<P> The result of this is a gel with proteins spread out on its surface . These proteins can then be detected by a variety of means, but the most commonly used stains are silver and Coomassie Brilliant Blue staining . In the former case, a silver colloid is applied to the gel . The silver binds to cysteine groups within the protein . The silver is darkened by exposure to ultra-violet light . The amount of silver can be related to the darkness, and therefore the amount of protein at a given location on the gel . This measurement can only give approximate amounts, but is adequate for most purposes . Silver staining is 100x more sensitive than Coomassie Brilliant Blue with a 40-fold range of linearity . </P> <P> Molecules other than proteins can be separated by 2D electrophoresis . In supercoiling assays, coiled DNA is separated in the first dimension and denatured by a DNA intercalator (such as ethidium bromide or the less carcinogenic chloroquine) in the second . This is comparable to the combination of native PAGE / SDS - PAGE in protein separation . </P> <P> A common technique is to use an Immobilized pH gradient (IPG) in the first dimension . This technique is referred to as IPG - DALT . The sample is first separated onto IPG gel (which is commercially available) then the gel is cut into slices for each sample which is then equilibrated in SDS - mercaptoethanol and applied to an SDS - PAGE gel for resolution in the second dimension . Typically IPG - DALT is not used for quantification of proteins due to the loss of low molecular weight components during the transfer to the SDS - PAGE gel . </P> <P> See Isoelectric focusing </P>

1. on what basis is electrophoresis able to separate molecules