Bio-Rad SmartSpec Plus Spectrophotometer - Manual (Page 11)

3. Background compensation. When using the DNA/RNA assay, you can choose to
have SmartSpec Plus automatically subtract background absorbance readings collected
at 320 nm from the A260 and A280 measurements. If the background subtraction option
is invoked, then the A320 is subtracted from the A260 and A280 readings before these
measurements are displayed and before they are used in the calculation of nucleic acid
concentration. The default condition is to not subtract the A320 background. You can
toggle background subtraction on and off by pressing Select.
4. Default type of Nucleic Acid. SmartSpec Plus can convert absorbance reading of nucleic
acid solutions into concentration. The conversion factor is determined by the type of
nucleic acid being measured. You can select the default type of nucleic acid in Setup,
so that when you press DNA/RNA, this type of nucleic acid will be shown first on the
display. You can choose another type of nucleic acid at any time by pressing Select.
The choices are double-stranded DNA (dsDNA), single-stranded DNA (ssDNA),
RNA, DNA oligo and RNA oligo. The factory default choice is dsDNA.
5. Default method to determine oligo molar extinction coefficient and molecular
weight. SmartSpec Plus uses the molecular weight and molar extinction coefficients of
oligonucleotides to convert the absorbance readings into mass (µg/ml) and molar
(pmol/µl) concentrations. You can input the molecular weight and molar extinction
coefficient directly if you know them, otherwise SmartSpec Plus will use one of three
methods to estimate them for you: Length, Composition or Sequence. The simplest
method to estimate either the molecular weight or the molar extinction coefficient is by
the length of the oligonucleotide. This method assumes an equivalent distribution of all
four nucleotides among the oligo. More accurate estimates can be calculated if you
specify the composition (i.e., the number of A’s, C’s, G’s and T’s or U’s) of the oligo
and the best estimate of molar extinction coefficient is calculated with the sequence of
the oligonucleotide.
Press Select to change the default to Composition (Compstn) and press Select again to
set the default to Sequence.
6. Default number of sample replicates. SmartSpec Plus has the ability to accept samples
(and standards) in replicate groups and to calculate a mean and standard deviation for
each sample (or standard) replicate group. The factory default number of sample
replicates is 1, but you can change the number of replicates to any number between 1 and 9.
Use the keypad to choose the number of sample replicates and press Enter or Setup
when finished. During most assays you can change the number of sample replicates by
choosing Options from the Ready Screen.
8
Substract A320 Background
for DNA/RNA? Yes >=Help
Select default type of
DNA/RNA: dsDNA >=Help
Select default method of
find oligo conc: length
Enter default number of
sample replicates: