Molecular Devices SpectraMax ABS User Manual

SpectraMax ABS and SpectraMax ABS Plus Microplate Spectrophotometers User Guide
20 5065390 C
Using a Plate Background OD
If your sample volumes are not identical or if you choose not to use a Plate Blank, then you
must use a Plate Background OD. Omitting a Plate Background OD results in artificially high
values after being normalized by the PathCheck technology.
To determine the Plate Background OD:
1. Fill a clean plate with water.
2. Read at the wavelengths you will use for the samples.
The average OD value is the Plate Background OD. If you intend to read your samples at more
than one wavelength, there should be a corresponding number of Plate Background OD
values for each wavelength.
Note: It is important that you put water in the wells and do not read a dry plate for the
Plate Background OD. A dry plate has a slightly higher OD value than a water filled plate
because of differences in refractive indices. Use of a dry plate results in PathCheck
technology normalized values that are lower than 1cm cuvette values.
Interfering Substances
Material that absorbs in the 900 nm to 1000 nm spectral region could interfere with PathCheck
technology measurements. Fortunately, there are few materials that do interfere at the
concentrations generally used.
Turbidity is the most common interference. If you can detect turbidity in your sample, you
should not use the PathCheck technology. Turbidity elevates the 900 nm measurement more
than the 1000nm measurement and causes an erroneously low estimate of pathlength. Use of
the Cuvette Reference does not reliably correct for turbidity.
Samples that are highly colored in the upper-visible spectrum might have absorbance that
extends into the near-infrared (NIR) spectrum and can interfere with the PathCheck technology.
Examples include Lowry assays, molybdate-based assays, and samples that contain
hemoglobins or porphyrins. In general, if the sample is distinctly red or purple, you should
check for interference before you use the PathCheck technology.
To determine possible color interference:
Measure the OD at 900 nm and 1000 nm (both measured with air reference).
Subtract the 900 nm value from the 1000 nm value.
Do the same for pure water.
If the delta OD for the sample differs significantly from the delta OD for water, then you should
not use the PathCheck technology.
Organic solvents could interfere with the PathCheck technology if the solvents have
absorbance in the region of the NIR water peak. Solvents such as ethanol and methanol do not
absorb in the NIR region, so the solvents do not interfere, except to cause a decrease in the
water absorbance to the extent of their presence in the solution. If the solvent absorbs
between 900nm and 1000nm, the interference would be similar to the interference of highly
colored samples. If you add an organic solvent other than ethanol or methanol, you should run
a Spectrum scan between 900 nm and 1000 nm to determine if the solvent would interfere
with the PathCheck technology.

Molecular Devices SpectraMax ABS Specifications

General

Brand	Molecular Devices
Model	SpectraMax ABS
Category	Measuring Instruments
Language	English