While it is not recommended, glass test tubes can be used in the Go Direct^® SpectroVis^® Plus Spectrophotometer (GDX-SVISPL). Extra caution should be used if you are using any organic solvent, as organic solvents can damage the spectrophotometer since it is made out of plastic. The cuvette holder for this spectrophotometer is 13.3 mm in diameter. So glass test tubes that are 13 mm in diameter should work in the device. We have tested glass test tubes from Flinn Scientific that are 13 and 12 mm in diameter. Both give decent spectra, but the test tubes that are 13 mm in diameter sit in the holder better and do not move around as much as 12 mm test tubes. For quantitative analysis, standard cuvettes should always be used. But for qualitative analysis of spectra, glass test tubes can be used.