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SEMI C3-0699 © SEMI 19 86, 1999 5 4.2.5.3 In sp ect the sampler vessel for a n y obvious physical defects, suc h as dents, gouges, b ent fittings, etc. Since the sampler is a pressurized v e ssel, it should be remov ed f…

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.

SEMI C3-0699 © SEMI 1986, 1999 6

The introduction of a gaseous sample into a carrier gas

stream is accomplished by means of a sample injection

valve. Valves for this purpose can be any of several

types, although the most commonly used are either

rotary or diaphragm valves using loops of stainless steel

tubing of a known volume. It is not necessary to

diagram such sample introduction systems for a

procedure unless the introduction system is unique to

the application by way of special conditions for safety

or other reasons critical to the accuracy of the sampling

technique.

6.3 Separations — It is an acceptable and common

practice to quantitate several gaseous impurities with a

single gas chromatographic separation. Occasionally a

single injected sample volume will undergo

"multidimensional" separation to achieve the necessary

analysis. Rotary valves, diaphragm valves or Dean's

pressure switching again are used to move impurities

from one separation medium to another, or from one

column to another. Where multidimensional techniques

are used, they should be accompanied by flowpath

diagrams which clearly indicate valving and their

appropriate positions. The valving sequences used

should have adequate explanation to clarify the

separations.

6.4 Columns — Columns used are generally of 3.2

mm (1/8 in.) o.d. and 2.2 mm (0.085 in.) i.d. stainless

steel of varying lengths and packed with one of many

solid supports. Columns may be specified by length and

packing material if these standard dimensions apply. If

another dimension or material is used for the column

itself, it should be specified by material type, and by

o.d. and i.d. in mm. Packing materials should be

specified by material, % coating and coating type if

applicable, and mesh size. Capillary columns are

assumed to be fused silica unless otherwise specified

and should be specified by i.d. in mm, film thickness in

µm, and length in meters. Column temperatures and

applicable program rates should be given for each

independently heated zone in degrees Celsius.

6.5 Carrier and Support Gases — Carrier and support

gas flow rates for all separations should be specified.

Carrier and support gases used should fall into the

general purity requirements in Table 2 and purity need

not be specified unless the analysis has specific purity

requirements for safety, accuracy, or component

lifetime. Flows should be specified in mL/min or

L/min, or as linear velocity for open tubular capillary

columns.

6.6 Detectors — Detector technolo gy should be

specified, and alternative detection may be assumed

equivalent for detectors of like selectivity and

sensitivity. Table 2 gives a reference of relative

detector sensitivity and is provided as a guideline only.

Detector parameters are less likely to be easily

formatted since detector technologies vary widely in

their specific parameters. All elements critical to

achieving like sensitivity must be included, such as

temperature, make-up gases and their flows, flame,

combustion or reaction gas ratios or flows, voltages,

currents, or any additional settings as outlined by the

detector manufacturer.

6.6.1 Detection limits must be speci fied for each

impurity for the actual methodology used. Because the

lower detection limit can be greatly influenced by

retention time for any impurity, it is important that the

detection limit be derived for the impurity within the

context of the method, and not solely on the

detectability of the detector. Detection limits are

assumed to be calculated on a mole/mole basis.

6.7 Operating Procedures — The standard procedure

assumed for the gas chromatographic analysis of most

gases is as follows:

1. Inject the calibration standard onto the column

using a gas sampling valve. Record the retention

time(s) and peak area(s) for all impurities detected.

2. Analyze the sample to be tested in the same

manner as the calibration standard.

3. Repeat 1.

4. Compare the average peak area of the calibration

standard with that of the sample being tested. (See

Calculation of Concentration, in Section 6.9.)

6.7.1 The method should specify an y additional valve

switching or special parameters which are necessary for

the successful analysis of the impurities specified for

the procedure. It must also specify the order of elution

if multiple impurities are detected.

6.8 Calibration — Calibration for these analytical

procedures is generally by external, single point

calibration. Calibration gas mixtures should be

specified and are assumed to be within the range

specified in Section 2.26. Calibration standards are

assumed to be made in a balance of gas representative

of the sample unless otherwise specified. If calibration

techniques other than external, point calibrations are

used, they must be described.

6.9 Calculation of Concentration — The calculation of

the concentration of impurity within the sample is based

on a comparison of the average peak area of the

impurity in the calibration standard, to the average peak

area of the impurity within the sample, based on the

formula:

Sample Peak Are

Standard Peak Are

Concentratio

of Standard

Concentratio

of Sample