Antares Analytical Technical Bulletin for October 2001

Subject: Poor Analytical Results for P, C, S, B, Se, As

Relevant Models: FSQ, DV, FoundryMate with 1/2 meter vacuum option - PST / PS1-6 / PS2000 Plasma series

These problems can also occur in the MOA, which will be written about in a later Bulletin

Relevant Matrix: Fe base (All), Non-Ferrous (primarily Pb, Sn, Cu alloys)

Symptoms:

• Poor repeatability on above elements but other major elements (for example: Ni, Cr, Mo in Fe Base .... Sb, Bi, in Pb / Sn) have good repeatability
• Poor Standardization "N" factor for the elements listed in "Subject" (N factor below 0.2 or above 2.00)
• Low intensity ratio even though high voltage setting is near or at maximum (9 on RS2 / RS3 / CMU equipped units or 7 on MC20 equipped units)

Most Probable Reason:

• Loss of far UV (ultraviolet) light transmission for wavelengths below 2000 Angstrom. All the above elements have wavelengths below 2000 A and these wavelengths require special circumstances to transmit from the analytical "spark" in the sample stand to the PMT detectors in the optical cell. Normal atmosphere will absorb these wavelengths below 2000 A so either vacuum or argon are required for transmission. Since normal glass will absorb ALL UV wavelengths below about 4000 A, all the optics in your Baird spectrometer are either quartz, MgFl (magnesium fluoride) or a MgFl / AlO2 coated diffraction grating.

Possible Causes of UV Loss:

• Dirty or discolored sample stand slide window: Solution: Clean slide window with suitable lens cleaner. Inspect the center portion of the window for a small brown discolored area about 10 to 15 mm in diameter. This brown discoloration will be caused by strong ultraviolet light "burning" the window and this UV burn can absorb the wavelengths below 2000 A. Sometimes this "UV burn" can be cleaned using 100% pure Acetone or Triclorethene. If Acetone or Triclorethene doesn't remove this UV burn then the window must be replaced. WARNING: Lens cleaner or other cleaner MUST NOT be used on the DV6-SN (Nitrogen) units. The DV6-SN uses MgFl windows and optics and must be cleaned by a special method. Please contact Antares Analytical for the correct procedure. This MgFl cleaning procedure is not in the DV6 Manual.

• No argon purge of the argon purged entrance optics. Solution: This is the entrance optics chamber located directly behind the sample stand where the Hg bulb (FSQ, DV2-5 and all Plasma Series) used for optical alignment is located. The DV6 / DV6E / FoundryMate do not use a Hg bulb for optical alignment. Under the optical chamber, behind the sample stand on all models, will be a small brass fitting connecting plastic tubing to the optical chamber. This plastic line brings a constant stream of argon from the gas panel to the chamber to eliminate air, because air also absorbs UV wavelengths below 2000A. There should be a small amount of argon pressure coming through this line. If there is no argon then adjust the constant flow setting on the gas panel. Use the Baird supplied manuals or contact Antares Analytical for advice.

• Dirty or UV burnt vacuum window:  Solution: Like the slide window, the vacuum window can eventually become dirty or UV burnt. Cleaning is done using the same method as for the slide window. This window is located on the vacuum cell door on the DV2 to 6 and all Plasma models. Bringing the unit to atmosphere and opening the cell door allows this window to be removed for cleaning. On the FSQ changing or cleaning this window should be done by a qualified Service Engineer only. On the FSQ removing & replainv this window involves removing the sample stand for access. The sample stand must be re-aligned after this window is changed and if this alignment isnot done correctly, your FSQ will not work correctly. Consult your Baird supplied manuals or contact us for advice before cleaning / changing this vacuum window.

• UV Burnt Entrance Mirror: (Applicable to the FSQ, DV2-5, all Plasma series only) Solution:  The entrance mirror, located inside the vacuum cell on all models, can not be cleaned and can only be replaced. This must be done by a qualified Service Engineer during a normal Maintenance visit. Replacement of this mirror requires precise re-alignment of the entrance optics and entrance mirror for correct miror replacement. Please contact Antares Analytical for more information. Mirror replacement and re-alignment is not in the Baird supplied manuals.

• UV Burnt or oil covered grating: Solution: The grating is the heart of the spectrometer's optical system. The grating can almost never be cleaned and NEVER should the grating be touched with ANYTHING as damage will occur. There are very certain times when a grating can be cleaned but ONLY with very special cleaning solution, using a very precise method and must be done only by a Qualified Service Engineer. Gratings on an FSQ or MOA can re replaced at the customer site and only by a trained Service Engineer. Antares Service Engineers do have this training and experience. The DV and Plasma gratings can not be replaced. On the FSQ sometimes oil from the vacuum pump can blow back into the optical system and deposit on the grating. This is usually caused by operator error when starting the spectrometer after a period of time it has been shut down. Incorrect shutdown and re-starting of the FSQ is almost always the main reason.

This monthly Technical Service Bulletin has been sent to you by the Technical Service Staff of Antares Analytical. Our purpose for sending this is to help the Baird spectrometer user get the lowest cost, best use of your Baird spectrometer. If you have any comments, suggestions for future Technical Bulletins, questions about the month's topics or questions / problems about your Baird spectrometer please contact us at:

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