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a change in the detector. If the compound changes in its form then the absorbance coefficient will also change which means the sensitivity of the assay will be affected. In the extreme example, the absorbance could be reduced by so much that the compound is no longer detected within the UV detector. The increase in biopharmaceutical compounds has highlighted this as an ever-increasing issue, since proteins can be very susceptible to degradation when exposed to a broad range of the electromagnetic spectrum.
applicability to a wide range of compounds. There are two formats that chromatographers use, one is a variable or fixed wavelength design and the other type is a diode array. The actual difference in terms of the operation is minimal, and the two types of detector are often used interchangeably. For the fixed wavelength detector, a UV/Vis light source is filtered to give the required wavelength, which results in the sample only being exposed to a single wavelength of light. With a diode array detection system, the sample is exposed to a full range of wavelengths, which are then captured by the array detector (Figure 2). This does not seem too significant, but for compounds which are sensitive to light this can be a significant difference resulting in the compound undergoing
The HelpDesk has discussed the importance of considering the effects of changing the instrumentation on the assay performance previously, and it is pertinent to reiterate this discussion. It is also important to consider that it is not just the pumps that can influence the performance of the assay and that the detector can also affect the very molecules that the chromatographer is trying to analyse. If changing the detector results in degradation of the analyte, then the sensitivity may alter, and in worse case situation complete loss of signal may be observed. As with all disciplines it is important not to make assumptions, and this is the case with assay development. It is important that the chromatographer understands how the analyte will be affected in each of the various stages of the analytical process to ensure that a robust assay is developed and that there are minimal issues when this assay is transferred.
References
1. L.R. Snyder, J.J. Kirkland, and J.W. Dolan, Introduction to Modern Liquid Chromatography, 3rd. ed. (Wiley, Hoboken, New Jersey, 2010)
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With numerous flow rate versions of all Precision gas generator models labs can build a gas solution tailored to their specific GC set up. Engineered with lab space in mind, the Precision Series generators can all be stacked with up to four units at a time, requiring a limited amount of lab floor-space.
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