Lake Michigan environmental survey : final report / [edited] by John C. Ayers.

were dissolved in a concentrated nitric acid - 3% hydrogen peroxide solution.
Water samples were freeze-dried to concentrate trace elements 100-fold. Because a large portion of benthos, zooplankton, and phytoplankton samples was
sediment contaminated, conclusions from these data should not be attempted.
Water and sediment data are ready for interpretation.
Phytoplankton, benthos, zooplankton and sediment samples were digested
in a concentrated nitric acid - 3% hydrogen peroxide mixture at approximately
90~C three to four hours. They were then centrifuged and decanted to separate
the soluble and insoluble phases. Originally filtration through either glass
fiber filters or membrane filters was attempted, but associated with this
method is a leaching of trace metals from both the filters and filtration
equipment and this technique was abandoned.
Fats of the various organisms did not go into solution. Collection and
processing of them yielded no significant amounts of the elements sought.
Being high enough in lake water, concentrations of Ca, Mg, Na, K, Zn and
Sr were measured directly. All other elements must be concentrated. Concentration was accomplished by low temperature and low pressure sublimation of
the sample. This was done with a freeze-drying unit. One liter of acidified
(approximately 2% nitric acid), filtered (0.45 v membrane filter) lake water
was freeze-dried to dryness; the residue was dissolved in ten milliliters of
10% nitric acid, giving a final 100-fold concentration. Concentration by
boiling could accomplish the same result, but we feared that the more volatile
elements would be lost to the atmosphere.
For analyses of the trace metals Co, Ni, Cu, Mn, and Fe in lake water, a
modification of an APDC-MIBK solvent extraction technique was tried. Both
non-reproducibility and a need to concentrate barium and molybdenum warranted
abandoning this method.
All analyses were performed using either Perkin Elmer and Jarrel Ash
atomic absorption units or a Beckman DU flame emission unit. Those done, at
least partly, by flame emission were Na, K, and Li.
Except for Sr, Ba, Ca, and P, all elements were measured directly or after
Brooks, R. R., B. J. Preselay, and I. R. Kaplan. 1967. The APDC-MIBK
extraction system for the determination of trace elements in saline waters by
atomic absorption spectrophotometry. Talanta 14: 809-816.

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