Investigation of retention mechanisms in HILIC chromatography ...
Investigation of retention mechanisms in HILIC chromatography ...
Investigation of retention mechanisms in HILIC chromatography ...
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pH Effect <strong>of</strong> Acetonitrile on pH <strong>of</strong> Ammonium Acetate [4]<br />
A Note on Buffer pH<br />
s<br />
pH w<br />
pH Measured Follow<strong>in</strong>g Addition <strong>of</strong> Organic<br />
12<br />
11<br />
10<br />
9<br />
8<br />
7<br />
6<br />
5<br />
4<br />
3<br />
pKa<br />
2<br />
2 4 6 8 10 12<br />
pH Measured Prior to Addition <strong>of</strong> Organic<br />
w<br />
pH<br />
w<br />
Measurements were taken at 25ºC.<br />
Triangle: 90.0% ACN,<br />
Square: 75% ACN,<br />
Diamond: 50% ACN,<br />
Circle: 32.5% ACN<br />
• Analyte pK a values have also been shown to be impacted by the<br />
presence <strong>of</strong> organic modifiers<br />
• Figure 2 shows the results <strong>of</strong> an NMR experiment conducted that<br />
explored the chemical shift <strong>of</strong> a proton near the ionizable group for<br />
amitriptyl<strong>in</strong>e <strong>in</strong> 90% acetonitrile. From data such as this, effective pK a<br />
values can be established for a variety <strong>of</strong> compounds.<br />
• Table 1 shows the results for several basic pharmaceutical compounds.<br />
The data <strong>in</strong>dicates that the effective pK a value for a basic analyte <strong>in</strong> 90%<br />
acetonitrile is approximately 1 pK a unit less than the aqueous-based<br />
value<br />
24/10/2012<br />
4