Instruments, misinterpretation

Personal Errors Finally, analytical work is always subject to a variety of personal errors, which can include the ability to see a change in the color of an indicator used to signal the end point of a titration biases, such as consistently overestimating or underestimating the value on an instrument s readout scale failing to calibrate glassware and instrumentation and misinterpreting procedural directions. Personal errors can be minimized with proper care. 

Quantitative fluorescence imaging techniques and FLIM in particular are becoming increasingly important in biological and biomedical sciences. Knowledge of instrumentation and data analysis is required to avoid misinterpretation of the experimental results and to exploit the wealth of information provided by these techniques. 

Successful flow cytometric analysis depends on adequate sample preparation (see Chapters 30-31), appropriate selection of probes or markers (see Subheading 2.), instrumentation, and data display and analysis. Each of these areas is interrelated and requires adequate attention to avoid the introduction of artifacts and misinterpretation of results. Flow cytometers tend to be excessively complicated and require a skilled operator for alignment and calibration, though manufacturers are introducing more compact, user-friendly data acquisition and image processing systems. 

It is often best to begin with purified proteins when studying the relationships between protein structure and function at the molecular level. The presence of multiple proteins often complicates data interpretation, as it is not clear if effects are due to protein interactions, variations in the ratio of proteins, or to other factors. In these studies it is advisable to select tests based on a fundamental physical or chemical property, since results are less likely to vary with the test conditions or instrumentation used. Unfortunately, it becomes less likely that the property under study will relate directly to function in a food system when such simplified (often dilute) systems are used. Something as seemingly insignificant as protein concentration in the model system can have a large influence on the results obtained. Also, the relative importance or contribution of a functional property to a complex food system can be misinterpreted in a purified model system. 

Control charts are designed to incorporate the entire process of the analytical measurement from sampling variability, instrument stability, calibration standards and sample preparation. The chart presents data in a framework that clearly shows whether corrective actions are necessary to ensure that results reported are correct, and allows extrapolation from sample results to conclusion about the whole population with known risks of error or misinterpretation. 

In the following sections the instrumentation used for the apphcation examples described in this chapter will be discussed in some detail. Specifically, the basic instrumental features of the two imaging systems, different possible measurement modes and the occurrence of instrument-related and sample-related artifacts and misinterpretations will be outiined. Because NIR imaging instruments are simpler in design, these will be discussed first. 

Wrong sample Inaccurate reagent preparation Misinterpreted instructions Unwarranted assumptions Sample misidentification Reagent decomposition or instrument malfunction Radionuclide cross-contamination... 

The vacuum also deteriorates remarkably due to steam admission with a corresponding rise in the temperature of the extrusion compound. As the temperature rises, the effect becomes more pronounced, because the partial pressure of the water in the clay increases at an accelerating rate [2], [3]. For vacuum-sensitive bodies/products, the use of a nonbarometric vacuum measuring instrument is recommened to preclude misinterpretation. The formulae describing the relationship between barometric and nonbarometric measuring techniques are presented in section 13.4. 

In previous sections of this chapter, we have discussed aspects of test and survey layout. The time investment to produce a visually appealing layout improves the data quality and minimizes problems caused by respondents confusion, misinterpretation, or misunderstanding of items. Some suggestions for improving instrument layout include ... 

BOX 2.3 Parallels between healthcare and aviation Misinterpretation of Instruments... 

Finally, we investigate some selected instrumental reasons that can lead to the misinterpretation of mass spectra. As discussed earlier, all MS types have their strengths and weaknesses that affect also the quality of your analytical result. Let us discuss these in the following on three scenarios ... 

Interrelationships among the Viscoelastic Material Functions. There is a continuing disagreement within the molecular viscoelasticity commimity about which of the above methods should be used to characterize a material (20). In fact, if one can obtain the zero shear rate viscosity and any of the other functions, these methods are all equivalent. The issue, however, revolves aroimd the fact that some features that appear in the dynamic modulus disappear if the compliance is used as the function to represent the data and vice versa. Also, some measurements are more or less dominated by the viscosity contribution. As a result, some problems of misinterpretation of data could be averted if workers who prefer modulus representations would calculate the compliances. In addition, those who measure the compliance should calculate the moduli in order to provide the data in the format that is more common in the field because of the large number of commercial instruments that obtain dynamic moduli. The advent of modern software packages that make the interrelationships easily calculated makes this dispute seem to go away. The pathways to determine the different material functions, one from the other, are shown in Figure 6. 

Wavelength axis calibration is also crucial to accurate analysis of difference Raman spectra. Although difference Raman is exceptionally sensitive to chemically caused band shifts, it is equally sensitive to instrument artifact band shifts and results can be easily misinterpreted if the stability of the wavelength axis is overestimated for the time frame over which the experiment occurs. Issues of wavelength axis calibration are discussed further below. 

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