Tuesday, December 16, 2008
Sunday, December 14, 2008
m/z (563.10761) is NOT the Molecular Ion? (II)

(1) Try to adjust the the capillary voltage: increase it a little bit each time.
If the the mass response of [M+H2O -H]- is decrease, the mass response of [M-H]- increase: then the m/z (563.10761) definitely is the molecular Ion.
If No such change happened, then the m/z (563.10761) definitely is NOT the Molecular Ion.
(2) From my view, the possibility of [M+H2O-H]( belongs to Molecular ion) is very low. Under ESI (-) negative mode, the trend of forming
the [M+HCOOmore high.
Doubt the H2O have that much acidity for forming the ion peak.
Monday, December 1, 2008
Where M/Z 425 from? ( II )
Where M/Z 425 from? ( I )
The molecular weight of your analyte is 548: 1st Mass is 549, 2nd Mass is 489, 3rd Mass are 471, 425.Here is HUGE challenge for the structural elucidation of your analyte.
From M/Z (471) to M/Z (425) , maybe belong the loss of Acetoxyl M/Z.
But it is NOT right because there are two Acyloxy in your analyte.
Will Update you by Monday Night.
Monday, November 17, 2008
Come on, Man: Don't be silly to send us this Newbie question? Are you want to test our GC knowledge?(1) Condition the GC Column according the manufacturer' recommend.
(2) Check the septum and the inlet, make sure NO cross-contamination -> inject the Blank.
(3) Optimize your method, change the Oven temp Ramp -> Higher the Initial temp, Low down the Temp Ramp.
(4) Low down the Split Ratio.
(5) Adjust the GC gas Flow Rate.
Sample Overload on Column? Example 2
Sample Overload on Column?
Sunday, October 26, 2008
How do you define the Limit of Detection?

In figure 5b, [M+Na-H2O]+ ion peak at m/z 475 was observed. The peak is hidden by back ground. How do you define the limit of detection?
(1) From the reviewer's point, you should explain why the Low response in the Mass Spectrum?(2) Optimize the Mass Spectrum of product ion: adjust the CID little by little, do not need to change the energy of cone voltage. low down the gas flow rate of CID, wait 10 min until equilibrium, increase the collision energy at Q2.
(3) If the Professor only care the Low response in the Mass Spectrum, here I have one "non-professional" shortcut: Inject twice in one time ( do not use the syringe pump), one could use low CID, other use high CID for about 2-5 min. Then use the second one as background to extract the First one. you definitely get high abundance on your mass spectrum. ( actually they are the same, but you could hide the response value in the Y axis, only put the abundance.)
Do not abuse the tip a lots, some reviewer hates that so much.
Good Luck...
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