The Blank Can Make a Big Difference in Oceanographic Measurements

It is hard to imagine a topic that seems more boring and trivial than the measurement of nothing. In a sense, determination of an analytical blank is exactly that — measurement of the signal associated with the absence of the property being detected. Although the magnitude and variability of an analytical blank may be very small compared to the oceanographic measurement, it must be determined as part of a calibration routine. For example, the blank for samples of particulate matter collected on filters consists of a filter that has been treated identically to field samples, except that no water with particles is drawn through it. Analysis of dissolved constituents requires measurements on samples that are analytically equivalent to field samples, but with no analyte present. It is the analyst’s responsibility to determine what constitutes the appropriate blank (e.g., purified water, artificial sea water, filtered sea water