Walker O. Smith
University of Tennessee

POC-PON Method:

Sampling

Samples are collected in 1 or 2 liter polypropylene bottles.  Water is
filtered onto precombusted (450 degrees C, 3 hours) 25mm Whatman GF/F
filters (nominal pour size 0.7 micron).  Just prior to end of
filtration, filter is rinsed with a weak HCl (0.01 N in filtered sea
water) to remove inorganic carbonates.  Filter is removed, placed in a
precombusted (525 degrees C, 2 hours) shell vial, and vial is capped
with precombusted (525 degrees C, 2 hours) aluminum foil.  Samples are
stored in a 60 degree C oven until processed

Procedure

    Sample Analysis

1.      Prior to analysis, the filters are kept dry in a 60 degree
oven, in precombusted (525 degree C, 2 hours) vials.
	
2.      The samples are placed in tin capsules and analyzed on a Carla
Erba EA1108-Elemental Analyzer.  One conditioning sample, two tin blank
samples, three standard samples, and three standard samples run as
unknowns are run to test the machines calibration each day. An average
of twenty to twenty-five POC/PON samples can be analyzed each day.  A
standard is run after approximately five POC/PON samples for
calibration.

    Standardization and blank determination

Acetanilide standards and tin blanks (empty tin sleeves) are measured
prior to each batch of samples. The standard is weighed in tin capsules
on a Sartorius XM 1000 P balance for calibration runs and test runs,
usually measuring between 90 and 250 micrograms.  Acetanilide is run as
an ordinary sample (test run) to test the accuracy of the calibration
of the machine each day.  Blanks are combusted 25mm Whatman GF/F
filters soaked in surface sea water and treated in exactly the same
manner. Data are collected and stored by a microcomputer.