I saw some brass color and rainbow pattern on my stainless steel quadrupole when I cleaned it. I previously done some analysis of lipids and pesticide with acidic solvent (1% acetic acid in H2O/ACN). I tried to remove them with methanol, but it didn't work. I would like to know if there's any method to bring it back. Also, how this would affect my signal?
The color you see on the quads is an oxidation of inox. Inox is a Cr/Ni rich iron alloy. Upon oxidation a chromium oxide layer is formed, the color is a result of interference of light on the layer interface.
One thing about quads: There relative position is really very critical, so whatever You do : do not disassemble the rods from there casing or apply force on them.
The best way is to clean them as one part.
As long as the construction is made of inox an ceramics only it is possible to clean them with a acetic acid solution (try 20%) in an Ultrasonic bath, Stronger cleaning can be done with 40% nitric acid. Make sure there are NO OTHER METALS involved : they will create a galvanic cell while cleaning with disastrous results. Rinse with Aqua dest. , methanol and dry in a stove at 100°C
NEVER USE ACID MIX
Mount the quad assembly (witch You kept as one part) again and make sure that the connecting wires remained in there original shape (High frequency: change in reactance ).
Personally I am not convinced That the condition (brass color) of your quads is the main problem, I would expect scanrate dependent mass- accuracy and resolution issue's not really signal loss at this stage. Check Your ion generation part (LC?GC?) first, then the electron multiplier. Keep the quad as last option.
The color you see on the quads is an oxidation of inox. Inox is a Cr/Ni rich iron alloy. Upon oxidation a chromium oxide layer is formed, the color is a result of interference of light on the layer interface.
One thing about quads: There relative position is really very critical, so whatever You do : do not disassemble the rods from there casing or apply force on them.
The best way is to clean them as one part.
As long as the construction is made of inox an ceramics only it is possible to clean them with a acetic acid solution (try 20%) in an Ultrasonic bath, Stronger cleaning can be done with 40% nitric acid. Make sure there are NO OTHER METALS involved : they will create a galvanic cell while cleaning with disastrous results. Rinse with Aqua dest. , methanol and dry in a stove at 100°C
NEVER USE ACID MIX
Mount the quad assembly (witch You kept as one part) again and make sure that the connecting wires remained in there original shape (High frequency: change in reactance ).
Personally I am not convinced That the condition (brass color) of your quads is the main problem, I would expect scanrate dependent mass- accuracy and resolution issue's not really signal loss at this stage. Check Your ion generation part (LC?GC?) first, then the electron multiplier. Keep the quad as last option.
Extra Warning:
If you intend to clean as above make sure the quads are plain inox and not a coated support. Some MS use cold plated quads or ceramics with a metal coating.
Actually only a small portion of your analyte will go into your MS, let alone as deep as the quadrupole. Contamination (and damage) usually happens first in the ion source, then capillary, then ion focusing, and finally quadrupole. If your sample is so acidic that can "corrode" your quadrupole, you better check whether your ion source is still in one piece.....
I agree with Kris that the main problem shouldn't be your quadrupole. Try injecting some standard using a syringe pump to see if there is anything wrong with your signal first.
Thank you all for our suggestions. Just one more thing, I need to run some experiments in -ve mode for some of the lipid. Would it be ok if I run it in 5 mM NH4OAc?
Rainbow pattern sometimes appears during localized corrosion. You must check occurence of pits on your quadrupole. INOX (AISI 304) is very susceptible to pitting.
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