GC calibration for acetaldehyde

[chuchu sun]

I am new to use GC, please help me with GC calibration and please bear with me for asking so many basic questions Thanks a lot

I want to use GC to measure the concentration of Acetaldehyde in drinks. the GC I use is agilent 6890 Series associated with FID

Previous report I found from library indicates that the result is analyzed using integrator

The manual I got saying acetaldehyde is calculated using 100% acetaldehyde, I don't think I can purchase so high purity acetaldehyde (if I am wrong, please recommend a supplier if you know one).
my question is:
what other external standard I can use? if a known percentage of acetaldehyde can be used, what is the difference between this and the 100% acetaldehyde? do I need make any changes or every procedure is the same?


Please let me know if I did not provide enough detail

Thanks you all for your help and time

[rb6banjo]

You will likely not find acetaldehyde at 100% purity. I don't know of any chemical that is available at 100% purity. Acetaldehyde is difficult to handle because it has such a low boiling point. When I use it, I generally add it by mass and I put some of my solvent in the volumetric flask and then tare the mass of the flask+solvent on the balance. Example:

Add 10 mL of methanol to a 25 mL volumetric flask.
Tare the mass of the flask and the solvent on the balance.
Add a number of drops of acetaldehyde to the solvent in the flask (let's say it results in 0.2485 g increase in mass).
Fill the flask to the mark with more methanol.

The concentration of AA in the methanol is: 0.2485 x 10^6/25 mL = 9,940 µg/mL (ppmv)

AA is very water soluble so you can prepare standards in water as well.

In a beverage (beer maybe), AA might be present at 1-2 µg/mL. So, to spike it into 10 mL of beer, I might add 5 µL of that solution:

9,940*0.005/10 = 4.97 µg/mL (added)

If the AA was only 98% pure:

9,940*0.98*0.005/10 = 4.87 µg/mL

After a very large dilution, the actual concentration is not affected by the purity a great deal. Obviously, it can't be grossly impure. If your reagent is reasonably pure, don't get too lost in that. In the end, you'll be within your ability to measure the analyte in your sample.

[AICMM]

chuchu sun,

Chem Service offers Acetaldehyde as both a neat and as a solution. rb6banjo is correct, very hard to handle (and nasty) so if you are dealing with the neat chilling syringes and what not is a good idea.

Best regards,

AICMM

[GC3]

chuchu sun,

Normally Acetaldehyde is analyzed in the gas phase of beverage grade CO2. CO2 is used to carbonate beverages. However, if it is to be analyzed in an aqueous fluid, the aqueous fluid cannot contain salts or sugars for direct injection onto the GC. There are some other special sampling techniques for organics in aqueous fluid, but they are more complex.

Jed

[MSCHemist]

I did it in citrus juices with HS-SPME. Acetaldehyde as mentioned is very volatile so it is necessary to chill both the container and gas tight syringe and add it to a volumetric flask with solvent in it. It also is prone to oxidation to paraaldehyde (trimer) and acetic acid.