In the context of TOC analysis, i want to investigate whether TOC analyzer is working fine. Therefore, i intend to run TOC analysis of the same samples three times so that i can observe whether the results are more uniform or not.
Running the same compound multiple times may not always help. Try running a standard or a compound whose TOC is known.
Hi Sajid,
I agree with the answer given above.
You can calculate the theoretical TOC value of a given compound as follows. For instance, suppose that you have a 500 mg/L phenol solution. Than, your theoretical TOC is computed as follows:
Molar mass phenol = 94.11 g/mole
Carbon mass of 1 mole phenol = 6 x 12 g/mole = 72 g/mole
Fraction of carbon mass in phenol = 72 g/mole / 94,11 g/mole = 0.765
Theoretical TOC volue: 0.765 x 500 mg/L = 382.5 mg/L TOC
Following this approach, you only need to calculate the theoretical TOC of your compound of interest with the method I have illustrated above. Finally, measure the TOC of such a solution with your TOC analyzer, in order to check whether the device presents reliable results.
Regards,
Niels
Niels Wardenier & V. N. Ravi Kishore V. , Thanks for your answers. I have run standard solutions but there was a marked deviation in results. That is why, i intend to know whether i can manipulate the programmer for TOC analyzer to run same sample multiple times. In this way, i would know whether the instrument is working properly or not. Please guide me in this context.
Running the sample again will be impossible. Normally during TOC analysis, your sample is first combusted, and than, the amount of CO2 being formed, is detected by near infrared spectroscopy. Due to the combustion, running this sample again will be not possible.
Dear Niels Wardenier, let me explain it for you what i want to do. In the programmer of TOC analyzer, i want to give a command in such a way that autosampler takes the sample again and again from the same vial. For instance i will run three same samples with different names i.e. A1, A2, and A3 and instruct the analyzer to take injections from same vial i.e. No. 1.
First understand what is causing the variation.
Is the variation sample dependent or is it uniform for all samples?
Dear Ravi Kishore, i tried multiple times with same concentrations but results are variable. I guess, the error is instrument dependent.
Unfortunately, I've seen similar variability over the last few years. We use an instrument that is calibrated regularly and a system suitability performed weekly. In our cleaning standards/samples, we can run the same solution in three separate vials and get %RSD as high as 20%. It should be noted that each vial is analyzed 5 times, disregarding the first two injections. The intra-vial RSD is typically low (0.5 - 2%). I have yet to determine why the inter-vial RSD are high. Any help with this would be greatly appreciated.
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