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SEMI C3.12-1102 © SEMI 1983, 2002 2 4.1.5.2 Set timing int erval on gas sampling val ve to 3:30 mi nutes. 4.1.5.3 Set timi ng interval #3 to 4: 20 minutes. 4.1.5.4 Do not change the initial sample flow setting once estab…
SEMI C3.12-1102 © SEMI 1983, 2002 1
SEMI C3.12-1102
SPECIFICATION FOR AMMONIA (NH
3
) IN CYLINDERS, 99.998%
QUALITY
This specification was technically approved by the Global Gases Committee and is the direct responsibility of
the North American Gases Committee. Current edition approved by the North American Regional Standards
Committee on August 29, 2002. Initially available at www.semi.org September 2002; to be published
November 2002. Originally published in 1983, previously published in 1994.
1 Description
1.1 Ammonia is a colorless, alkaline gas having a
pungent odor. Ammonia dissolves readily in water. It is
shipped as a liquified gas under its own vapor pressure.
It is combustible.
2 Specifications
2.1 QUALITY: 99.998%
Impurities
Maximum Acceptable Level
(ppm)*
Carbon monoxide (CO) 1
Hydrocarbons C
1
– C
3
1
Nitrogen (N
2
) 5
Oxygen (O
2
) 2
Water (H
2
O) (v/v) 3
TOTAL LISTED IMPURITIES 12
*An analysis of significant figures has not been considered. The
number of significant figures will be based on analytical accuracy and
the precision of the provided procedure.
NOTE 1: This specification applies to the gas phase of the
cylinder as delivered.
3 Physical Constants (for information only)
Metric Units US Units
Molecular weight 17.031 17.031
Boiling point at 1 atm –33.4°C –28.2°F
Density of gas at 0°C (32°F)
and 1 atm
0.771 kg/m
3
0.0481 lb/ft
3
Specific gravity of gas at 0°C
and 1 atm (air = 1)
0.597 0.597
Density of liquid at 21.1°C
(70°F)
608.7 kg/m
3
38.00 lb/ft
3
4 Analytical Procedures
NOTE 2: Observe proper safety procedures for handling and
venting the ammonia sample.
NOTE 3: Introduce the calibration standard as many times as
necessary to achieve the desired precision.
NOTE 4: All the gases used in the analysis of the sample
should contain not more than 10% of the specified value of
the component of interest unless otherwise specified.
NOTE 5: All carrier lines, carrier pressure regulators and
sample containers are to be constructed of stainless steel and
cleaned. The systems must be assembled without pipe threads,
PTFE tape or polymeric seal materials.
4.1 Carbon Monoxide, Oxygen and Nitrogen — This
procedure is for the determination of carbon monoxide,
oxygen and nitrogen in ammonia using a gas
chromatograph with a helium ionization detector.
NOTE 6: Due to the extreme sensitivity of the helium
ionization detector, the system is to be helium leak tested to a
maximum of 10
–7
atm-cc/sec.
4.1.1 Detection Limits — 25 ppb (mole/mole) carbon
monoxide, 30 ppb (mole/mole) oxygen, 50 ppb
(mole/mole) nitrogen.
4.1.2 Instrument Parameters
4.1.3 Columns:
Column 1: HayeSep A or equivalent, 100/120 mesh, 3.28
m (10 ft) by 3.2 mm (1/8 in.) 0.085 ID.
Column 2: HayeSep A or equivalent, 100/120 mesh, 3.28
m (10 ft) by 3.2 mm (1/8 in.) 0.085 ID.
4.1.3.1 Carrier Flow: 30 mL/min helium, minimum of
99.9999% purity having a maximum of 40 ppb carbon
dioxide.
4.1.3.2 Sample Volume: 1.0 mL.
4.1.3.3 Temperatures:
Detector 125°C
Columns 27°C
4.1.3.4 Determine the breakdown voltage of the
detector. Set operating voltage at 10 volts below
breakdown.
4.1.4 Calibration Standards — 1–2 ppm (mole/mole)
carbon monoxide, 2–3 ppm (mole/mole) oxygen, 5–6
ppm (mole/mole) nitrogen, balance helium (having a
total of other impurities of less than 1 ppm).
4.1.5 Operating Procedure
4.1.5.1 Set timing interval on sample select valve to 10
seconds.
SEMI C3.12-1102 © SEMI 1983, 2002 2
4.1.5.2 Set timing interval on gas sampling valve to
3:30 minutes.
4.1.5.3 Set timing interval #3 to 4:20 minutes.
4.1.5.4 Do not change the initial sample flow setting
once established.
4.1.5.5 Obtain a continuous flow of the calibration
standard using a clean stainless steel line (0.02 in. ID).
4.1.5.6 Inject the calibration standard onto the
precolumn with the gas sampling valve. Record the
retention times and peak areas. Order of elution is
nitrogen, oxygen, and carbon monoxide.
4.1.5.7 Repeat Section 4.1.5.6 until reproducibility of
the reading is better than 1% of full scale.
4.1.5.8 Inject the sample to be tested in the same
manner as the calibration standard. Record the retention
times and peak areas.
4.1.5.9 Repeat Section 4.1.5.8.
4.1.5.10 Compare the average peak areas of the
calibration standard to that of the ammonia sample
being tested. Calculate the concentrations of carbon
monoxide, oxygen and nitrogen, using the formula
below. The result may not exceed the specification in
Section 2 of this standard.
Sample Pea
k
Area
Standard Peak
Area
×
Concentration
of Standard
=
Concentration
of Sample
4.2 Hydrocarbons C
1
−
C
3
— This procedure is for the
determination of hydrocarbons C
1
– C
3
in ammonia.
The sample should be gas phase and analyzed using a
gas chromatograph with a flame ionization detector.
NOTE 7: It is good practice to keep carrier gas flowing
through the instrument. This prevents the back-diffusion of
moisture and carbon dioxide in the air from contaminating the
column.
NOTE 8: When not analyzing samples, the dual column
switching valve should be set at the molecular sieve position
to prevent the silica gel column from drying out.
NOTE 9: The silica gel column will, after repeated use, tend
to dry out. This will manifest itself by the peaks of each
component becoming separated farther and farther apart.
Overall sensitivity will drop as the peak areas decrease due to
the peaks spreading out more and more.
NOTE 10: The condition of the silica gel column is restored
by allowing the carrier gas to pass through the water-saturated
silica gel trap that has been provided. (Normally the carrier
gas bypasses this trap.)
NOTE 11: The flame should be extinguished when not in use;
also the air and hydrogen is shut off; and the helium flow
reduced.
4.2.1 Detection Limit — 0.1 ppm (mole/mole).
4.2.2 Instrument Parameters
4.2.2.1 Columns:
Column 1: 13X molecular sieve, 3.2 mm (1/8 in.) by
3.2 mm (1/8 in.) ss, or equivalent.
Column 2: Silica gel (saturated) 4.6 m (15 ft) by 3.2
mm ss, or equivalent.
4.2.2.2 Carrier Flow: 50 mL/min helium.
4.2.2.3 Sample Volume: 5 mL.
4.2.2.4 Column Temperature: 40°C
4.2.2.5 Sample Flow: 150 mL/min.
4.2.2.6 Air Pressure and Flow: As specified by the
instrument manufacturer’s instructions.
4.2.2.7 Hydrogen Pressure and Flow: As specified by
the instrument manufacturer’s instructions.
4.2.3 Calibration Standards — 5–10 ppm (mole/mole)
methane in nitrogen, 5–10 ppm (mole/mole) ethane, 5–
10 ppm (mole/mole) propane in nitrogen.
4.2.4 Operating Procedure
4.2.4.1 Install the column switching as shown in Figure
1. Place the dual column switching valve in the
molecular sieve column position for methane analysis.
Use the silica gel column position for the analysis of C
2
– C
3
compounds.
4.2.4.2 Ignite the flame following the instrument
manufacturer’s instructions. Allow the system to
stabilize for 15 minutes. (This is also indicated by a
stable signal output.)
4.2.4.3 Inject the methane in nitrogen standard onto the
molecular sieve column to determine the retention time
for methane.
4.2.4.4 Inject the ethane and propane in nitrogen
standard onto the silica gel column to determine the
retention times for these compounds.
4.2.4.5 Inject the calibration standard onto the desired
column to determine the peak area for the compound of
interest. Record the retention times and peak areas.
4.2.4.6 Inject the sample to be tested in the same
manner as the calibration standard. Record the retention
times and peak areas.
4.2.4.7 Repeat Section 4.2.4.6.
SEMI C3.12-1102 © SEMI 1983, 2002 3
4.2.4.8 Compare the average peak areas for at least
three runs each of the calibration standard to that of the
ammonia sample being tested. Calculate the
concentration of hydrocarbons C
1
– C
3
, using the
formula below. The result may not exceed the
specification in Section 2 of this standard.
Sample Pea
k
Area
Standard Peak
Area
×
Concentration
of Standard
=
Concentration
of Sample
4.3 Water — The method for the determination of
water in ammonia is based on its decomposition by the
reaction 2NH
3
→ N
2
+ 3H
2
, which occurs completely
and irreversibly when ammonia is passed over a nickel
catalyst at 1000°C. Water passes through the catalyst
unchanged. Therefore, the water content of ammonia
may be determined by measuring the dewpoint of the
stream of hydrogen and nitrogen produced by
decomposition of ammonia.
NOTE 12: The system should be checked for leaks prior to
use to preclude atmospheric contamination of the sample.
NOTE 13: The moisture analyzer must be calibrated
according to the manufacturer’s specified method prior to use.
4.3.1 Apparatus (shown in Figure 2)
4.3.1.1 The nitrogen and ammonia are connected to a
tee with 3.2 mm (1/8 in.) OD stainless steel tubing,
keeping the lines as short as is practical.
4.3.1.2 The nitrogen may be fed from a regulator.
4.3.1.3 The ammonia should be fed through a stainless
steel needle valve.
4.3.1.4 The furnace is a Lindberg Model 54032 or
equivalent, with an Inconel reaction tube. The reaction
tube is 0.6 m (24 in.) long by 25 cm (1 in.) OD and
terminates in 3.2 mm (1/8 in.) swaged tubing
connectors.
4.3.1.5 The reaction tube is filled with nickel lumps,
MCB Catalog number NX305 or equivalent.
4.3.1.6 The outlet of the furnace is connected by a 1.2
m (4 ft) by 3.2 mm (1/8 in.) OD stainless steel tubing to
a moisture analyzer suitable for determining the
concentration of water should be a mixture of hydrogen
and nitrogen at the specified concentration. This length
of tubing is required to permit adequate cooling of the
gas between the furnace and the moisture analyzer.
4.3.1.7 The outlet of the moisture analyzer is connected
to the inlet of a 0-10 CFH flowmeter.
4.3.1.8 The outlet of the flow meter is connected to an
appropriate vent for the disposal of ammonia, nitrogen
and hydrogen.
4.3.2 Operating Procedure
4.3.2.1 Start a nitrogen purge flow of approximately 5
CFH.
4.3.2.2 Set furnace to 950°C and allow to equilibrate
(approximately 1.5 to 2 hours).
4.3.2.3 With the ammonia cylinder valve closed,
disconnect the tubing from the cylinder outlet and open
the ammonia inlet needle valve to allow the ammonia
sample line to purge with nitrogen. Reconnect the
tubing to the cylinder outlet and close the needle valve.
4.3.2.4 Shut off the nitrogen flow.
4.3.2.5 Open the ammonia cylinder valve and adjust
the needle valve to obtain a flow of approximately 5
CFH.
4.3.2.6 Gradually increase the furnace temperature,
periodically testing the gas for the presence of ammonia
by placing a piece of wet red litmus paper in the vent
stream. If ammonia is present, the paper will turn blue.
When ammonia is no longer found, the appropriate
catalyst temperature has been reached.
4.3.2.7 Measure the concentration of water in the
nitrogen and hydrogen stream, following the
instructions of the moisture analyzer manufacturer.
Periodically test the vent stream for the presence of
ammonia, as described in Section 4.3.2.6, and adjust the
furnace temperature as necessary.
4.3.3 Reporting of Measurement
4.3.3.1 Double the water concentration obtained in
Section 4.3.2.7 to correct for the doubling of gas
volume by the decomposition of the ammonia.
4.3.3.2 Subtract twice the concentration of oxygen (as
measured by the procedure specified in Section 4.3) in
the sample from the concentration of water calculated
in Section 4.3.3.1. This is necessary because oxygen in
the ammonia reacts with the hydrogen formed by
decomposition to produce additional water.
4.3.3.3 The concentration of water calculated in Section
4.3.3.2 in the ammonia may not exceed the limit
specified in Section 3.