In-Country Method Validation of a Paper-based, Smartphone-assisted Iron Sensor for the Food Fortification Programs

Objectives

Food fortification programs and food companies in low-income settings, such as in the case of Mexico, lack the ability to monitor the micronutrients added to staples entering local markets. The purpose of the present work is to validate a user-friendly sampling kit and quantify the final error parameters of a paper-based, smartphone-assisted sensor (Nu3px) for the determination of iron in corn flours within the context of Mexico's food fortification program.

Methods

Corn flour samples (n = 45) from local brands (n = 6) were collected from supermarkets, convenience stores, and directly from companies in the States of Querétaro, Cuautitlán, Saltillo, and Cuetzalan, Mexico. Iron content was analyzed using atomic emission spectroscopy (AES) and Nu3px. The final error parameters were quantified via method validation final experiments, i.e., replication and comparison of methods experiments. Qualitative categorization of samples (i.e., accept/reject batch) was applied to evaluate Nu3px's against Mexico's fortification policy (cutoff = 40 μg Fe/g flour). A user-centered design process was applied to develop and evaluate a sampling kit consisting of low-cost measuring utensils.

Results

Iron content in fortified Mexican corn flours varied widely (23–39%). Nu3px's random error was 12% (replication experiment, n = 5) and its bias was 1.79 ± 9.99 μg Fe/g flour (comparison of methods experiment, n = 45). The true mean difference between Nu3px and AES was zero (p > 0.05) and both methods had similar variance (F = 2.40; P > 0.05). AES and Nu3px classified the iron content above/below the cutoff in the same way (100% match, Χ2 = 16.41, P = 0.01). The affordable and user-friendly sampling kit added some random error, but the mean difference was equal to zero (P > 0.05). Both sampling procedures were correlated (r = 0.952, P = 0.01).

Conclusions

An affordable, user-friendly, and equipment-free sample preparation kit for corn flour samples showed similar precision to using analytical tools. The sample preparation kit along with the paper-based, smartphone-assisted assay measure iron within the performance parameters required for its application to monitor batch quality in the corn flour fortification program in Mexico.

Funding Sources

Fulbright Garcia-Robles Fellowship, 2019.

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