Calibration

[punt]

Hi,

In doing calibration for GC, if the area is fluncating between a range of 900 to 1100, is it best to use the median which is 1000 for our calibration?
so that our standard conc. will be able to fluncated between 10 %.
because when i have calibrate at near area 900,, my verification standard has always been higher than the real value.
nyone has any experience?

Thank you

[AICMM]

punt,

Rather than calibrate with such a large swing in area it would be better to figure out why the large swing in area. More information on the application and there are plenty of people that will try to help reduce the swing in areas.

Best regards.

[aldehyde]

What type of sample? What type of inlet, detector, column? What are your flow rates, temperature programs, and what gases are you using?

[punt]

Hi,

I am analysis H2S in calibration gas, split/splitless inlet, HP-1 capillary column, helium as carrier, SCD detector, 2.5ml/min for carrier flow.
Could it be due to the nature of the compound I am analysing that cause the big flunctation in the area count. The area is stable in the same day, but fluncating a bigger range on different days. Usually wat is the frequency for GC re-calibration?

Thank you

[AICMM]

punt,

By implication, you are shooting H2S by syringe since you discuss splitless/split inlet? That is highly likely to be the source of your variance although H2S is a difficult component to measure.

Do you have a gas sampling valve available?

Best regards.

[punt]

Hi,

The H2S was not injected using a syringe, it is injected thru a gas sampling valve passing thru a split and splitless liner. Can loss occur at the inlet?

Thank you

[Don_Hilton]

back pressure through the sampling valve can change the quantity of gas present (PV=nRT). So do you have a way to ensure the pressure at the gas sampling valve is the same each time when you sample?

[Palki]

Hi Punt,
we have the same problem, H2S have the fluctuation in area on SCD....
for example COS have reproducible area counts...and also other higher organosulfuric compounds...

We inject H2S containing calibration gases through 100°C vapourizer and
1mL loop. First two-three injections are different...but then it is OK...

I mean fluctuation of H2S area is due to the compound nature....

Peter

[punt]

Hi Palki,

are you refering to repeated injection or injection on different days?
The problem i encounter are non-repeatable results on different days.
But continous injection on the same day and same time, the area is quite consistent.

Thank you