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Dr. Harish L. Rao ☆ India, 2007-10-24 15:23 (6818 d 15:50 ago) Posting: # 1249 Views: 7,414 |
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Dear Group Members, We use API Sciex LC-MS/MS systems with Analyst 1.4.2 software. During study sample analysis, can we set the Area Threshold parameter based on the LLOQ response? If so, what % of LLOQ response should be the Area Threshold? Thanks & regards, Dr. Harish L. Rao |
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Helmut ★★★   Vienna, Austria, 2007-11-02 18:45 (6809 d 11:28 ago) @ Dr. Harish L. Rao Posting: # 1267 Views: 6,536 |
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Dear Harish! ❝ During study sample analysis, can we set the Area Threshold ❝ parameter based on the LLOQ response? If so, what % of ❝ LLOQ response should be the Area Threshold? This is a tricky question - especially for LC-MS/MS... Since I expect your method uses an internal standard (IS), your LLOQ response is based on the ratio of analyte/IS. Therefore it's difficult to set an area threshold for integration - the data system simly 'does not know' the suitable 'LLOQ response' - which in a strict sense can only be established based on the calibration curve for the particular batch. What you can do is establish some kind of minimum area of the limit of detection (LOD), which generally is 1/3 - 1/10 of the LLOQ. By this you
Although the human brain is a perfect pattern recognition system (especially if you have seen many thousands of chromatograms), you should have an SOP in place guiding you through re-integration in a consistent and traceable way. — Dif-tor heh smusma 🖖🏼 Довге життя Україна! ![[image]](https://static.bebac.at/pics/Blue_and_yellow_ribbon_UA.png) Helmut Schütz ![[image]](https://static.bebac.at/img/CC by.png) The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes |
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vishal vayeda ☆ 2008-01-01 09:53 (6749 d 20:20 ago) @ Helmut Posting: # 1446 Views: 6,392 |
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Dear Sir, As per my knowldge area threshold require to neglet those area of the chromatogram which are no need to quantify so you can put whatever value as area thresold but it should be less then the area which you found at LLOQ level. e.g. if the area of LLOQ is 12345 so you can put area thresold value less then the LLOQ area so whatever peak having the area less then area threshold will not reflect in your chromatogram. plese correct me if i am wrong. Regards, Vishal Vayeda -- Edit: Full quote removed. Please see this post! [HS] |
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Helmut ★★★ Vienna, Austria, 2008-01-02 02:57 (6749 d 03:16 ago) @ vishal vayeda Posting: # 1450 Views: 6,105 |
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Dear Vishal! ❝ As per my knowldge area threshold require to neglet those area of the ❝ chromatogram which are no need to quantify ... So far so good.  ❝ ... so you can put whatever value as area thresold but it should be ❝ less then the area which you found at LLOQ level. As said in my previous post, it's not that easy - at least for internal standards methods... ❝ e.g. if the area of LLOQ is 12345 so you can put area thresold value less ❝ then the LLOQ area so whatever peak having the area less then area ❝ threshold will not reflect in your chromatogram. Simple example (sample at LLOQ): Analyte area 12345 IS area 246900 Ratio analyte/IS 0.05 Now you are loosing 5% somewhere in the sample transfer process, getting Analyte area 11723 IS area 234555 Ratio analyte/IS 0.05 (=unaffected!) If you would have set the threshold to 12345, the analyte would not have been integrated (in other words, you would report the sample as BLQ, which is not correct). Just remember that it's OK at LLOQ to have an inaccuracy of ±20% together with precision of 20%. If you set the area threshold to the analyte's response calculated at LLOQ for the average internal standard area from the CC, you will miss roughly 1/3 of samples by pure chance! I agree with Rajendra, that the threshold should be set somewhere between LOD and 50% of LLOQ. — Dif-tor heh smusma 🖖🏼 Довге життя Україна! Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes |
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rajendra ☆ India, 2007-12-27 07:34 (6754 d 22:39 ago) @ Dr. Harish L. Rao Posting: # 1428 Views: 6,122 |
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Dear Sir, Area Threshold Parameter in LC-MS/MS, it should be less than 20% of your LLOQ response. |
Ing. Helmut Schütz