m******k
发帖数: 92 | 1 Can any MS expert help me out here? I use API3000 trying to detect certain
compounds. The method was set up, just like what I did for other compounds.
The first injection was just solvent (MeOH) but I saw unusually high
baseline. Changed to different column, same problem. Changed to different
method, fine． Ｃｈａｎａｇｅｄ ｔｏ ｏｔｈｅｒ ｓａｍｐｌｅｓ， ｆｉｎ
ｅ ａｓ ｗｅｌｌ． Ｎｅｖｅｒ ｓａｗ ｔｈｉｓ ｈｉｇｈ ｂａｓｅｌｉｎ
ｅ ｂｅｆｏｒｅ．I checked the method again but I don't see a problem. Is
that sort of contamination in the line or in the ion sou |
e*****r
发帖数: 379 | 2 very simple ja. but i am too sleepy now |
m******k
发帖数: 92 | 3 have u wake up yet.....please |
L****r
发帖数: 333 | 4 改变方法后，基线又降下来了， 说明SOURCE没有被污染，当基线很高的时候，看看都
是什么离子，可能溶剂污染了。希望能有更好的建议。 |
m******k
发帖数: 92 | 5 谢谢建议！我也觉得source应该没有污染，在这个injection后 跑了其他的sample 很
正常，不过用的也是同样的溶剂。因为我用的是triple quadrupole MRM, 设定了要看
我要的化合物，所以没有看到其他的离子。我会把溶剂换掉试试看。也可能是我inject
的MeOH污染了。都换掉都换掉。
而且这两个化合物，carry over还挺严重的，方法可能也要改。。。。
【在 L****r 的大作中提到】
: 改变方法后，基线又降下来了， 说明SOURCE没有被污染，当基线很高的时候，看看都
: 是什么离子，可能溶剂污染了。希望能有更好的建议。
|
m******k
发帖数: 92 | 6 still have the problem.............can anyone help????? seems only see this
high baseline for this method! Solvent is totally fine!! |
S***x
发帖数: 2012 | 7 跟你的ion pair有关。
如果灵敏度不是问题，就调调DP和CE. MP可以用ACN,还不行的换ion pair或者试试
negative
.
【在 m******k 的大作中提到】
: Can any MS expert help me out here? I use API3000 trying to detect certain
: compounds. The method was set up, just like what I did for other compounds.
: The first injection was just solvent (MeOH) but I saw unusually high
: baseline. Changed to different column, same problem. Changed to different
: method, fine． Ｃｈａｎａｇｅｄ ｔｏ ｏｔｈｅｒ ｓａｍｐｌｅｓ， ｆｉｎ
: ｅ ａｓ ｗｅｌｌ． Ｎｅｖｅｒ ｓａｗ ｔｈｉｓ ｈｉｇｈ ｂａｓｅｌｉｎ
: ｅ ｂｅｆｏｒｅ．I checked the method again but I don't see a problem. Is
: that sort of contamination in the line or in the ion sou
|
w**********8
发帖数: 1755 | 8 1.你“Ｃｈａｎａｇｅｄ ｔｏ ｏｔｈｅｒ ｓａｍｐｌｅｓ”，你的MRM方法和那
个certain compound一样吗？
2.你所说的high baseline，是指出现在MRM的某一个transition里还是所有的？
3.你把mobile phase换成ACN，看看还会有那么高的background吗？
4.所谓carry over的问题，是不是inject太多样品了，稀释一下，如果还不行，就改
gradient方法吧。
我和楼上看法一样，估计是ion pair的问题。如果条件允许，换成negative ion mode
好了。 |
L****r
发帖数: 333 | 9 #
Dear group members,
Welcoming the LC-MS/MS users to comment on the plausible causes for
high background noise observed sometimes in LC-MS/MS analysis. What
are the different attributing factors responsible for high to very
high baseline level and what are the different measures to reduce the
baseline.
Also how best can we explain the rise in baseline level while doing
analysis in SIM mode compared to MRM mode.
Looking forward to have your responses.
Regards
Neel K Mohan
Back to the Top
# On 7 |
m******k
发帖数: 92 | 10 Thanks for replying!
Sensitivity is good, proved by other samples. I tuned the instrument for
these particular compounds and got optimized DP and CE, those are what I
used in the method. You think the DP and CE need to adjusted? MP is ACN.
【在 S***x 的大作中提到】
: 跟你的ion pair有关。
: 如果灵敏度不是问题，就调调DP和CE. MP可以用ACN,还不行的换ion pair或者试试
: negative
:
: .
|
|
|
m******k
发帖数: 92 | 11 Thanks!
1. No, different MRM method based on different compound. I just wanted to
see if the instrument sensitivity was the problem.
2. The high baseline showed up when I injected the blank solvent (ACN). The
MRM method was set to look at two compounds (two sets of Q1/Q3), for both
channel I could see high baseline but apparently the baseline in one channel
is way higher than the other.
3. I'm using ACN as the mobile phase. I even changed the LC method from
gradient to isocratic, 60% ACN all the
【在 w**********8 的大作中提到】
: 1.你“Ｃｈａｎａｇｅｄ ｔｏ ｏｔｈｅｒ ｓａｍｐｌｅｓ”，你的MRM方法和那
: 个certain compound一样吗？
: 2.你所说的high baseline，是指出现在MRM的某一个transition里还是所有的？
: 3.你把mobile phase换成ACN，看看还会有那么高的background吗？
: 4.所谓carry over的问题，是不是inject太多样品了，稀释一下，如果还不行，就改
: gradient方法吧。
: 我和楼上看法一样，估计是ion pair的问题。如果条件允许，换成negative ion mode
: 好了。
|
S***x
发帖数: 2012 | 12 How can you test sensitivity for Compund A by using Compound B?
For different compounds, same instrument may have different sensitivity.
Auto tune can help, but it may not be the best method. You can use auto tune
method as start point to make the adjustment.
Also, please check the spary needle to make sure it's not too close.
【在 m******k 的大作中提到】
: Thanks for replying!
: Sensitivity is good, proved by other samples. I tuned the instrument for
: these particular compounds and got optimized DP and CE, those are what I
: used in the method. You think the DP and CE need to adjusted? MP is ACN.
|
S***x
发帖数: 2012 | 13 If you want to check sensitivity, the best way will be calibration.
Comparing with last time calibration data, you can find whether sensitivity
changed or not.
The
channel
【在 m******k 的大作中提到】
: Thanks!
: 1. No, different MRM method based on different compound. I just wanted to
: see if the instrument sensitivity was the problem.
: 2. The high baseline showed up when I injected the blank solvent (ACN). The
: MRM method was set to look at two compounds (two sets of Q1/Q3), for both
: channel I could see high baseline but apparently the baseline in one channel
: is way higher than the other.
: 3. I'm using ACN as the mobile phase. I even changed the LC method from
: gradient to isocratic, 60% ACN all the
|
S***x
发帖数: 2012 | 14 就怕negative没有碎片
mode
【在 w**********8 的大作中提到】
: 1.你“Ｃｈａｎａｇｅｄ ｔｏ ｏｔｈｅｒ ｓａｍｐｌｅｓ”，你的MRM方法和那
: 个certain compound一样吗？
: 2.你所说的high baseline，是指出现在MRM的某一个transition里还是所有的？
: 3.你把mobile phase换成ACN，看看还会有那么高的background吗？
: 4.所谓carry over的问题，是不是inject太多样品了，稀释一下，如果还不行，就改
: gradient方法吧。
: 我和楼上看法一样，估计是ion pair的问题。如果条件允许，换成negative ion mode
: 好了。
|
m******k
发帖数: 92 | 15 Thanks a lot!
You right negative does not give fragment, I have to use positive mode. And
yes the sensitivity to different compounds are different. I just wanted to
see if the instrument works fine and if there is contamination through the
line. I have checked the needle the position I thought it should be ok with
the flow rate 0.25 mL/min....spray area is about the right position to the
orifice. I will move it away try to see if there is a difference. I never
run these two compounds before so d
【在 S***x 的大作中提到】
: 就怕negative没有碎片
:
: mode
|
b*****r
发帖数: 203 | 16 It is likely due to methanol contact with the silicon or other plastic
backing of the lid. Try to run LC-MS/MS with the injection without the lid
and see if you see less noise. |
S***x
发帖数: 2012 | 17 Right,you can run auto tune first. Then adjust by FIA.
Few weeks before, I use auto tune for a compound. The baseline is 10000 high
.....
So I have to increase both DP and CE a lot. Finally I have a reasonable
background.
And
with
I
【在 m******k 的大作中提到】
: Thanks a lot!
: You right negative does not give fragment, I have to use positive mode. And
: yes the sensitivity to different compounds are different. I just wanted to
: see if the instrument works fine and if there is contamination through the
: line. I have checked the needle the position I thought it should be ok with
: the flow rate 0.25 mL/min....spray area is about the right position to the
: orifice. I will move it away try to see if there is a difference. I never
: run these two compounds before so d
|
m******k
发帖数: 92 | 18 OK! Really! I never had a problem with auto tune until these two compounds..
..I have a ref I tried the parameters people reported in that paper but didn
't work either....I will do it ASAP.
Thanks a lot!
high
【在 S***x 的大作中提到】
: Right,you can run auto tune first. Then adjust by FIA.
: Few weeks before, I use auto tune for a compound. The baseline is 10000 high
: .....
: So I have to increase both DP and CE a lot. Finally I have a reasonable
: background.
:
: And
: with
: I
|
m******k
发帖数: 92 | 19 Thanks...Trying.
【在 b*****r 的大作中提到】
: It is likely due to methanol contact with the silicon or other plastic
: backing of the lid. Try to run LC-MS/MS with the injection without the lid
: and see if you see less noise.
|
