Rapid analyses of oil and fat content in agri-food products using continuous wave free precession time domain NMR † L. A. Colnago, a * R. B. V. Azeredo, b A. Marchi Netto, c F. D. Andrade d and T. Venâncio e Time-domain nuclear magnetic resonance (TD-NMR) is one of the most popular solutions for quality control in the food industry. Despite the recognized success of TD-NMR in quality control and quality assurance, the speed by which samples can be characterized by TD-NMR techniques is still a concern, primarily when considering online or high-throughput applications. Therefore, to enhance the speed of TD-NMR analysis, we developed rapid methods based on steady-state free precession of nuclear spins, which we denoted continuous wave free precession (CWFP). CWFP substantially increases the sensitivity of TD-NMR compared with free induction decay or spin-echo detection, which are traditionally used. The objective of this paper was to present the physical background of CWFP and review its recent developments and applications in fat and oil quantifications in agri-food products. Copyright © 2012 John Wiley & Sons, Ltd. Keywords: continuous wave free precession; steady-state free precession; time domain NMR; oil and fat; agri-food products; online NMR; high-throughput NMR Introduction Most of the traditional methods for food analysis are time consum- ing, destructive, and/or performed in multiple steps. Therefore, several investigators have reported the application of spectroscopic methods to complement or even replace the traditional methods used in food quality control and assurance (QC/QA). [1–6] Among all of the spectroscopic methods, time domain nuclear magnetic resonance (TD-NMR) has been the most popular solution for quality control in the industrial sector. [1–3,7,8] Time domain nuclear magnetic resonance also is known as low-field NMR or low-resolution NMR. The analyses are primarily performed on low-cost benchtop spectrometers with permanent magnets. The low intensity of the magnetic field and the lack of magnetic field homogeneity do not allow the detection of chemical shift, which eliminates the application of the Fourier transform. In general, TD quantifica- tions are based on the analysis of the amplitude (absolute or relative) of the free induction decay and/or spin-echo. Importantly, both relaxometry and diffusometry, which also are part of the TD-NMR routine experiments, are inserted as filters in a specific pulse sequence [9] or performed as an independent measurement. [10] Nuclear magnetic resonance was first used to measure oil content in an agri-food product (i.e. corn seeds) in 1963. [11] This analysis was performed with a continuous wave NMR spectrom- eter. The advent of pulsed TD-NMR instruments 40 years ago initiated efforts to develop a small bench-top NMR analyzer that was dedicated to animal and vegetable oil and fat analysis. [1] Today, TD-NMR is an off-the-shelf NMR solution that is recog- nized as a standard international method for several agencies. [12–17] Despite its recognized success in the QC/QA context, the speed by which samples can be characterized by TD-NMR techniques is still a concern, primarily when considering online or high-throughput applications. Therefore, to enhance the speed of TD-NMR analysis, several authors have been develop- ing instrumentation and applications of online NMR for analysis of agri-food products such as avocado, cherry, lemon, orange, olive, and pear. [18–22] We have been developing online NMR method for measur- ing oil/fat content and quality based on steady-state free precession (SSFP) of nuclear spins, denoted continuous wave free precession (CWFP). [23–29] Continuous wave free precession has several interesting features, including a substantially increased sensitivity [23,24] compared with detection of free induction decay FID or spin-echo, which are traditionally used in the TD-NMR context. * Correspondence to: Luiz Alberto Colnago, Embrapa Instrumentação, Rua XV de Novembro 1452, São Carlos, SP, Brazil 13560–970. E-mail: colnago@cnpdia. embrapa.br a Embrapa Instrumentação, São Carlos, São Paulo, Brazil b Instituto de Química, Universidade Federal Fluminense, Niterói, Rio de Janeiro, Brazil c Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, São Paulo, Brazil d Instituto de Química de São Carlos, Universidade de São Paulo, São Carlos, São Paulo, Brazil e Departamento de Química, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil † This article is published in Magnetic Resonance in Chemistry as a special issue on Magnetic Resonance in Food-Dealing with Complex Systems, edited by Belton and Capozzi. Magn. Reson. Chem. 2011, 49, S113–S120 Copyright © 2012 John Wiley & Sons, Ltd. Special Issue Review Received: 3 June 2011 Revised: 2 September 2011 Accepted: 21 September 2011 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/mrc.2841 S113