Whether as standalone instruments or high performance liquid chromatography (HPLC) detectors, UV-Vis spectrophotomters are indispensible for measuring analyte concentrations in a variety of areas. These instruments are important in scientific research, academic teaching, and QA/QC laboratories studying pharmaceuticals, proteins, DNA, solar panels, semiconductors, and coatings.
In the 1930s, vitamin research indicated that several vitamins, particularly vitamin A, absorb ultraviolet (UV) light. Spurred by the American government’s interest in measuring vitamin content in soldiers’ rations using ultraviolet and visible (UV-Vis) light, this research culminated in the commercial launch of UV-Vis spectrophotometers in the early 1940s. Although modern UV-Vis spectrometers differ greatly from the first instruments, all operate on the same basic principle—light intensity is measured from UV-Vis source lamps before and after the light passes through a sample. The amount of light absorbed corresponds to the molecular concentration in the sample. Xenon lamps have replaced older tungsten and deuterium lamps, resulting in better quality of data analysis.
UV-Vis spectrophotometers from different manufacturers come in a variety of detection wavelength ranges, spanning from 175 nm to 3,300 nm, but as a guideline you can generally group a UV-Vis spectrophotometer into one of the following three ranges: up to 175 nm, 190 to 900 nm, and up to 3,300 nm.
UV-Vis spectrometers come in four basic models: low-cost single-beam, dual-beam, array-based, and handheld. Single-beam techniques must apply a correction for the loss of light intensity as the beam passes through the solvent. Dual-beam spectrometers use a second solvent reference cell and perform the correction automatically. Single- and dual-beam benchtop instruments use a broad spectrum lamp as the light source, and most use a photomultiplier tube as the detector while some instruments employ photodiode array detectors.
Handheld instruments are usually dedicated to one wavelength and analyte, for example, for water testing in the field. Handhelds employ single wavelength lightemitting diode light sources and photodiode detectors.
Array-based instruments use a very broad-spectrum tungsten lamp emitting between 200 and 1000 nm, and use a photodiode array or charge-coupled device as the detector. Array instruments do not scan the UV-Vis spectrum in the traditional sense, but rather send and collect the entire spectrum at once. Array instruments are useful when spectra must be acquired quickly, for example, from an HPLC trace or fast kinetics experiments.
Over 80 percent of the respondents have either a singlebeam or dual-beam model.
Traditional UV-Vis techniques require liquid samples to be transferred to a cuvette and placed in the instrument for measurement. This approach wastes time and affects the quality of the data: first, it can require you to wait for the sample to stabilize to ambient temperatures, which can be detrimental to the sample; second, it demands that you clean the cuvette between measurements.
The growing popularity of UV-Vis stems from its ease of use and the speed of the analysis. Many vendors are introducing instruments that eliminate the need for cuvettes, saving time and money, while reducing sample handling errors. After discarding the pipette tip and wiping the spectral window surfaces clean, the instrument is ready for the next sample.
In addition, software and automation improvements have helped to turn UV-Vis instruments into true analyzers for use in the lab or in the field.
Over 40 percent of the respondents use their UV-Vis spectrophotometer at least once a day.
|Several times daily||36%|
|Once a day||7%|
|Several times each week||33%|
|Once a week||6%|
|Two to three times a month||8%|
|Once a month||2%|
|Less than once a month||6%|
Future improvements in UV-Vis spectrophotometers will focus on ease-of-use, portability, and applicationspecific instruments. UV-Vis analysis of solid samples and materials continues to grow in areas such as solar cell research, semiconductor products, and coating materials. Advances in light sources will provide new developments in conventional spectrophotometers and handheld UV-Vis instruments while further development in remote sensors will enable more types of samples to be measured outside the laboratory.
Performance is the most important factor to respondents in their decision-making process. A general understanding of the effects of each performance attribute on the outcome of the measurements will help to improve the results from the UV-Vis test. The required performance tests include wavelength accuracy, UV and visible absorbance accuracy, UV and visible stray light, and resolution. Other factors such as noise, baseline flatness, and stability could also affect the performance. Luckily, many of the newer instruments offer a selfcalibration check.
Manufacturers recommend potential buyers first consider the applications for which they will be using the spectrophotometer to determine the detection range they require and consider any future applications that may require a broader range. Next, choose what range of stray light performance you are comfortable with for your application and budget.
Top ten factors / features in the decision-making process:
|Better sensitivity and resolution||86%|
|Ease of maintenance/Low operating costs||84%|
|Faster acquisition and analysis of data||69%|
For more information on UV-Vis Spectrophotometers, visit www.labmanager.com/spectrophotometers
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