grab samples

B. Reagents
Chelating reagent: ammonium pyrrolidinedithiocarbamate (APDC) or sodium diethyldithiocarbamate
(DEDC). Make up a 5% solution with deionized-distilled water. Extract at least twice with methyl
isobu tyl ketone (MIBK).
Methyl isobutyl ketone (MIBK) (distilled).
C. Extraction
(I) Place 50 ml of solution in a 250-ml acid-washed separatory funnel. Add 2 ml ofchelating reagent
and add 5 ml of MIBK.
(2) Shake thoroughly for abou t 3 min and save the upper (extract) layer for analysis.
D. Analysis
For flame conditions, adjust the spectrometer settings as above. It may be necessary if the metal
concentrations are very low to use the flameless attachment of the atomic absorption spectrometer. Check
manufacturer's handbook.
Note: Where greater sensitivity is required the flameless method can be employed. In all methods, however,
it is well known that difficulties can arise through contamination from reagents, samplers, and
containers.
6.11 Extra Notes on Metal Analysis
I. Quantity of MIBK
The quantity of MIBK extraction solvent determines the concentration factor. It should be noted that
no extraction is 100% efficient and the solubility of MIBK in water is 2%.
II. Contamination
( I) The purity of the MIBK is im proved by distillation.
(2) Only high purity acids should be used when the sample is acidified for storage.
(3) Any chelating reagent should be extracted twice before use.
(4) Care should be taken that all glassware is thoroughly washed in conc. nitric acid and deionizeddistilled
water.
III. Atomic Fluorescence Spectroscopy
A number of authors have suggested measuring metal concentrations by atomic fluorescence rather
than atomic absorption because this method has lower detection limits. However, most laboratories do not
have the necessary instrumentation or expertise.
IV. Anodic Stripping Voltametry
This technique is still under development and has not received the degree of acceptance accorded to
atomic absorption approaches.
6.12 Mercury (Cold Vapour Atomic Absorption Technique)
I. Concentrations
Average river water"" 0.08 j.tgl I
Nearshore sediments"" 390 j.tg/kg (Loring 1975)
Coastal seawater 0.058-0.071 j.tgl I (Cranston and Buckley 1972)
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