By Anonymous on Monday, May 17, 2004 - 05:37 pm:
Any body have idea about a moeity with MW 74. I have a Mass Spectrum, four peaks distribute at 462,536, 610, 684. Interval is same, 74.
thank you
By Kostas Petritis on Tuesday, May 18, 2004 - 01:52 am:
Anonymous,
These are siloxanes coming either from your chromatographic column or from some plastifiers. What is your LC-MS system?
Kostas
By Anonymous on Wednesday, May 19, 2004 - 02:22 pm:
Thank you! It is waters ZQ. Do you think this is elution of column Silicon Gel?
By Anonymous on Wednesday, May 19, 2004 - 02:27 pm:
Now I increased the scale of MS, and found 758,832...,how can I determine where this information is from?Thank you.
By Anonymous on Wednesday, May 19, 2004 - 03:44 pm:
looks to be close to trimethylsilyl (CH3)3Si -- encapping stripping?
or dimethylsiloxane (CH3)2SiO -- polymerises in MS after RP ligand has been stripped?
By Kostas Petritis on Wednesday, May 19, 2004 - 11:00 pm:
It can also be volatile polylydimethylcyclosiloxanes that can be found in plastic materials. Have a look at the following article, which is relevant with the type of pollution you described. You'll see that your MS spectra will be very much alike... (but as I said it can be column bleed).
J Mass Spectrometry, 2003, 38, 523-525.
Kostas
By Anonymous on Friday, May 21, 2004 - 07:34 am:
Polydimethylsiloxanes are components in vacuum grease, which is sometimes used to lubricate o-ring seals and ground glass connections. Check your HPLC solvent reservoirs and see if your bottle openings have ground glass necks. If so, consider replacing the bottles with ones without ground glass necks.
Kevin