple heating program. Once the coil is dry, 25 μl of an iodide solution is added to the coil. The solution is dried and vaporized at high current. The atomic emission signal for In at 451.1 nm is monitored. In the presence of iodide, InI is formed and the In emission signal is attenuated. This attenuation is proportional to iodide concentration with a method detection limit of 0.6 mg l^{− 1} iodide using an In concentration of 10 mg l^{− 1}, and 3 mg l^{− 1} iodide using an In concentration of 50 mg l^{− 1}. Linear calibration curves span a range of two orders of magnitude. Analysis of a deionized water sample spiked with 50 mg l^{− 1} iodide gives a recovery of 100% and a precision of 5.5% relative standard deviation. Analysis of a tap water sample spiked with 50 mg l^{− 1} iodide gives a recovery of 140% and a precision of 7.1% relative standard deviation. The poor accuracy for the tap water analysis may arise from the reaction of In with other halides in the sample. This is the first report of determination of a halogen using the tungsten coil atomizer.