差别分析(Differential analysis)
表达增高的点（Up-regulated spots）
表达降低的点（Down-regulated spots）
只在样品或对照品中出现的特异性点
差别分析示意图
表达上调
表达下调的点(right)
2DE常见问题及解决办法(Troubleshooting)
Too much salt in the sample (disturbs IEF)
Hint:
Include an acetone precipitation to remove salts and other contaminants
Charged impurities in the sample
Hint:
Include an acetone precipitation to remove salts and other contaminants
Impurities in the sample or rehydration solution
Hint:
Include an acetone precipitation to remove salts and other contaminants
Prepare new rehydration solution with pure reagents
underfocused (Focusing time not long enough)
Hint:
Prolong the focusing time of the IEF
Gel surface during polymerization not overlaid with destilled water (or too low amount of water used)
Hint:
Apply at least 1 ml to overlay the gel surface
No uniform gel polymerization (e.g. impurities at gel cassettes, air bubbles in the polymerized gel)
Hint:
Clean gel cassettes with ethanol
Cast the slab gel slowly (approx. 1 min)
Overlay the gel carefully with destilled water 
Not all proteins (especially high molecular mass proteins) saturated with SDS
Hint:
Use 0.15 % instead of 0.1 % (w/ v) SDS in the 1 x SDS buffer for SDS-PAGE
High sample load (protein disturbs separation of other spots or may not be fully saturated with SDS)
Hint:
Lower the protein amount
Impurities on or within the 2-D gel still present during silver staining
Hint:
Clean the gel cassettes prior casting with ethanol
Incubate the 2-D gels long enough (and with at least 100 ml/ gel) in fixing and washing solution prior staining
