The ERETIC method (Electronic REference To access In vivo Concentrations) provides a reference signal, synthesized by an electronic device, which can be used for the determination of absolute concentrations. The results presented here demonstrate the accuracy and precision of the method in the case of (1)H high resolution NMR. Five tubes were filled with D(2)O solutions of trimethylamine hydrochloride (TMA) 3.84 mM and sodium lactate at concentrations ranging from 5.25 to 54.11 mM. Results obtained with the ERETIC method were compared to those obtained by using TMA as an internal reference. The standard deviations were the same for the two methods and always lower than 1% of the mean. The accuracy (difference between true value and measured value) was slightly better for the ERETIC method than for the internal reference. No significant variation was observed when the experiments were performed over 56 h. Measurements were repeated once a month during three months. As the values obtained showed a standard deviation of only 3%, we can conclude that the ERETIC method has a good stability and only requires monthly calibration. Furthermore, it must be noted that nothing is added to the sample and that the reference signal frequency can be freely chosen to fall within a transparent region of the spectrum.

A new method for absolute quantitation of MRS spectra is presented. This method is not based on a reference peak, derived from a real NMR signal, but rather on a synthesized NMR reference produced by an electronic device, transmitted by a broad-band antenna to avoid quality factor variations. This signal is therefore received at the same time as the sample signal. The reference line produced is stable in time (maximum variation lower than 2%) and allows precise and accurate measurement of absolute concentrations (mean error lower than 3%) in vitro and in vivo.