Bland-Altman plots.

<p>Differences (Δ) of measured substance loss between various methods were plotted against the mean measured values. Hatched line and dotted lines = mean and 95% Confidence Intervals of the difference. Solid grey line = zero-line. Solid black line = ordinary least square regression line. Relative bias between methods is indicated if pΔ<0.05. The slope (R) of the linear regression line is given, and proportional bias was assumed if p<0.05.