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Chapter 5: Problem 13

Define the following terms: instrument precision, injection precision, intra- assay precision, intermediate precision, and interlaboratory precision.

Short Answer

Expert verified
These precision terms describe consistency and variability in measurements across different analytical contexts and configurations.

Step by step solution

01

Define Instrument Precision

Instrument precision refers to the consistency or repeatability of measurements when conducted by the same instrument under the same conditions. It describes how much variation in measurements can be attributed to the instrument itself when it is used repeatedly without changing any other factors.
02

Define Injection Precision

Injection precision pertains to the consistency and repeatability of multiple injections of the same sample within an analytical run. It reflects the ability of the instrument to produce close results for successive injections without significant variation.
03

Define Intra-assay Precision

Intra-assay precision, also known as within-run precision, is a measure of the variability when identical samples are tested multiple times within a single assay. This precision helps assess the repeatability of a test during a single run by the same operator using the same setup.
04

Define Intermediate Precision

Intermediate precision, also referred to as within-laboratory precision, measures the variation in results when tests are conducted on different days, by different analysts, with different equipment in the same laboratory environment. This assesses the robustness of methods under normal lab variations.
05

Define Interlaboratory Precision

Interlaboratory precision is a metric for the variation in results obtained when the same sample is tested across different laboratories. This precision measures the reproducibility of test results when factors like location, analysts, and equipment can vary significantly.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Instrument Precision
Instrument precision is all about how consistent an instrument is when it takes the same measurement multiple times under identical conditions.
Imagine using a ruler to measure a pencil several times. If the ruler shows the same length every time, it has good instrument precision.
In a laboratory, this concept is crucial for ensuring that an instrument doesn't introduce variability into the measurements.
  • The key is repeatability 鈥� can the instrument deliver the same results repeatedly?
  • Instrument precision helps scientists trust their tools and the data they collect.
Consistency allows researchers to make clear, decisive interpretations of their experiments.
Injection Precision
Injection precision focuses on the ability of an analytical instrument to produce reliable results from successive injections of the same sample.
Think of it like using the same syringe to inject colored dye into water repeatedly. If each injection creates a solution with the same shade, the injection precision is high.
This precision ensures that the method delivers uniform results without significant changes between different injections.
  • It helps in detecting potential errors in handling and methodological execution.
  • Injection precision is vital in processes like chromatography, where consistency is key.
Providing repeatable results bolsters confidence in the analytical procedure.
Intra-assay Precision
Intra-assay precision, or within-run precision, gauges how consistent test results are when identical samples are tested several times during a single run.
Picture baking multiple batches of cookies with the same dough. If the taste and look are identical, you have good intra-assay precision.
In laboratories, achieving this precision ensures the reliability of tests in a single assay.
  • It's concerned with the repeatability of the process within one continuous operation by the same technician.
  • This helps to ensure the protocol and setup are not the source of variability.
By maintaining high intra-assay precision, tests become dependable and trustworthy.
Intermediate Precision
Intermediate precision is about consistency in test results when minor changes occur within a single laboratory.
Imagine you鈥檙e cooking several times on different days, using slightly different utensils and still achieving the same flavor each time. This represents intermediate precision.
This type of precision assesses how robust methods are under typical laboratory variations, such as different days, analysts, or apparatus.
  • It tests the stability of methods against day-to-day changes.
  • Intermediate precision is essential for long-term reliability within a lab environment.
This stability allows results to stay reliable over weeks and even months, highlighting robust testing standards.
Interlaboratory Precision
Interlaboratory precision looks at how much results might vary when a test is carried out in different labs.
Imagine having a recipe that tastes the same no matter who makes it or where it is made. That's the goal of interlaboratory precision.
This form of precision ensures that data remains consistent across different locations, tools, and teams worldwide.
  • It evaluates the reproducibility of a measurement method under diverse conditions.
  • Ensuring high interlaboratory precision helps standardize methods internationally.
This uniformity confirms that any scientific findings can be universally accepted and applied.

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Most popular questions from this chapter

Verifying constant response for an internal sfandard. When we develop a method using an internal standard, it is important to verify that the response factor is constant over the calitration range. Data are shown below for a chromstographic analysis of naphthalene \(\left(\mathrm{C}_{10} \mathrm{H}_{2}\right)\), using deuterated naphthalene \(\left(\mathrm{C}_{10} \mathrm{D}_{\mathrm{s}}\right.\) in which \(\mathrm{D}\) is the isotope \({ }^{2} \mathrm{H}\) ) as an internal standard. The two compounds emerge from the column at almost identical times and are measured by a mass spectrometer, which distinguishes them by molecular mass. From the definition of response factor in Equation \(5-11\), we can write $$ \frac{\text { Area of analyte signal }}{\text { Area of standard signal }}-F\left(\frac{\text { concentration of analyte }}{\text { concentration of standard }}\right) $$ Prepare a graph of peak area ratio \(\left(\mathrm{C}_{10} \mathrm{H}_{\mathrm{s}} / \mathrm{C}_{10} \mathrm{D}_{\mathrm{k}}\right)\) versus concentration ratio \(\left(\left[\mathrm{C}_{10} \mathrm{H}_{\mathrm{k}}\right]\left[\mathrm{C}_{10} \mathrm{D}_{\mathrm{k}}\right]\right)\) and find the slope, which is the response factor. Evaluate \(F\) for each of the three samples and find the standard deviation of \(F\) to see how "constant" it is. \begin{tabular}{ccccc} Sample & \(C_{10} \mathrm{H}_{\mathrm{s}}\) \((\mathrm{ppm})\) & \(C_{10} D_{\mathrm{s}}\) \((\mathrm{ppm})\) & \(C_{10} H_{\mathrm{k}}\) peak area & \(C_{10} D_{\mathrm{s}}\) peak area \\ \hline 1 & \(1.0\) & \(10.0\) & 303 & 2992 \\ 2 & \(5.0\) & \(10.0\) & 3519 & 6141 \\ 3 & \(10.0\) & \(10.0\) & 3023 & 2819 \\ \hline \end{tabular}

An unknown sample of \(\mathrm{Cu}^{2+}\) gave an absorbance of \(0.262\) in an atomic absorption analysis. Then \(1.00 \mathrm{~mL}\) of solution containing \(100.0 \mathrm{ppm}(=\mu \mathrm{g} / \mathrm{mL}) \mathrm{Cu}^{2+}\) was mixed with \(95.0 \mathrm{~mL}\) of unknown, and the mixture was diluted to \(100.0 \mathrm{~mL}\) in a volumetric flask. The absorbance of the new solution was \(0.500\). (a) Denoting the initial, unknown concentration as \(\left[\mathrm{Cu}^{2+}\right]_{\mathrm{i}}\), write an expression for the final concentration, \(\left[\mathrm{Cu}^{2+}\right]_{\mathrm{f}}\), after dilution. Units of concentration are ppm. (b) In a similar manner, write the final concentration of added standard \(\mathrm{Cu}^{2+}\), designated as \([\mathrm{S}]_{\mathrm{f}}\). (c) Find \(\left[\mathrm{Cu}^{2+}\right]_{\mathrm{i}}\) in the unknown.

What is the purpose of a blank? Distinguish method blank, reagent blank, and field blank.

Tooth enamel consists mainly of the mineral calcium hydroxyapatite, \(\mathrm{Ca}_{10}\left(\mathrm{PO}_{4}\right)_{6}(\mathrm{OH})_{2}\). Trace elements in teeth of archeological specimens provide anthropologists with clues about diet and diseases of ancient people. Students at Hamline University measured strontium in enamel from extracted wisdom teeth by atomic absorption spectroscopy. Solutions were prepared with a constant total volume of \(10.0 \mathrm{~mL}\) containing \(0.750 \mathrm{mg}\) of dissolved tooth enamel plus variable concentrations of added Sr. $$ \begin{array}{cc} \begin{array}{c} \text { Added Sr } \\ \text { (ng/mL }=\mathrm{ppb} \text { ) } \end{array} & \begin{array}{c} \text { Signal } \\ \text { (arbitrary units) } \end{array} \\ \hline 0 & 28.0 \\ 2.50 & 34.3 \\ 5.00 & 42.8 \\ 7.50 & 51.5 \\ 10.00 & 58.6 \\ \hline \end{array} $$ (a) Find the concentration of \(\mathrm{Sr}\) and its uncertainty in the \(10-\mathrm{mL}\) sample solution in parts per billion \(=\mathrm{ng} / \mathrm{mL}\). (b) Find the concentration of \(\mathrm{Sr}\) in tooth enamel in parts per million \(=\mu \mathrm{g} / \mathrm{g}\). (c) If the standard addition intercept is the major source of uncertainty, find the uncertainty in the concentration of Sr in tooth enamel in parts per million. (d) Find the \(95 \%\) confidence interval for Sr in tooth enamel.

Detection limit. Low concentrations of \(\mathrm{Ni}^{2+}\)-EDTA near the detection limit gave the following counts in a mass spectral measurement: \(175,104,164,193,131,189,155,133,151,176\). Ten measurements of a blank had a mean of 45 counts. A sample containing \(1.00 \mu \mathrm{M} \mathrm{Ni}^{2+}\)-EDTA gave 1797 counts. Estimate the detection limit for Ni- EDTA.
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