1.5 - Interferences in Analysis
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Extraction Techniques
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today, we will start with the extraction of organics from water. Can anyone explain what extraction means in this context?
Isn't it about separating the organic compounds from the water sample?
Exactly! We're focusing on very low levels, usually in the nanogram per liter to microgram per liter range. We use solvents that are immiscible with water. Can anyone name a couple of those solvents?
Hexane and dichloromethane!
Perfect! And why do we need to be careful with these solvents?
Because they are hazardous and we need to manage waste properly.
Great point! Remember, waste management is a crucial part of using hazardous substances.
So to summarize, we use extraction to pull organics from water with careful selection of solvents while managing waste.
Understanding Interferences
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now, let's talk about interferences. Who can tell me what interferences mean in analysis?
They’re substances that affect the measurement of the analyte we care about.
Exactly! If we're analyzing PAHs, other substances like oils might interfere. How do we address these interferences?
We have to filter the sample before performing extraction, right?
Yes! Filtration removes any suspended solids that could give false readings. Always remember, interferences are specific to what we're analyzing.
So if I’m analyzing for PAHs, oils and metals are interferences?
That's correct! Always consider the context of your analysis.
The Role of Filtration
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Let's go deeper into filtration. Why is it vital before liquid-liquid extraction?
It removes solids that can interfere with our results.
Exactly! There are various filter types available. What factors should we consider when choosing a filter?
Pore size and ease of use!
Correct! While a smaller pore size captures more particles, it also slows the process down. What do we typically use for TSS analysis?
We usually go for a 1 micron filter because it’s efficient.
Well done! Remember, the right filter size is a balance between efficiency and effectiveness.
The Relationship Between Organic Carbon and Interferences
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now I want to link organic carbon content to our discussions about interferences. Why is TOC important?
It helps understand how much organic matter is in the sample, affecting measurements!
Exactly! If you have a high TOC, it might skew your results when measuring specific compounds.
So we need to correct our values to get accurate analysis?
Yes, that’s essential! Always consider all constituents in your sampling.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section delves into the extraction methods for organic compounds from water and emphasizes that various factors, such as turbidity and the presence of other compounds, can lead to interferences that affect analytical accuracy. Understanding and mitigating these interferences is crucial for reliable water quality assessment.
Detailed
Interferences in Analysis
In this section, we discuss the techniques involved in extracting organic compounds (denoted as A) from water sources, particularly at low concentrations of nanograms per liter or micrograms per liter. The extraction process primarily utilizes liquid-liquid extraction (LLE), which involves adding an immiscible solvent like hexane or dichloromethane to the water sample so that the organic compounds can migrate from the water phase into the organic phase. While effective, the method introduces the risk of interferences — substances in the sample that may affect the analysis of the target analyte.
The concept of interferences is explained relative to what is being analyzed. For instance, if both polycyclic aromatic hydrocarbons (PAHs) and oils are present in water, and the goal is to quantify PAHs, the oils would interfere with accurate PAH measurement. If a water sample is extracted without prior filtration, it may also contain total suspended solids (TSS) that further complicate the analysis.
Key Points:
- Interferences: Defined as substances that can alter the results of an analysis for a specific target compound (like PAHs) but are not interfering when measuring overall composition.
- Filtration: Recommended before LLE to remove suspended solids and improve accuracy.
- Selection of Solvents: It’s important to choose solvents that are effective but also take waste management into account, as compounds like dichloromethane are hazardous and require careful disposal.
This understanding is critical in water quality assessment and in ensuring that methods used are both effective and environmentally sustainable.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Understanding Interferences
Chapter 1 of 4
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
When extracting water, especially from sources like wastewater treatment plants, all kinds of materials in the sample can also be extracted. This includes not only the target analyte but also organic carbon and solids. If a sample from a turbid lake is collected and solvents such as hexane or dichloromethane are added, numerous materials will be extracted. This leads to the question: what exactly constitutes interference?
Detailed Explanation
In the analysis of water samples, various pollutants and materials can interfere with the detection of the specific chemical (let's call it 'A') you are trying to analyze. An interference is defined in relation to a specific analyte or group of analytes that you want to study. For instance, if you are measuring the concentration of polynuclear aromatic hydrocarbons (PAHs), the presence of oil or metals in the same sample could skew the results because they also get extracted during the process. Therefore, interferences are not absolute—they depend on the context of what you are trying to analyze. This means you might need to develop methods to isolate the targeted analyte from these potential interferences.
Examples & Analogies
Think about baking a cake. If you want a vanilla cake but accidentally drop in chocolate chips and nuts, they can alter the final flavor. In this case, the chocolate chips and nuts are the 'interferences.' Just like in the analysis of chemicals, where specific substances can interfere with your primary target, getting the 'cake' (or results) you want requires careful selection and separation of your ingredients.
Filtration Before Liquid-Liquid Extraction
Chapter 2 of 4
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Prior to carrying out liquid-liquid extraction (LLE), it is essential to filter the samples. This step helps in removing any solids that might interfere with the analysis. The correct procedure involves first collecting the sample, then filtering it to eliminate solids before proceeding to LLE.
Detailed Explanation
Filtration is a crucial step in sample preparation. When you analyze a water sample, you are particularly interested in the dissolved substances. However, if there are solid particles (like dirt or organic debris), they may interfere with your measurement of 'A'. To avoid this, the sample must be filtered to separate out these solids. This step ensures that only the intended analytes are present in the liquid phase for accurate analysis. Failure to filter could result in measurement inaccuracies, affecting the quality and reliability of your data.
Examples & Analogies
Think of washing fruits before eating them. If you grab a handful of grapes from the garden without rinsing, you might end up with bits of dirt or bugs. Similar to how washing helps you enjoy clean fruit, filtering a water sample ensures that what you analyze is free from unwanted solids that could distort the results.
Choosing the Right Filter Paper
Chapter 3 of 4
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Different types of filter papers are available based on pore sizes, such as 0.1 microns, 0.4 microns, and larger sizes like 1 micron. Selecting the appropriate filter paper depends on the analysis objective, particularly the types of particles you wish to separate from the water sample.
Detailed Explanation
When filtering a water sample, choosing the right filter paper is crucial. The pore size of the filter determines which particles can pass through and which will be retained. A smaller pore size (e.g., 0.1 microns) can filter out more particles but requires more pressure to push water through, making the process slower. Conversely, a larger pore size (like 1 micron) allows for quicker filtration but may let smaller particles through. The choice of filter thus relies on balancing the need for thoroughness in separating particles and the efficiency of the filtration process.
Examples & Analogies
Imagine using a colander to drain pasta. If your colander has large holes, some small pieces of pasta might slip through. If it has very fine mesh, these pieces won’t get through, but it will take longer to drain the pot. Similarly, choosing a filter size is about finding the right balance between speed and thoroughness when cleaning your water sample.
Impact of Filter Size on Analysis
Chapter 4 of 4
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Using a filter size of 1 micron is standard for analyzing total suspended solids (TSS). Filters smaller than this may provide more thorough separation but may not significantly improve mass measurement, given the tiny weight difference of particles below this threshold.
Detailed Explanation
In TSS analysis, the standard practice is to use a 1 micron filter. This size is sufficient to separate larger debris while still allowing for efficient filtration. Filters smaller than 1 micron may take too long to work and may clog easily, making them impractical. Even if a smaller filter could theoretically capture more particles, the contribution of particles smaller than 1 micron to the overall mass is minimal, thus providing negligible improvement in the analysis. Hence, standardizing the use of a 1 micron filter helps achieve a good balance of efficiency and accuracy.
Examples & Analogies
Consider using a sieve with a very fine mesh to sift flour. While using a very fine mesh will catch more particles, it also takes significantly longer to sift the flour. In baking, speed and efficiency matter, so using a medium sieve ensures you get the job done in a timely manner without significantly compromising quality.
Key Concepts
-
Liquid-Liquid Extraction: Extraction technique to separate organics by using an immiscible solvent.
-
Interference: Substances affecting the analysis of a target measure.
-
Total Suspended Solids (TSS): Solids that remain in suspension in water that could impact analysis.
Examples & Applications
Extracting PAHs from contaminated water using dichloromethane as the solvent.
The impact of oils and metals on the measurement of PAHs during analysis.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
To prevent a mess when samples we assess, filter first then extract, to keep results correct.
Stories
Imagine you're fishing in a clear lake; you want to catch one type of fish. If you throw in bread and worms, you'll catch more than just fish! Filtering helps you target.
Memory Tools
F.I.L.E: Filter first, Investigate interferences, Liquid extraction, Evaluate results.
Acronyms
PAOH
Pairs of Analytes Often Harm results – indicating that multiple substances can interfere with analysis.
Flash Cards
Glossary
- LiquidLiquid Extraction (LLE)
A method to separate organic compounds by adding an immiscible solvent to a water sample.
- Interference
A substance that affects the measurement of a target analyte.
- Total Suspended Solids (TSS)
Solids suspended in water that can interfere with the analysis of dissolved substances.
- Filtration
The process of separating solids from a liquid using a filter.
- Turbidity
Cloudiness or haziness in water caused by large numbers of individual particles.
Reference links
Supplementary resources to enhance your learning experience.