Ross Geddes (personal communication, 16 November 2005) suggests that the word captivation here could be an error for captivity, the word that is used elsewhere in the text to refer to being held captive by Satan:
The Oxford English Dictionary, under captivation, explains that the original meaning for this word was general and referred to “taking or holding captive”. Over time, however, the word has taken on a purely figurative meaning, referring to “the attention, mind, fancy, affections” being held captive. The Book of Mormon’s single use of captivation in Alma 9:28 is based on the literal sense of being held captive. The OED provides only one citation (from the early 1600s) with this meaning; there the reference is to the return of the Jews from their Babylonian captivity in the sixth century BCE (original spelling retained):
All the other OED citations, from 1656 to 1878, have only the figurative meaning. It may be that the general meaning of captivation here in Alma 9:28 is one more example of the archaic vocabulary in the Book of Mormon text. There is no need to suppose that captivation is somehow an error in the early transmission of the text. In fact, one would expect the error to go in the other direction: namely, for captivation with its literal meaning to be replaced by the very frequent captivity (which occurs 61 times in the text). The critical text will maintain the original captivation here in Alma 9:28.
Summary: Maintain in Alma 9:28 the unique occurrence of the word captivation in the text; its meaning here is general and is identical to the meaning of the word captivity (which occurs very frequently in the text).