Multielement geochemical data missing value and below detection limit imputation

Introduction The precise measurement of small concentrations of elements from chemical analyses is limited due to instrument sensitivity. Such concentrations are known as the detection limit (DL). Given the increasing popularity of multivariate data analysis tools to identify patterns within geochemical data, which often require all data to be represented by real values, methods for imputing missing or below DL (BDL) values are required. BDL values are often either removed completely or replaced with a constant value such as half the BDL (Carranza, 2011; Hron and others, 2010). Where additional information is available, such as with multivariate data, BDL values can be imputed using methods that assess the conditional similarities between samples within data space.