Camlab Limited

Buy Smarter – what questions should you ask when buying a Spectrophotometer?

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Courtesy of Camlab Limited

Spectrophotometers are relied on by a wide range of laboratories, for tests ranging from specific parameters, like chlorine or metals concentrations, right through to complex analyses of reaction kinetics.

When choosing a spectrophotometer the range of specifications and price is vast, so take the time to list the features you need before you buy and make sure you choose the right one.

Water Analysis or Laboratory use?

The first choice to make is whether you want to test water with predefined methods, with the speed and convenience of pre-measured reagents, or if you want the flexibility to design your own methods and test a wider range of analytes.

Water Analysis Spetrophotometers Fast, simple to use, pre-defined methods for direct readings of standard parameters

Water analysis spectrophotometers use pre-programmed methods and ready to use reagents (tablets, powder sachets (also known as powder pillows) or tubes or vials, to give a direct reading of a set parameter. For example you might use powder pillows to directly measure free Chlorine in mg/L, or tablets to read out the hardness of your water sample.

These allow a simple to use system to get direct results of concentration. They also have the benefit of reagents coming as pre-measured doses, so there is no need to weigh or measure out exact amounts, simply add the number of sachets or pillows the instructions state.

Popular models include the Hach DR3900, the Hach DR1900, the Palintest 7500, the Lovibond MultiDirect or the Lovibond MD610.

When choosing a water analysis spectrophotometer you should ask;

  • What parameters do I need to test, and at what levels?
    • e.g. Chlorine at 2mg/L, Iron at 1 to 5mg/L, COD from 150 to 1,000 mg/L…
  • What reagent format do you prefer?
    • Some tests are fixed, for example all COD tests are usually in the form of a tube or vial, but others can come in a range of formats; tablets, powder sachets (powder pillows), liquid drops, or even test strip mounted reagents. Each method has benefits and drawbacks, so this is down to personal preference.
  • How much are the reagents for these tests?
    • And are they regularly stocked, or should I order ahead?
  • Are any other items needed for these tests?
    • For example COD vials require a micropipette to add the right volume of water, and a reactor block to digest the sample.
  • How many test methods are available on this unit?
    • In case you need to add more in the future
  • Will I only need to work with water samples?
    • If this is a no, then this type of unit may not be for you
  • Do I need the unit to be portable?
    • Many models are battery powered to use in the field, but do check the methods you need are portable – some need a digestor which must be mains powered!
  • What connectivity does the unit offer?
    • Some models can connect via RS232, Bluetooth or other methods to download results.
  • What accessories are available?
    • Most models offer a carry case, a mains adaptor, or other accessories to make using the instrument easier.
  • What service support is available?

Laboratory Spectrophotometers A wider range of options, design your own tests, more versatile for sample volumes and types

If your samples are not water, or if you want to test for different analytes or design your own more complex method, a lab spectrophotometer may be a better choice.

This type of unit offers complete flexibility to design your own tests for any analyte that is active in the UV or visible range – for example some pharmaceuticals (e.g. aspirin) are UV active at a particular wavelength, but there would not be a pre-defined method in a water spectrophotometer for these. A lab spectrophotometer will allow you to create your own calibration curve, then measure unknown samples relative to this, to track any analyte of interest.

There is still an array of options available, so make sure you pick the right instrument by asking…

  • What is the wavelength range?
    • You may need to measure samples only in the visible or in UV and visible ranges
  • What is the bandwidth?
    • This will affect how finely you can tune your results
  • What outputs are available?
    • Many units allow results to be downloaded by USB, RS232 or SD card to either standard files like CSV or to their own software for analysis.
  • What modes does the unit offer?
    • Many units have built in photometrics, concentration or kinetics modes as well as the standard absorbance and transmittance.
  • What sample size do you usually work with?
    • Standard 1cm cuvettes need a few ml of sample, but specialised units are available for very small sample types, such as the Genova Nano by Jenway that can take a reading from just 0.5µL of sample
  • What accessories are available?
    • Many instruments offer adaptors for specialised cells, printers or software for data analysis.
  • Are cuvettes included?
  • What warranty is available?
    • Find out the length of warranty but also how you can make a warranty claim.
  • Is IQ/OQ documentation available?
    • For some units installation qualification and operation qualification procedures are available, if your lab requires this make sure it is available for your chosen model.
  • What service support is available?

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