Hellma offers the TrayCell in two different lengths. The ‘short’ TrayCell 105.810-UVS fits well in devices where the sample compartment is closed with a cap. The ‘long’ TrayCell 105.800-UVS makes pipetting easier in devices with deep sample compartments.
The properties of the two measuring cells are otherwise identical. Spacers can be used in both models to achieve various center heights as necessary. Your TrayCell can therefore be used problem-free in spectrophotometers with different center heights. If you are unsure as to which center height you require, tell us the details of your device and we will recommend the most suitable TrayCell.
As is the case when using cuvettes, you should be careful to ensure that the TrayCell stands straight and stable in the light path. To achieve the best possible reproducibility of measurement values, we recommend always inserting the TrayCell in the same direction, with the Hellma logo facing the front, and leaving it in the holder between measurements.
The smaller the path length, the higher the concentrations of samples that can be measured within the linearity range of the spectrophotometer or sample testing system. In contrast to the customary cuvettes with their 10 mm path length, the 1 mm path length cap offers a ‘dilution factor’ of 10, and the cap with a 0.2 mm path length even provides a ‘dilution factor’ of 50. This factor therefore indicates the extent of dilution that would be necessary in a conventional cuvette (virtual dilution factor).
The TrayCell consists of quartz glass and metal components, and must therefore be handled with care. While the quartz glass components are highly resistant to laboratory cleaning agents, no caustic or corrosive cleaning agents should be used on metal components. We recommend using lint-free swabs or lint-free lab cloths for cleaning. Samples can be recovered beforehand using a pipette, and the remainder is then wiped away using a swab or lab cloth. If necessary, final cleaning may be performed with a solvent used for the sample.
The TrayCell is characterized by its use of low solarization fiber optics. It permits a measuring range of between 190 and 1,100 nm.
It is not possible to simply use a second TrayCell and follow the usual procedure for taking reference measurements in a double beam spectrophotometer. The differences in the optical characteristics of the fibers are too great to allow any sensible comparisons to be drawn. Baseline correction is sufficient in the majority of cases, however, making such comparisons unnecessary for standard measurements. If you need to improve the signal-to-noise ratio, we recommend reducing the reference beam to an intensity of around 20%. This can easily be achieved using a simple aperture in the reference beam path.
Depending on the sample being analyzed (double-stranded or single-stranded DNA or RNA, oligomers, etc.) we see nucleic acid concentration ranges from around 6 to 8,500 ng/μl for an absorbance range of 0.025 – 1.7. In the case of proteins, measurements should only be taken up to a maximum absorbance of 1, since the scattering above this level would no longer ensure linearity as defined by the Beer-Lambert law. For a protein with an absorbance of 1 at a concentration of 1 mg/ml, the concentration range with a TrayCell would be 0.1 – 100 mg/ml. This concentration range varies depending on the specific absorption coefficients of the individual proteins.
For further information see also chapter '6. Measuring range' in the User manual
The maximum absorbance that can be measured is limited by the linearity range of the spectrophotometer used. The highest performance spectrophotometers available on the market permit measurements up to a maximum absorbance of 10. Statements in the literature referring to far greater absorbance ratios should be understood as theoretical values. These ‘theoretical’ absorbance ratios indicate the results that could be expected if we were able to measure undiluted samples in cuvettes with 10 mm path lengths. When using a path length of 0.2 mm (factor 50), the absorbance range of a spectrophotometer with a linear measuring range up to 1.7 would equate to a ‘theoretical’ absorbance of up to 1.7 x 50 (factor) = 85 in a 10 mm cuvette.
The ability to measure highly-concentrated samples is determined by the linear absorbance range of the spectrophotometer used. The type of sample being measured also plays a role, as proteins, for example, can only be measured correctly up to an absorbance of 1. By using different path lengths with the TrayCell, even highlyconcentrated proteins can be measured. (See also question 7)
Yes. As the window is slightly indented and measurements are performed in the horizontal plane, the liquid is unable to escape. To achieve the best results, we recommend using the cap with the 0.2 mm path length where possible, or the 0.1 mm path length cap that is available as an optional accessory.
Check that a sufficiently large sample quantity has been pipetted onto the window. The volume should be equivalent to the minimum quantity recommended for a given path length. Some pipettes are not precise enough for transferring small sample volumes. If in doubt, increase the sample volume a little. In the case of very low volumes, we recommend pipetting samples directly onto the mirror inside the cap. Check whether the spectrum is showing a high noise level, that could cause the measurement signal to fluctuate. Provided that the concentration and/or absorbance of the sample lies within the measuring range, an extended integration period will improve the measurements.
At room temperature, the TrayCell measuring head, including the cap, is resistant to many organic solvents, acids up to pH ≥ 2 and alkaline solutions up to pH ≤ 10.
Please find in the Download section the TrayCell User manual; you will find in chapter 9 a list of the compounds for which a chemical resistance of the measuring head of the TrayCell is given at room temperature.