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A short class with Sarah and her students. The other ways are under More.
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Welcome everyone! Today, we will explore what a surrogate is. Can someone tell me why we might use one?
Isn't it because it behaves like the analyte we're interested in?
Exactly! A surrogate mimics the analyte's properties during the extraction. It allows us to estimate how much analyte we can expect to recover.
What if the surrogate doesn’t behave like the analyte?
Good question! If the surrogate's behavior deviates from that of the analyte, our recovery calculations can be misleading, leading to inaccuracies.
Remember the acronym SURE: Surrogate Utilized for Recovery Estimation. It helps you remember the main purpose of a surrogate!
Nice mnemonic! Can we continue with the example?
Next, let’s talk about the extraction process. We add 50 ml of hexane to our sample to extract the surrogate. Why do we use hexane?
Hexane is a nonpolar solvent, right? It helps extract nonpolar compounds.
Exactly! And after shaking, we take out 40 ml for analysis. Can anyone explain why we don’t take all 50 ml?
Some of the hexane might not separate properly, right?
Yes, it’s often because of the difficulty in separating phases. Good point! So, fingering finger for those small residual amounts can impact our recovery rates.
Now, who remembers the efficiency of extraction we discussed previously? Connect that to the extraction process.
It affects how much of the analyte and surrogate we recover, right?
Now, let’s focus on why we concentrate our samples. Why do we reduce the volume from 40 ml to 1 ml?
To increase the concentration for better detection in the instrument!
Precisely! By concentrating the sample, you're minimizing the volume and maximizing the chance of detecting lower concentrations of the analyte.
And then we calibrate the instrument with known values, right?
Absolutely! Calibration ensures we can interpret the responses from our analyses accurately. If we get an instrument response of 80,000 units, how do we relate that to the mass of the analyte?
We use the calibration equation to find the mass!
Great! And keep in mind the formula: Response = 60000 * mass – it’ll help you connect the dots.
Finally, we need to back calculate to find out how much analyte we recovered based on the surrogate response. If our instrument gave us a total of 1.3 nanograms in our 1 ml sample, how do we find the recovery?
We need to compare that to the original amount we added, right?
Exactly! So if we added 100 micrograms, how does that relate?
We find the percentage recovery by comparing the recovered mass to what we initially added.
Correct! It’s crucial to perform these calculations accurately to interpret the efficacy of the extraction and the analysis.
Could errors in our calculations affect our results?
Absolutely! Always check your units and ensure accuracy. Accuracy is key in reporting what you find.
Compounds used to mimic analytes for accurate recovery calculations.
The method employed to isolate compounds from a sample.
Reducing sample volume to enhance detection of target analytes.
The process of setting instrument parameters to ensure accurate measurements.
A key metric that indicates the effectiveness of the analytical process.
In a study where a surrogate is added to a water sample, if the original concentration is 100 micrograms and the instrument returns a recovery of 70 micrograms, the recovery rate is 70%.
For soil samples, after extraction and analysis, if it is determined that 50 nanograms of an analyte are recovered from a 100 nanograms sample added, the recovery rate would be 50%.
For surrogates, it's really quite clever, they mimic analytes, helping us measure!
Imagine a detective (the surrogate) following a suspect (the analyte) to understand the case (the recovery process) better. The detective's journey shares insight into how much the suspect behaves in various situations.
M.A.R.C.: Measure - Analyze - Recover - Calculate, steps to follow during recovery analysis.
SURE: Surrogate Utilized for Recovery Estimation.
Term
Recovery Rate
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Term
Calibration
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Term
Surrogate
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A compound added to a sample that behaves similarly to the analyte of interest and is used to estimate recovery rates.
The process of separating a substance from a mixture, typically done to isolate specific compounds for analysis.
The process of reducing the volume of a solution to increase the amount of solute per unit volume.
The process of adjusting the instrument's response based on known concentrations of a standard to ensure accurate results.
The percentage of an analyte that is recovered during the analytical process, compared to the amount that was originally present.
This section discusses the calculation of the recovery of an analyte using a surrogate compound in environmental analysis, detailing the procedural steps and underlying principles.
In this section, the process of calculating the recovery of an analyte of interest in a sample using a surrogate compound is outlined. It illustrates the methodology by detailing the extraction steps, volume and concentration adjustments, and how to use calibration data to determine the mass of the analyte based on instrument response.
This section focuses on Calculating Recovery of an analyte using a surrogate compound, a critical aspect of quantitative analysis in environmental chemistry. The surrogate is a known compound that behaves similarly to the analyte in the extraction process, allowing analysts to estimate how much of the analyte was recovered during analysis.
Definition of Surrogates: The section opens by defining a surrogate and its role in analytical chemistry, emphasizing its similarity to the analyte of interest, which aids in identifying recovery rates.
Mass Calculation of the Surrogate: A specific example employing a 1-liter sample with a 1 ml addition of a 100 mg/L surrogate solution is provided. The amount added is calculated as 0.1 mg, which sets the groundwork for recovery calculations.
Extraction Process: The extraction method is explained in depth; 50 ml of hexane is added to the sample. The process includes discussing liquid-liquid extraction techniques and the practicalities of sample handling.
Concentration Steps: After extraction, the hexane layer containing the surrogate is reduced to 1 ml for analysis to improve the detection capability. The necessity of concentration is explained concerning enhancing instrument response.
Calibration and Response: A critical formula for calculating the mass based on calibration response is shared (60,000 times the mass of analyte). The calculated response from an instrument (80,000 units) correlates to an estimated mass leading toward determining recovery rates.
Back Calculations for Recovery: The section describes back-calculating to determine how much surrogate was initially in the sample before analysis, emphasizing the importance of accounting for recovery rates to estimate the analyte concentration accurately.
Common Errors: It stresses the importance of unit conversions and the potential errors that may arise during calculations, providing insights into maintaining accuracy during analysis.
Recovery Indicators: The final parts discuss how surrogate recovery corresponds to the analyte and the complexities of solid and liquid sample recoveries, including challenges of extraction efficiencies.