Concentration of the Analyte:
As per Beer and Lambert's law, the plot of absorbance versus the concentration of absorbing substance should be a directly line while ε and b are constant. The path length could always be held constant but there are a few factors that affect ε and it is found which at high concentration, ε is not constant. Thus, at higher concentrations (>10-3 mol dm3) there might be deviation from the law.
Temperature
The temperature is not considered as a significant factor since ordinarily the measurements are made at a constant temperature. Therefore, changes in temperature sometimes might shift ionic equilibrium and the absorptivity. For instance, the colour of acidic ferric chloride solution changes from yellow to reddish brown on heating because of change in λmax and absorptivity.