basic difference

[mass]

What is the basic difference between lcms/ms of sciex 2000,3000 and 4000 only sensitivity?

Let me know regarding this issue other than sensitivity part.

How mass can be measured? based on Q1 length? what are the parameters taking into consideration while measurement of mass.



massnmass@yahoo.com

[MG]

I know very little about the 2000, but I can say some things about the 3000 vs. 4000.

The 4000 has the probe, whether ESI or APCI, at a 90 degree angle from the orifice, and pointed downward, same as the Agilent sources have been for years. The 3000 has the ESI probe at a 45 degree angle to orifice, and APCI probe is on-axis (zero degree angle). AB/Sciex claims this allows the 4000 to handle more abuse (salts and other matrix crud) without dirtying the source. I have yet to form an opinion on this claim.

The 4000 can handle higher flows in ESI, 1mL/min and perhaps higher, without splitting. The 3000 has trouble above 0.5mL/min. Since I am not a fan of wasting solvent, I have not had the opportunity to test this capability much.

With the 4000, it is easier to remove the curtain plate and clean it, it just snaps on and off by hand. With the 3000, some screws must be removed. It is also easier to clean the orifice and Q0, although the instrument must still be vented for this. Also, the 4000 does not have the focusing ring as the 3000 did, so that is one less item to clean/replace and one less parameter to adjust (there is no "FP" on the 4000).

Sensitivity-wise, the 4000 is definitely more sensitive than the 3000 in ESI mode. In APCI mode, I have made fewer comparisons, but so far I have not seen the sensitivity improvement in that mode.

[mass]

Mr. MG,

can you explain how the mass canbe calculated in the instrument? on which basis it will take the mass, what is the principle behind that? It is based on the length of the ion travelled? by considering kinetic energy?
Please let me know regarding this issue.

can anybody help me?

[MG]

It's been so long since I've had to think about it much, that I'm probably not the best person to ask. I'll give it my best shot.

There are four metal rods, or they can be other material with a metal coating. Ideally they are hyperbolic in shape, though on some models they are circular because it is easier to make them that way. An alternating voltage in the radio-frequency regime is applied to the rods, and a DC voltage is superimposed. The ratio of RF to DC amplitude determines what mass has a stable trajectory through the rods. Quads act as a mass filter. A narrow range of masses make it through the rods, and others are kicked-out. In a selected ion monitoring (SIM) experiment, the potentials on the rods are held constant, and only one nominal mass (plus or minus about 0.3 to 0.5 mass units usually, depending upon how the resolution is set) makes it through the rods. Quads are most efficient in this mode, because all ions of interest are allowed through, not discarded. In a scanning experiment, the potential is varied rapidly so that the selected mass is ramped through a given mass range. However, the quads are still acting as a mass filter, and at any given instant in time, only one mass is allowed through and all others are discarded. This is less efficient, because at any given time during the experiment, most of the signal is being discarded.

I do not know what factor the length of the rods have on the resolution or mass range. But quads do not work in the same way as a Time of Flight analyzer, where the travel time down the flight tube is used to measure mass.

[mass]

MG,

Can you give any websites which will help me regarding this issue. And also any websites which will improve my knowledge in Mass spectroscopy.
I will be very thankful to you, if you send the URLs.


Regards

[MG]

Jeol has some tutorials:

http://www.jeol.com/ms/essays.html