grab samples

(8) Add 3 g of20- 30 mesh high quality zinc to Erlenmeyer flask and connect the scrubber assembly.
Make sure all connections are very tigh t.
(9) Allow 30 min for complete evolution of arsenic. Warm slightly to release all arsine.
(10) Measure abundance at 535 nm with reagent blank as reference.
Note: An alternative method for which special apparatus is required is atomic absorption analysis. In this
method, the arsine is generated as above, except the gas is passed on to an argon-hydrogen flame of an
atomic absorption spectrometer rather than into the silver diethyldithiocarbamate solution. An
electrodeless discharge lamp is preferred over a hollow cathode lamp for the spectrometer (APHA et
aJ. 1975). Methods for the analysis of arsenic in seawater are currently undergoing development - in
particular the use of the graphite furnace approach holds some merit. The most severe problem arises
because of the volatility of arsenic and its compounds.
References
ALLEN, S. E. (ed. ) 1974. Chemical analysis of ecological materials. Blackwell Scientific Publications, Oxford and Edinburgh. 565 p.
AMERICAN PUBLIC HEALTH ASSOCIATION , AMERICAN WATER WORKS ASSOCIATION, AND WATER POLLUTION CONTROL FEDERATION.
1975 , Standard methods for the examination of water and wastewater. 14th ed, Washington, D .C. 1193 p.
6.14 Cyanide
I. Principles
( I) Cyanide salts within the sample are converted to hydrogen cyanide under acidic conditions.
Because hydrogen cyanide has a boiling point of 26°C, it can be easily isolated by distillation. Many
complex cyanide salts are not attacked by this method. Addition of mercury and magnesium salts aid in
this breakdown. (APHA et aJ. 1975).
(2) If an auto-analyzer is available, the Aldridge-Konig method (photometric) can be used
(Caspieri et aJ. 1970). The method outlined here will be manual analysis of cyanide.
II. Summary of Method (Fu ller 1969)
Liberated hydrogen cyanide is trapped in sodium hydroxide solution creating sodium cyanide salts.
After distillation, this solution is reacted with chloramine-T to create cyanogen chloride. The cyanogen
chloride is then reacted with pyridine-pyrazolone reagent creating a blue dye, the absorbance of which can
be measured at 620 nm. Extraction of the dye in n-butyl aJchol and measuring the absorbance at 630 nm
gives increased sensitivity (Minimum detection concentration: 0.02 mg/ I).
III. Interferences
Sulphides should be removed by the addition of powdered lead carbonate in the alkaline trap. This
will cause precipitation oflead sulphate. Avoid adding large quan tities of lead.
Other interferences are removed during distillation.
IV. Reagents
( I ) Conc. sulphuric acid
(2) I N sodium hydroxide
(3) 34 g/ 500 m I mercuric chloride sol u tion
(4) 51 g/ 100 m! magnesium chloride solution
(5) Glacial acetic acid
(6) I % aqueous chloramine-T solution (prepare daily)
45