Introduction

In the field of material evaluation, it is desirable to analyze the components of samples in a simple and convenient manner. As an optional accessory for the JASCO Palmtop Raman spectrometer, JASCO offers a dedicated Vial holder that allows easy qualitative evaluation of liquid and powder samples using disposable vials.

<Liquid measurement using Raman spectroscopy>
Since Raman spectroscopy allows spectroscopic information at the laser focal point to be obtained, measurements can be performed with the sample still in a glass vial (Fig. 1).

Fig. 1 Measurement through vial

Liquid samples may need to be measured outside the container by dropping them onto a plate or introducing them into a capillary tube. However, in the case of highly volatile samples, some evaporation will occur during the measurement, resulting in an incorrect spectrum. By placing the sample in a vial and keeping the lid on, an accurate Raman spectrum can be measured while preventing sample evaporation.

<Vial holder>
The dedicated JASCO Vial holder is an optional accessory that is simply inserted into the tip of the Palmtop Raman spectrometer (Figure 2), and allows measurements to be made with liquid or powder samples placed in 2 mL vials. This keeps the distance between an objective lens and the sample constant and reduces the time and effort required for focusing on the sample, which can be considerable for Raman measurements. Additionally, the dedicated JASCO Vial suppresses photoluminescence from glass at an excitation wavelength of 785 nm.

In this report, we describe measurement results for acetone, methanol and ethanol, all of which are highly volatile liquids.

Experimental

Samples: Acetone, methanol, ethanol
System: PR-1w Palmtop Raman Spectrometer
Accessories: Vial holder,  2 mL Screw vial, amber, Cap with septum

Fig. 2 Vial holder

Parameters:
Excitation wavelength: 785 nm
Laser output power: 50 mW
Exposure time:    1 sec
     Accumulations:        10

Keywords

Qualitative analysis, acceptance test, screening, Palmtop Raman spectrometer, Vial holder

Results

The measured spectra are shown in Figure 3. The three compounds have a relatively similar structure and molecular weight, but they exhibit completely different spectra.

Fig. 3 Raman spectra of three volatile liquids

Spectra acquired using the JASCO Palmtop Raman spectrometer can also be searched for using a general-purpose database.

Conclusion

Using the JASCO Vial holder together with the dedicated JASCO Vial allowed easy and reliable measurements of highly volatile liquids. This holder can be used to measure both powder and liquid samples. After measurement, the vials are disposable, and a new vial is used for subsequent measurements, allowing more efficient sampling inspections for screening purposes.