p**********m
发帖数: 472 | 1
accuracy
standards
dramatic though.
i am looking for smaller than 5ppm.
after temperature change, i hardly can get 5ppm accuracy even with lockmass.
will it be harm to qtof if temperature change dramatically on daily basis.
withine 5oC range. |
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p**********m
发帖数: 472 | 2 yes, that is true. we are not familiar with MS.
but if i calibrate qtof just before I use it, will temperature variation
matters? |
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L****r
发帖数: 333 | 3 Agilent 的QTOF 应该贵很多，原因是其解决了一个困扰多年的技术，Watersd的软件很
容易上手， 看楼主喜欢了。 |
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b****u
发帖数: 2771 | 4 and stability
I am quite happy with the integration of chipcube to the QTOF enabling fast
data acquisition and robust performance at both chromatography and mass
spec ends. (note. You have to get familiar with the whole thing first. It
takes me 3 months to grasp the whole thing from scratch)
however, agilent needs to expedite their software support for proteomic
applications. their core business focus on small molecules, and slowly
moving toward protein field (correct me if I am wrong)
I don't |
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y*****s
发帖数: 1047 | 5 劳驾哪位对instrumentation熟的来解释一下，包子答谢
QqQ应该是最高的，我想虽然没100%，应该有个八九十吧
QTof我感觉很难超过20%
QLinearTrap感觉比QTof高，没有50%，应该有个30-40%
对QOrbitrap和LinearTrapObitrap不太了解，前者感觉类似于QTof，需要离子的简谐振
动同相位，能够有20%吗？后者要trap两次恐怕还不如QTof。
我的感觉对吗？ |
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b*******g
发帖数: 1309 | 6 你这个应该叫transmission efficiency，QQQ,从形成离子进入Q1开始算，到Q3，效率
超过90%，好像在95%以上，所以要提高LOD必须在ionization source 跟Q0上下功夫。
举个例子AB Sciex 的6500跟5500 的区别就是source enhance 2倍LOD，Q0（Qjet)
enhance 2倍2LOD，共计4倍LOD
QTOF 的ion transmission主要是损失在 flight 过程中，另外TOF的pulse frequency
并不慢，大部分仪器都在 20kHz 左右，就是0.05ms一次。
速度慢在仪器跟电脑之间的传输，没想到吧，每个TOF的spectrum在被digitization过
后从instrument到电脑需要的时间在ms ，这段时间TOF只能idle等digitizer
clearance
所以QTOF效率取决于duty cycle time跟飞行过程中的离子损失。QQQ现在的duty cycle
一
般可以到2-5ms per MRM，但是QTOF最快能到10ms，一般只能到50ms。意味着同样的时... 阅读全帖 |
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b*******g
发帖数: 1309 | 7 我对 Q-exactive 一直有疑虑，
一旦扫描速度上去了，resolution 就跟TOF 差不多了
综合扫描速度跟resolution，顶级的QTOF还是比Q-exactive好些
但是Q-exactive 还是比顶级QTOF便宜些，另外Q-exactive可调分辨率，这样用起来比
较灵活一些 |
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b*******g
发帖数: 1309 | 8 先回答TOF的问题，你的理解不是很正确。
应该是放慢QTOF scan 速度 (就是增加 duty cycle 时间）增加灵敏度，但是跟
resolution无关。
一个pulse的时间，比如5ns的pulse跟50us的flight time 都是不能改变，或者很难改
变。必须加高pulse的电压才能缩短飞行时间（或者把flight tube该短）。缩短飞
行时间才能增加pulse frequency。
能改变的就是每个cycle里面pulse的数量， 如果做100个pulse是5ms （100X0.05ms）
加上digitizting 时间（假设10ms， 我还没查到具体数据，在2ms到几十之间），这样
一个cycle是15ms
如果增加到400个pulse，一个cycle就是30ms.
每个cycle产生一张谱图，每个谱图是所有pulse信号的叠加。100个pulse的信号只有
400 个pulse的1/4. 如果pulse数继续增多，dwell time（简单看就是digitizing时间
）不会减少，但是占的比例就越来越少，说所以信号损失越来越少。
所以说放慢QTOF sc... 阅读全帖 |
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L****r
发帖数: 333 | 9 4分分析化学杂志
一片GC-MS
一篇LC-QTOF
谢谢 |
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px
发帖数: 853 | 10 My lab has 1 LC-MS-MS(micromass), 1 LC-MS(HP), 1 QTOF(micromass),
1 MSengine. Another LC-MS is coming soon. |
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b*******g
发帖数: 1309 | 11 我知道你说的意思
我说的是现在or未来的方法就是把 MRM的transition 直接整合到QTOF里面去，因为
TOFscan的速度越来越快，不再需要MRM那样只scan 一个或两个fragment ion，而是直
接在 MS2里面选择一两个fragment ion。用MS2的 某些 ion的 peak area 来定量，同
时MS2也提供了sequence的信息
另外你说的MS1的信息给我另外一个灵感，哈哈，谢谢。。。。
Ms1 |
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s******a
发帖数: 252 | 12 Q-executive, QQQ, QTOF 分别大概多少钱？
先谢了。 |
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K******S
发帖数: 10109 | 13 Q-Exative是Thermo的，基本上30大几万就能拿下，因为Thermo很聪明，定的价钱正好
是Share Instrument Grant的价位，Triple Quad很多公司都有，一般的30-40万就能拿
下，QTOF贵的可能要70-80万，现在Agilent比较好划价，因为他们想抢占一些市场。 |
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b*******g
发帖数: 1309 | 14 QTOF 价格也在降
AB tripleTOF5600 跟Agilent 6550 现在都是550K左右
如果上nanosource可能在600K左右。
刚开始确实卖到750K，太黑了。 |
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K******S
发帖数: 10109 | 15 FTICR是需要很多Attention，不过Alan marshall好像说过生产的FTICR比能熟练的造作
FTICR的人多，所以应该就业不错，不知道是否属实
其他的就Case By Case了，我上学的时候用Thermo的比较多，基本上24小时连轴转，平
均一年出一次问题，ABSciex的那个QTOF天天需要Attention。
其实Ms一般都很Robust，很多时候就算坏了自己也修不了，因为里面就是一堆的Boards
。坏了就换。反而倒是HPLC需要不停地Trouble Shooting和维护 |
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b*******g
发帖数: 1309 | 16 哈哈，我们这里 AB TripleTOF 正常工作时间跟down机时间是 50/50
我们这个区那个工程师忙死了。。。。
所以我的实验室一定要买一台Agilent QTOF，跟一个AB 的tripleTOF
TripleTOF坏了至少可以用Agilent的做点事情
Boards |
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w********3
发帖数: 39 | 17 你这个是很typical 的peptide mapping. 你去找个facility 都可以给你做，用
multiple enzyme digest,光用trypsin是不够的，还要Glu-c, Asp-N啥的。然后基本能
做到99-100%的recovery.当然你得有纯化的蛋白，大概需要10ug.还有质谱得是lc
coupled with orbitrap 或者qtof. FT-ICR应该不行，扫描速度太慢。
LC- |
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v**********m
发帖数: 5516 | 18 公司合成时会出specification，AAA通常是做过的，会给出(weight of多肽/weight of
样品)的纯度。那些一起干燥出来的小分子如醋酸盐等都会加重样品的表观重量。这个
只会对绝对浓度有影响,另外小分子对后续的生物实验影响不大，透析一下就可去除。
我觉得LZ应该是更关心多肽内部的纯度，合成步骤多时肯定有一些会少掉某些AA，那些
多肽杂质如果太多，会影响后续的生物研究。此类杂质只能用RP-HPLC鉴定，LCMS能更
一步的定性多肽杂质。这些多肽杂质和目的多肽性质理化接近，只能过制备柱进一步纯
化。
LZ的质谱图貌似MALDI-TOF，这个质谱样品的matrix非常杂，有些杂质也许是样品本身
带的，也可能是学校的facility质谱机器太脏导致的。如果能走LC-ESI-QTOF或TOF，基
本能确定多肽杂质在总多肽里所占的比例。 |
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i******g
发帖数: 90 | 19 这么一点vacumn变化应该属于正常的吧。我用的xevo qtof 也经常有在这个范围变化，
不知道和实验室温度变化有没有关系，不过lockmass调整后就没什么问题了。 |
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p**********m
发帖数: 472 | 20 室内温度到底对tof 的影响有多大. mass accuracy 老是drift on daily basis.
可能是温度问题吗 ,我们实验室也是一会儿冷一会儿热的. |
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k********s
发帖数: 320 | 21 Q-tof accuracy is very temperature dependent. For good accuracy you need to
use lockspray or at least adjust Veff using Leucine Enkephalin on daily
basis. |
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H********f
发帖数: 289 | 22 Yes, Q-tof mass accuracy is very temperature dependent--since TOf tubes are
made of metals, and metals expand or contract when temperature increase/
decrease, so you have to use internal lock mass or lock spray to correct for
the mass shift, when temperature changes. |
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p**********m
发帖数: 472 | 23 does it mean I need to recalibrate everytime using NaI in order to get good
accuracy.
are
for |
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k********s
发帖数: 320 | 24 1. If you use external lockmass (lockspray)- which gives you better accuracy
than internal lockmass, then you don't need to recalibrate.
2. If you don't use lockmass but rather use Leu or other reference standards
to adjust Veff, and if the change of Veff is very small, then you don't
need to recalibrate - according to Water's engineer. However, based on my
experience, fresh calibration does give you improved accuracy - not dramatic though.
3. What is your RMS from calibration?
4. What's the acc |
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k********s
发帖数: 320 | 25 1. Are you using Q-tof premier or not?
2. Did you use W mode?
3. What is your nominal mass accuracy, less than 0.1 amu I hope?
4. What did you use in lockspray lock mass?
5. Is the mass you are looking for very different from your lock mass?
6. Is the signal of the mass you are looking for very different from
that of your lock mass?
7. Did you make sure that when you do mass measurement, the cps of your
analyte is <200? i.e take signal from tail if the intensity is too high?
8. Did you use on-th |
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k********s
发帖数: 320 | 26 Please do not tell me that you mass instrument is in a room with no
temperature control.
lockmass.
basis. |
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p**********m
发帖数: 472 | 27 yes, we do not have temperature control room. |
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p**********m
发帖数: 472 | 28
i use q-tof micromass
what do you mean w mode?
after adjusting vteff, it will be less than 0.1amu.
raffinose, does it matter?
200-400 amu difference. does it matter?
what do you mean signal difference?
they told me q-tof has auto adjustment for dead time correct.
i guess I use post run mass measurement.
really do not on the fly lockmass?
Thanks so much for your patience. |
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k********s
发帖数: 320 | 29 In that case whoever you work for does not know anything about MS
operation. |
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N******o
发帖数: 25 | 31 Please discuss your preference. |
|
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b****u
发帖数: 2771 | 33 what is ur primary application? |
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N******o
发帖数: 25 | 34 Big molecules.
在 blyuyu (Think +) 的大作中提到: 】 |
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a***k
发帖数: 563 | 35 micromass质谱做的好
agilent的不如流 |
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s*******c
发帖数: 179 | 37 scan speed and mass accuracy over a wide concentration range and mass range. |
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b****u
发帖数: 2771 | 38 intact proteins or peptides? |
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L****r
发帖数: 333 | 39 QTRAP做MS/MS功能强大，做peptide没问题，但QTRAP的m/z 上限是1500， 如果楼主用
QTRAP测蛋白的话， 就要用multiplecharge，但QTRAP的resolution不高，建议楼主用
QTOF。 |
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b*******g
发帖数: 1309 | 40 I bet what you mentioned is ESI-Q-TOF,
ESI-Q-TOF is similar as ESI-QqQ
TOF used here instead of Q is to improve mass accuracy.
QToF is much cheaper than FT MS, but the mass accuracy is also good (1-5ppm)
, and the scan speed is very fast, so it become more and more popular.
With the MALDI source, there is instrument called MALDI-ion trap-TOF,
produced by Shimadzu. Ion trap is used to select and fragment ions, then you
can do MS/MS or more.
There are also some home-made MALDI-quadrupole-TOF instr... 阅读全帖 |
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j*********1
发帖数: 109 | 42 本人在这个组，刚刚group发布了beta版本。有兴趣的可以试着用用。说是用于
metabolomics，其实对LC-MS的数据普遍可用，需要upload 两组data进行对比分析。
Announcement:如下
The Scripps Center for Metabolomics is pleased to announce XCMS Online, a
new user-friendly approach to process metabolomics data.
XCMS Online provides the same high-quality metabolomic analysis that you are
used to but in a user-friendly, web-based format. XCMS Online allows users
to easily upload LC/MS metabolomic data that can then be processed with a
few simple mouse clicks. Predefi... 阅读全帖 |
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b*****y
发帖数: 175 | 43 My protein was eluted in 0.3% vitamin C in H2O and lyophilized (vitamin C
was intended to prevent any Met oxidation of my protein). Since I know
highly acidic pH is not good for LC-MS so I tried three different approaches:
1. directly dissolve in ammonium bicarbonate and adjust pH to 8
2. directly dissolve in ammonium bicarbonate and dialyzed against ammonium
bicarbonate (3 changes in 6 hrs) and the final pH is 8
3. dissolve in ammonium bicarbonate and buffer exchanged to 3M guanidinium
hydrochl... 阅读全帖 |
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y*****s
发帖数: 1047 | 44 损失大部分是难免的，只考虑离子产生的总时间里有多少比例可以到最后一级, 这能叫
duty cycle吗
QqQ是流水线，出了Q1进q2,出了q2进Q3
QTof出了collision cell只有一个脉冲时间里的进到Tof，完了再进下一个脉冲的，脉
冲之间的间隔应该比脉冲本身占的比重多不少吧
Linear Trap 一段时间打开进离子，然后扫描，完了再打开进离子，不知道扫描时间和
收集离子时间哪个占的比重大
Orbitrap 只看过thermo的一些广告，似乎是 c trap 打开进离子，然后一个脉冲送到
orbitrap扫描，然后c trap再打开收集离子。不知道c trap 收集离子的时间，脉冲时
间和orbitrap扫描时间的长短都是多少。当然前面还有一个Q或者linear trap |
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