ESTD vs ISTD

Hello!

I wouldn't say either is inherently better.  Each has benefits and disadvantages.  We have many methods (LC and GC) that are ESTD and many that are ISTD.  

I'd say that the main issue we have had with ESTD is that injection amounts need to be reliably accurate and consistent. So cheap sloppy syringes, poor injection technique (if manual injection), partially plugged syringes, poorly maintained injectors, less than optimum split flow control can pose problems.  

For ISTD's sample preparation is critical as you need to add an exact and known amount of ISTD.  We have problems with this when people get sloppy with sample prep.  It can also be a challenge to find an appropriate ISTD.  It can't co-elute with anything in your sample, it can't react with anything in your sample, it has to be stable, it has to be compatible with your sample prep (soluble in the matrix).  It has to be detectable via the mode you use.  When I am setting a method up and I have the option of choosing the internal standard myself, I try to select one that is chemically similar the the compound(s) that I am trying to quantify.  And elutes near the compound(s) of interest.  

You can definitely use both quantification methods, but that would require a custom report or some type of add on macro to have it generate automatically.  

Hello!

I wouldn't say either is inherently better.  Each has benefits and disadvantages.  We have many methods (LC and GC) that are ESTD and many that are ISTD.  

I'd say that the main issue we have had with ESTD is that injection amounts need to be reliably accurate and consistent. So cheap sloppy syringes, poor injection technique (if manual injection), partially plugged syringes, poorly maintained injectors, less than optimum split flow control can pose problems.  

For ISTD's sample preparation is critical as you need to add an exact and known amount of ISTD.  We have problems with this when people get sloppy with sample prep.  It can also be a challenge to find an appropriate ISTD.  It can't co-elute with anything in your sample, it can't react with anything in your sample, it has to be stable, it has to be compatible with your sample prep (soluble in the matrix).  It has to be detectable via the mode you use.  When I am setting a method up and I have the option of choosing the internal standard myself, I try to select one that is chemically similar the the compound(s) that I am trying to quantify.  And elutes near the compound(s) of interest.  

You can definitely use both quantification methods, but that would require a custom report or some type of add on macro to have it generate automatically.