Calibration for Quantification

Today, we will discuss the role of surrogates in quantification. Can anyone tell me what a surrogate is?

I think it's something that's added to help measure the main analyte?

Exactly! Surrogates are compounds added to assess the recovery of the actual analyte during analysis. This is crucial for achieving reliable results. Let's remember this with the acronym 'SURE' - Surrogate for Understanding Recovery Efficiency.

So, if the surrogate behaves like the analyte, it helps us understand how much of the analyte we can recover?

Precisely! Now, why do you think it's important to calculate recovery rates?

To ensure our measurements are accurate and account for any losses during processing?

Exactly right! The recovery rate indicates how effective our extraction methods are.

Let's now look at the extraction process. What are some methods we can use to extract analytes from a sample?

I remember you mentioned liquid-liquid extraction last class.

Exactly! Liquid-liquid extraction often involves shaking a sample with a solvent. What happens to the analyte during this process?

The analyte moves from the water phase into the solvent phase, right?

Correct! However, during extraction, we lose some compounds due to incomplete separation. We commonly use hexane as a solvent. Can anyone explain why we concentrate the extract after extraction?

To increase the sensitivity for detection of the analytes in the sample right?

Exactly! Concentrating helps us in detecting even trace amounts. Using the mnemonics 'SISS' - Sensitivity through Increased Sample Size - we can remember the goal here.

Now, let’s discuss calibration. After obtaining a sample response from the instrument, what must we do next?

We need to use the calibration curve to determine the concentration of the analyte?

Correct! The calibration curve relates instrument response to the mass of analyte. If I told you that the equation is response equals 60,000 times mass, how would you find mass from a known response?

To find the mass, we would divide the response by 60,000?

Great! And what does that mass represent?

It shows how much of the analyte was present in our sample initially!

This back calculation is essential, revealing the efficiency of our extraction. Just remember, 'CALC' - Concentration And Loss Calculation in our Analytical process!

Lastly, let's talk about recovery calculations. If we added 100 micrograms of a surrogate and recovered 1.67 micrograms, how would we determine our recovery percentage?

We divide the recovered mass by the added mass and multiply by 100, right?

Exactly! This tells us how effective our method was. We can capture this with the phrase 'Happy Recovery: Recovered Mass Over Added Mass Times 100'.

What would a low recovery percentage indicate?

It would suggest either losses during the extraction process or issues with our calibration method. Ensuring we understand this is key to quality control in our analyses.