Dilution factor

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

3 posts Page 1 of 1
Hello all,
I have some confusion in sample preparation and calculation. I am asking question giving two situations

situation 1: During Benzoic acid analysis of juice, 5 ml of juice sample is taken in 25 ml vf and volume is made up to the mark with buffer. Aliquot of the final solution is injected into hplc system. Suppose 8 ppm benzoic acid is obtained from hplc in sample aliquot. Then the benzoic acid in the juice is calculated as
=8*25/5
=40 mg/L
situation 2: During Benzoic acid analysis of tomato sauce(which is semi solid material), 5 g of sauce sample is taken in centrifuge tube and 25 ml buffer is added into 5 g sauce. Aliquot of the final solution is injected into hplc system. Suppose 6 ppm benzoic acid is obtained from hplc in sample aliquot. Then the benzoic acid in the sauce is calculated as
=6*25/5
=40 mg/kg
My question is, what is correct calculation for situation 2, where sample is not completely dissolved in buffer? What is the correct dilution factor in calculation for situation 2?
is it 6*25/5
or 6*(25+5)/5
or 6*{25+(5-Moisture content of 5 g sample)}/5
Or we have to use weight of total solution/ weight of sample as dilution factor?
what is the accurate way of calculation for analysing those semi solid samples which are not completely dissolved in buffer?
thanks in advance
Suraz wrote:
Hello all,
I have some confusion in sample preparation and calculation. I am asking question giving two situations

situation 1: During Benzoic acid analysis of juice, 5 ml of juice sample is taken in 25 ml vf and volume is made up to the mark with buffer. Aliquot of the final solution is injected into hplc system. Suppose 8 ppm benzoic acid is obtained from hplc in sample aliquot. Then the benzoic acid in the juice is calculated as
=8*25/5
=40 mg/L
situation 2: During Benzoic acid analysis of tomato sauce(which is semi solid material), 5 g of sauce sample is taken in centrifuge tube and 25 ml buffer is added into 5 g sauce. Aliquot of the final solution is injected into hplc system. Suppose 6 ppm benzoic acid is obtained from hplc in sample aliquot. Then the benzoic acid in the sauce is calculated as
=6*25/5
=40 mg/kg
My question is, what is correct calculation for situation 2, where sample is not completely dissolved in buffer? What is the correct dilution factor in calculation for situation 2?
is it 6*25/5
or 6*(25+5)/5
or 6*{25+(5-Moisture content of 5 g sample)}/5
Or we have to use weight of total solution/ weight of sample as dilution factor?
what is the accurate way of calculation for analysing those semi solid samples which are not completely dissolved in buffer?
thanks in advance


You want the final result in mg/kg so you take the 5g and add 25ml buffer and assume the sample is not soluble in the buffer, but the benzoic acid is.

Now you have a result from the instrument as 6ppm benzoic acid which is 6 mg/L

You have 25ml of buffer so you have 6mg/L in 0.025L = 0.15mg in the solution.

This means you had 0.15mg in the 5g of sauce which would be 0.03mg/g or 30mg/kg benzoic acid in the sauce. If the sauce was 50% water, then you can correct the concentration for the water as (30mg/kg)/0.5 = 60mg/kg dry weight. So you have a result of 30mg/kg wet weight or 60mg/kg dry weight.

If you add 25ml of buffer at above assuming 1 as density you would have 30ppm w/w for the initial answer, if you bring it to 25ml total volume you would have 30ppm w/v. If you used a graduated cylinder to measure out 5ml of sauce then bring to total of 25ml you have 30ppm v/v.

Mixed units for semi soluble samples are always a little confusing, so I normally like to use the dry weight to correct for the moisture in the sample.

Another alternative is to weigh 5g of wet sauce, then dry at room temperature over night then do the normal solid/liquid extraction by adding 25ml of buffer, that gives you the most accurate result per wet weight and you don't have to do any extra calculations.
The past is there to guide us into the future, not to dwell in.
Thank you for very good reply
3 posts Page 1 of 1

Who is online

In total there is 1 user online :: 0 registered, 0 hidden and 1 guest (based on users active over the past 5 minutes)
Most users ever online was 1117 on Mon Jan 31, 2022 2:50 pm

Users browsing this forum: No registered users and 1 guest

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food & Beverage, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry