Ruggedization techniques

Optimization of the Analytical Method by Utilizing Ruggedization Techniques... 

Because the number of data points is low, many of the statistical techniques that are today being discussed in the literature caimot be used. While this is true for the vast majority of control work that is being done in industrial labs, where acceptability and ruggedness of an evaluation scheme are major concerns, this need not be so in R D situations or exploratory or optimization work, where statisticians could well be involved. For products going to clinical trials or the market, the liability question automatically enforces the tried-and-true sort of solution that can at least be made palatable to lawyers on account of the reams of precedents, even if they do not understand the math involved. 

In the following, an example from Chapter 4 will be used to demonstrate the concept of statistical ruggedness, by applying the chosen fitting model to data purposely corrupted by the Monte Carlo technique. The data are normalized TLC peak heights from densitometer scans. (See Section 4.2) ... 

One of the key aspects in developing a method for regulatory analysis is method ruggedness. The more rugged a method, the less susceptible it is to failure or to excessive variations due to differences in equipment, analyst technique, and other differences that are typically present among laboratories. Several factors contribute to poor method ruggedness insufficient testing by the developer, excessive method complexity, and a failure of the developer to identify and communicate critical points. 

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

Some more recent field techniques have focused on the location of the preparation of field fortification samples and have taken some of the responsibility for the preparation of the field fortification samples from the field personnel and placed them with the analytical laboratory. For example, it is becoming more common for the analytical laboratory to prepare air sample field fortifications in the analytical laboratory, freeze them, and ship them to the field for use in a frozen state. Whereas there may be some advantage to this technique in that the air tube fortification samples may possibly be fortified more accurately in the laboratory under controlled conditions than if done in the field, there are some inherent scientific problems with this method. First, one reason for the field fortification is to test the ruggedness of the field techniques of the researcher under extreme field conditions. Second, the act of freezing and thawing the sorbent matrix within the air mbe itself may have an impact on the recovery of the analyte from the air tube after exposing the sorbent to field conditions... 

A review of ruggedness testing methods is presented in Chapter 3 and in Chapter 5 examples are given. In these chapters procedures are described that test the robustness or ruggedness of existing methods. Hence, incorporating robustness explicitly in analytical techniques (see Section 1.1) is not discussed. 

HPLC is a complex analytical methodology that involves the development of a unique method for each new application. This method development often requires the optimisation of several method conditions to achieve a desired selectivity and sensitivity [12,13]. HPLC is also one of the most commonly applied analytical techniques and is in widespread use throughout the pharmaceutical industry for applications as diverse as quality control, stability studies and clinical trials. These two reasons mean that HPLC has been the focus of most research into ruggedness testing procedures because it is most likely to require extensive ruggedness... 

Concentration in the sample (c). This is normally calculated using both peak areas and peak heights as it is a good idea to postpone the selection of a calibration technique until after the ruggedness study. Mean number of theoretical plates, N, there are several methods to calculate N. The following calculation is often employed due to its convenience as it uses values which are previously collected as part of the data handling. 

The results of a ruggedness study can help in the definition of a suitable calibration technique. 

It is imperative to also consult the vendor to determine an adequate number of valves for spray weight testing. If the metered chamber is plastic, valves totaling at least twice the number of the vendor s mold impressions should be tested to guarantee complete evaluation of the lot of valves. The spray weight methodology conducted on valves can drastically influence the results. Because the valve is a mechanical device, the way in which it is actuated is technique-oriented. Manual actuation versus automatic actuation can cause variation in the results. Method ruggedness is essential in evaluation of the valve performance. 

Raman spectroscopy has its main strength in the combination of a fairly high chemical selectivity and a true remote sensing capability. In comparison, NIR has been used extensively in the manufacturing industry due to its ruggedness and simplicity with respect to interfacing of probes to process vessels. However, due to fairly poor spectral selectivity it has to be paired with multivariate data evaluation and is thus sometimes considered as a black box technique. Mid-IR, on the other hand, offers a high selectivity and is also well established... 

The outcome of the different exercises should be discussed among all participants in technical meetings, in particular to identify random and/or systematic errors in the procedures. Whereas random errors can be detected and minimised by intralaboratory measures, systematic errors can only be identified and eliminated by comparing results with other laboratories/techniques. When all steps have been successfully evaluated, i.e. all possible sources of systematic errors have been removed and the random errors have been minimised, the methods can be considered as valid. This does not imply that the technique(s) can directly be used routinely and further work is likely to be needed to test the robustness and ruggedness of the method before being used by technicians for daily routine measurements . 

However, TSI-LC/MS applications did not completely capture the imagination of chemists and biologists in the pharmaceutical industry. TSI- LC/MS was overshadowed by its unpredictable performance and questionable ruggedness when compared to HPLC with ultraviolet (UV) detection. This perception was the case, in part, because pharmaceutical researchers were ready for a universal LC/MS system, but with very few limits. Simple methods to handle small and large molecules, combined with a gentle technique for ionization, were needed. Researchers were not content with the unique capabilities of TSI-LC/MS. They wanted few boundaries for applicability with familiar levels of analytical performance (i.e., similar to LC/U V). This requirement was not necessarily derived from an analytical perspective, but rather an industry perspective, which ultimately forms the basis of acceptance. Whether this requirement... 

The ruggedization of the analytical procedure was performed by applying statistical screening techniques to minimize the effort required and, therefore, reduce the time and the cost substantially. The statistical approaches used in this study were those first introduced by Plackett-Burman (3.) and Youden-Steiner (4). Both techniques reduce the required effort since they use balanced incomplete block design experiments which can clearly indicate the non-affecting parameters from those that may have an effect. In this study the important variables of the analytical method were identified by using the Plackett-Burman technique. 

The effect of each variable in the ruggedness test is determined by the difference between the average high and low levels, as is done in the Plackett-Burman design. However, the Youden technique, as modified by Steiner, differs from the Plackett-Burman technique in that the Youden-Steiner experiment is performed in duplicate, and the standard error is estimated differently. An estimate of the experimental error is calculated by equation 5. ... 

In practice, however, due mainly to a number of technical difficulties, most of which are attributable to lack of column ruggedness, it has yet to be shown that the theoretically predicted potential of CEC will fulfill its promise and result in a widespread routine technique. In the past 5-8 years, there has been a sustained effort in the separations community to understand theoretical aspects, based on which new developments arose in the field of column technology [9,13,14], application [4,5], and detection [7]. A number of these observations are summarized here, with an emphasis on their bearing on extending the application range of CEC. 

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