gradient mixing

[jusuom]

Does anyone remember historical facts (or have suitable material) on gradient mixing in LC? - When first introduced (low-pressure vs. high-pressure mixing), when started to be in common use, etc.

Thank you!

[Andy Alpert]

Gradient mixing was in use by the early 1970's, although isocratic applications were still common in the chromatography literature until around 1980. All of the mixing I encountered from 1974-79 was high pressure. In 1979, Varian introduced its first HPLC system (I believe it was the 5000 model), which featured low-pressure mixing via solenoid valves. I don't recall any low-pressure mixing before that. If you want specific references, I recommend that you go to an academic library and look through issues of Journal of Chromatography from the 1970's.

[MaryCarson]

Gradients were used in chromatography back when chemists and biochemists poured slurry into glass tubes to make their own columns--much earlier than the 1970s, I would think. Two bottles with mobile phase A and mobile phase B, connected by tubing and with a stirbar in A can make a reasonably reproducible gradient using nothing more than gravity feed.

I, of course, am much too young to have ever done such a thing myself

[Johnny Rod]

What's the advantage of high-pressure mixing over low pressure?

[Andy Alpert]

Lower system volume between the point of mixing and the top of the column.

[jusuom]

Any additional information/memories from the people working with HPLC during 70's and 80's?

Additional question, what is your opinion on the most important innovations in the area of HPLC instruments/packing materials/particles during the 80's ant 90's?

[mirac_han]

low pressure mixing give good result than high pressure because low gradient delay.
ı have been reading a book about chromatography; said the first chromatography detector is human eye. ıt ıs the origin of the hplc adventure.

[Andy Alpert]

I'm afraid I disagree. With low pressure mixing, the blended solvents have to travel through the pumphead, pulse dampener, pressure transducer, etc. and all the connecting tubing in between before reaching the injector valve and the column. That introduces some delay compared with high-pressure mixing, where the solvents are blended just upstream from the injector valve.

HPLC instrumentation: The innovation in the 1990's that stands out for me is the introduction of computerized data acquisition programs that worked well and were reasonably easy to use. They displaced integrators and strip chart recorders. This was made possible by the increase in performance and decrease in price of personal computers.

[Johnny Rod]

I'm with Andy on the advent of data systems, it's so much easier to reprocess, check integration, look for small peaks, carry out calculations like tailing factor etc. We still have some integrators... where are my scissors?

[Csaba]

...--much earlier than the 1970s

As poined out, these techniques were used already in the 40:ths at least by biochemists. I did preparative salt gradient chromatographic labs in my first biochemistry course at the university 1976. On-line detectors were to expensive, so we collected eluent in tubes and measured manually the absorbance in each tube, and then measured the bioactivity of enzymes in some of the tubes.