Flexible sampling options, short analysis times, small form-factor, and superior identification capabilities are the best known benefits of 785 nm handheld Raman systems. Let’s dive a bit deeper and check out how low laser powers and resolution contribute to this growing list.

Short analysis times and low laser powers both preserve battery life for a system—a necessity for handheld Raman in field applications. Low laser powers also pose less risk of sample degradation for safer analysis of unknown materials.

MIRA’s (Metrohm Instant Raman Analyzer) unique spectrometer design collects data in very short analysis times with an excellent signal-to-noise ratio (SNR). A comparison of high (green) and low SNR (grey) in Figure 1 illustrates how noise in a low-resolution spectrum can occlude peak resolution. Ultimately, high SNR means more peak information for optimal library matching.

XTR®: The novel fluorescence rejection technique for improved 785 nm performance

Wavelength can be very influential when deciding on a Raman system, e.g., 532 nm for strong signal or 1064 nm for reduced fluorescence – but 785 nm Raman with fluorescence rejection gives users the best of both worlds. Approximately 20–30% of materials fluoresce under excitation at this wavelength. However, patented algorithms on MIRA XTR DS (Figure 3) eXTRact fluorescence from the 785 nm Raman spectrum for fluorescence-free material ID.
 

Find out more about MIRA XTR DS in our free White Paper and related blog article.

Fluorescence-free 785 nm material ID with MIRA XTR DS

The evolution of handheld 785 nm Raman spectroscopy: Raman extraction from fluorescence interference

The benefits of Raman eXTRaction are impressive:

• Non-technical users can quickly and easily collect high quality data anywhere for diverse material identification applications
• XTR makes possible the analysis of thousands of highly colored, organic, and/or complex samples
• High resolution spectra enhance library matching capabilities, providing fast and accurate material ID
• The incredibly high SNR spectra provided by XTR, even when sampling fluorescent materials, enables direct, sensitive analysis of even low concentration components

Chemicals

Raman can be a powerful tool for synthetic development of chemical compounds or in research laboratories because its specificity makes chemical identification, detection, and characterization quick and easy. However, organic substances can also be some of the most problematic materials under 785 nm interrogation. XTR overcomes this issue, as shown in the example here.

Synthetically useful molecules often have multiple bonds, and are also likely to exhibit fluoresce in the Raman spectrum. Consider folic acid, a B vitamin that is also useful as a synthetic material because of its extended saturation and numerous functional groups. Folic acid does fluoresce under Raman interrogation, but nonetheless, XTR produces a very high-resolution spectrum.

Dyes

Dyes and highly colored materials nearly always fluoresce under Raman interrogation, and the broad, featureless baseline of fluorescence obscures signature peaks. This can be compounded in complex materials and mixtures.

Here, a highly colored food product (Koolaid® drink mix) was interrogated by handheld Raman. The top (blue) spectrum is an excellent example of the strong fluorescence from analysis of dyes with 785 nm Raman. XTR routines extract the signal from target material well enough that Allura Red (FD&C Red 40) can be positively identified in MIRA Cal DS.

Nutraceuticals and dietary supplements

Dietary supplements are often composed of large doses of vitamins, minerals, fiber, and antioxidants that are sourced from vibrantly colored fruits and vegetables. Nutraceuticals and dietary supplements are less regulated than pharmaceuticals, but Raman can be used to confirm the identity of a supplement.

Quercetin is a plant pigment with antioxidant and anti-inflammatory effects that is used as an ingredient in dietary supplements, beverages, and foods. MIRA XTR DS can produce a distinct spectrum from quercetin with intense, well-resolved signature peaks, despite fluorescence. 

Authentication of saffron

The challenge of identifying low-grade or counterfeit saffron lies in the variety of strategies used to give the appearance of a pure mixture—e.g., added dyes and the inclusion of inauthentic flower parts. This is a demonstration of the power of MISA (Metrohm Instant SERS Analyzer) for simple, portable food authentication.
 

Find out more about MISA in our blog article.

Combat food fraud: Meet MISA

SERS contributes its own inherent fluorescence-reduction capabilities here. In this comparison of Raman and SERS analysis of pure saffron, the SERS background (in orange) is much less affected by fluorescence. This supports very sensitive detection of Sudan 1, a toxic dye used in very low concentrations to mimic saffron’s rich color.
 

Learn more about saffron authentication in the following Application Note.

Trace Detection of Toxic Dye in Saffron – Protecting consumer safety with MISA 

Pesticides on raisins

Raisins are consumed around the world as a healthy snack. However, the heavy use of pesticides in countries with poor regulation turns this snack into a potentially harmful food product. Acetamiprid is a widely used neonicotinoid pesticide that has a role in bee colony collapse and is now regulated at a maximum residue level of 0.5 µg/g (500 ppb) in Europe.

Simple and effective sample extraction techniques support portable, flexible, on-site SERS analysis. Here, a highly volatile solvent was used to extract the target compound. Quick evaporation of a large volume of supernatant (800 µL instead of the 200 µL generally used) improves detection to ppb levels. With this treatment, peaks for acetamiprid are visible down to 0.5 µg/g (in orange).