abnormal result

Dear Harith,

Thank you for your enquiry.

You are using a double beam UV/Visible spectrophotometer.

There are a number of reasons for seeing apparently negative values on a UV/Visible spectrophotometer. They include the following:-

• The blank and sample/standards have been reversed in time or spatial positions. The sample/standard should be placed in the beam closest to the front of the instrument.

• No blank, or an inappropriate blank has been used. The blank must be of exactly the same composition as the sample/standard, but without the analyte of interest.

• The spectrophotometer has not been zeroed on the blank. In the case of a double beam spectrophotometer, you should place the blank in both cell positions and zero.

• The sample/standard is undergoing a chemical reaction, is precipitating out, or has air bubbles.

• Inappropriate cuvette/s (cell/s) are used, in terms of cuvette wall composition, path length, working fill volume.

• Inappropriate cell holder/s are used, so that the appropriate part of the cell does not have contact with the light beam.

• An inappropriate wavelength of measurement is used.

• If the values you see are in terms of concentration units, then it may be that an inappropriate calibration curve, or part of the calibration curve is being used.

If you would like to elaborate on your query, please contact me directly and send me your full contact details.

If you have any further queries, please contact me directly and send me your full contact details.

Kind regards,

Ade Kujore