Objective: To evaluate alternative methods for radiochemical purity testing of indium (In)-111 capromab pendetide after the discontinuation of instant thin-layer chromatography silica gel (ITLC-SG) strips.

Design: Descriptive experimental study.

Setting: United States in 2009.

Participants: Not applicable.

Intervention: Paper chromatography using Whatman 3MM strips, paper chromatography using Whatman 31ET strips, and mini-column chromatography using silica Sep-Pak cartridges were evaluated in the radiochemical purity testing of 13 consecutive vials of In-111 capromab pendetide prepared for clinical patient imaging procedures.  These methods also were evaluated by testing 7 aliquots of In-111 capromab pendetide that had been spiked with 5% to 15% In-111 pentetate (diethylene triamine pentaacetic acid).

Main outcome measures: Correlation coefficients, radiochemical purity values for each method compared with ITLC-SG, and procedure times.

Results: Correlation coefficients of 0.988, 0.996 and 0.979 were found for ITLC-SG compared with Whatman 3MM, Whatman 31ET and silica Sep-Pak, respectively.  Compared with ITLC-SG, mean (+/- SD) radiochemical purity values differed by -0.8 +/- 0.8 (range -2.5 to 0.4) for Whatman 3MM, -0.8 +/- ?0.6 (-2.3 to 0) for Whatman 31ET and -0.5 +/- 1.2 (-3.6 to 0.7) for silica Sep-Pak.  The approximate time required to develop the chromatography strip or elute the mini-column was 3, 14, 5 and 6 minutes for ITLC-SG, Whatman 3MM, Whatman 31ET and silica Sep-Pak, respectively.

Conclusion: All three methods evaluated were acceptable alternatives to ITLC-SG for radiochemical purity testing of In-111 capromab pendetide.  Based on its slightly higher correlation to ITLC-SG, slightly tighter SD and range, and slightly shorter development time, Whatman 31ET is preferred in our facility.