Chromatography Forum

Have somebody tried to detec lactose by HPLC-MS/MS or HPLC-DAD? I am trying to detect lactose in milk with LOD below 0.03 %.

If I'm interpreting this correctly, 0.03% (w/v) would be equal to 0.3 mg/mL = 0.3 micrograms/microliter. Assuming a typical injection volume of, say 10 microliters, that would be 3 micrograms on-column per injection. That should be well within the working range of something like RI detection. Barring issues with interferences, why would you need to use LC-MS/MS?

This is easily achievable on standard LC equipment with ELSD detection.

http://www.waters.com/waters/library.ht ... d=10179824

Download the applications book and it's application WA64095

Thanks a lot,
I will let you know how it goes!

Can anybody share the mass spectrum of lactose by lc ms/ms?
I am working on lactulose by lc/ms/ms. Lactulose have M.W. 342. For Posivtive ESI, I could not find the M+1 ion, 343. I found m/z 360. Can anybody help to explain this?

Thanks

Jen

Can anybody share the mass spectrum of lactose by lc ms/ms?
I am working on lactulose by lc/ms/ms. Lactulose have M.W. 342. For Posivtive ESI, I could not find the M+1 ion, 343. I found m/z 360. Can anybody help to explain this?

Thanks

Jen

looks like ammonium adduct, [M+NH4]+. what is your eluent composition?

Hola Carol.
You can analyze lactose by LC MS; but sometime this could be too much?? depending of what your requirements are. lactose can be analyzed by simple UV/Vis spectrofotometry with an enzynatic method; faster and easier but maybe not too much precise.
Other way is use Elechtrochemical detector.

Can anybody share the mass spectrum of lactose by lc ms/ms?
I am working on lactulose by lc/ms/ms. Lactulose have M.W. 342. For Posivtive ESI, I could not find the M+1 ion, 343. I found m/z 360. Can anybody help to explain this?

Thanks

Jen

Jen,
look at the following for ESI -ive MS/MS
683.22 [2M-H], 341.11 [M-H], 281.09, 179.05, 161.05, 101.02
when I use the CID energy 15 eV, the following ratio was obtained
683.22 [2M-H], 31%
341.11 [M-H], 100%
281.09, 6%
179.05, 15%
161.05, 30%
101.02, 1%
you can get another ion with High energy, such as 221, 143 and 119
(Lactose C12H22O11 MW= 342.115663, [M-H] = 341.107838, [2M-H] = 683.224049)

This is obtained from my system only, I'm not sure it same as others.

Jetjamnong

Hi Jetjamnong
You are using the ESI negavitve ion, I am using ESI posivtive ion. Is there any advantage of Negative ion over Positive ion in this application?

Thanks

Zhen

Jen,

Most people do quantitation of sugars in negative mode where you are generating the M-1 ion.
Some people try to generate positive adducts and quantitate that but quantitation of an adduct
can be unreliable. As others have pointed out there are more linear and easier to use detectors
for sugars such as RI and ELSD.

Hi Jetjamnong

Thanks for the information, I will try the negative mode.
Zhen