Recommended Spectrum Acquisition Parameters

It is difficult to be specific about the actual instrumental parameters for spectrum acquisition because these are dependent on both the instrument type and the method of sample preparation. The following are guidelines for average situations  

Normal sample, modern FTIR spectrometer 1-4 minute scan time, with spectral resolution of 2-4 cm providing a signal-to-noise ratio (S/N) of between 1000 1 and 10,000 1. If a spectrum is to be used for qualitative purposes only, then a S/N of approximately 1000 1 to 2000 1 is normally adequate and is typically obtained in well under 1 min often within a few seconds. For quantitative apphcations, or applications involving spectral subtraction or resolution enhancement techniques, higher signal-to-noise performance is required. Note that scanning for more than 256 scans may approach a point of diminishing returns in terms of spectral quality and S/N improvement (limited by the law, and the performance of the 

Normal sample, older-style dispersive spectrometer 3- to 10-min scan, with a slit program (integrated scan mode) equivalent to 3-5 cm (average value), providing a S/N of 500 1 or better. 

Low transmission sample (microsample or optically opaque material) 2- to 8-min scan, with a spectral resolution of 4-8 cm , providing a S/N of 500 1 or better. The use of a MCT detector is suggested for samples with an overall transmission of 5%T or less, especially in the absence of an optimizing accessory (such as a beam condensor for microsamples). When using a MCT detector, it is important that the potential for nonlinearity is appreciated. Also, it is important to be aware of the occurrence of detector saturation, which will lead to extreme nonlinearity, and spectral distortion. 

Irrespective of the final selection of data acquisition parameters, full documentation of the experimental details should be recorded with all spectra, especially if regulated procedures are followed. Also, as a general rule, it is recommended that good laboratory practice guidelines are adopted throughout. 

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Figure 2 HMBC spectrum recorded on a sample of 50 mmol cyclosporine dissolved in C6D6 using the standard HMBC pulse sequence depicted in Figure 1 and recommended acquisition and processing parameters.27...

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