Basic Photometric Mode
Measures Absorbance, %T and Concentration with entry of Concentration Factor or the Concentration of the standard. Units such as ug/mL, mg/mL, mg/L, g/L, ppb, ppm, %, I.U., mM/L, M/L may be selected or other units may be entered via the keypad. Continuous display of the result means there is no need to press a button to read.
Quantitative
Up to 10 standard solutions may be used to establish calibration equation curve. There is a choice of four methods for fitting a curve through the calibration points: Linear fit. Linear fit through zero, square fit and cubic fit.
There are three kinds of correction method:
- Single wavelength method
- Iso-absorbance (two wavelength method): The absorbance at the measurement (peak) wavelength is measured relative to the absorbance at a second (valley) wavelength. This minimizes the effects of cell difference and turbidity
- Three-point: The absorbance of the peak itself is measured by subtracting the calculated tangent joining the valleys on each side of the peak.
Wavelength Scanning
The wavelength scan intervals are 0.1, 0.2, 0.5, 1, 2, 5nm, and Hi, Medium and Low scan speeds are available. Scan speeds vary from 100 to1000 nm/min. Wavelengths are scanned from high to low so that the instrument waits at high wavelength. This minimizes the degradation of UV sensitive samples. Precise control of filter and lamp changes means that their effects are not seen on the final scan. Post-run manipulation includes re-scaling axes, curve tracking and peak picking.
Kinetics
This mode may be used for time course scanning or reaction rate calculations. Abs. vs. time graphs are displayed on the screen in real time. Wait time and measurement time up to 12 hours may be entered with time intervals of 0.5, 1, 2, 5, 10, 30 secs and 1 min. Post-run manipulation includes re-scaling, curve tracking and selection of the part of the curve required for the rate calculation. Rate is calculated using a linear regression algorithm before multiplying by the entered factor
DNA/Protein
Concentration and DNA purity are calculated:
Absorbance ratios 260nm/280nm or 260nm/230nm
With optional subtracted absorbance at 320nm
DNA Concentration =62.9 x A260 - 36.0 xA280 or 49.1 x A260 - 3.48 x A230
Protein Concentration =1552 x A260 -757.3 x A280 or 183 x A260 - 75.8 x A230
Other wavelengths and factors may be entered
Multi-Wavelength
Up to 10 wavelengths may be entered, allowing the measurement of multiple wavelengths on a series of samples.
Performance Validation
for the GLP compliant laboratory SpectroQuest spectrophotometers may be automatically self-calibrated on switch-on, using the 656.1nm deuterium emission line. This function may be repeated at any time. The wavelength accuracy may be checked using the "WL Validity" program (wavelength calibration standards required). The absorbance accuracy at several wavelengths may be checked using the "Accu Validity" program.