here you can useful sites for the answers:

http://www.chromatographyonline.com/precision-internal-standard-and-external-standard-methods-high-performance-liquid-chromatography

http://www.lcresources.com/discus/messages/5134/1469.html?ThursdayJune2120010907am

https://www.quora.com/What-is-the-difference-between-internal-and-external-standard-calibration

will wait your respone,

kind reagrds

Still waiting your participation.

Regards

may be the question is not visible to all

May this could help 

Internal standard versus external standard calibration: 

https://www.google.it/url?sa=t&source=web&rct=j&url=http://www.scielo.br/scielo.php%3Fscript%3Dsci_arttext%26pid%3DS0100-40422010000400041&ved=0ahUKEwjNpsndicjTAhVCPxoKHfLkA9YQFghNMAs&usg=AFQjCNFM-uH83AxrtWCMBWWy_OLSyiHNZw&sig2=WvkIPp_o_WW2f_OPHyHXrQ

Regards

lets start again:

www.scielo.br/pdf/qn/v33n4/41.pdf

regards

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regards