7.4: Sample Containers

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Sample Containers

Most experiments using absorption of emissions spectroscopy interrogate samples that are gases, liquids or solutions. The exception to these are solid samples that can be mounted in the spectrometer. Spectroscopy experiments with gases are generally accomplished with long-path cells that are either sealed or through which the gas flows. For liquids and solutions cuvettes are the most common sample containers.

The key characteristics for sample containers are:

1) the window material or cuvette material is transparent in the spectral region of the experiment

2) the window, cell or cuvette material does not reactive with the sample

3) the path length of the cell is matched to the experiment and instrument

4) the cell volume is matched to the sample.

Pictured in Figure 7.4.1 is a 10 cm pathlength demountable cell useful for absorption experiments with gases such as iodine vapor. It is often difficult to fit a longer pathlengh cell in the sample compartment of a benchtop UV- Vis spectrophotometer. If a longer pathlength is required, multipath cell with pathlenghts up to 100 m are commercially available.

10 cm cell.jpg

Figure \(\PageIndex {1}\): A 10 cm pathlength demountable cell for absorption experiments with gases. Demountable means the cell can be disassembled, say for cleaning or changing the windows, and then reassembeled.

Cuvettes for experiments for liquids and solutions can be purchased with pathlengths ranging from 0.1 cm to 10 cm and the pathlenghts are precise to +/- 0.05 mm. The volume of sample held can be between 1.4 and 35 milliliters (macro), between 0.7 ml and 1.4 ml (semi micro) and between .35 and 0.7 (micro). Cuvettes are constructed with two polished sides for absorption spectroscopy and with four polished sides for emission spectroscopy. Cuvettes can be purchased individualy or in matched sets of 2 or 4. Shown in Figure 7.4.2a is a quartz macro cuvette. for absorption spectroscopy and Figure 7.4.2b is a semi micro cuvette for emission spectroscopy.

Figure \(\PageIndex {2}\): (a) A 1.0 cm pathlength macro cuvette absorption experiments (b) A 1.0 cm pathlength semimicro cuvette for emission experiments.

The most common materials for windows and cuvettes for experiments in the UV and visible regions are shown in Table 7.4.1.

Material	Useful spectral range
Glass (BK-7)	340 - 2500 nm
Fused Silica (IR grade)	240 - 3500 nm
Fused Silica (UV grade)	190 - 2500 nm
Polystyrene (PS)	340 - 800 nm
Polymethylmethacrylate (PMMA)	280 - 900 nm
Saphire	250 - 5000 nm

Note: Brand-UV cuvettes are disposable plastic cuvettes with a short wavelength cutoff reported to be 230 nm