Quantification of calcium in the cuticle of the fly larva
Exeretonevra angustifrons was undertaken at the micron scale
using wavelength dispersive X-ray microanalysis, analytical standards,
and a full matrix correction. Calcium and phosphorus were found to be
present in the exoskeleton in a ratio that indicates amorphous calcium
phosphate. This was confirmed through electron diffraction of the
calcium-containing tissue. Due to the pragmatic difficulties of
measuring light elements, it is not uncommon in the field of entomology
to neglect the use of matrix corrections when performing microanalysis
of bulk insect specimens. To determine, firstly, whether such a
strategy affects the outcome and secondly, which matrix correction is
preferable, phi-rho (z) and ZAF matrix corrections were contrasted with
each other and without matrix correction. The best estimate of the
mineral phase was found to be given by using the phi-rho (z)
correction. When no correction was made, the ratio of Ca to P fell
outside the range for amorphous calcium phosphate, possibly leading to
flawed interpretation of the mineral form when used on its own.