Detection of Lead in Bullet Wipe Using Sodium Rhodizonate

The sodium rhodizonate spot test is commonly used as a verification test for the presence of lead, primarily for the detection of lead deposits on fabric as a result of firearm discharge. Upon treatment of the fabric with the light yellow sodium rhodizonate solution, a pink complex of lead forms. Further treatment of the sample with dilute hydrochloric acid produces a purple complex specific to lead. The first objective of this study has been to determine the limit of detection (LOD) of this test on white cotton fabric. No research has been published using other rhodizonate salts for lead detection. It is known that sodium rhodizonate exhibits a separate color change (blue-violet) in the presence of calcium ions. It is proposed that using this dark calcium rhodizonate spray solution may exhibit a more contrasting background for the observation of the pink spots due to lead, especially on dark cloth. Upon synthesizing the calcium rhodizonate salt, tests were performed to compare the LOD of this high contrast test to the standard sodium rhodizonate test. As previous studies have shown, sodium rhodizonate solutions are quickly reduced to tetrahydroxyquinone. When prepared in pH 2.8 buffer, the lifetime of the solution increases from one hour to approximately ten hours, as measured by UV-Vis spectroscopy. However, to date, no studies have estimated the \u27usable\u27 lifetime of rhodizonate solutions for visual forensic analysis. This study estimated this \u27usable\u27 lifetime of both the sodium and calcium salts via a time controlled set of visual analyses