.check_isotopic <- function(isotopic) {
if (length(isotopic) != 1L) {
stop("Only one \"isotopic\" is possible.",
call. = FALSE)
}
if (!is.character(isotopic)) {
stop("The provided isotopic is not \"any\", \"labeled\", or \"unlabeled\".",
call. = FALSE)
}
if (!any(tolower(isotopic) %in% c("any", "labeled", "unlabeled"))) {
stop("The provided isotopic is not \"any\", \"labeled\", or \"unlabeled\".",
call. = FALSE)
}
}
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