State of California

Air Resources Board

Method 426

Determination of Cyanide Emissions

from Stationary Sources

Adopted: January 22, 1987

Method 426 - Determination of Cyanide Emissions from Stationary Sources

1. APPLICABILITY AND PRINCIPLE

1.1 Applicability
This method is for determination of cyanides in aerosol and gas emissions
from stationary sources. Cyanide is defined as cyanide ion and complex
cyanide converted to hydrocyanic acid (HCN) by reaction in a reflux
system of a mineral acid in the presence of magnesium ion.

1.2 Principle
Particulate and gaseous emissions are extracted isokinetically from the
stack and passed through an impinger-filter train where the cyanide is
collected on a glass-fiber filter and in a solution of sodium hydroxide. The
combined filter extract and impinger solution are analyzed for cyanide by
either titrating with standard silver nitrate in the presence of a silver
sensitive indicator or by colorimetric procedure using Chloramine-T with
either pyridine-barbituric acid or pyridine-pyrazolone color forming
reagents.

2. RANGE AND SENSITIVITY

The titration procedure using silver nitrate with p-dimethylamino-benzal-

rhodanine indicator is used for measuring concentrations of cyanide greater than
1 mg/L (0.25 mg/250 mL of absorbing liquid). The detection limit for this
procedure is 0.3 mg/L.

The colormetric procedure has an optimum working range of 0.02 - 1 mg/L, and
a detection limit of 0.01 mg/L.

3. INTERFERENCES

Sulfides adversely affect the colorimetric and titration procedures. Samples that
contain hydrogen sulfide, metal sulfides or other compounds that may produce
hydrogen sulfide during the distillation should be distilled by the procedure
described in Section 6.3.3.2. The apparatus for this procedure is shown in
Figure 3.

Positive errors may occur with samples that contain nitrite and/or nitrate. During
the distillation, nitrite and nitrate form nitrous acid which reacts with some
organic compounds to form oximes. These compounds will decompose under
test conditions to generate HCN. The interference of nitrite and nitrate is
eliminated by pretreatment with sulfamic acid.

January 1987 CARB Method 426 Page 1

 Since oxidizing agents may decompose most of the cyanides, they must be
removed during sample recovery (Section 6.2.1.1).

If the analytical method herein recommended does not give the desired
sensitivity in the presence of interfering substances in the sample, the tester may
select an equivalent procedure, subject to the approval of the Executive Officer.
The tester must then produce data to demonstrate that the method is equivalent,
and substantiate this data through an adequate quality assurance program
approved by the Executive Officer.

4. APPARATUS

The following sampling apparatus is recommended. The tester may use an

alternative sampling apparatus only if, after review by the Executive Officer, it is
deemed equivalent for the purposes of the method.

4.1 Sampling Train

A schematic diagram of the sampling train is shown in Figure 1. This is
similar to the CARB Method 5 sampling train with some minor changes
which are described below.

4.1.1 Probe Nozzle, Probe Liner, Pitot Tube, Differential Pressure

Gauge, Filter Holder, Filter Heating System, Metering System,
Barometer and Gas Density Determination Equipment. Same as
Method 5, Sections 2.1.1 to 2.1.6, and 2.1.8 to 2.1.10,
respectively.

4.1.2 Impingers. Four impingers are connected in series with glass

ball joint fittings. The first, third, and fourth impingers are of the
Greenburg-Smith design modified by replacing the tip with a 1-
cm (0.5 in.) I.D. glass tube extending to 1 cm from the bottom of
the flask. The second impinger is of the Greenburg-Smith
design with the standard tip.

The first and second impingers shall contain known quantities of

0.1 N NaOH (Section 6.1.3). The third shall be empty, and the
fourth shall contain a known weight of silica gel or equivalent
desiccant.

In the case of sources which produce significant levels of carbon

dioxide, the tester may substitute sodium bicarbonate for sodium
hydroxide in the first and second impingers.

January 1987 CARB Method 426 Page 2

 o o
A thermometer which measures temperatures to within 1 C (2
F), should be placed at the outlet of the fourth impinger.

4.2 Sample Recovery.

The following items are needed:

4.2.1 Probe Liner and Probe Nozzle Brushes, Petri Dishes, Plastic
Storage Containers, Rubber Policeman and Funnel. Same as
Method 5, Sections 2.2.1, 2.2.4, 2.2.6 and 2.2.7, respectively.

4.2.2 Wash Bottles. Glass (2)

4.2.3 Sample Storage Containers. Alkali resistant polyethylene

bottles. Impinger and probe solutions and washes, 1000 mL.
Use screw-cap liners that are either rubber-backed Teflon or
leak-free and resistant to attack by alkali.

4.2.4 Graduated Cylinder and/or Balance. To measure the volume of

condensed water to within 2 mL, or the weight to within 1 g. Use
a graduated cylinder that has a minimum capacity of 500 mL,
and subdivisions no greater than 2 mL. (Most laboratory
balances are capable of weighing to the nearest 0.5 g or less).

4.2.5 Funnel. Glass, to aid in sample recovery.

4.3 Analysis.
The following equipment is needed:

4.3.1 Reflux distillation apparatus assembled as shown in Figure 1 or

Figure 2. The boiling flask should be of 1 liter size with inlet tube
and provision for condenser. The gas absorber may be a
Fisher-Milligan scrubber.

4.3.2 Microburet. 5.0 mL (for titration).

4.3.3 Spectrophotometer suitable for measurements at 578 nm or 620

nm with a 1.0 cm cell or larger.

4.3.4 Reflux distillation apparatus for sulfide removal as shown in

Figure 3. The boiling flask should be of 1-liter size with inlet tube
and provision for condenser as in 4.3.1. The sulfide scrubber
may be a Wheaton Bubbler #709682 with 29/42 joints, size 100

January 1987 CARB Method 426 Page 3

 mL. The air inlet tube should not be fritted. The cyanide
absorption vessel should be the same as the sulfide scrubber.
The air inlet tube of this absorber should be fritted.

4.3.5 Flow Meter. Such as Lab Crest with stainless steel float (Fisher
11-164-50).

4.3.6 Erlenmeyer Flasks. 125-mL. 24/40 .

4.3.7 Whatman No. 42 filter paper (or equivalent).

4.3.8 Volumetric Flasks. 100-mL, 250-mL and 1000-mL.

4.3.9 Balance - Analytical. Capable of accurately weighing to the

nearest 0.0001 g.

5. REAGENTS

Unless otherwise specified, use ACS reagent grade chemicals or equivalent.

Mention of trade names or specific products does not constitute endorsement by

the California Air Resources Board.

5.1 Sampling.
The following reagents are needed:

5.1.1 Glass Fiber Filters, Silica Gel, Crushed Ice and Stopcock
Grease. Same as Method 5, Sections 3.1.1, 3.1.2, 3.1.4 and
3.1.5, respectively.

5.1.2 Water. Deionized, distilled, to conform to ASTM Specification

D1193-77, Type 3. If high concentrations of organic matter are
not expected to be present, the analyst may omit the potassium
permanganate test for oxidizable organic matter.

5.1.3 Sodium Hydroxide Solution, 0.1 N. Dissolve 4.0 g NaOH in

deionized distilled water, and dilute to 1 liter with water.

5.2 Sample Recovery.

5.2.1 Sodium Hydroxide Solution, 0.1 N. Same as 5.1.3 above.

5.2.2 Sodium Hydroxide Solution, 10 N. Dissolve 40 g NaOH in

January 1987 CARB Method 426 Page 4

 deionized distilled water, and dilute to 100 mL.

5.2.3 Ascorbic acid, crystals.

5.2.4 Potassium iodide-starch test paper (KI-starch paper).

5.3 Analysis.
The following reagents are needed:

5.3.1 Water. Same as 5.1.2 above.

5.3.2 Sodium Hydroxide Solution, 1.25 N. Dissolve 50 g of NaOH in

deionized distilled water, and dilute to 1 liter.

5.3.3 Dilute Sodium Hydroxide Solution, 0.25 N. Dilute 200 mL of

1.25 N sodium hydroxide solution (5.3.2) to 1000 mL with
deionized distilled water.

5.3.4 Sulfuric Acid, 18 N. Slowly add 500 mL of concentrated H2SO4

to 500 mL deionized distilled water.

5.3.5 Sodium Dihydrogenphosphate, 1M. Dissolve 138 g of

NaH2PO4.H2O in 1 liter of deionized distilled water. Refrigerate
this solution.

5.3.6 Standard silver nitrate solution, 0.0192 N. Prepare by crushing

approximately 5 g AgNO3 crystals and drying to constant weight
o
at 40 C. Weigh out 3.2647 g of dried AgNO3, dissolve in
deionized distilled water, and dilute to 1000 mL (1 mL = 1 mg
-
CN ).

5.3.7 Stock Cyanide Solution. Dissolve 2.51 g of KCN and 2 g of KOH

in 900 mL of deionized distilled water. Standardize with 0.0192
N AgNO3 (Section 5.3.6). Dilute to appropriate concentration so
-
that 1 mL = 1 mg CN .

5.3.8 Intermediate standard cyanide solution. Dilute 100.0 mL of

-
stock cyanide solution (1 mL = 1 mg CN ) to 1000 mL with
-
deionized distilled water. (1 mL = 100.0 ug CN ).

5.3.9 Working standard cyanide solution. Prepare fresh daily by

diluting 100.0 mL of intermediate cyanide solution to 1000 mL
with distilled water and store in a glass stoppered bottle (1 mL =

January 1987 CARB Method 426 Page 5

 -
10.0 ug CN ).

5.3.10 Cyanide Calibration Standards. Pipet 0.0, 1.0, 2.0, 5.0, 10.0,
15.0 and 20.0 mL of the working cyanide standard solution
(5.3.9) into 250-mL volumetric flasks. To each flask, add 50 mL
of 1.25 N sodium hydroxide, and dilute to 250 mL with deionized
distilled water. These working standards contain 0.0, 0.04, 0.08,
-
0.20, 0.40, 0.60 and 0.80 mg CN /L, respectively. Prepare as
needed, additional standards at other concentrations in a similar
manner.

5.3.11 Rhodanine indicator. Dissolve 20 mg of p-dimethyl-amino-

benzalrhodanine in 100 mL of acetone.

5.3.12 Chloramine-T solution. Dissolve 1.0 g of white, water-soluble

Chloramine-T in 100 mL of deionized distilled water and
refrigerate until ready to use. Prepare fresh daily.

5.3.13 Color Reagent - One of the following may be used:

5.3.13.1 Pryidine-Barbituric Acid Reagent. Place 15 g of

barbituric acid in a 250 mL volumetric flask and
add just enough distilled water to wash the sides of
the flask and wet the barbituric acid. Add 75 mL of
pyridine and mix. Add 15 mL of conc. HCl, mix,
and cool to room temperature. Dilute to 250 mL
with deionized distilled water and mix. This
reagent is stable for approximately six months if
stored in a cool, dark place.

5.3.13.2 Pyridine-pyrazolone solution.

(a) 3-Methyl-l-phenyl-2-pyrazolin-5-one reagent,

saturated solution. Add 0.25 g of 3-methyl-1-
phenyl-2-pyrazolin-5-one to 50 mL of distilled
o
water, and heat to 60 C with stirring. Cool to
room temperature.

NOTE: It is imperative that this synthesis be

performed as directed.

(b) 3,3'Dimethyl-1, 1'-diphenyl-[4,4'-bi-2

pyrazoline]-5,5'dione (bispyrazolone): Dissolve

January 1987 CARB Method 426 Page 6

 0.01 g of bispyrazolone in 10 mL of pyridine.

(c) Pour solution (5.3.13.2a) through non-acid-

washed filter paper. Collect the filtrate.
Through the same filter paper pour solution
(5.3.13.2b) collecting the filtrate in the same
container as filtrate from (5.3.13.2a). Mix until
the filtrates are homogeneous. The mixed
reagent develops a pink color but this does not
affect the color production with cyanide if used
within 24 hours of preparation.
.
5.3.14 Magnesium chloride solution. Weigh 510 g of MgCl2 6H2O into
a 1000 mL flask. Dissolve and dilute to 1 liter with deionized
distilled water.
.
5.3.15 Lead acetate. Dissolve 30 g of Pb(C2H3O2) 3H2O in 950 mL of
deionized distilled water. Adjust the pH to 4.5 with acetic acid.
Dilute to 1 liter.

5.3.16 Sulfamic acid.

6. PROCEDURE

6.1 Sampling.
Because of the complexity of this method, testers should be trained and
experienced with the test procedures in order to ensure reliable results.

6.1.1 Pretest Preparation. Follow the same general procedure

described in Method 5, Section 4.1.1, except the filter need not
be weighed.

6.1.2 Preliminary Determinations. Follow the same general procedure

described in Method 5, Section 4.1.2.

6.1.3 Preparation of Collection Train. Follow the same general

procedure given in Method 5, Section 4.1.3, except place 100
mL of 0.1 N NaOH in each of the first two impingers, leave the
third impinger empty, and transfer approximately 200 to 300 g of
preweighed silica gel from its container to the fourth impinger.
Assemble the train as shown in CARB Method 5, Figure 5-1.

6.1.4 Leak-Check Procedures. Follow the general leak-check

January 1987 CARB Method 426 Page 7

 procedures given in Method 5, Sections 4.1.4.1 (Pretest Leak-
Check), 4.1.4.2 (Leak-Checks During the Sample Run), and
4.1.4.3 (Post-Test Leak-Check).

6.1.5 Sampling Train Operation. Follow the same general procedure

given in Method 5, Section 4.1.5. For each run, record the data
required on a data sheet such as the one shown in CARB
Method 5, Figure 5-2.

6.1.6 Calculation of Percent Isokinetic. Same as Method 5, Section

4.1.6.

6.2 Sample Recovery.

Begin proper clean-up procedure as soon as the probe is removed from
the stack at the end of the sampling period.

Allow the probe to cool. When it can be safely handled, wipe off all
external particulate matter near the tip of the probe nozzle and place a
cap over it. Do not cap off the probe tip tightly while the sampling train is
cooling, as this would create a vacuum in the filter holder, thus drawing
liquid from the impingers into the filter.

Before moving the sampling train to the cleanup site, remove the probe
from the sampling train, wipe off the silicone grease, and cap the open
outlet of the probe. Be careful not to lose any condensate that might be
present. Wipe off the silicone grease from the glassware inlet where the
probe was fastened and cap the inlet. Remove the umbilical cord from
the last impinger and cap the impinger. The tester may use ground-glass
stoppers, plastic caps, or serum caps to close these openings.

Transfer the probe and filter-impinger assembly to a cleanup area, which

is clean and protected from the wind so that the chances of contaminating
or losing the sample are minimized.

Inspect the train prior to and during disassembly and note any abnormal
conditions.

Check the pH of the impinger solutions to ascertain that the pH is still

basic, and that the test was a valid one.

Treat the samples as follows:

6.2.1 Container No. 1 (Filter). Carefully remove the filter from the filter

January 1987 CARB Method 426 Page 8

 holder and place it in a glass sample container containing 50 mL
of 0.1 N NaOH. Carefully transfer any visible particulate matter
and/or filter fibers that adhere to the filter holder gasket with a
dry Nylon bristle brush and/or sharp-edged blade.

6.2.1.1 Oxidising agents. If oxidising agents are known or

suspected to be present, test and treat the sample
as follows. Test a drop of the sample with
potassium iodide-starch test paper (KI-starch
paper). A blue color indicates the need for
treatment. Add ascorbic acid, few crystals at a
time, until a drop of sample produces no color on
the indicator paper. Then add an additional 0.6 g
of ascorbic acid for each liter of sample volume.

6.2.1.2 Preservation. Samples must be preserved with 2

mL 10 N sodium hydroxide (5.3.2) per liter of
sample (pH ≥ 12) at the time of collection.

6.2.2 Container No. 2 (Probe). Taking care that dust on the outside of
the probe or other exterior surfaces does not get into the
sample, clean all surfaces that have been exposed to the
sample (including the probe nozzle, probe fitting, probe liner,
and front half of the filter holder) with 0.1 N NaOH. Place the
wash in a glass sample storage container. Measure and record
(to the nearest 2-mL) the total amount of 0.1 N NaOH used for
each rinse. Perform the rinses with 0.1 N NaOH as follows:

Carefully remove the probe nozzle and rinse the inside surface
with 0.1 N NaOH from a wash bottle. Brush with a Nylon-bristle
brush, and rinse until the rinse shows no visible particles, after
which, make a final rinse of the inside surface. Brush and rinse
the inside parts of the Swagelok fitting with 0.1 N NaOH in a like
manner until no visible particles remain.

Rinse the probe liner with 0.1 N NaOH. While squirting the
sodium hydroxide rinse into the upper end of the probe, tilt and
rotate the probe so that all inside surfaces will be wetted with the
0.1 N NaOH. Let the 0.1 N NaOH drain from the lower end into
the sample container. The tester may use a glass funnel to aid
in transferring liquid washes to the container. Follow the rinse
with a probe brush. Hold the probe in an inclined position, and
squirt 0.1 N NaOH into the upper end as the probe brush is

January 1987 CARB Method 426 Page 9

 being pushed with a twisting action through the probe. Hold the
sample container underneath the lower end of the probe, and
catch any liquid and particulate matter brushed from the probe.
Run the brush through the probe three times or more until no
visible sample matter is carried out with the 0.1 N NaOH and
none remains on the probe liner on visual inspection. With
stainless steel or other metal probes, run the brush through in
the above prescribed manner at least six times, since metal
probes have small crevices in which particulate matter can be
entrapped. Rinse the brush with 0.1 N NaOH and quantitatively
collect these washings in the sample container. After the
brushing, make a final rinse of the probe as described above. It
is recommended that two people clean the probe to minimize
loss of sample: Between sampling runs, keep brushes clean
and protected from contamination.

After ensuring that all joints have been wiped clean of silicone
grease, brush and rinse with 0.1 N NaOH the inside of the front
half of the filter holder. Brush and rinse each surface three
times or more, if needed, to remove visible particulate matter.
Make a final rinse of the brush and filter holder.

After all washings have been collected in the sample container,

test a drop of the sample with potassium iodide-starch test paper
(KI-starch paper). A blue color indicates the need for treatment.
Add ascorbic acid, a few crystals at a time, until a drop of
sample produces no color on the indicator paper. Then add an
additional 0.6 g of ascorbic acid for each litre of sample volume.

Samples must be preserved with 2 mL 10 N sodium hydroxide

per liter of sample (pH ≥ 12) at the time of collection.

Tighten the lid on the sample container so that the fluid will not
leak out when it is transported to the laboratory. Mark the height
of the fluid level to determine whether leakage occurs during
shipment. Label the container to clearly identify its contents.

Rinse the glassware a final time with water to remove residual

NaOH before reassembling. Do not save the final rinse water.

Repeat the test for oxidising agents (6.2.1.1) and then preserve
the sample (6.2.1.2).

January 1987 CARB Method 426 Page 10

 6.2.3 Container No. 3 (Silica Gel). Check the color of the indicating
silica gel to determine if it has been completely spent, and note
its condition. Transfer the silica gel from the fourth impinger to
the original container and seal. The tester may use a funnel to
pour the silica gel and rubber policeman to remove the silica gel
from the impinger. It is not necessary to remove the small
amount of particles that may adhere to the impinger walls and
are difficult to remove. Since the gain in weight is to be used for
moisture calculations, do not use any water or other liquids to
transfer the silica gel. If a balance is available in the field, the
tester may follow the procedure for Container No. 2 under
Section 6.4 (Analysis).

6.2.4 Container No. 4 (Impingers). If the volume of liquid is large, the

tester may place the impinger solutions in several containers.
Clean each of the first three impingers and connecting
glassware in the following manner:

1. Wipe the impinger ball joints free of silicone grease and

cap the joints.

2. Rotate and agitate each impinger, so that the impinger

contents might serve as a rinse solution.

3. Transfer the contents of the impingers to a 500-mL

graduated cylinder. Remove the outlet ball joint cap and
drain the contents through this opening. Do not separate
the impinger parts (inner and outer tubes) while
transferring their contents to the cylinder. Measure the
liquid volume to within + 2 mL. Alternatively, determine
the weight of the liquid to within + 0.5 g. Record in the log
the volume or weight of the liquid present, and the
occurrence of any color or film in the impinger catch. The
liquid volume or weight is needed, along with the silica gel
data, to calculate the stack gas moisture content (see
Method 5, Figure 5-3).

Determine the pH of the impinger solution to ascertain

whether it is still basic and whether the test was a valid
one.

4. Transfer the contents to Container No. 4.

January 1987 CARB Method 426 Page 11

 5. Note: In steps 5 and 6 below, measure and record the
total amount of 0.1 N NaOH used for rinsing. Pour
approximately 30 mL of 0.1 N NaOH into each of the first
three impingers and agitate the impingers. Drain the 0.1
N NaOH through the outlet arm of each impinger into
Container No. 3. Repeat this operation a second time;
inspect the impingers for any abnormal conditions.

6. Wipe the ball joints of the glassware connecting the

impingers free of silicone grease and rinse each piece of
glassware twice with 0.1 N NaOH; transfer this rinse into
Container No. 3. (Do not rinse or brush the glass-fritted
filter support). Repeat the procedure described in Section
6.2.1.1 above.

Mark the height of the fluid level to determine whether

leakage occurs during transport. Label the container to
clearly identify its contents.

6.2.5 Sample Blanks (Container No. 5). Prepare a blank by placing an

unused filter in a glass container, and adding a volume of
recovery solution identical to the total volume in Containers No.
1, 2 and 4. Process the blank in the same manner as the
sample.

6.3 Sample Preparation.

6.3.1 Container No. 1 (Filter). Cut the filter into strips and transfer the
strips and all loose particulate matter into a 125-mL Erlenmeyer
flask. Rinse the petri dish with 10 mL of 1.25 N NaOH to insure
a quantitative transfer and add to the flask. Pipet 25 mL of 1.25
N NaOH into the flask. Cap the flask, place on a shaker and
shake for at least 30 minutes at moderate speed to complete the
extraction.

6.3.2 Containers No. 2 and No. 4 (Probe and Impingers). Check the
liquid level in Containers No. 2 and/or No. 4 to determine
whether any sample was lost during shipment. Record
observations on the analysis sheet. If a noticeable amount of
leakage has occurred, either void the sample or take steps,
subject to approval by the Executive Officer, to adjust the final
results. Combine the contents of Containers No. 2 and No. 4
with the filter extract (6.3.1) for analysis.

January 1987 CARB Method 426 Page 12

 6.3.3 Distillation Procedure.

6.3.3.1 Samples without sulfide. Place 500 mL of the

combined sample (Section 6.3.2) or an aliquot
diluted to 500 mL in the 1 liter boiling flask. Pipet
50 mL of 1.25 N sodium hydroxide (5.3.2) into the
absorbing tube. If the apparatus in Figure 1 is
used, add distilled water until the spiral is covered.
Connect the boiling flask, condenser, absorber
and trap as shown in Figure 1 or Figure 2.

Start a slow stream of air entering the boiling flask

by adjusting the vacuum source. Adjust the
vacuum so that approximately two bubbles of air
per second enter the boiling flask through the inlet
tube. Proceed to Section 6.3.5.

6.3.3.2 Samples that contain sulfide. Place 500 mL of the

combined sample (6.3.2) or an aliquot diluted to
500 mL in the 1-liter boiling flask. Pipet 50 mL of
1.25 N sodium hydroxide into the absorbing tube.
Add 25 mL of lead acetate solution (5.3.15) to the
sulfide scrubber. Connect the boiling flask,
condenser, scrubber and absorber as shown in
Figure 3. The flow meter is connected to the outlet
tube of the cyanide absorber.

Start a stream of air entering the boiling flask by

adjusting the vacuum source. Adjust the vacuum
so that approximately 1.5 liters per minute enter
the boiling flask through the air inlet tube. The
bubble rate may not remain constant while heat is
being applied to the flask. It may be necessary to
readjust the air rate occasionally. Proceed to
6.3.5.
- -
6.3.4 If samples contain NO3 and/or NO2 , add 2 g of sulfamic acid
(5.3.16) after the air rate is set through the air inlet tube. Mix for
3 minutes prior to addition of H2SO4.

6.3.5 Slowly add 50 mL 18 N sulfuric acid (5.3.4) through the air inlet
tube. Rinse the tube with deionized distilled water and allow the

January 1987 CARB Method 426 Page 13

 airflow to mix the flask contents for 3 minutes. Pour 20 mL of
magnesium chloride solution (5.3.13) into the air inlet and wash
down with a stream of water.

Heat the solution to boiling. Reflux for one hour. Turn off the
heat and continue the airflow for at least 15 minutes. After
cooling the boiling flask, disconnect the absorber and close off
the vacuum source.

Drain the solution from the absorber into a 250 mL volumetric

flask. Wash the absorber with deionized distilled water, and add
the washings to the flask. Dilute to volume with deionized
distilled water.

6.3.6 Sample Blank (Container No. 5). Treat in the same manner as
the sample (Sections 6.3.3 to 6.3.5). Use the absorbance
obtained for the blank to correct the sample measurement.

6.4 Analysis.

6.4.1 Colorimetric Procedure. Sample (Containers No. 1, No. 2 and

No. 4.). Withdraw 50 mL or less of the solution from the 250-mL
volumetric flask (Section 6.3.3.1 or 6.3.3.2) and transfer to a 100
mL volumetric flask. If less than 50 mL is taken, dilute to 50 mL
with 0.25 N sodium hydroxide solution (5.3.3). Add 15.0 mL of 1
M sodium dihydrogenphosphate solution (5.3.5) and mix.

6.4.1.1 Pyridine-Barbituric Acid Method. Add 0.5 mL of

chloramine T (5.3.12) and mix. See Notes 1 and 2.
After 1 to 2 minutes, add 5 mL of pyridine-
barbituric acid solution (5.3.13.1) and mix. Dilute
to volume with distilled water and mix again. Allow
8 minutes for color development then measure the
absorbance at 578 nm in a 1 cm cell within 15
-
minutes. Read ug CN /50 mL from the calibration
curve obtained in Section 7.2. If the absorbance
does not fall within the range of the calibration
curve, repeat the procedure using a smaller
aliquot.

6.4.1.2 Pyridine-Pyrazolone method. Add 0.5 mL of

chloramine T (5.3.12) and mix. See Notes 1 and 2.
After 1 to 2 minutes, add 5 mL of pyradine-

January 1987 CARB Method 426 Page 14

 pyrazolone solution (5.3.13.2) and mix. Dilute to
volume with distilled water and mix again. After 40
minutes, measure the absorbance at 620 nm in a 1
cm cell. Read the concentration of the sample (ug
-
CN /50 mL) from the calibration curve obtained in
Section 7.2. If the absorbance of the sample does
not fall within the range of the calibration curve,
repeat the analysis using a smaller aliquot.

NOTE 1 Some distillates may contain compounds that have

a chlorine demand. One minute after the addition
of chloramine T, test for residual chlorine with KI-
starch paper. If the test is negative, add an
additional 0.5 mL of chloramine T. After one
minute, recheck the sample.

NOTE 2 If more than 0.5 mL of chloramine T is used with

the pyridine-pyrazolone color reagent, this will
prevent the color from developing.

If more than 0.5 mL of chloramine-T is used with

the pyridine-barbituric acid color reagent, this will
accelerate the rate at which the color fades.

6.4.2 Titration Procedure. If the sample contains more than 1 mg of

-
CN /L, transfer the distillate (6.3.3), or a suitable aliquot diluted
to 250 mL, to a 500-mL Erlenmeyer flask. Add 10-12 drops of
the benzalrhodanine indicator. Titrate with standard silver nitrate
solution (5.3.6) to the first change in color from yellowish-brown
to pink. Titrate the blanks using the same amount of sodium
hydroxide and indicator as in the sample.

The analyst should familiarize himself with the end point of the
titration and the amount of indicator to be used before actually
titrating the samples. A 5- or 10-mL microburet may be used to
obtain a more precise titration.

6.4.3 Sample Blank (Container No. 5). Follow the same procedure
used for the sample (Section 6.4.1 or 6.4.2 above). Use the
same aliquot size as that used for the sample.

6.4.4 Container No. 3 (Silica Gel). The tester may conduct this step in
the field. Weigh the spent silica gel (or silica gel plus impinger)

January 1987 CARB Method 426 Page 15

 to the nearest 0.5 g; record this weight.

7. CALIBRATION.

7.1 Sampling Train Calibration.

Calibrate the sampling train components according to the following
sections of Method 5: Probe Nozzle (Section 5.1); Pitot Tube (Section
5.2); Metering System (Section 5.3); Probe Heater (Section 5.4);
Temperature Gauges (Section 5.5); Leak-Check of the Metering System
(Section 5.6); and Barometer (Section 5.7).

7.2 Spectrophotometer.
Pipet 50 mL of each calibration standard (5.3.10) into a 100-mL
volumetric flask, and treat according to Section 6.4.1. These standards
-
will contain 0.0, 2.0, 4.0, 10.0, 20.0, 30.0 and 40.0 ug CN /50 mL.

With the spectrophotometer at 620 nm for pyridine-pyrazolone, or 578 nm

for pyridine-barbituric acid, use the reagent blank (7.2) to set the
absorbance to zero. Determine the absorbance of the standards, and plot
-
net absorbance versus ug CN /50 mL. Draw a smooth curve through the
points. The curve should pass through the origin.

7.2.1 Samples without sulfide. It is not imperative that all standards

be distilled in the same manner as the samples. However, it is
recommended that at least two standards (a high and low) be
distilled and compared to similar values on the curve to ensure
that the distillation technique is reliable. If distilled standards do
not agree within ±10% of the undistilled standards, the operator
should find the cause of the apparent error before proceeding.

7.2.2 Samples that contain sulfide. It is imperative that all standards

be distilled in the same manner as the samples. Standards
distilled by this method will give a linear curve, but as the
concentration increases, the recovery decreases. It is
recommended that at least 3 standards be distilled.

7.3 To check the efficiency of the sample distillation, add an increment of

cyanide from either the intermediate standard (5.3.8) or the working
standard (5.3.9) to 500 mL of sample to insure a level of 20 ug/L.
Proceed with the analysis as in Section 6.3.3.

January 1987 CARB Method 426 Page 16

8. CALCULATIONS.

8.1 Nomenclature

At = Aliquot of total sample added to the still, mL (6.3.3)

Ad = Aliquot of distillate taken for color development, mL

(6.4.1).
-
Cc = ug CN from the calibration curve

Vd = Volume of distillate after dilution, mL (6.3.3)

Vt = Total volume of cyanide sample after final dilution, mL

(6.3.2)

mt = Total cyanide in sample, mg

3
Cs = Concentration of cyanide in the stack gas, mg/m , dry
basis, corrected to standard conditions of 760 mm Hg
o o
(29.92 in. Hg) and 293 K (528 R).

Qt = Aliquot of sample used for titration, mL

T = Volume of AgNO3 for titration of sample, mL

B = Volume of AgNO3 for titration of blank, mL

8.2 Dry Gas Volume.

Using the data from this test, calculate Vm(std) the total volume of dry gas
o
metered corrected to standard conditions (20 C and 760 mm Hg), by
using Equation 5-1 of Method 5. If necessary, adjust Vm(std) for leakages
as outlined in Section 6.3 of Method 5. See the field data sheet for the
average dry gas meter temperature and average orifice pressure drop.

8.3 Volume of Water Vapor and Moisture content.

Using data obtained in this test and Equations 5-2 and 5-3 of Method 5,
calculate the volume of water vapor Vw(std) and the moisture content Bws of
the stack gas.

8.4 Total Cyanide in Sample.

Colorimetric Procedure. Use the following equation to calculate the

January 1987 CARB Method 426 Page 17

 -
amount of CN in the sample:
-3
10 x V t x V d Cc
mt = Eq. 1
At x Ad

Titration Procedure. Use the following equation to calculate the amount of

-
CN in the sample:
(T - B) x V t x 250
mt = Eq. 2
A t x Qt

8.5 Total Cyanide Concentration in Stack Gas.

Use the following equation to calculate total cyanide concentration in the
stack gas:
K x mt
Cs = Eq. 3
Vm(std)

Where:
3 3
K = 1.00 m /m if Vm(std) is expressed in metric units.
3 3
K = 35.31 ft /m if Vm(std) is expressed in English units.

8.5 Isokinetic Variation and Acceptable Results.

Same as Method 5, Sections 6.11 and 6.12, respectively. To calculate Vs
the average stack gas velocity, use equation 2-9 of Method 2 and the data
from this field test.

9. ALTERNATIVE TEST METHODS FOR TOTAL CYANIDE.

9.1 NIOSH Method 7904 (Reference 10.4).

Airborne cyanides (gas and aerosol) are collected on a cellulose ester
membrane filter and in a KOH bubbler. Because the particulate cyanide
collected on the filter can liberate HCN which is trapped in the bubbler, the
method cannot distinguish between HCN formed in this manner and HCN
originally present in the air. Cyanide concentration is determined with an
ion-specific electrode.

Interferences are significant. Sulfide, iodide, bromide, cadmium, zinc,

January 1987 CARB Method 426 Page 18

 silver, nickel, cuprous ion, and mercury are named as elements or
compounds which affect the performance of the ion-specific electrode.
Except for sulfide, the method does not propose remedies for minimizing
or eliminating these interferences.

10. BIBLIOGRAPHY.

10.1 American Society for Testing and Materials. Annual Book of ASTM
Standards. Part 31; Water, Atmospheric Analysis. Philadelphia, Pa.
1974. p. 40-42.

10.2 U.S. Environmental Protection Agency/Office of Solid Waste, Washington,

D.C., Method 9010. In "Test Methods for Evaluating Solid Waste-
Physical/Chemical Methods" SW-846 (1982).

10.3 EPA-600/4-79-020. Method 335.2. In "Methods for Chemical Analysis of

Water and Wastes" (Final report)/J.F. Kopp et al. Environmental
Monitoring and Support Laboratory, Cincinnati, OH. March 1983.

10.4 NIOSH Manual of Analytical Methods, 3rd ed., Method 7904, Cyanides,
Aerosol and gas. U.S. Department of Health and Human Services DHHS
(NIOSH) Publ. No. 84-100. Feb, 1984.

10.5 Same as Method 5, Citations 2 to 5 and 7 of Section 7.

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