Environmental Express MicroBloc - Manual (Page 12)

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HotBlock: Operation and Instruction Manual MicroBlock TM Distillations
Total Cyanide Distillation with the MICROBLOCK TM
Figure 2 - Cyanide Glassware
Cold Finger
C5210
Slip Connector
Absorption
Impinger
C5217
Vacuum Inlet
Distillation
Head
C5216
Reaction
Absorption
Flask
C5012
Drain
Water
Inlet
1.0 SCOPE AND APPLICATION
1.1 This method replicates US EPA
method number 335.4 titled
“Determination of Total
Cyanide by Semi-Automated
Colorimetry”. It is applicable
for the determination of total
cyanide in drinking, ground,
surface, and saline waters,
as well as, domestic and
industrial wastes, and soils.
1.2 The standard range is typically
5 to 500μg/L. Lower detection
limits can be achieved by
using a longer path length
flow cell in the analysis step
when using an automated
continuous flow analyzer.
2.0 SUMMARY OF METHOD
2.1 The cyanide as HCN is
released from metal-cyanide
complexes by means of
an acidic manual reflux-
distillation whereby the
HCN gas that is formed is
separated from the sample
matrix and absorbed in a
dilute solution of sodium
hydroxide. The distillate can
be analyzed for cyanide by
semi-automated colorimetry,
manual colorimetry,
titrimetric, or ion-selective
electrode.
2.2 Reduced volume versions of this method that use the same reagents and molar ratios as in the original method are
acceptable provided they meet the quality control and performance requirements stated in the method.
3.0 INTERFERENCES
There are several known interferences with this method.
A few of these are:
Aldehydes Thiocyanates Nitrate-nitrite
Thiosulfates Chlorine Sulfides
Some of these interferences are reduced or eliminated by the distillation process. For example, the nitrate-nitrite
interference is eliminated by addition of sulfamic acid during the distillation step. Further, the addition of
magnesium chloride, which acts as a catalyst, will promote the breakdown of refractory iron-cyanide complexes. The
reagent preparations for these two interferences will be summarized in the REAGENT PREPARATION SECTION. For all
other pretreatment procedures refer to the US EPA method number 335.4.
4.0 CHEMICALS REQUIRED – DISTILLATION ONLY
4.1 Sodium Hydroxide
4.2 Sulfuric Acid, 18N
4.3 Magnesium Chloride, if refractory iron-cyanide complexes are present