I tryed the example of the link you suggested:
(xset1 <- xset[which(xset@peaks[,"mz"]<600 & xset@peaks[,"mz"]>100),] )
but the R consol give this error:
Errore in xset[which(xset@peaks[, "mz"] < 600 & xset@peaks[, "mz"] > 100), : object of type 'S4' is not subsettable
Do you have any further suggestion?? :?: