5061-084-REV-1
LIGHTWAVE 3 & 3+ SPECTROPHOTOMETERS USER’S MANUAL
40
TROUBLESHOOTING
Negative absorbance
readings
• Sample measurements will be negative absorbance reading if the absorbance value
of the reference is higher than the sample.
• Negative readings can also result if reference and sample are interchanged or if
the sample is very dilute and close to the absorbance of the reference.
Unexpected results
• Bubbles or contamination in the sample or reference can result in considerable errors.
• Incorrect cuvette orientation. Rotate by 90˚ and repeat.
• Incorrect cuvette material for UV measurement wavelengths.
• Wrong pathlength selected in software.
• Contact your supplier for advice on the minimum concentrations that can be measured.
Absorbance higher
than expected
• Incorrect sample reference.
• Incorrect cuvette orientation.
• Incorrect cuvette material for measurement wavelengths.
• Wrong pathlength selected in software.
• Contamination in sample or on cuvette.
• Check baseline, if greater than 0 A toggle background
correction or us an appropriate reference sample.
• Possible incorrect optical alignment. Contact technical support.
Absorbance lower
than expected
• Incorrect sample reference.
• Check sample and reference for contamination.
• Check sample and reference samples are not the same.
• Incorrect cuvette material for measurement wavelengths.
• Wrong pathlength selected in software.
• Check the beam height and buffer sample volume.
• Check baseline, if greater than 0 A toggle background correction or us an
appropriate reference sample.
• Possible stray light issue. Contact technical support.
Poor reproducibility
• Insufficient sample in cuvette.
• Cuvette in wrong orientation.
• Cuvette material unsuitable for wavelengths used.
• Concentration of sample too low or too high. For best results, the measured sample
absorbance using a 10 mm pathlength cuvette should ideally be between 0.1 and 1.0 A.
If absorbance is >1 A, measurement is no longer in the most linear range.
• Particulates in sample. Absorbance measurements will not be accurate with turbid samples.
• Possible noise or measurement stability issue. Contact technical support
Instrument start up
reported failure
• Check the cell holder is empty.
• Check original 18V dc supply is connected and is fully engaged.
• Report persistent failures to technical support.
