Preparation Of New Metal Capillary Column And Its Application In High Temperature Gas Chromatography

High temperature gas chromatography (HTGC) is a very effective and convenient way for analysis such as crude oil, triglycerides, geoporphyrin and some other high molecular weight compounds. There are some limitations to use polyimide-coated fused silica capillary column for the HTGC analysis with final temperature up to 410℃. Even the "high temperature" polyimide polymer coating when maintained at 370℃or higher temperature for any reasonable length of time, begin to degrade thermally. Mico-fissures are formed in the exposed fused silica surface and expand into cracks, leading to spontaneous breakage of the flexible capillary coil. Aluminum-clad fused silica capillary is difficult to disconnect from the oven without breakage after 24 hour' use at 400℃. The reason may be the thermal coefficient different. Stainless capillary columns can withstand very high temperature, but the deactivated process is very time-consuming and complicated, and also when the stainless capillary use a lone time, the metal active center can be exposed.Based on high-temperature gas chromatography of these problems encountered, polyimide-coating fused silica capillary columns were used as starting material, trough the process of surface treatment, sensitization, activation, electroless plating, the metal form on the surface of polyimide coating. Through the contrast experiment of electroless plating metal capillary with polyimide coating capillary column in very high temperature, we found that the electroless plating metal protect the polyimide, make the capillary column break temperature increased(the final temperature is 410℃), and prolong the lifetime of the capillary in high temperature .We also try another in situ self-metallization method. First, the polyimide coating capillary column immerse into solution of NaOH(0.4M),then make ion exchanged in solution NiCl₂(0.4M), finally the capillary surface form metal nickel by the effect of thermal reduction. The results show that the self-metallization capillary column is also thermal stable. Secondly, hydroxy -terminated methyl polysiloxane is prepared by hydrolysis of dimethyldichlorosilane in ammonia solution environment. In order to remove the lower molecular-weight materials, fractionations lead high molecular material precipitate. It is easier for high molecular polymer coat on the capillary columns.The high molecular polymer hydroxy - terminated methyl polysiloxane is coated on the electroless plating metal capillary columns by static coating method. The final overall film thickness 0.2um is obtanined ,the column was palced in oven bonding and crosslinking in very high temperature (obove 380℃). This electroless plating metal capillary column show excellent chromatography column efficency and have a good thermal stable temperature ability( withstand 410℃). At last ,we use this column to analysis liquid paraffin ,solid paraffin, ethlene cracker and crude oil. We found that the electroless metal capillary column coated with hydroxy-terminated methyl polysiloxane show very good column efficiency and have a peak shape even at very high temperature.This electroless plating metal capillary columns shows excellent performance in the field of HTGC. We use a very simple method (electroless plating, and in situ self-metallization) to make the polyimide coating fused silica capillary surface form a layer of metal nickel. The nickel layer would protect the polyimide from oxygen. So this methods improve its heat-resistant temperature, prolong its service life at high temperatures.