Technical FAQ

What do Mw, Mn, Mz, Mp and Pd stand for?
From:putus.org Author:putus.org Time:1/21/2009 9:06:49 PM Count:

Mw: Weight-average molecular weight 

Mn: Number-average molecular weight

Mz: Z-average molecular weight          

Mp: Peak molecular weight

Pd: Polydispersity, Pd= Mw/Mn

OBG:Oat Beta Glucan

 

1.The comparison between Pullulan GPC standard and OBG GPC standard

 
Size exclusion chromatography (SEC) is frequently applied in industries and many labs for Mw and Mw distribution (MwD) determination because of its time and cost efficiency. Since the retention volume of SEC depends on the hydrodynamic volume rather than Mw, the use of globular coil-type standards Pulluan(P)-82, leads to a significant overestimation of Mw of many plant and fungal polysaccharides with flexible chain conformation. In this research, we developed Mw standards with linear structure and expanded chain conformation. The standard kits were characterized and compared with the performance of P-82.
 
Materials:
Lentinus edodes  (PLE ), Guar galactomannan (GG ),  CM-cellulose (CMC )
Shodex P-82, PS-OBG-Mw( From Putus Macromolecular company)
 
Methods:
GPC and laser LLS
 
Results:
Figure 1:Characterization of a General Mw Standards Kit produced by Putus, with comparison to Pullulan-82
 

Mw standards
Mw
range
SEC Profile
Mark-Houwink
Equation exponent
Chain Conformation
Pullulan-82
5.9K, 11.8K, 22.8K, 47.3K, 112K, 212K, 404K, 788K
 
 
PS-OBG-GMw
11K, 31K, 81K, 191K, 290K,  500K, 720K, 890K
 
 
 
 
 

0.56 in water     Globular coil
 
 
 

0.71 in water   Expanded flexible

 
Table 1:the Mw of the samples by GPC and LLS
Samples
Mw1
Mw2
Mw3
PLE
707k
1160k
790k
GG
122k
331k
112k
CMC
130k
354k
148k
 
Mw1 : determined by PS-OBG-GMw
Mw2:determined by Pullulan-82
Mw3: determined by LLS
 
The three polysaccharides in Table 1 were widely accepted to adopt expanded chain conformation in solution. The Mw determined by using Putus standard was demonstrated to be more accurate than by using Pullulan-82, compared to their real Mw measured by LLS. Using P-82 to determine Mw of expanded chain leads to a significant overestimation.

 

2. The comparison between Dextran GPC standard and OBG GPC standard

 

PS-OBG-30(from Putus): oat beta glucan standard ,Mw:31,000D, Pd: 1.02

GPC standard 25(from Sigma): Dextran GPC standard, Mw:25,000, Pd: 1.30

Conclusion: From this two pictures, we can find the Pd of PS-OBG-30 is  narrower  than the GPC Standard Dextran 25.