Values below detection limit in compositional chemical data

Samples representing part of a whole, usually called compositional data in statistics, are commonplace in analytical chemistry say chemical data in percentage, ppm, or mu g g(-1). Their distinctive feature is that there is an inherent relationship between all the analytes constituting a chemical sample as they only convey relative information. Some compositional data analysis principles and the log-ratio based methodology are outlined here in practical terms. Besides, one often finds that some analytes are not present in sufficient concentration in a sample to allow the measuring instruments to effectively detect them. These non-detects are usually labelled as