Column degradation

Preparing a Volatile Sample Gas chromatography can be used to separate analytes in complex matrices. Not every sample that can potentially be analyzed by GG, however, can be injected directly into the instrument. To move through the column, the sample s constituents must be volatile. Solutes of low volatility may be retained by the column and continue to elute during the analysis of subsequent samples. Nonvolatile solutes condense on the column, degrading the column s performance. 

TBT exists in solution as a large univalent cation and forms a neutral complex with CH or OH . It is extremely surface active and so is readily adsorbed onto suspended particulate material. Such adsorption and deposition to the sediments limits its lifetime in the water column. Degradation, via photochemical reactions... 

Elevated temperatures may be used with SynChropak GPC or CATSEC supports if necessary for solubilization, speed, or reduction of band spreading. Such conditions are not recommended for routine analyses, however, because column degradation is enhanced as temperatures are raised. 

Figure 6.3 Nonspecific protein adsorption as a result of column degradation. White circles indicate eluted column peak heights of a new column. Black diamonds indicate eluted peak heights after the column was treated with 50 wash cycles. See text for discussion. (Data from P. Gagnon, 1997, Validated Biosystems Quarterly Resource Guide for Downstream Processing, 2(1), 1, http //www.validated.com/revalbio/library.html.)...

From Table V it is an Inescapable fact that a small pore enhances the degradation. For PS the 7-column set had no 10 pore-size column, and yet the whole extra battery of 6 higher pore-size columns degraded PS less than the one low pore-size column. The PI results are similarly Illustrative. When just one low... 

The /3-diketonates are usually thermally stable and may be fused or volatilized with little or no decomposition. These complexes were tested by gas-liquid chromatography without evidence for on-column degradation.252 However, some retention of fluorodiketonato complexes was due to reaction in the stationary phase or with active sites.253 The sublimation enthalpy of tris(trifluoroacetylacetonate)vanadium(III) is 118 2kJmol-1 and the evaporation enthalpy is 77.8 0.8 kJ mol-1.254 At 300-470°C there is decomposition of [V(acac)3] acetone, CO and CO2 are the products.255... 

For quantitation, a minimum resolution (Figure 23-10) of 1.5 between the two closest peaks is desired so that neighboring peaks are separated. For ruggedness, a resolution of 2 is even better. That way, resolution is still adequate if small changes in conditions or slow deterioration of the column degrades the resolution. 

Tailing peaks Column degradation Evaluate column using standards... 

JL Glajch, JJ Kirkland, J Kohler. Effect of column degradation on the reversed-phase high-performance liquid-chromatographic separation of peptides and proteins. J Chromatogr 384 81-90, 1987. 

Column degradation can be caused by too low pH or too high temperature. Columns should be operated in a pH range of 2.5-7.5 at ambient temperature. 

We have already discussed the use of a saturation column between the pump and injector to protect the main column against column degradation caused by high pH buffers. Another function of this column is to provide filters (the column inlet and the outlet frits) before the injector. I have seen unusual pumps that flaked Teflon off the pump seal this ended up plugging the injector. An in-line filter would have prevented the problem, which required tearing down the injector to remove the plugging. 

Silica is the most widely used support. In LSC and SEC it is used by itself in LLC it is coated with a liquid phase, and in BPC and IEC its surface is reacted with a modifier to give it special surface characteristics. Above a pH of about 8 it is sufficiently soluble in aqueous solutions that significant column degradation results with extended usage, thus limiting its use to the lower pHs. 

The column temperature was also an important factor to successfully join IPC with atomic absorption spectrometry in the online speciation of Cr(HI) and Cr(VI) [37], Some concerns for high temperature methods include column stability [38] and potential on-column degradation of analytes [39]. 

---