precision problem

[sreenivas]

hi sir,

iam facing problem with GC calibration.

The details are
Gas chromatograph; Make : Shimadzu; Model GC-2010
Standard ; 1250ppm of biphenyl in n-heptane, 5 injections in single vial
Capillary column; BP-1 30m,0.53mmID,1µm
Injection Volume;2µl
Column oven Temp; 130°C
Injector Temp; 250°C
Detector Temp;250°C
Split Ratio;1:1
Viscosity delay time ;0.2sec
Column flow;10 ml/min
total flow; 23 ml/min

And finally we get the %RSD is 3.9 against 2.0%.

please find What problem going with these parameters.

Thanking you sir
Sreenivas.B
Divi's laboratories ltd
Vizag
Mail;bobburi496@gmail.com

[Peter Apps]

A split ratio of 1:1 combines all the disadvantages of splitless and split injections. Either go for splitless with a splitless tiem of about 30 s and a purgefl owo f 30 ml/min, or go with a split injection - your concentration is plenty high enough to use split. Also a 2 ul injection gives a bigger vapour cloud than 1 ul, which can also cause problems. If you need splitless or a 1:1 split and a 2 ul injection to get big enough peaks than you probably have a problem with the detector.

Peter

[MSCHemist]

I'm not sure about Shimadzu but Agilent instruments cannot generate a <5:1 split reliably due to the extremely low gas flow to the inlet. That is likely the source of your problems. I agree with Peter, Go splitless with a low injection volume and short splitless time or go at least 5:1 split with a larger volume. I tried a pulsed split when doing headspace with a 3:1 split and was getting RSD's near 20% due to that issue so I went 5:1.

[Bigbear]

I agree with the above statements, and will add, you should consider reducing your injection volume. In our Agilent instruments the largest inlet liner can contain only 990ul of vapor.