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Fig. 1. (a) Calibration line for F. Glasses with different Fe contents were used from ~0.4 to ~14 wt% (Table 1). There is an almost linear correlation (R2 = 0.9962) with increasing Fe content. The 95.45% confidence line indicates that the error (2 SD) on the F content because of Fe is relatively small (±40 μg/g) up to ~9 wt% and increases (±80 μg/g) at higher concentrations. (b) Calibration line for Br that quantifies the effect of Al in the analysis signal. Our glasses have an Al2O3 content ranging from ~1 to ~18 wt% (Table 1). The excess Br signal we get from Al also shows a linear relation (R2 = 0.9891) with an increasing amount of Al inside the samples. Based on the 95.45% confidence lines, the error (2 SD) at the excess Br for Al concentrations higher than 12 wt% is ±20 μg/g, while it increases significantly at concentrations less than 2 wt%, probably due to the absence of glasses with very low Al contents. (c) Calibration line for I shows the effect of Ca-interference on the I measurements. The Ca compositional range of our glasses is from 0.4 to ~14 wt% (Table 1). The correlation between the glasses with different Ca contents and the excess I in the signal of the analysis has a linear correlation (R2 = 0.9958). The 95% confidence lines show that the error (2 SD) at the excess I for Ca concentrations from ~5 to ~14 wt% is ±20 μg/g, while it increases at low concentrations (<2 wt%) at 40 μg/g.