Development and testing of a novel micro-Raman probe and application of calibration method for the quantitative analysis of microfluidic nitric acid streams

Abstract

To simplify and improve the safety of reprocessing used nuclear fuel, an initial assessment was made of Raman microscopy applied to microfluidic volumes with a view toward the on-line spectroscopic measurement of highly radioactive solutions. This study compares a microscopic Raman probe (excitation focal point diameter 70 μm) to a larger, well studied probe (excitation focal point diameter 125 μm) used in prior investigations. This was done by chemometrically modeling and predicting concentrations of HNO solutions (0 M to 8 M) as they flowed through microfluidic cells based upon spectra from each probe. Spectra recorded for each probe using the same static HNO solution set contained in 2 dram glass vials were used as training sets to produce models for the respective probes. Modeling required baseline, normalization and smoothing preprocessing to compensate for a reduced path length between the static glass vial training set (4 cm) and the reduced path length flow cell (1 cm), wide ranging solution concentrations, and the associated non-linear spectral changes, and abrupt and uneven concentration changes of flowing solutions. The micro-Raman probe is able to produce spectra that may be analyzed chemometrically to accurately predict the concentration of flowing HNO solutions down to microliter volumes. Based upon RMSECV and RMSEP modeling statistics concentration predictions of the micro-Raman probe are comparable to those obtained for a macro-Raman on identical samples.

Micro-Raman Technology to Interrogate Two-Phase Extraction on a Microfluidic Device

“…Note, the channel width of the MFD is 300 μm, while the focal point diameter of the Raman excitation laser is 69 μm. This allows for accurate measurement of solutions within the MFD channel. , Both Raman probe and MFD can be held stationary or the MFD can be moved relative to the probe. Moving the MFD to interrogate solutions down the length of the MFD allows for the exploration of kinetic parameters on the chip, giving multiple target measurement points down the channel …”

“…For solutions less than 2 M, three bands were observed associated with nitrate ion in accordance with the unperturbed nitrate ion being trigonal planar geometry within the D3h point symmetry group. 21,47 The 1048 cm −1 band is the most intense band observed and is assigned to the ν 1 symmetric stretch; the band located at 1411 cm −1 is assigned to the ν 3 asymmetric stretch; and the 719 cm −1 band assigned to the ν 4 in-plane deformation. They are assigned to the A 1 , E′, and E′ modes, respectively.…”

“…The novelty of the methodology and technique lies in the fact that this work can measure interfacial transfer in real time, without further chemical work up, is in situ and does not require aliquots for sample analysis, and is nondestructive. Building on a recently developed micro-Raman probe, , and methodology for online measurement in a two phase Lewis Cell extraction system, , methods were advanced to collect Raman spectra in aqueous and organic phases online as they were pumped down the microchannel of a single channel MFD in a segmented plug flow pattern. The flow rate may be adjusted to obtain steady 1:1 volumes for the alternating droplets .…”

Design of Electrochemical Microfluidic Detectors: A Review

“…[176] Raman spectroscopy offers non-destructive detection of many organic compounds, biomaterials and metal oxides. [177,178] A unique advantage of Raman spectroscopy used in microfluidics is that water molecules do not have any strong characteristic peak, therefore it would not convolute or mask the signals collected from the targeted molecules. Also, it is possible that quantitative detection can be achieved by pre-calibrating the characteristic peaks.…”

Measuring Nd(III) Solution Concentration in the Presence of Interfering Er(III) and Cu(II) Ions: A Partial Least Squares Analysis of Ultraviolet–Visible Spectra

“…The RMSEP value is 0.003 M and the similar values between RMSECV and RMSEP indicate the model is robust enough to handle some degree of variation which is expected for an unknown sample. 39 The RMSEP showed the model is robust enough to accurately quantify Nd 3þ in the presence of both interferents even though no single training set sample included both interferents. With both interferents present, the percentage error of validation set A is below 7%.…”