Preamble

Simultaneous Determination Nitric Microfluidic Li-Hua Zhang Hong-Juan Department Radiochemistry, China Institute Atomic Energy, Beijing 102413, China.

Abstract

simultaneous quantification actinides acids nuclear reprocessing critical, conventional absorption spectroscopy faces fundamental limitation: reliance single, fixed optical length, which forces compromise between sensitivity dynamic range multiple analytes. constraint particularly problematic

analysis

radioactive materials glovebox environments. Herein, present monolithic microfluidic fabricated poly-methyl methacrylate (PMMA) integrates multiple, distinct optical lengths single platform overcome limitation. features self-aligning channels seamless optical fiber coupling UV-Vis spectrometers, enabling simultaneous measurements. employing partial least squares regression (PLSR) deconvolute mutually interfering spectra nitric acid, demonstrate concurrent determination these species under their individual optimal conditions. chip-based platform drastically reduces sample reagent consumption simplifies workflow single pipetting step, offering decisive advantages safe, high-throughput

analysis

within radioactive gloveboxes representing paradigm spectral measurement nuclear cycle.

Key words : Microfluid chip, uranium, nitric acid, PLSR

Introduction

Absorption spectrometry remains cornerston analytical technique quantification actinides, particularly uranium plutonium, within nuclear reprocessing streams. previous studies established various on-line off-line

methods

simultaneous determination uranium, plutonium, nitric complex matrices fundamental constraint persists: these conventional approaches singular, fixed optical length analytes. inherent limitation compromises analytical sensitivity dynamic range certain species, their optimal absorbance values cannot attained concurrently.

Introducing multiple lengths accommodate different analytes leads instrumental complexity, elevated

reagent consumption, cumbersome operational protocols significant disadvantages

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radioactive samples within glove boxes. Another drawback conventional measurement

methods

difficulty manipulating quartz cuvettes bulky gloves inside glovebox, making prone slipping shattering, which consequently compromises operational efficiency.

Microfluidic technology offers compelling paradigm address these challenges enabling flexible integration miniaturization operational units monolithic platform.

Compared conventional benchtop systems, microfluidic chips orders magnitude smaller, require microliters sample reagents, offer rapid

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excellent mass-transfer efficiency context spent-fuel reprocessing, these attributes translate decisive advantages: drastic reduction sample volume potential automation minimize radiation exposure personnel equipment, thereby extending equipment service life.

Furthermore, deployment within glove boxes curtails generation radioactive waste significantly reduces instrument footprint. ability integrate multiple analytical processes single further simplifies workflows enhances overall efficiency. integration absorption spectroscopy microfluidic chips effectively mitigate limitations conventional methods.

On-chip measurements dramatically reduce sample consumption.

Crucially, distinct optical lengths monolithically fabricated single chip, enabling simultaneous, multi-component

analysis

under their respective optimal conditions without complex external optical realignment. incorporation optical fiber technology further facilitates seamless coupling spectroscopic instrumentation these microfluidic devices. broader research community actively explored utility microfluidics within nuclear cycle, generating wealth knowledge online process monitoring.

Investigators successfully coupled microfluidic devices suite spectroscopic techniques, including Raman, UV-Vis, X-ray fluorescence (XRF) spectrometry, achieve quantitative

analysis

various radionuclides, consistently reporting analytical fidelity robust performance metrics [5-11] study, present multi-channel microfluidic integrated UV-Vis

spectrometers optical fiber coupling. Chemometric models developed enable simultaneous determination nitric utilizing distinct, on-chip optical lengths. approach overcomes limitation conventional methods, where nitrate quantified simultaneously compromise length (e.g., excessively absorbance aqueous samples near-infrared region.

Experimental Section Design Fabrication Poly-methyl methacrylate (PMMA) selected substrate material excellent optical transmittance 287-2600nm) UV-Vis-NIR range chemical resistance nitric -irradiation tolerance 50kGy multi-channel microfluidic assembled substrates.

Micro-channels optical features fabricated high-precision micro-milling using carbide end-mills, followed thermal compression bonding permanent sealing micro-channels uniform cross-section incorporated three distinct optical paths lengths optical featured self-aligning fiber channels. interface spectroscopy instruments, pigtailed silica fibers (core diameter: inserted light source spectrometer opposite these self-aligning channels. apertures alignment channels precisely dimensioned match fiber connectors, ensuring repeatable straightforward positioning.

Input Bleeder Optical Micro-lenses deliberately omitted channel terminations. reason micro-milling cannot produce optically smooth surfaces required functional lenses;

rough-surfaced lenses would introduce stray light scattering peaks obscure critical analytical features. compensate optical losses inherent lens-free configuration, windows separating self-alignment channels micro-channel thinned during fabrication process.

Furthermore, mirrors which serving total internal reflection elements, micro-milled along sides optical (Fig.2).

These mirrors mirrors served function: laterally confining probe within intended while preventing optical crosstalk adjacent channels Reagents Solutions Nitric analytical grade) Nickel nitrate hexahydrate (Ni(NO analytical grade) purchased Macleans Reagent (Shanghai) limited company. uranium standard solution obtained Department Radiochemistry, China Institute Atomic Energy. aqueous solutions prepared using deionized water (resistivity Instrumentation Setup balanced deuterium halogen light source (AvaLight-D (H)-S-BAL) together spectrometers:

AvaSpec-HSC1024x58TEC-EVO UV-Vis region AvaSpec-NIR512-2.5-HSC-EVO near-infrared region. simultaneous determination nitric achieved using fabricated multi-channel microfluidic chip. instrumental arrangement illustrated Light source split beams bifurcated optical fiber, branch inserted self-aligning channels optical paths chip. separate collection fibers inserted opposing channels guide transmitted light spectrometers. coupled spectrometer nitric quantification,

while coupled UV-Vis spectrometer quantification. Spectral acquisition spectrometers synchronized, displayed composite spectrogram.

Glovebox Optical fibre spectrometer

UV-Vis spectrometer

Integration multichannel optical system: Schematic photograph setup Experimental Procedure experimental protocol simultaneous measurement follows. positioned custom stage, fiber optic connectors securely inserted self-aligning channels (Fig.4). aliquot sample solution pipetted injection port, filling entire microchannel optical paths (total volume: ensure consistent measurements. volume provided sufficient flushing prevent cross-contamination between samples.

After spectral acquisition, solution expelled waste container. process repeated samples. streamlined procedure, requiring pipetting injection, particularly advantageous glovebox operations. obviates cumbersome steps associated cuvette-based methods, cleaning waste handling, thereby significantly increasing analytical throughput while minimizing sample consumption (Table1).

Slide photograph multichannel stage; photograph optical chip.

Total

Method

Chemometric

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nitric exhibit characteristic absorption peaks visible (Vis) near-infrared (NIR) regions, respectively.

Significant spectral interference between these species precludes univariate calibration.

Consequently, multivariate calibration models based partial least squares regression (PLSR) developed simultaneous analysis. theoretical principles detailed other literature training comprising samples varying concentrations nitric prepared.

Spectral acquired microfluidic construct validate models using Unscrambler software.

Discussion

Optical Performance Calibration On-Chip System validate optical performance custom-designed chip, which differs conventional cuvettes, absorption spectra solutions measured. standard solutions 5.0g/L,10.0 g/L,80.0g/L constant matrix) analyzed verify response stability linearity.

(a,b,c) absorbance measurement absorbance units, A.U.) concentration different optical path(a.2mm;b.5mm;c.10mm);(d) linear relationship between absorbance concentrations (VI). shown spectral absorption intensity systematically increased concentration across three optical lengths.

Calibration curves established characteristic absorption demonstrating excellent linearity 0.99) length. molar extinction coefficients derived on-chip measurements benchmarked against literature values (Table2). coefficients agreement, length yielding closest match; minor deviations attributed differences solution acidity instrumental conditions. length literature values

introduction

solution chip, absorption spectrum continuously monitored 48-hour period, acquired 10-minute intervals. illustrates resulting absorption spectra, wherein hundreds individual scans acquired duration nearly perfectly superimposed.

Stability quantify signal stability, relative standard deviations (RSD) absorbance discrete wavelengths calculated. determined below validat exceptional stability on-chip spectral analysis.

Simultaneous Determination Nitric prepared. detailed composition samples presented Table /(g/L) mol/L) /(g/L) /(mol/L)

Spectra samples acquired under identical conditions using deionized water blank (Fig.7). observed, samples concentrations 60.00, 65.0, exhibited absorbance saturation therefore excluded calibration Consequently, chemometric models developed using training samples samples independent samples external validation model.

Based absorption spectra nitric acid, optimal wavelength ranges selected develop their respective calibration models. model demonstrated robust performance, characterized standard errors calibration (SEC) prediction (SEP), coefficient regression (Table5). t-test comparing predicted reference values yielded t-statistic 0.05), confirming significant difference validating model predictive accuracy.

Similarly, model exhibited excellent performance SEC/SEP values coefficient regression. t-test 0.18, 0.05) further corroborated model robustness. detailed

results

presented

analytical software models simultaneously, enabling real-time, on-line

analysis

concentration readout components. Reference Prediction Relative Reference Prediction Relative value/( value/( value/(mol/L) value/(mol/L) t-test |T|=0.31 =2.78 |T|=0.18 =2.77

Conclusions

demonstrated PMMA-based microfluidic integrates multiple fiber-guided spectroscopy simultaneous determination nitric nuclear reprocessing liquors. demonstrated robust performance, calibration curves exhibiting excellent linearity stability. molar extinction coefficient measured on-chip consistent literature values, affirming accuracy approach. coupling on-chip Vis-NIR spectroscopy PLSR, achieved simultaneous determination nitric acid. approach lowers limit detection order magnitude compared previous techniques, which constrained single, compromise length. microfluidic platform offers decisive advantages traditional cuvette-based analysis, including operational simplicity, drastic reduction reagent consumption radioactive waste generation.

These features particularly suitable automated

analysis

within gloveboxes, leading substantial improvement analytical throughput nuclear reprocessing applications.

contributions manuscript written through contributions authors. authors given approval final version manuscript.

Conflicts interest There conflicts declare. availability authors confirm supporting findings study available within article.

Acknowledgements financially supported Nuclear Radiochemistry Fundamental Technology Research Project (BJ19001203) China Institute Atomic Energy.

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