GENERAL55980

• Permit No: M1988112
• IBM Index Class Name: General Documents
• Doc Name: STANDARD TEST METHODS FOR CYANIDE IN WATER AUTOMATED METHODS FOR TOTAL CYANIDE & DISSOCIABLE CYANIDE
• Media Type: D
• Archive: No

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~~) D 4374
6,5.4 For more information refer to Appendix X2, Ni-
trate-Nitrite Interference.
6.6 Meta! Cations:
6,6.1 Metal cations do not interfere with total cyanide
measurement, because UV eradiation breaks down all the
cyanide complexes. Formation of metal cyanide complexes
in field samples is not considered a source of interference to
the measurement of dissociable cyanide since the objective is
not to measure the strong cyano complexes.
6.6.2 On the other hand, addition of some metallic
catalytic compounds doting the analytical procedure is not
desirable and may constitute significant errors. Dramatic
inhibition occurs when mercuric chloride and, to a lesser
extent, cuprous chloride were added as catalysts (8). Magne-
sium chloride, while not causing any problems, did not
demonstrate amy favorable catalytic action. Thus no catalyse
should be added.
6.6.3 Due to its high volatility, mercury when present at
concentrations >I mg/L distills over with the cyanide
causing negative interference. Most samples do not contain
mercury at this high level.
6.7 Aldehydes:
6.7.1 Aldehydes react with cyanide and cause negative
interference (probably due to formation of nitrites). This
interference is noticeable at formaldehyde concentrations of
0.5 mg/L and above. Both total cyanide amd dissociable
cyanide ate affected by the presence of aldehydes and
significant cyanide losses occur.
6.7.2 Treatment with silver nitrate (7, 9) gave erratic
results, whereas ethylene diamine was found to be reasonably
effective.
6.7.3 The addition of 2 mL of 5 % ethylene diamine
solution per 100-mL sample gives complete recovery of total
cyanides in presence of up to 50 mg/L formaldehyde.
Recovery of dissociable cyanides is not complete. Variable
losses occur depending on the levels of cyanide, aldehyde,
and amount of ethylene diamine added.
6.7.4 For more information refer to Appendix X3,
Aldehyde Interference.
6.8 Fatty.4cids:
6.8.1 Mineral oils do not cause any interferences. Fatty
acids up to 100 mg/L are tolerated by the cyanide automated
system. Higher concentrations of fatty acids interfere me-
chanically with the automated thin film distillation tech-
nique. Apparently the presence of fatty acids leads to the
escape of gases through the waste trap system. In addition
fatty acids may distill over and form soap with the NaOH
absorbing solution and interfere with the cyanide
colorimetric determination.
6.8.2 Excessive amounts of fatty acids can be removed by
liquid-liquid extraction. Extraction at a pH 6-7 as suggested
by Kruse and Mellon (5) caused significaot cyanide losses up
to 50 %. ExtraMion at pH 12 with trichlorotrifluoroethanes,
hexane, or isooctane is adequate and cyanide recoveries are
satisfactory (about 90 %). Use a solvent volume about I'/S of
the sample. One or two extractions should reduce the fatty
acids below the interfering level. Salting out effect by the
s Trichlorotriauoronhane is commonly known az Freon, of equivalent.
addition of NaCI (5 to 8 g per 500-mL sample) enhances the
extraction and separation.
6.9 Potential Cyanide Forming Mau~rials and Thiocva-
nate:
6.9.1 Several substances, namely cyanate, thiocyanate,
nitrobenzene, urea, thiourea, glycine :tnd cysteine, were
investigated to determine if they hydrolyze or break down
under [he experimental conditions and interfere with the
cyanide determination.
6.9.2 None of these materials gave interferences in the
acid dissociable cyanide measurement.
6.9.3 Only the sulfur containing substances give variable
positive interferences with the total cyanide determination.
Thiocyanate gives cyanide values on t.n equimolar basis.
Each I mg/L thiourea produces a respo Ise of about 5 µg/L
CN. cysteine interferes only at very high levels and can be
considered negligible up to 100 mg/L. Thiourea and cysteine
aze not likely to be found in significart concentrations in
natural or wastewater. On the other hand, thiocyanate can be
determined (9) and subtracted from the total cyanide mea-
surement. (See Test Method D 4193.)
7. Apparatus
7.1 Automated Analysis Modulesb, as follows:
7.1.1 Sampler with Stirrer, 20 samples per hour (1:1).
7.1.2 Proportioning Ptemp.
7.1.3 Colorimeter, with a 580-nm filter and a 1 S-mm flow
cell.
7.1.4 Recorder.
7.1.5 Printer (optional).
7.2 Manifold, the flow diagram and details of which are
presented in Fig. 1. Note the thin film distillation unit and
the ultraviolet (UV) irradiator.
7.3 Thin Film Distillation Unit (6):
7.3.1 The unit is made of borosilicate glass tubing and a
schematic is presented in Fig. 2. It corsists of a horizontal
tube (A), 8-mm inside diameter (10-mtn outside diameter),
25 cm long, and is slightly tilted downwards with a slope of
about 5°. The tube accommodates the continuous flaw of
acidified samples. The horizontal tub: is connected to a
vertical tube (B), 5-mm inside diameter and 170 mm long, to
carry the HCN gas evolved to the absort~er. The non-distilled
portion of the acidified sample flows to the waste trap (C).
7.3.2 Waste Trap-The waste trap is a two piece unit.
The inside piece connects to the distillation unit by a 12/5
spherical join[ and clamp (S/P No. C6120-I, size 12). This
inner piece is placed into the outer jacketing 200 by 22-mm
outside diameter tube by means of a 19/22 ground glass
joint. When in operation, the nondistilled waste flows by
gravity from [he distillation unit to :he inner piece and
continues downwards [o the bottom of'.he outer tube. When
the outer tube has been filled, the waste exits from the side
outlet.
7.3.3 Heating and Temperature Control-The unit basi-
cally consists of an aluminum bar and temperature control
components, The aluminum bar (Fig. 2) dissipates heat to
the thin film of the acidified sample. The temperature of the
"Suitable AutoAnalvzer II modulo arc available from Ttthnicon Inc..
Tarrytown NY. Similar equipment rrom other manufacturers may also be suiuble.
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