Frequently Asked UV/Visible Spectrophotometer Questions

Below is a selection of frequently asked questions.  In addition, the answers to many queries may be found in user manuals and other Cecil documentation.  Otherwise, please contact us on  or

telephone +44 (0) 1223 420821, for detailed information and answers to your queries.

We would like to use this type of instrumentation in our laboratory, but no one has any knowledge or experience of its use.  Please could you advise?

We do appreciate that this may be a daunting prospect, we at Cecil Instruments have experienced chemists and biologists who should be able to help.  In the first instance please read our document/s on the use of our relevant spectrophotometers, which should provide the background on the theory and use of spectrophotometer models.  We also can provide application notes for methods of analysis of specific compounds, within specific sample groups.  

I have just switched on my brand-new Cecil spectrophotometer, although the red lights illuminated for a few moments, my screen is blank.  My spectrophotometer is at the start of its two year warranty, please arrange for me to return it to the factory?

At this stage, it would be prudent to first check the variable screen contrast control.  The screen contrast and brightness may be varied by yourself.  Sometimes in a new spectrophotometer, the contrast control has been inadvertently set to dim.  Ensure that no red lights are illuminated then adjust the screen contrast and brightness by pressing the UP and DOWN arrow keys to achieve the desired screen contrast and brightness.

Which wavelength should I use for the measurement of my given analyte in my sample?

In order to determine the specific wavelength for making a measurement, you may perform a wavelength scan of an analytical standard in the presence of the sample matrix.

A wavelength scan is a plot of Absorbance on the y axis and wavelength on the x axis, for a particular analyte.

The single wavelength which gives rise to the largest clearly resolved Absorbance value, may be used for the measurement of the analyte of interest in your sample. This specific wavelength is often the Lambda max of the analyte of interest.  Be sure to make a wavelength scan of your sample blank and check that your Lambda max is only attributable to the analyte of interest.

Is there a difference between a cuvette and a cell?

No, these terms are interchangeable, although the use of the word ‘cell’ is now more popular.

There is a bewildering choice of cuvettes/cells, which ones should I use?

Please bear in mind the following points:-


Wavelengths of the visible region (generally around 325 to 1,100 nm) may be used with cuvettes made of optical glass or plastic.

Wavelengths of the ultraviolet region (generally around 190 to 325 nm) require cuvettes made of materials such as quartz, silica or special plastics.

Z height

This is the height from the bottom of the cell compartment, to the  vertical centre of the light beam passing through the  inserted cell.  Please choose a cuvette with a Z height which matches that of your spectrophotometer.  All of the Cecil spectrophotometers have a Z height of 15 mm.


10 mm is standard, however, if you are expecting samples/standards to have very high Absorbance readings, then pathlengths smaller than 10 mm may be used.  If you are expecting samples/standards to have very low Absorbance readings, then pathlengths greater than 10 mm may be used.

Available volume of sample/standard/blank

If you are using a 10 mm pathlength cell and have copious amounts of sample/standard/blank, then a macro cell with a working volume of around 2.5 mL may be used.  If you have more limited volumes, then semi-micro, micro, ultra-micro or nano cells may be used.

Please bear in mind that in order to properly accommodate your chosen cuvette  within the spectrophotometer cell compartment, you will need to use an appropriate cell holder.

My samples are meant to be pale blue colours, but the blue colours which I see are very dark and the spectrophotometer Absorbance readings are all 9999.  Please help.

It appears that your samples are too concentrated to be read.  You may use one of two options.  Either dilute you samples with measured volumes of blank and then scale up your final results data accordingly.  Or, use cells of pathlength smaller than 10 mm.  If you use smaller path length cells, you may need to use a cell spacer to reliably hold the cell in position within your spectrophotometer.  These principles apply in reverse to very dilute samples.

I think that I have done everything correctly, the right wavelength, cell material, cell holder, cell path length, blank, correct sample treatment, correct sample dilution, no precipitation or bubbling of the liquid sample, the sample compartment lid is closed and no tubing or cables are blocking the light entering and exiting the cell, but I am obtaining really erratic Absorbance data.  Please could an engineer arrange to visit, as I think that there is something wrong with the spectrophotometer.

Check the Z height of the cell which you are using.  The Z height or dimension of a UV/Visible spectrophotometer is the distance from the bottom of the spectrophotometer cell compartment to the vertical centre of the light beam passing through the inserted cell. The Z height of all Cecil spectrophotometers is 15 mm, so that of your cell should also be of a 15 mm Z height.

If we assume that you are not using a nano type cell, then the following solutions may also apply.

Please see the diagram below, which shows the height of sample in a filled cell.

Please note how the whole of the light beam must fully pass though the liquid contained in the cell.  Is your

cell adequately filled.

Please check that the linear portion of the calibration curve is being used for sample measurements.

I wish to use 1 µL samples, I know that Cecil has the traditional quartz cuvettes with low fill volumes, but they are tricky to use.  Is there anything else?

Cecil Instruments are able to offer nano wipe clean cells, such as the Tray cell, BioDrop and Nano Stick devices. They may be used with the Cecil spectrophotometers.

I note that many Cecil UV/Visible spectrophotometers have a USB port, can I use that port to directly attach the spectrophotometer to a printer?  

The printer manufacturers constantly change their printer drivers, Cecil Instruments, in common with other spectrophotometer manufacturers cannot keep up with the changes.  

Hence we provide DataStream software, which will enable most of our spectrophotometers to collect data onto a PC and then print from the PC.  DataStream software is very fast and easy to load onto a suitable PC, and is very easy to use.  All of the functions which the Cecil spectrophotometer performs on a stand-alone basis, may be performed using the equivalent DataStream PC keys.

Some of our spectrophotometers do have integral printers.  

In the case of those of our spectrophotometers which also have an RS 232 port, we do know that the Epson LX 300 + dot matrix printers are generally compatible.

Can I use DataStream software on my Linux computer and Apple PCs?

DataStream software is designed for use on the Windows operating systems of PCs.  It is compatible with Windows 98, Vista, XP, 7 , 8 and 10.

I have lost the original user manual, which accompanied the spectrophotometer when I originally purchased it.  I cannot find a section on your site for user manuals.

Sorry, but our replacement manuals are not available electronically. This is because different versions of the same instrument model may be in use, and we wish each specific replacement manual to match the exact version of the instrument, which a person may be using.

Hence we can only supply hard copy replacement manuals.  Please contact your local distributor for ordering details.

On placing the order with the distributor, please provide the serial number of the spectrophotometer concerned, so that the appropriate version of the manual is sent.

I have a Cecil double beam spectrophotometer, but the results are expressed as negative values.

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

We have recently purchased an identical model as a replacement, can we still use the same factors to express our concentration results?

Although both instruments are of the same model, different instrument components, such as, lamps, cams and filters have been used for each instrument.  These components, and their interactions will give rise to slight differences between each instrument.  If you need accurate data, you will have to obtain new factors, by making up new calibration curves and using the factors from each of your new calibration curves.

In addition, if your original Lambda max was obtained on an extremely narrow Absorbance peak, you may first have to obtain a new Lambda max.

I use my spectrophotometer in a regulated laboratory.  Our SOPs require us to check the wavelength and Absorbance calibrations at regular intervals.  How regular should these intervals be?

This really depends on how critical your measurements will be and how often measurements are made.

Many laboratories opt for a calibration check once a month.  These laboratories also ensure that performance standards are used every time a sample is measured.

We use calibrated filters/sealed liquid standards to check wavelength and Absorbance calibrations.  How often should we replace these standards.

If we assume that the standards have not been stored under damp conditions, or have not been exposed to light (except when in use), or to extremes of heat, and have not incurred damage, they may be replaced or have their calibration checked approximately every one to three years.