PARAROSANILINE METHOD FOR THE DETERMINATION OF
SULFUR DIOXIDE IN THE ATMOSPHERE --
TECHNICON II AUTOMATED ANALYSIS SYSTEM
EPA Designated Equivalent Method Mo. EQS-0775-002
July 1975
U. S. Environmental Protection Agency
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
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25 July 1975
PARAROSANILINE METHOD FOR THE DETERMINATION OF SULFUR
DIOXIDE IN THE ATMOSPHERE -- TECHNICON II AUTOMATED ANALYSIS SYSTEM
EPA Designated Equivalent Method No. EQS-0775-002
1. Principle and Applicability
1.1 A stable dichlorosulfitomercurate complex, formed by absorp-
tion of S00 from air in a potassium tetrachloromercurate solution, is
(1}
reacted with pararosaniline and formaldehyde in the required amountsv '
by controlling the flow rates of sample and reagents. A pararosaniline
methyl sulfonic acid dye is formed. The absorbance is measured colori-
metrically and converted to an electrical signal. The signal is dis-
played in either digital or analog form on a readout device.
1.2 The method is applicable to integrated sampling of S02 in
ambient air over periods of from 1 to 24 hours. Collected samples are
transferred to a laboratory and analyzed by an automated procedure.
2. Range and Sensitivity
2.1 Concentrations of sulfur dioxide in the range of 25 to 1050
2
yg/sm * (0.01 to 0.40 ppm) can be measured under the conditions given.
One can measure concentrations below 25 yg/sm by sampling larger volumes
of air, but only if the absorption efficiency of the particular system
is first determined. Higher concentrations can be measured by using
smaller gas samples, a larger collection volume, or a suitable dilution
of the collected sample. Beer's Law is followed through the working
analytical range of 0.02 - 1.4 yg S02/ml.
2.2 The lower limit of detection of sample analysis is estimated
to be 0.02 yg S09/ml.v ' This value would represent a concentration of
3 o
4 yg S02/sm * (0.0015 ppm) in a 24 hour sample or about 7 yg S02/sm
(0.003 ppm) in a 1 hour sample. However, the minimum detectable concen-
3
tration for the overall method is 25 yg S09/sm , unless the reliability
3
of measurements of concentrations less than 25 yg/sm can be established
by determining the absorption efficiency at low levels.
*Micrograms per standard cubic meter. Standard conditions are 25°C and
760 mm Hg for this method.
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3. Interferences
3.1 The effects of the principal known interferences have been
minimized or eliminated. Interferences by oxides of nitrogen are elim-
(1 3}
inated by sulfamic acid, ' ozone by time-delay/ ' and heavy metals
by EDTA (ethyl enedi ami ne-tetraacetic acid, disodium salt) and phosphoric
acid/1' 4^ At least 60 yg Fe (III), 10 yg Mn (II), and 10 yg Cr (III)
in 10 ml absorbing reagent can be tolerated in the procedure. No signifv
cant interference has been found with 10 yg Cu (II) and 22 yg V (V).
4 . Precision, Accuracy, and Stability
4.1 An estimate of the relative standard deviation for one-hour
samples at a concentration of 980 yg S02/sm (0.37 ppm) is 5.0 percent.
Estimates of the relative standard deviation for 24-hour samples at
concentrations of 100, 350, and 900 yg S02/sm3 (0.037, 0.13, and 0.34
ppm, respectively) are 4.2, 0.4, and 0.8 percent respectively.
4.2 No data, on accuracy are available.
4.3 The presence of EDTA enhances the stability of S00 in solu-
(5)
tion, and the rate of decay is independent of SO^ concentrationv ' but
is not independent of temperature. At 22°C, loss of S02 occurs at the
rate of 1% per day. Samples stored at 5°C (e.g., in a refrigerator) for
30 days show no detectable loss of SO^.
To minimize loss of SO^, samples should be refrigerated as
soon after collection as possible. Refrigerated shipping containers
("Trans Temp"3 temperature controlled shipping containers available from
Cole-Parmer Co., 7425 North Oak Park Avenue, Chicago, 111. 60648 have
been found to be satisfactory) can be used to transport samples from a
field monitoring site to the laboratory for analysis.
aMention of specific products and/or vendors does not imply endorsement
by the Environmental Protection Agency.
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5. Apparatus
5.1 Sampling
5.1.1 Absorber, 1 hour sampling. An all-glass midget
impinger having a 25 mm outside diameter (O.D.), a total capacity of 30
ml, and a 1 mm diameter orifice having a clearance from the bottom of
the impinger of 4 ± 1 mm. An impinger meeting these specifications is
commercially available from a number of manufacturers.
5.1.2 Absorber, 24 hour sampling. A polypropylene absorp-
tion tube 32 mm in diameter and 164 mm long, with a polypropylene two-
port closure (rubber stoppers are unacceptable because they cause high
and variable blank values). The closure must be fitted with an 8 mm
O.D., 6 mm I.D. glass orifice tube approximately 152 mm long having the
end drawn out to form an orifice of 0.4 ± 0.1 mm and positioned to allow
a clearance of 6 mm from the bottom of the tube.
5.1.3 Air Sample Probe. Teflon, polypropylene, or glass
tube with a polypropylene or glass funnel at the end.
5.1.4 Moisture Trap. Polypropylene tube equipped with a
two-port closure. The entrance port of the closure is fitted with
tubing that extends to the bottom of the trap. The unit is loosely
packed with glass wool to prevent moisture entrainment. (Figure 1.)
5.1.5 Filter. Membrane filter of 0.8 to 2.0 urn porosity.
5.1.6 Pump. Capable of maintaining a vacuum greater than
0.7 atmosphere at the specified flow rate.
5.1.7 Flow Control and Measurement Devices.
5.1.7.1 Flow Control Device. Any device capable of
maintaining a constant flow rate (± 2 percent) can be used. For one
hour sampling (0.5 1/min), a 23-gauge hypodermic needle 16 mm long
(Figure 1) or a needle valve (Figure 1-A) is suggested. For 24-hour
sampling (0.2 1/min), a 27-gauge hypodermic needle 10 mm long is sug-
gested. In either case the needle valve or critical orifice must be
protected from particulate matter and moisture entrainment.
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5.1.7.2 Flow Measurement Device. Properly calibrated
flow measuring device such as rotameter, wet test meter, bubble flow-
meter, etc.
5.1.8 Diagram. The arrangement of the component parts for
atmospheric sampling is shown in Figure 1.
5.2 Analysis
5.2.1 A Technicon II automated analysis system (manufac-
tured by Technicon Instruments Corporation, Tarrytown, New York 10591),
consisting of the components described below, is used for the analysis.
Figure 2 shows the arrangement of components.
5.2.2 Sampler IV turntable, Technicon Part No. 171-A017-
03E. Set for 40 samples/hour and a 6:1 ratio of sample to wash time.
5.2.3 Proportioning pump III, Technicon Part No. 133-AOOO-
05L. Capable of maintaining the flow rates indicated in Figure 2. Pump
tubing for the Proportioning Pump II must be poly (vinyl chloride) or
other inert tubing for sample and reagent. Silicone tubing is used for
air injection.
5.2.4 Sampler Probe. Made of Kel-F, poly (chlorotri-
fluoroethylene), or glass. Because of the corrosive properties of the
TCM absorbing reagent, no metal should contact the sample solution.
5.2.5 Flow Rates. Sample and reagent flow rates are
specified in Figure 2. The different flow rates are obtained by selecting
pump tubing of the proper inside diameter. Deviation from these flow
rates is acceptable only to the extent that a proper calibration curve
and acceptable quality control checks are obtained.
5.2.6 Mixing Coils. Technicon Part Nos. 157-B089 and 157-
B095, 20 turn, 2 mm I.D. glass coils.
5.2.7 Heating Bath. Technicon Part No. 157-B273-06, 40-
45°C heated coil, total volume 5.4 ml.
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5.2.8 Colorimeter and Voltage Stabilizer. Technicon Part
Nos. 199-A001.04J and 161-A007-01 respectively, with proper filters for
measurement of absorbance at 560 nm. Interference filters should have a
spectral bandwidth not greater than 20 nm. The filters should be checked
with an accurate spectrophotometer, at least quarterly, to assure maxi-
mum transmittance at the specified wavelength.
5.2.8.1 Flow cell, 15 mm long with an I.D. of 2 mm.
5.2.9 Readout Device. A mv strip chart recorder or digital
volt meter of proper range.
6. Reagents. All reagents should conform to ACS specifications for
reagent grade materials unless otherwise specified.
6.1 Sampling
6.1.1 Distilled water. Must be reagent water as defined
by ASTM procedure TT93-66 part 6.3 (Consumption of potassium perman-
ganate
6.1.2 Absorbing Reagent [0.04 M Potassium Tetrachloromer-
curate (KM)].
CAUTION: Mercuric chloride and TCM are very poisonous,
particularly when concentrated. Avoid contact with skin,
and especially with eyes. Avoid generating dust or
breathing dust. Keep away from food. Wash hands after
handling it. Do not take internally.
Dissolve 10.86 g mercuric chloride, 0.066 g EDTA ( ethyl enedi ami netetra-
acetic acid, disodium salt), and 6.0 g potassium chloride in distilled
water and bring to mark in a 1,000 ml volumetric flask. The pH of this
reagent must be 4.0 ±1.0. ' The absorbing reagent is normally stable
for 6 months. If a precipitate forms, discard the reagent.
6.2 Analysis
6.2.1 Sulfamic Acid (0.17 percent). Dissolve 1.7 g of
sulfamic acid in distilled water and bring to mark in 1000 ml volumetric
flask. Prepare fresh daily.
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6.2.2 Formaldehyde (0.2 percent). Dilute 5 ml of formal-
dehyde solution (36-38 percent) to 1,000 ml with distilled water.
Prepare fresh daily.
6.2.3 Pararosaniline Dye (PRA). The dye must have a wave-
length of maximum absorbance at 540 nm when assayed in 0.1 M sodium
acetate-acetic acid (6.2.3.2).
6.2.3.1 Stock PRA Solution (0.20%). A specially
purified (99-100 percent) solution of pararosaniline is commercially
available in the required 0.20 percent concentration (Harleco Company,
Gibbstown, New Jersey 08027), but must be assayed. Alternatively, PRA
dye may be prepared from the crystalline form, purified according to the
procedure of Scaringelli, et al. , and assayed.
6.2.3.2 PRA assay procedure. One ml of the stock
solution (0.20%) is diluted to the mark in a 100 ml volumetric flask
with distilled water. A 5 ml aliquot of that solution is then trans-
ferred to a 50 ml volumetric flask. Five milliliters of 1 M sodium
acetate-acetic ac-fd buffer (6.2.3.4) is added, and the mixture is then
diluted to 50 ml volume with distilled water. After 1 hour the absor-
bance is determined at 540 nm with a spectrophotometer. The assay of the
PRA is determined by the formula
1 PRA a«Qav = Absorbance „ m
A PKA assay grams of dye taken* x K (1'
For 1-cm cells and a spectral bandwidth of less than 11 nm, K = 21.3.
*Assume 0.1 gram of dye taken when assaying the Harleco solution.
6.2.3.3 PRA Working Reagent.
CAUTION: Always use extreme care in handling concentrated acid.
Add it slowly. Protect eyes from splatters.
To a 200 ml volumetric flask, add 16 ml stock pararosaniline solution.
Add an additional 0.2 ml stock solution for each percent the stock
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assays below 100 percent as calculated by Equation 1. Then add 25 ml of
concentrated (85%) phosphoric acid and dilute to volume with distilled
water. This reagent is stable for at least 9 months.
6.2.3.4 Buffer (Acetate-Acetic acid, 1 M). In a 100 ml
volumetric flask, dissolve 13.61 grams of sodium acetate trihydrate in
approximately 50 ml of distilled water. Then add 5.7 ml of glacial
acetic acid and dilute to volume with distilled water. (This buffer
should have a pH of 4.7.)
6.3 Calibration
6.3.1 Preparation of Sulfite-TCM Standards.
6.3.1.1 Stock Iodine Solution (0.1N). Place 12.7 g
iodine, 40 g potassium iodide and 25 ml distilled water in a 1000 ml
volumetric flask.. Stir until dissolved, then dilute to volume with
distilled water.
6.31.1.2 Iodine Solution (0.01 N). Transfer 50 ml of
0.1 N Stock Iodine Solution to a 500 ml volumetric flask and dilute to
mark with distilled water.
6.3.1.3 Starch Indicator Solution. Triturate 0.4 g
soluble starch and 0.002 g mercuric iodide (preservative) with a little
distilled water, and add the paste slowly to 200 ml boiling distilled
water. Continue boiling until solution is clear, and transfer to a
glass stoppered bottle.
6.3.1.4 Stock Sodium Thiosulfate Solution (0.1 N).
Dissolve 25 g sodium thiosulfate (Na2S203'5H20) in 500 ml of distilled
water, add 0.1 g sodium carbonate to the solution, and dilute to 1000 ml
with distilled water. Allow the solution to stand one day before
standardizing. To standardize, accurately weigh to the nearest 0.1 mg,
1.5 g primary standard (or best available grade with an assay of 99+
percent) potassium iodate previously dried at 180°C for 3 hours and
dilute to volume in a 500 ml volumetric flask. To a 500 ml iodine
flask, pi pet 50 ml of potassium iodate solution. Add 2 g potassium
iodide and 10 ml of 1 N hydrochloric acid. Stopper the flask, and after
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8
5 minutes, titrate with stock sodium thiosulfate solution to a pale
yellow. Add 5 ml of starch indicator solution and continue the titra-
tion until the blue color disappears. Calculate the normality (N ) of
the stock solution:
Ns = y- x 2.80 (2)
where: N = Normality of stock sodium thiosulfate solution
V = Volume of sodium thiosulfate required, ml
W = Weight of potassium iodate, grams
o on - (1000 mg/g) (0.1 dilution factor)
^'ou ~ 214 g KI03/mole
6 equivalents/mole
6.3:;1.5 Sodium Thiosulfate Titrant H). 01 N). Pipet
100 ml of the stock sodium thiosulfate solution into 1000 ml volumetric
flask and dilute to the mark with freshly boiled distilled H20. The
normality (Nt) of the sodium thiosulfate titrant is:
L
Nt = 0.100 Ns (3)
where: N. = Normality of the sodium thiosulfate titrant
0.100 = Dilution factor
N = Normality of stock sodium thiosulfate solution (from
Equation 2)
6.3.1.6 Stock Sulfite Solution. Dissolve sufficient
anhydrous Na^SO., or Na2S20(- in 1000 ml of recently boiled, cooled distilled
water to give a solution containing approximately 500 yg SOp/ml . The
required amount of either compound can be calculated as follows:
grams of Na2S03 = 5JL. (4)
grams of Na2S205 = ^Zl. (5)
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Note: The assay of the reagent used should be 0.97 or greater.
Have reagents ready to analyze this solution immediately.
6.3.1.7 Analysis of Stock Sulfite Solution. The actual
concentration of the solution is determined by adding excess iodine and
back-titrating with standard sodium thiosulfate solution. To back-
titrate, pi pet 50 ml of the 0.01 N iodine into each of two 500 ml iodine
flasks (A and B). To flask A (blank) add 25 ml distilled water and to
flask B (sample) pipet 25 ml sulfite solution. Stopper the flasks and
allow to react for 5 minutes. Prepare the working sulfite-TGM solution
(6.3.1.8) at the same time iodine solution is added to the flasks. By
means of a buret containing standardized 0.01 N sodium thiosulfate,
titrate each solution in turn to a pale yellow. Then add 5 ml starch
solution and continue the titration until the blue color disappears.
Record the volumes of sodium thiosulfate used to titrate the blank (A)
and the sample (B).
6.3.1.8 Working Sulfite-TCM Calibration Standard.
Pipet 20 ml of the-standardized sulfite solution into a 500 ml volumetric
flask and dilute to the mark with 0.04 M TCM. Calculate the concen-
tration of sulfur dioxide in the working solution:
(A - B) (Nt) (32,000)
yg S02/ml = |g x 0.04 (6)
where: A = Volume sodium thiosulfate for blank, ml
B = Volume sodium thiosulfate for sample, ml
N, = Normality of sodium thiosulfate titrant from Equation 3
32,000 = Mi 11iequivalent wt. of S02, yg
25 = Volume standard sulfite solution, ml
0.04 = Dilution factor
This solution is stable for 30 days if kept at 5°C (refrigerator). If
not kept at 5°C, prepare daily.
6.3.2 Alternate preparation of calibration standards: use
of SOp-Permeation Devices. Sulfur dioxide permeation tubes, available
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10
as Standard Reference Materials 1625, 1626, and 1627 from the National
Bureau of Standards, can be used as the source of S0? for preparing
calibration standards in lieu of the NapSO., or Na^S^Cr.
7. Calibration
7.1 Sampling
7.1.1 Flowmeter or Hypodermic Needle. Calibrate flowmeter
or hypodermic needle against a calibrated flow measurement device, such
as a wet test meter, bubble flowmeter or other reliable volume measure-
ment standard.
7.2 Analysis
7.2.1 Procedure with Sulfite Solution.
7.2.1.1 Prepare calibration standards by dilution of
the working sulfite-TCM standard (Sec. 6.3.1.8) and subsequent dilution
of the 1.0 yg SOp/ml standard as indicated below. Use absorbing reagent
for all dilutions.
Standard Volume of standard Diluted to Concentration
(yg S0/ml) (ml) (ml) (yg St
20 7.0 100 1.4
20 5.0 100 1.0
20 2.0 100 0.4
1.0 10.0 100 0.10
1.0 4.0 100 0.04
1.0 2.0 100 0.02
7.2.1.2 Start up the analyzer and start reagents flowing
through the system. The sample in the flow cell must be free of bubbles
during operation. Refer to manufacturer's instructions for general
operating procedures. It should be noted that the sample and reagent
flow rates listed in Figure 2 are measured values, and are intended only
as a guide to the user in obtaining optimum sensitivity.
7.2.1.3 Set the electronic zero by turning the display
rotary switch to the zero position and adjusting the zero control (screw-
driver adjustment) for zero percent of scale.
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11
7.2.1.4 Set the electronic full scale by turning the
display rotary switch to the full scale position and adjusting the full
scale control (screwdriver adjustment) for 100 percent of scale.
7.2.1.5 Set the display rotary swtich to the normal
operation mode. With unreacted absorbing reagent flowing through the
flow cell, adjust the baseline to zero percent of full scale.
7.2.1.6 Once a stable baseline is obtained, span the
colorimeter by introducing a 1.0 yg S02/ml calibration standard and
adjusting the standard calibration control so that a recorder response
of 71.4% of full scale is obtained (when using the specified range of 0
to 1.4 yg SOp/ml). Repeat several times to verify the setting. If the
calibration standard concentration is not exactly 1.0, the recorder
response should be adjusted proportionately.
7.2.1.7 Introduce the calibration standards at the
beginning, near the middle, and at the end of each day's analyses.
Record the percent response for each peak and substract the baseline.
7.2.1.8 Plot net response in percent of full scale for
all three calibrations (y-axis) versus the corresponding concentration
in yg SOp/ml (x-axis). Draw or compute the straight line best fitting
the data to obtain the calibration curve. Determine a new calibration
curve for each day's analyses.
7.2.2 Procedure with S02 Permeation Devices
7.2.2.1 General Considerations. Atmospheres containing
accurately known amounts of sulfur dioxide, at levels of interest, can
be prepared by diluting the output of a permeation tube with known
amounts of clean dilution air.^ '
7.2.2.2 Preparation of Standards and Calibration Curve.
Prepare a series of six atmospheres containing SOp concentrations from
25 to 470 yg S02 per standard (25°C, 760 mm Hg) cubic meter (yg S02/sm3).
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12
Sample each atmosphere, using similar apparatus and taking exactly the
same air volume as will be used in atmospheric sampling, to generate
calibration standards. Calculate the concentration of S0£ in the
standard as follows:
yg S02/sm x F x T
ug so2/mi = v x 1000 (7)
where: yg S0~/ml = concentration of standard
3
yg S02/sm = concentration of atmosphere
F = flow rate, in standard (25°C, 760 mm Hg) liter per
minute (sl/min)
T = sampling time, minutes
V = volume of absorbing solution, ml
1000 = Factor to convert liters to cubic meters (1/m )
This procedure can be used to generate calibration standards over the
range 0.08 to 1.4 yg S02/ml. Standards in the range 0.02 to 0.08 yg
S02/ml can be prepared by dilution of more concentrated standards. Once
prepared these standards are used to prepare a calibration curve as
directed in 7.2.1.7 and 7.2.1.8.
8. Procedure
8.1 Sampling. Procedures are described for short-term (1 hour)
and for long-term (24 hour) sampling. One can select different combina-
tions of sampling rate and time to meet special needs, but sample volumes
and air flowrates must be adjusted so that the linearity is maintained
between absorbance and concentration over the dynamic range.
8.1.1 1 Hour Sampling. Add 10 ml TCM solution to a midget
impinger and insert it into the sampling system, Figure 1. Collect
sample at approximately 0.5 liter/minute for 1 hour, using either a
critical orifice or a needle valve and rotameter as shown in Figure 1 or
Figure 1-A, to control flow. Shield the absorbing reagent from direct
sunlight during and after sampling by covering the impinger to prevent
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T3
deterioration. Determine the volume of air sampled by multiplying the
average flow rate, measured before and after sampling, by the time in
minutes and record the atmospheric pressure and temperature. Remove and
stopper the impinger. If the sample must be stored before analysis,
keep it at 5°C in a refrigerator (4.3).
8.1.2 24 Hour Sampling. Place 50 ml TCM solution in the
absorber and collect the sample at 0.2 liter/minute for 24 hours, usually
from midnight to midnight. Make sure no entrainment of solution occurs.
During collection and storage protect the sample from direct sunlight.
Determine the total air volume by multiplying the average air flow rate,
measured before and after sampling, by the time in minutes. The correc-
tion of 24-hour measurements for temperature and pressure may be difficult
and is not ordinarily done; however, the accuracy of the measurement
will be improved if meaningful corrections can be applied. If storage
is necessary, refrigerate at 5°C. (4.3).
8.2 Analysts
8.2.1 Sample Preparation. After collection, if a precipi-
tate is observed in the sample, remove it by centrifugation.
8.2.1.1 1 Hour Samples. Bring sample back to 10 ml with
distilled water.* Delay analyses for 20 minutes to allow any ozone to
decompose.
8.2.1.2 24 Hour Samples. Bring sample back to 50 ml
with distilled water.* Delay analyses for 20 minutes to allow any ozone
to decompose.
8.2.2 Sample Analysis. Fill the test cups with samples
and place on the turntable. One quality control sample, a 1.0 yg S
*This assumes loss of volume due only to water evaporation.
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14
calibration standard (7.2), is included after every 10 samples, followed
by enough test cups filled with unreacted absorbing reagent to provide a
baseline check. The quality control sample must produce a response
within ±3.9 scale percent of the value indicated by the day's cali-
bration curve for the analyses to be valid.
Sample analysis, net yg SCL/ml , is determined directly from
the calibration curve (7.2). Samples which exceed the highest cali-
bration standard are diluted up to 5:1 with absorbing solution until the
sample falls within the range of the calibration curve. A randomly
selected 5-10% of the samples should be rerun to maintain an internal
quality assurance program.
9. Sampling Efficiency. Collection efficiency is above 98 percent;
efficiency may fa
10. Calculations
3 ( 8 9
efficiency may fall off, however, at concentrations below 25 yg/sm . v '
10.1 Air Volume. Convert the volume of air sampled to the volume
at standard conditions of 25°C and 760 mm Hg (On 24-hour samples, this
may not be possible) as follows:
VR = v
where: VR = Volume of air at 25°C and 760 mm Hg, standard liters.
V = Volume of air sample, liters
P = Average barometric pressure, mm Hg.
t = Average temperature of air sample, °C
10.2 Sample Concentration. This is determined graphically from
the calibration curve or computed from the slope and intercept values,
in yg S02/ml .
10.3 S09 Concentration in Air Sample. This is calculated in yg
3
S02 per standard cubic meter (yg SO^/sm ) as follows:
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15
., yg S09/ml x V«. x 1000
yg S09/snr = n—^ .— x D (9)
* VR
where: yg S02/ml = Sample analysis
VQ = Volume of collected sample, ml
3
1000 = Factor to convert liters to cubic meters (1/rri )
Vp = Volume of air sampled, standard liters
D = Dilution factor of samples exceeding 1.4 yg S02/ml;
D = 1 if sample was not diluted.
3
10.4 Conversion of yg/sm to ppm. If desired, the concentration
of sulfur dioxide may be calculated as ppm S02 as follows:
ppm S02 = yg S02/sm3 x 3.82 x 10"4 (10)
11. Maintenance. Cleaning of the apparatus after each use is necessary
to prevent contamination of subsequent analyses. Consult manufacturer's
instructions for cleaning procedures. Alkaline materials should not be
used because of the formation of a precipitate with TCM.
12. Waste Disposal. Since the absorbing solution contains mercury,
waste solution from the analysis should be treated prior to disposal or
shipment for reclamation. The following procedure is suggested. '
12.1 To each liter of waste solution, add sodium carbonate (about
10 grams) until neutral and 10 grams of granular zinc or magnesium.
12.2 Sodium hydroxide may have to be added if a neutral solution
is not obtained with sodium carbonate.
12.3 Stir the solution for 24 hours in a hood. CAUTION: Hydrogen
gas will be released during this process.
12.4 After 24 hours, the solid material (mercury amalgam) will
have separated. Decant and discard the supernatant liquid.
12.5 Quantitatively transfer the solid material to a convenient
container and allow to dry.
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16
This procedure removes greater than 99% of the mercury from the absorbing
solution.
13. Potential Sources of Error. Sulfur dioxide present in the air
surrounding the Technicon analysis system can cause errors in the auto-
3
mated analysis. When using the small, 2 cm Technicon IV sample cups,
an error may result from the diffusion of .SOp into the filled sample cup
as it sits on the turntable. The error can be minimized by using larger
sample cups such as disposable culture tubes in place of the small
sample cups, by setting the sampling probe so that it nearly touches the
bottom of the culture tube, and by filling the tubes to the top. This
technique increases the time required for the SOp to diffuse to the
point of sampling.
Also, because room air is used to segment the sample stream, contami-
nation due to SOp in the surrounding air could cause a shift in the
nominal baseline response and a false increase in response due to absorp-
tion of SOp into the sample as it passes through and is mixed with
analysis reagents. If such contamination is suspected, the air should
be purified by passing it through a solution of TCM.
14. References
1. Scaringelli, F. P., Saltzman, B. E., and Frey, S. A., "Spectro-
photometric Determination of Atmospheric Sulfur Dioxide," Anal.
Chem. 39. 1709 (1967).
2. Logsdon, 0. J. II and Carter, M. J., "Comparison of Manual and
Automated Analysis Methods for Sulfur Dioxide in Manually Impinged
Ambient Air Samples." EPA-Region V, 1819 West Pershing Road,
Chicago, Illinois 60609.
3. Pate, J. B., Ammons, B. E., Swanson, G. A., Lodge, J. P., Jr., "Nitrite
Interference in Spectrophotometric Determination of Atmospheric Sulfur
Dioxide," Anal. Chem., 37^, 942 (1965).
4. Zurlo, N. and Griffini, A. M., "Measurement of the SOp Content of Air
in the Presence of Oxides of Nitrogen and Heavy Metals," Med.
Lavoro, 53, 830 (1962).
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5. Scaringelli, F. P., Elfers, L., Norn's, D., and Hochheiser, S.,
"Enhanced Stability of Sulfur Dioxide in Solution," Anal. Chem.,
42, 1818 (1970).
6. ASTM Standards (Water; Atmospheric Analysis), Part 23. October 1969.
(p. 225.)
7. Federal Register. 36_, 22386-22387 (November 25, 1971).
8. Urone, P., Evans, J. B., and Noyes, C. M., "Tracer Techniques in
Sulfur Dioxide Colorimetric and Conductimetric Methods," Anal. Chem.,
37., 1104 (1965).
9. Bostrom, C. E., "The Absorption of Sulfur Dioxide at Low Concen-
trations (pphm) Studies by an Isotopic Tracer Method," Intern. J.
Air Uater Poll.. 9, 333 (1965).
10.* Thompson, R. J., J. Air Pollut. Contr. Ass.. 2]_, 428 0971).
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TEFLON OR GLASS
7
TO INVERTED
FUNNEL
/Nl—
NEEDLE VALVE
ABSORBER FOR
24 hr. SAMPLING
NOTE -A MIDGET IMPINGER IS
USED FOR 1 HOUR SAMPLING.
Figure 1 a. Alternate flow control.
TRAP
Figure 1. Sampling system.
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PART#
133-AOOO-05L
HEATING
BATH
PART WO.
157-8273-06
RECORDER
TO WASH RECEPTACLE
n.o-r.,n MIXING COILS
?»/ \ ™js
000 000
COLORIMETER
PART NO. 199-A001.04J
WASTE
PUMP
(ml/min)
(1.8) TCM
(0.32) AIR
(0.56) SAMPL7E
(0.32) SULFAMIC ACID
(0.10) FORMALDEHYDE
(0.16) p-ROSANILINE
(0.60) FROM FLOW CELL
PART WO. 171-A017-03E
Figure 2. Technicon II automated sulfur dioxide analysis system.
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