Part 1 – Types of Calibrations
In previous blog posts on TO-15A and OTM-45 I’ve expressed strong opinions about calibration acceptance criteria. While the acceptance criteria is important, I thought I’d step back and delve more deeply into calibrations, starting with the different types of calibration. A calibration is just a way to convert your instrument response to a known of analyte, and then to a concentration based on injection amount and sample preparation steps, but there are several different flavors of calibration to choose from, and choosing the best one requires you to weigh the advantages and disadvantages. The following post will highlight some of those differences, therefore hopefully enabling you to make the best educated decision for your lab.
Part 2 – Curve Fits and Weighting
Once you’ve determined that, the next step is how to mathematically go from a response reading to a concentration. Be warned, this blog will be a bit math heavy.
Part 3 – Dealing with Zero Points
In this installment I’ll cover issues around the calibration zero point. This is a topic that many methods give little guidance on, and various methods can handle it very differently; so it’s easy to be confused over what best practices are, and hopefully I can clear up some confusion. When I talk about zero points in calibrations, there are two different things to consider. First, whether a zero point or blank needs to be included in the calibration, and second, whether a calibration curve should be forced through zero. I’ll go over how these might affect your calibration before discussing some examples of how various EPA methods handle them.
Part 4 – Calibration Acceptance
In this post we’ll cover how to tell if your calibration is accurate. The previous posts have been a bit dense and math heavy, but the TL;DR on this one is pretty simple: r2 is bad and you shouldn’t use it.
Part 5 – Accuracy, Precision and Detection Limits
In this post we’ll talk about how calibrations affect your results, focusing especially on low-level accuracy, precision, and detection limits.
Part 6 – Linearity and Calibration Spacing
Starting with this post we’ll be looking more at the practical considerations of how to make a calibration, starting with how to choose your calibration points.
Part 6 (Continued) – Even More On Calibration Spacing
In this post we delve deeper into calibration spacing and revisit some of the assumptions we made in the previous post.
Part 7 – Internal Standards, Surrogates, and Isotope Dilution
In this post of our calibration series, we demystify the differences between extracted internal standards and surrogates.
Part 8 – Low Level Replicates
Does changing from duplicate to triplicate (or from triplicate to quadruplicate) determination in the highest variation region improve the calibration performance? Find out in this blog post!
