What is the difference between a surrogate standard and an internal standard

This solution is added to each sample and will check the internal standard recovery through the entire sample preparation process. Lastly, a question that I am always asked, is if there is another way to improve the workflow to reduce the risk of poor analyte recoveries?

Well, I have done this type of testing with groups of chemists. Some are much better than others. However, I have noticed the loss is much less when utilizing sample prep automation, rather than a full manual hands-on process. Although, EPA method Therefore, EPA method For more information on internal standard implementation at the start of an extraction and how it is carried out, please click on the button below to download our latest application note. Topics: epa method Michael has been practicing analytical chemistry for over 20 years which, combined with his 11 years at the company and his many years of service and customer support, provides him with a significant amount of experience in application areas such as environmental, food and beverage, pharmaceutical and industrial.

Michael enjoys working closely with customers and coworkers using his knowledge and experience to assist them with their laboratory challenges and workflow hurdles. April 1, at PM Michael Ebitson.

What is the difference between an Internal Standard and Surrogate? Sounds familiar right? In this case, you would try to use a compound that is somewhat chemically similar, but would not be found in your sample, i.

Any time you choose in internal standard, you have to validate that it does correct for small amounts of variation within the analytical process. Download as a pdf. Remember me. You will be logged off in seconds due to inactivity. Technical Tips. I'm not sanguine about the accuracy of "semi-quantitation" of using D4 or D5 for compounds such as D15 through D25, either Please, see what you think, and thank you?

Hi Matt The preparation of the plaques is not part of "sample prep" as an analyst would understand it. The sample prep begins when you have the plaque and you dump it into the extraction solvent.

How many samples do you have to do, and how variable are they? It might be best to do an external calibration with a select few of the cyclics if you can get them as pure compounds and then to estimate recovery by extracting some samples twice and comparing the peak area from the first and second extracts.

Then apply the recovery to correct the results. Or use an exhaustive extraction. Peter Apps. Hi Peter, Quite agreed on the prep of the plaque Agreed also on the suitability of D4 and D5 as either a surrogate out of the question or an IS.

Idea is to create a QC method unfortunately? Variability of these cyclics is high even within a single plaque I'm getting some resistance on this idea.

And as usual, it seems agreed on the approach you suggest for estimating recovery extracting twice. The procedure of extraction seems to me to be exhaustive work done before my time, and with great care, it seems to me --reviewed the data for this Hi Matt If your extraction is exhaustive then your main source of variability will be sample mass, and the various volumes along the extraction and concentration if you do that pathway.

You can eliminate the effects of sample mass by always calculating back to actual mass, and a lot of the volume errors either by adding a standard into the extraction solvent this could even be an alkane for example, all it is doing is tracking volume or by check weighing at each stage.

I don't see much advantage to using one standard to correct for sample prep and another one for instrument variability - one standard can do both jobs. You could do this with an internal standard calibration - use e. The most likely source of problems at the intrument stage is inlet discrimination so you need ISs with a range of MWs similar to your cyclics'. I don't see any particular advantgaes to this approach compared to external calibration.

Good Evening, Everyone, Peter, my thanks for being a sensible fellow and a good teacher. Yes, my plan is to calculate these cyclics back to their mass in the original sample. Very much agreed with the idea that there is little advantage in using one standard to correct for prep and one for instrument variability Tangaloomaflyer's idea and thank you again for that appearing earlier in this thread is pretty much the same as the one Peter suggested immediately above I can use the "surrogate" in this case as an internal standard Thank you, and Tom Jupille, for your responses!

I am a little late seeing this post but it reminds me of some of the early work I did looking for Glucoraphanin in broccoli extracts. The reference works all used Sinigrin as a "surrogate standard" where they calibrated using Sinigrin and used that calibration curve to quantify Glucoraphanin. We always used the actual Glucoraphanin to calibrate with, and we had different results than the people using Sinigrin. The response factor is close between the two compounds, but not exactly the same.

If you want a general idea of how much of a compound you have you can use a similar compound or "surrogate" standard to calculate the compound of interest, but if you are looking for a more accurate quantification you will need the actual compound to be sure of your values.

In this work, the surrogate was very different from how it is defined in Environmental work. The past is there to guide us into the future, not to dwell in. The word "surrogate" seems to be used in the sense as "a substitute for" the standard s I don't have rather than as how an environmental chemist would understand a "surrogate standard" My thanks for your input as well. Interesting how word usage can cause such horrible confusion Matt, you are not the only one confused by the "surrogate" as the environmental analysts use it.