are also several ways to classify such
instruments, which unfortunately often
overlap. For example, instrumentation can
be classified by sampling mechanisms
(fibre optics, rotating cups for ground
samples, bulk samplers for unground
samples, liquid samplers), by function
(general purpose or dedicated to a single
analyte or several similar analytes), by
portability (bench top, luggable, meter), by
optical design (grating, filter, light-emitting
diodes, FTNIR, single detector, integrating
spheres, diode array, charged coupled
devices, etc.), or by wavelength range (NIR,
SWNIR, SWNIR/NIR, MIDIR, etc.). While
there can be considerable overlap, all
possible combinations are not available, at
least not for analysing feedstuffs.
The user of NIR for analysing feed-
stuffs has many options at the present time.
In addition, there are many other instru-
ments still in use which were made by
companies that no longer exist or have
been purchased by other companies. For
example, the model 6500 scanning mono-
chromator presently manufactured by
FOSS-NIRSystems is the successor to
instruments in the 6000 series made by
previous owners of NIRSystems (Perstorp,
Pacific Scientific, Neotec). While some of
these older instruments may be in working
condition and perfectly suitable for a given
project, one should consider that these
instruments may not be repairable without
heroic efforts and, unless precautions are
taken to allow calibration transfer, one may
end up with a useless collection of spectra.
The problem is not with the instrument
manufacturers, so much as with the
advances in electronics which have made
many spare parts impossible to get. Also,
many systems once relied on proprietary
computer systems for which keyboards,
monitors, power supplies, etc. are no
longer available (personal experience).
Finally, in purchasing an instrument for
NIR work, the potential buyer should care-
fully consider future plans in addition to the
immediate needs. Portable instruments
using fibre optic cables might seem a great
overall choice since they can be used in the
laboratory or in the field, but they generally
have very small fibre optic bundles which
means a small area of illumination. This can
be fine for solutions or even finely ground
homogeneous powders or solids, but would
not be optimal for work with bulk quantities
of heterogeneous materials. Also, they are
often limited to the SWNIR or lower part of
the NIR, although this is changing. If one
wants or needs the region from 1800 to
2500 nm, then many of these are not
adequate. The same applies to the LED-
based instruments.
The same type of thinking applies to
dedicated versus general purpose instru-
ments. If all one needs is an instrument to
measure moisture in feedstuffs, why
purchase a general purpose instrument
costing ten times more, which would also
be more difficult to use and maintain?
Alternatively, many general purpose scan-
ning monochromators can be purchased
with accessories to use a wide variety of
cells (liquid, powders, bulk), attachments
(diffuse reflectance, transmission, fibre
optic probes), spectral ranges (visible
through the NIR), software packages and so
on. The only drawbacks are cost and lack
of easy portability.
Finally, while FTNIRs appear to be
making big inroads in the NIR field, they
have not as yet been directed at feedstuff
analysis. The companies producing them
are aiming almost completely at the indus-
trial need for quality checking of incoming
raw material using discriminate analysis
and, since virtually no work has been done
using FTNIRs on feedstuffs, it is difficult to
judge their suitability.
For further information on instrument
designs, advantages, disadvantages, etc. the
reader is referred to some of the following
references: Griffiths and de Haseth (1986);
McClure (1987); Marten et al. (1989);
Workman and Burns (1992) or the Internet,
where many companies provide a wealth
of information.Applications to Feed Chemistry
In Table 9.2 are listed some of the feedstuff
determinations for which NIR has beenUse of Near Infrared Reflectance Spectroscopy 199