42-14
COPPER, continued
Testing zero concentration samples, the limit of detection was 1.7 µg/L
Cu. The limit of detection was calculated as three times the standard
deviation when testing zero concentration samples (adapted from
Analytical Chemistry, 1980, 52, 2242-2249).
INTERFERENCES
The following may interfere when present in concentrations exceeding
those listed below:
Aluminum 60 mg/L
Cadmium 10 mg/L
Calcium 1,5000 mg/L
Chloride 90,000 mg/L
Chromium (Cr
6+
) 110 mg/L
Cobalt 100 mg/L
Fluoride 30,000 mg/L
Iron 6 mg/L
Lead 3 mg/L
Magnesium 10,000 mg/L
Manganese 140 mg/L
Mercury 3 mg/L
Molybdenum 11 mg/L
Nickel 60 mg/L
Potassium 60,000 mg/L
Sodium 90,000 mg/L
Zinc 9 mg/L
Chelating agents, such as EDTA, interfere at all levels unless either the
Digesdahl or vigorous digestion (Section I) is performed.
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment: see
Interferences, pH (Section I)
SUMMARY OF METHOD
The porphyrin method is very sensitive to trace amounts of free copper.
The method is free from most interferences and does not require any
sample extraction or preconcentration. Interferences from other metals
are eliminated by the copper masking reagent. The porphyrin indicator
forms an intense, yellow-colored complex with any free copper present
in sample.
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