Standard analyses minimum frequency

There is no experimentally established optimum frequency for the distribution of samples. The minimum frequency is about four rounds per year. Tests that are less frequent than this are probably ineffective in reinforcing the need for maintaining quality standards or for following up marginally poor performance. A frequency of one round per month for any particular type of analysis is the maximum that is likely to be effective. Postal circulation of samples and results would usually impose a minimum of two weeks for a round to be completed and it is possible that over-frequent rounds have the effect of discouraging some laboratories from conducting their own routine quality control. The cost of proficiency testing schemes in terms of analysts time, cost of materials and interruptions to other work has also to be considered. 

For standard analysis windows (e.g. Hanning, Hamming,) the cutoff frequency is inversely proportional to the window length, CO/, 4% IT. The first condition implies that T > 4A CO min The window must be longer than 4 times the period corresponding to the interval between the closest frequencies. The last constraint above implies R < 774, i.e. successive analysis windows must have a minimum overlap of 75%. The larger the cutoff frequency, the larger the minimum overlap between successive analysis windows. 

For reliable data, the concentration of the components of the mixture must be determined. Measuring peak Intensities and then relating these values to the amount of each component present is practically impossible by standard analytical techniques for this system. In order to do quantitative analysis, first, frequencies must be found that are unique to each component and, second, Intermolecular Interactions must be at a minimum. Re-examining Figure 3, reveals that only the carbonyl stretching mode at 1685 cm" may be free of overlap. The difficulty presented by these systems (natural rubber-peroxide and polybutadlene-peroxlde) provides a test of the sensitivity of the FTIR spectrometer. 

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