You've set up your tables incorrectly. When you start suffixing field names with numbers, its time for a new table. Further, you do that and this issue you've posted about becomes trivial--just one DCount into that new table.
That table will have this structure:
tblSamples
SampleID, autonumber, primary key
IDTblQcMeasurements, number, foriegn key to TblQcMeasurements
SampleNumber, number, this will hold the suffix on the end of all those samples
SampleValue, ?, this field will hold whatever value is currently in all those sample fields
That's it. Those 4 fields can now hold an unlimited number of samples for your data. Instead of filling in 5 fields in TblQcMeasurements you would add 5 rows to tblSamples for them.