Figure 4.

The dependence of relative error of peak areas on peak SNR in 1D ¹³C NMR spectra. From these data, power regression was used to define an empirical relationship between relative error (RE) and SNR: RE = 0.62(SNR)^−0.66. RE was calculated as the sd of three measurements made on the same sample divided by the average peak area. Measurements were made on a sample of [U-¹³C₆]Glc with a low SNR and on a mixture of Ala, citrate, Glu, Asp, and malate at higher SNR. Errors are ±1 sd (n = 3). Inset, Line-fitting of a representative peak from a 1D ¹³C NMR spectrum. Line-fitted peaks are indicated with dashed lines. Peak annotations indicate the cumomer abundance defined by the area of the line-fitted peak; 1 corresponds to the presence of ¹³C at positions 1 to 6 in citrate (standard numbering), 0 corresponds to the presence of ¹²C, and x corresponds to either ¹³C or ¹²C.