小中大
电压升不上去有好几种原因，通过我自己的经验和资料搜索，我认为有以下几点可能：
1. 有些样本就算用了clear-up kit，除盐效果也不是100%，比如细胞样本如果在收获是用PBS这种含150mM NaCl的PBS洗，做western没关系，但在2-D上就有干扰，所以有些protocol中建议把NaCl换成250mM的sucrose。Kit的操作也很关键，比如起始量不要过多等等。
2. GE手册P70原文：Voltage limit not reached: The ionic strength of the rehydration solution is too high; reduce the IPG buffer concentration; use a mixed-bed ion-exchange resin to remove ionic breakdown products of urea or other additives. Desalt the sample or prepare the sample so that the salt concentration is less than 10 mM.
3. GE手册p71原文：Voltage too low or does not reach maximum set value: Prepare the sample to yield a salt concentration less than 10 mM. The recommended IPG Buffer concentration is 0.5%. A maximum of 2% is advisable only if sample solubility is a problem. High conductivity can also arise from the use of poor quality urea or other denaturants. Urea is also prone to decomposing to charged breakdown products. Higher conductivity salts and ionic impurities in the sample can raise the conductivity of the strip.
Shorter length IPG strips (e.g. 7 cm strips) will not reach 8000 V. The distance between the electrodes is shorter so that the voltage gradient (V/cm) required to reach the 50 μA current limit is reached at a lower overall voltage.
