Mantis 5000 Especificaciones descargar pdf (Pagina 71)

9. Click the Setup button and check the parameters. Normally, the setup parameters for

the application should match those used for the baseline scan. If using a previously

defined baseline correction, retrieve the correct baseline.

10. Click the Start button.

11. If the standard reference option was used for the baseline scan, the reflectance

spectra is generated automatically. If the simple or zero baseline correction was selected,

multiply the sample scan data by the spectral reflectance factors for the calibrated

reflectance standard.

Small Sample Masking Techniques

Small samples that do not completely fill the sample reflectance or transmission port

should be measured using masking techniques. Masking in this case may be necessary if

only to mount the sample at the appropriate port. When using the small spot kit to

measure the reflectance or transmission of samples smaller than the port diameter, both

the reference and the sample can be masked such that the port is filled completely.

Generally a black mask is used to prevent reflectance from the mask adding to the

reflectance of the sample. Another reason for a black mask is consistency - a black mask

is always the same and easy to make. The reflection off the black mask is very small and

does not contribute to the reflectance properties of the sample. Simple and effective

masks can be prepared from a piece of cardboard. A manila file is excellent because it is

thin and easily manipulated. The mask must be constructed large enough to fill the port.

The internal surface of the mask should be painted black with flat black Krylon™ paint

or its equivalent. The illustrations in the figures above and below demonstrate the use of a

mask at the transmission and reflectance ports, respectively. The following guidelines

will help when constructing masks:

• The mask surface area should cover the entire transmission or reflectance port.

• The mask aperture should be in the same profile of the sample surface, but

slightly smaller in size.

• The sample beam should overfill the mask aperture.

• The baseline scan should be collected during reflectance measurements with the

reflectance standard in the same mask geometry. For transmission measurements,

the masked port constitutes the 100% transmission standard.

Note

There are two negatives of using a mask in your analyses. Firstly, using a mask at

either the transmission port or the sample reflectance port reduces the throughput

of the accessory and energy seen by the detector. Secondly, using a mask at the

sample reflectance port upsets the balance between the sample and reference beams

because the reference beam strikes the high reflectance inner surface of the sphere.

If the spectrophotometer is operating in single beam mode, of course, this is not a

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Mantis 5000 Especificaciones Pagina 71