To demonstrate that the method will be reliable at various contaminant concentrations, accuracy must typically be assessed at different concentration levels—whether carbendazim is present at 10 ppb, 100 ppb, or even 1000 ppb.
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Explore This IssueJune/July 2012
Method precision. Method precision is typically evaluated simultaneously with method accuracy, where the precision can most simply be determined through repeated measurements of standard additions control samples. Most laboratories prefer to assess precision by taking at least three measurements at each concentration level, although more measurements are ideal.
Method selectivity and specificity. Accuracy and precision are certainly key elements to method development and performance evaluation, but is the method selective for the compound of interest? Selectivity and specificity are key method criteria that ensure that the observed measurement is due to the presence of the compound of interest and that the compound of interest can be identified reliably even in the presence of many other components in the sample.
The power of LC/MS/MS technology enables method development scientists to assess selectivity and specificity quickly, accurately, and reliably. LC/MS/MS incorporates three key selection criteria, HPLC retention time, the distinct molecular mass of the compound, and the distinct mass of one or more fragments of the compound (characterized breakdown products based on the chemistry of the compound), to confirm that the analysis is selective and specific for the compound of interest.
Additionally, through the use of linear ion trapping technology, compound fragmentation is taken a step further, and a fourth dimension of selectivity is incorporated. With linear ion trapping LC/MS/MS technology, a complete product fragment scan can be evaluated, including the masses of all breakdown products of the compound and the relative abundance of each. These four points of selectivity make LC/MS/MS a powerful tool for quick and reliable method development.
Method robustness. Regulators and food producers often survey many samples to evaluate the breadth of a problem or crisis. This is why method robustness is also critical in responding to a food crisis. Perhaps multiple chemists are preparing solutions and samples, multiple HPLC columns or instruments are used, and instruments are required to run repeated injections for many hours at a time. It is important that these elements do not affect method performance or the reliability of results.
Well-rounded robustness studies are often quite difficult to complete for a new method created in response to a food crisis, primarily due to the time constraints labs face in trying to get the method up and running quickly. As a result, labs often choose to keep their methods as simple as possible, using the most sensitive and reliable instrumentation possible. Fewer procedure variables can be a key factor in ensuring method robustness.
Method sensitivity. All of these elements of the method are important, but if the method is not able to detect the compound of interest at concentrations relevant to what is regulated in the global food import/export markets, then the method has no value. As a result, method sensitivity is a critical consideration in the method development process. Technology plays a key role in enabling labs to achieve the sensitivity required for an analysis.
For the analysis of carbendazim in orange juice samples, for example, sensitivity was essential. Because the compound is not approved by the U.S. government for use on oranges, it is not allowed at any level in oranges or orange products, and highly sensitive methods are key to accurately assessing violations.