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Dear All:

I am having difficulty in understanding the principle for preparation of standards.

My objective is to develop a calibration curve for ethanol using n-propanol as the internal standard. My range of concentrations for ethanol will be from 80% to 100%.

I usually prepare individual mass fractions of ethanol (i.e., 8g ethanol and 2g of water) and then from this solution I take 1g and add 0.1g of water to dilute it. I use a 4 place analytical balance and weigh accurately the mass. I use a small vial for making the sample prep.

My question is what should be the weight of n-propanol that I should add in each of the varying concentrations of ethanol (i.e, 80,90,95 and100)? Should the weight of n-propanol vary or should it be constant?What should be the concentration of n-propanol that I should add to these ethanol solutions?

I am using a HP 5890 series II with FID and HP-5 column.

Please provide some guidance at the earliest. Thanks in advance.

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You have only to know what concentration of internal standard is. It does not matter constant it or not. To simplify calculations use constant concentration.

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I run a EtOH method where I use propanol as the ISTD (1N)or (0.031 mL per Liter). You should use a different column. There are columns made for EtOH testing (ALC-1). When making the STDs you should use volume and calulate the wieght of the volume. I think EtOH has a denisty of 0.78 g/mL. The same amount of ISTD should be added to each STD.

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Hello:

Thanks for the tip. Can you please tell me how you are preparing the ethanol standards? If u can provide information in detail on this regard it would clear many confusions I have related to this issue.

Thank you

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For 100 ml solution at 80 % weight/volume: use 80 g of alcohol, 1 ml ISTD and the rest of water. Try a run if you can see the ISTD (propanol), if not increase the amount of ISTD. I dont remember exactly but i belive if you mix ethanol and water that give volumic contraction, verify this.