"Hybrid" macro-ATR: estimating acquisition time
Generally we recommend that for each sample, you acquire a low resolution overview map of your sample, before focusing on a region of interest at higher resolution, while maintaining the single contact between the ATR crystal and your sample. This allows us to observe regions of specific interest of your sample as well as regions of best contact between the crystal and your sample. Therefore for each sample, estimate the time required for both the low and high resolution map:
Low resolution overview map:
In macro-ATR mode using a pinhole of 0.3 mm, the beam size on your sample is 3.8 µm. However, for the "low resolution map" we could use an x and y step size of 10 µm over a 200 x 200 micron area. That gives a total of 400 points (spectra) in the map, as calculated by ((200/10) x (200/10)). Obtaining spectra averaged from 16 scans, approximates 6 seconds per spectra (at 4 cm-1 resolution). Therefore the total map time is calculated to be:
(400 x 6)/60 = 40 minutes
High resolution overview map:
Without changing the contact between the sample and the ATR crystal, a high resolution map can be performed based on the information obtained from the above overview map. For example, an area of 120 x 120 µm will be mapped at an x and y step size of 3 micron, with each spectra averaged from 16 scans, the time taken is:
((120/3) x (120/3) x 6)/60 = 160 minutes (1 hour and 40 minutes)
Therefore, considering both the high and low resolution maps you would estimate approximately 2.5 hours of mapping per sample for these specific acquisition parameters.