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SEMI C3-0699 © SEMI 19 86, 1999 4 3.2.2 By connecting th e container be i n g sampled directly to the an alytical equipment. 3.2.3 By selecting a representative c y l i nder fro m the cylinders in the lot. 3.3 L iquid Sa…

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SEMI C3-0699 © SEMI 1986, 19993
2.19 physical properties — physical properties shall
not usually be employed for specification purposes; for
information, however, representative values for a
particular gas, as supplied, may be included as an item
in the monograph for that gas.
2.20 quality — the quality is determ ined by
subtracting the sum of the maximum acceptable gas
phase impurity levels, expressed in percent, from 100.
The result is truncated after the first significant figure
which is not a nine. The quality does not represent an
assay.
2.21 rare gas — any of the six gases, all noble,
comprising the extreme right-hand group of the
Periodic Table; namely helium, neon, argon, krypton,
xenon, and radon.
2.22 rounding numbers — the follo wing rules for
rounding of measured or calculated values shall be
employed:
2.22.1 When the figure next beyond t he last place to
be retained is less than 5, leave unchanged the figure in
the last place retained.
2.22.2 When the figure next beyond t he last place to
be retained is greater than 5, increase by 1 the figure in
the last place retained.
2.22.3 When the figure next beyond t he last place to
be retained is 5 and there are no figures beyond this 5 or
only zeroes, (a) increase by 1 the figure in the last place
retained if it is odd, or (b) leave the figure unchanged if
it is even.
2.22.4 When the figure next beyond t he last place to
be retained is 5 and there are figures other than zeroes
beyond this 5, increase by 1 the figure in the last place
retained.
2.22.5 Obtain the rounded value in on e step by direct
rounding and not in two or more steps of successive
rounding.
2.23 specific gravity — the ratio of the mass of a gas
to the mass of an equal volume of air at a specified
temperature. For liquids, it is the ratio of the mass of
the liquid to the mass of an equal volume of water.
2.24 specification and specification limits — the
specification limit should fall above or in the range of
the result and its uncertainty.
2.25 temperature — temperature va lues shall be
expressed in degrees Celsius.
2.26 tolerances in measurements — use the following
guidelines for mixture tolerances:
2.26.1 Mixtures should be specified b y the major
component and the concentration of the desired minor
component(s).
2.26.2 All component gases shall adhere to the
appropriate SEMI specification, if available.
2.26.3 The impurity levels in the mix ture shall not
exceed the algebraic sum of the impurities specified for
the designated components.
2.26.4 Mixtures shall be prepared according to the
following mixing tolerances:
Concentration of Minor
Component
Preparation Tolerance Level
10 - 99 ppm ± A 20%
100 - 999 ppm ± A 10%
0.1 - 50% ± A 5%
2.26.5 Standards used to verify mixin g tolerance
(henceforward called Certified Standards) shall meet
the following requirements:
Range Preparation
Tolerance of Each
Minor Component
Analytical
Accuracy of Each
Minor Component
0 - 9.9 ppm To Be Determined To Be Determined
10 - 99 ppm ± A 10% ± A 3%
100 - 999 ppm ± A 5% ± A 2%
0.1% - 50% ± A 4% ± A 2%
2.27 Calibration Standards — Calibration standards
shall be as close as practical to specification and may
not exceed ten times (10×) the specification unless
specifically excepted in procedure.
3 Samples
3.1 Sample Size — The quantity o f gas/liquid in a
single sample container shall be sufficient to perform
the analysis for all the listed specifications. If a single
sample does not contain a sufficient quantity of
gas/liquid to perform all of the required analyses,
additional samples from the same source shall be taken
under similar conditions.
3.2 Gaseous Samples — Gaseous samples shall be
representative of the gaseous supply. Sampling shall be
performed in accordance with one of the following:
3.2.1 By withdrawing a sample from the supply
container through a suitable connection into the sample
container. (For safety reasons, the sample container and
sampling system must have a rated service pressure at
least equal to the pressure in the supply container.)
SEMI C3-0699 © SEMI 1986, 1999 4
3.2.2 By connecting the container being sampled
directly to the analytical equipment.
3.2.3 By selecting a representative c ylinder from the
cylinders in the lot.
3.3 Liquid Sampling (Vaporized) — Vaporized liquid
samples shall be representative of the liquid supply.
Sampling shall be in accordance with one of the
following:
3.3.1 By vaporizing liquid from the supply container
in the sample tubing.
3.3.2 By flowing liquid from the sup ply container into,
or through, a suitable container in which a
representative sample is collected and then vaporized.
3.4 Liquid Samples (Liquified Compressed Gases) —
A direct connection between the liquid phase of
liquified compressed gas containers and the analytical
equipment can be achieved, provided suitable flash
vaporization is obtained.
3.5 Lot Acceptance Tests — These are analyses
performed on the gas/liquid in the shipping container,
or a sample thereof, which is representative of the lot.
(The terms “lot” and “batch” may be used
interchangeably.)
3.6 Lots — One of the following is to be used:
3.6.1 No specific quantity or any qu antity of product
agreed upon between the supplier and the customer.
3.6.2 All of the product supplied during the contract
period.
3.6.3 All of the product supplied or containers filled
during a calendar month.
3.6.4 All of the product supplied or containers filled
during seven consecutive days.
3.6.5 All of the product supplied or containers filled
during a consecutive 24-hour period.
3.6.6 All of the product supplied or containers filled
during one eight-hour shift.
3.6.7 All of the product supplied in one shipment.
3.6.8 All of the product supplied in one shipping
container.
3.6.9 All of the product supplied in the container(s)
filled on one manifold at the same time.
3.7 Number of Samples Per Lot — The number of
samples per lot shall be in accordance with one of the
following:
3.7.1 One sample per lot.
3.7.2 Any number of samples agreed upon by the
supplier and the customer.
4 Sampling
4.1 For gases provided in cylinder s, a sample can be
taken directly for analysis. For gases provided in bulk
quantities or cylinders where direct sampling is not
appropriate, a sample may be taken per SEMI sampling
procedures.
4.2 Sampling Procedures
4.2.1 Cryogenic Liquid Sample — Liquid Samples for
Oxygen, Nitrogen, and Argon, using the TTU-131/E
sampler.
WARNING: DO NOT USE THIS PROCEDURE
FOR THE SAMPLING OF LIQUID HYDROGEN.
4.2.2 Applicable Document — Military Specification
MIL-S-27626D 16 August 1979, Amendment 1, 24
April 1981.
4.2.3 General Description — The TTU-131/E
cryogenic sampler is a small, portable pressure vessel
used to receive, vaporize, and contain a representative
sample of cryogenic liquid from a supply source. The
vaporized sample is withdrawn as a gas for analytical
purposes.
4.2.4 Theory — The sampler is used to isolate a small
but representative quantity of cryogenic liquid and
vaporize the major component and all volatile
impurities to form a homogeneous gas sample suitable
for analysis. The cryogenic liquid is used to cool a
shielding space and sampling cup prior to admitting the
liquid to the sampling cup. The purpose of pre-cooling
the sampling cup is to prevent concentrating impurities
which could result when the warm cup causes the liquid
to vaporize, leaving behind impurities with higher
boiling points.
4.2.4.1 When the cup is adequately cooled, the
sampling valve is opened, allowing liquid to fill the
cup. When the sampling valve is closed, the liquid is
trapped in the cup and will vaporize as a result of
atmospheric heating. Once the sample is trapped, the
flow of liquid is stopped.
4.2.5 Preparation for Sampling
4.2.5.1 The sample should be kept in the same product
service to avoid sample contamination. If a product
change is required, always thoroughly purge the
sampler or evacuate to 100 microns prior to taking the
sample.
4.2.5.2 When taking the sample, the s ampler is to
remain secured to the bottom half of the case and
MUST be in an upright position.
SEMI C3-0699 © SEMI 1986, 19995
4.2.5.3 Inspect the sampler vessel for any obvious
physical defects, such as dents, gouges, bent fittings,
etc. Since the sampler is a pressurized vessel, it should
be removed from service if any damage is apparent.
4.2.6 Sampling Procedure
4.2.6.1 Remove cover.
4.2.6.2 Loosen inlet and outlet fittings dust caps
located on side of the vessel.
CAUTION: SAFETY GLASSES AND
PROTECTIVE GLOVES ARE REQUIRED WHEN
OPERATING THIS EQUIPMENT. SAMPLING
SHOULD BE DONE ONLY IN WELL
VENTILATED AREAS.
4.2.6.3 Relieve pressure in vessel thro ugh vents in
dust caps by cautiously opening inlet sampling valve.
4.2.6.4 When gauge indicates atmosph eric pressure
and flow ceases, close inlet sampling valve and remove
dust caps.
4.2.6.5 Connect fill hose to supply tan k and inlet
fittings of sampler.
4.2.6.6 Open supply tank outlet valve. Gas and liquid
will begin to flow from the sampler outlet.
CAUTION: WHEN OXYGEN IS SAMPLED,
SOME ADDITIONAL PRECAUTIONS MUST BE
OBSERVED. IF THERE IS NO FACILITY SUCH
AS A CLEAN CONCRETE PAD ON WHICH THE
LIQUID OXYGEN CAN EVAPORATE SAFELY,
IT WILL BE NECESSARY TO CATCH THE
LIQUID OXYGEN IN A CLEAN, PREFERABLY
SEAMLESS ALUMINUM BUCKET. USE A LINE
WITH MINIMUM INSIDE DIAMETER OF ONE-
HALF INCH TO DIRECT THE LIQUID OXYGEN
INTO THE BUCKET. FURTHERMORE, IT IS
IMPORTANT THAT THERE IS NO
RESTRICTION IN THIS LINE BECAUSE THE
BACK PRESSURE DEVELOPED MAY BE
SUFFICIENT TO CAUSE THE LIQUID IN THE
CUP TO OVERFLOW INTO THE LARGE
CHAMBER. ON WARMUP, THE PRESSURE IN
THE SAMPLER COULD BECOME EXCESSIVE,
PARTICULARLY IF THE SAMPLE WERE
SUBCOOLED, NECESSITATING THE
REPLACEMENT OF THE SAFETY RELIEF
DEVICE.
4.2.6.7 Allow sampler to cool until a s teady flow of
liquid appears at outlet.
CAUTION: AVOID CONTACT WITH THE
FLOW OF CRYOGENIC LIQUID. THE
EXTREMELY LOW TEMPERATURE CAN
CAUSE PAINFUL INJURIES.
4.2.6.8 Open inlet sampling valve completely to allow
liquid to enter sampling cup.
4.2.6.9 After 30 seconds, close sampling valve.
4.2.6.10 Close supply tank outlet valve.
4.2.6.11 Disconnect fill hose.
4.2.6.12 Invert sampler for five minutes to allow
sampling cup to empty and provide vaporization of
liquid.
4.2.6.13 At ambient temperature the sa mpler should be
at 400-500 psig, indicating that a good sample was
obtained. A lower pressure would indicate a leak in the
sampler or that the cup was not filled with liquid. If
there is any doubt, release gas from sampler and take
another sample.
4.2.6.14 Re-install inlet and outlet fitting caps. Do not
tighten.
4.2.6.15 Affix a tag identifying the product to the inlet
sampling valve handwheel.
4.2.6.16 Install cover.
4.3 Gas Phase Sample — (To Be Determined)
4.4 Liquid Sample — (To Be Dete rmined)
4.5 Delivery to Analytical Instruments — (To Be
Determined)
5 Quantification (To Be Dete rmined)
5.1 Linear Response
5.1.1 Direct Comparison
5.1.2 Calibration Curve
5.2 Non-Linear Response
5.2.1 Direct Comparison
5.2.2 Calibration Curve
6 Gas Chromatography
6.1 The analysis of many gaseous impurities in bulk
and specialty gases is done by means of a gas
chromatography separation of impurities from the gas
matrix and quantification using a broad range of
sensitive and sometimes selective detectors. This
section will provide a guide for the format and
representation of such a procedure. Figure 1 is designed
to represent the format for submission of such
methodology.
6.2 Sample Introduction — By its nature, gas
chromatography implies the use of carrier gases into
which the gaseous sample is injected and carried into
the separation medium, either solid or liquid in nature.