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.
By Anonymous on Friday, June 11, 2004 - 08:16 am:
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.
By Anonymous on Saturday, June 19, 2004 - 04:48 pm:
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.
By Anonymous on Monday, June 21, 2004 - 03:53 pm:
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.
By Anonymous on Tuesday, June 22, 2004 - 01:38 pm:
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.