Antares Analytical Technical Bulletin for

January 2003

Subject: Argon Systems for Baird Spectrometers, Part 1

Relevant Models: All DV series, FSQ,  Foundrymate, ICP, MAX II, HA10 /12 used for metals analysis. This does not apply to MOA / FAS spectrometers

Relevant Matrix: Not Applicable

Background: All Baird spectrometers, actually all OES spectrometers being used for metals analysis will use argon for one or more of the following purposes A) as a burning medium in the sample stand, B) for optical purging or flushing, C) for controlling various spectrometer functions.

 Sample Sparking: Baird spectrometers use a capacitive discharge source (KH3-5 or HR400 although some of the older Baird HA or DV1-2 systems can use the PZ1 or QG2-3 sources) optimized to burn in an inert argon atmosphere at the sample stand.  No gas, poor gas, or incorrect gas flow at the sample can and will give inaccurate sample results. Any inert gases, except nitrogen, can be used but argon is normally used for costs reasons. 

Optical Purging:  Part of the optical path needs to be purged by an inert gas (normally argon for costs reasons) to allow transmission of UV wavelengths (wavelengths below 2000 Angstroms, usually P, S, C, B, Se, and Sn & As if ferrous base). On the Baird FSQ, ICP and all

·         DV series this is done using a low flow constant gas purge set at the gas panel. Nitrogen could be used but because of the low gas requirements for a constant optical purge, the added costs for a separate gas system is not economical.

·         The Baird OneSpark will use a constant purge of the CCD camera optical cell. Because the CCD uses a chilled head, vacuum can create a “fogging” affect on the CCD lens so nitrogen can be used. The OneSpark does have the basic gas system to accept nitrogen, but this option would have been needed to be ordered when the unit was built.

Controlling Spectrometer Functions: The DV6 / DV6SN / DV6E uses a high pressure gas line from the argon panel to push down the sample clamp during sample analysis and to open the entrance solenoid during the expose portion of the sample analysis cycle. These are the only 2 functions on any Baird spectrometer which are controlled by gas pressure.

Basic Argon System Design: All gas systems on all Baird metals spectrometers are built along the same basic design. The difference is the ICP series spectrometers has a system to purge the entrance optics and supply a high pressure gas flow to the torch. 

Argon Supply: Required for all Baird spectrometers is a supply of minimum 99.996% pure argon with a maximum of 5 PPM (parts per million) of oxygen. A Certificate of Purity should be received from the argon supplier on a regular basis.

·         An argon purifier can be used which will allow a lower (and less expensive) purity argon to be used down to a maximum of 99.95%. There is a cost tradeoff though because of the cost to purchase / maintain the argon purifier. However in cost analysis an argon purifier can pay for itself in as little as 2 years, depending on the local cost of argon.

·         Argon purifiers usually do not need periodic maintenance to do their job correctly. Please see the section below on the care & feeding of Argon Purifiers.

·         Usually a commercial tank of gaseous argon is sufficient for most Baird metal spectrometers, however if several spectrometers are being used  or your spectrometer is used on a constant 24 / 7 basis, it is probably more cost effective to install a liquid argon supply.

·         ICP spectrometers, because of the large amount of argon required, are almost always used with a liquid argon supply.

Gas Control Panel: This is the panel mounted on the lower left side of the spectrometer (DV / HA /  ICP series) or right below the spectrometer shelf. (FSQ) It’s purpose is to regulate the incoming gas pressure, regulate the gas pressure to the spectrometer, direct the gas to the correct lines, and mount the various gas relays.

Constant Purge Adjustments: Because the entrance optics / sample stands require a constant purge of argon, to maintain an inert gas environment, all constant gas purges are also controlled from the rear of the gas panel by one or more needle valves which are part of the gas panel plumbing.

The DV series with KH 3-5, QG, PX or RE1 source came with one gas flow indicator per sample stand. On the front of the panel will be a rotary knob which will control the gas pressure during the sample analysis cycle (flush-preburn-expose).  When not analyzing a sample, there will be a constant flow indicated … usually between 3-4 SCFH. This will be a combination of the constant flow to the sample block and another constant flow to the entrance optics.

o        Take off the side panel so the rear of the gas panel can be accessed. There will be 2 rotary valves visible. The top will be used to adjust the constant purge to the sample stand. This gas flow is not critical and (in our opinion) can be set to 1 SCFH, though the manual states 3 SCFH. 

o        This is because at the start of a sample analysis cycle, the flush uses a 20 SCFH gas flow for 2 –3 seconds to “flush” the sample stand of atmosphere. Starting with both valves closed, adjust the top so the flow meter reads a constant 1 SCFH.

o         The lower valve will be used for the entrance optics constant purge. Adjust the valve until the flow meter shows 3 SCFH. Though the meter will show a total of 3, this will be  cumulative 1 & 2. SCFH.

o        The flush / preburn / expose gas flow is set to 20 SCFH

The DV and FoundryMate Series with HR400 / TR300 source is similar to the DV series with KH source. The constant purge for the entrance optics & sample stand flows are set the same way to the same level. The difference is in the flush / preburn / /expose gas flow. Originally the HR400 was set at 11 SCFH but later HR400 supplied units were set to 17 SCFH. Our suggestion is to try both gas flows and see which gives the best analytical result. We have never noticed any difference between an 11 & 17 SCFH gas flow.

FSQ Gas Panel: The early FSQ was manufactured with either a 1 or 3 flow indicator gas panel. The later models FSQ had the single flow meter and the gas flows are set up as described above for the DV spectrometer. Be sure to use the correct source (HR400 or KH5) as the FSQ could be equipped with either.

Earlier model FSQ were equipped with a 3 flow indicator gas panel. The .03 to 3.0 SCFH meters are used for the entrance optics purge and the sample stand purge. These should be set a 1.0 and checked periodically. The 2 to 20 SCFH flowmeter is set to 20 during the flush / preburn / expose cycles.

Problems and Solutions with various Argon System components will be covered in February Tech Bulletin.

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This Technical Bulletin is written by Gerry Smith, Technical Services Manager of Antares Analytical. Having spent 22 years with Baird in various capacities, including many years as Final Test / Calibration Manager and Senior Service Engineer, International Operations, he or any of our Technical Support Staff, are well qualified to answer any Technical or Applications problems you may have.

For further information or access to past monthly Technical Bulletins covering a variety of subjects, please visit our website (still under development) at www.antaresanalytical.com 

This bulletin is meant for informational purposes only and it not meant as a substitute for Service performed by a qualified Service Engineer. Any use of this information is done strictly at the discretion of the user. Antares Analytical is not responsible for any misfortune which results as the result of use of these Technical Bulletins, in place of service by a Qualified Service Engineer.