Means and method for controlling eluent gradient in liquid chromatography

Apparatus for controllably varying the apportionment gradient between two eluents flowing into the column of a liquid chromatograph comprising:

• a first function generator for generating a substantially linear, monotonically varying pilot signal y arising between predetermined limits;
• means for varying the slope of said pilot signal whereby said pilot signal may be caused to arise between said limits in a lesser or greater time period;
• a second function generator coupled to said first function generator for receiving said pilot signal y and outputting a signal A in response thereto, said signal A having upper and lower limits and characterized by the expression
• A = x .multidot. G(y)
• where G is an operator such that G(y) is a monotonic non-linear function and x is a predetermined constant value, said second function generator comprising means for selectively varying the value of x to thereby vary the difference between the upper and lower limits of signal A;
• and
• eluent apportioning means coupled to said function generator and responsive to said outputted signal A for varying the proportion of two eluents.

A control system for effecting a non-linear gradient between two eluents in a liquid chromatograph and for selectively expanding and contracting the range of the gradient without varying the shape thereof, comprising:

• a clock stage for producing clock pulses;
• means for adjustably varying the rate of said clock pulses;
• a counter receiving said clock pulses and producing a digital output signal in response thereto;
• a digital-to-analog converter for converting said digital signal into an analog pilot signal y extending between predetermined limits;
• means for producing a first signal representing a desired initial eluent ratio;
• means for producing a second signal representing a desired final eluent ratio;
• first summing means for receiving said first and said second signals and outputting a range signal x representative of the difference therebetween;
• a function generator responsive to said pilot signal y and said range signal x to output gradient signal A where
• A = x .multidot. y.sup.m
• said function generator including means for varying the effective value of m;
• and
• means for combining said gradient signal A with said first signal.

A system for controlling the gradient between two eluents in a liquid chromatograph, comprising:

• function generator means for producing a first, non-linear signal over a given range during a first, run period;
• control means responsive to said signal for determining the instantaneous ratio of the eluents;
• and
• means for causing said function generator means to produce a second non-linear signal over said given range during a second, reset period which is shorter than said run period.

A method for controlling the ratio between two eluents in a chromatograph system, comprising:

• developing a periodic, digital signal which arises at a determinable rate;
• converting said digial signal to a substantially linearly-increasing analog signal y which extends between fixed limits;
• operating upon said substantially linearly-increasing signal y with an operator G to produce a non-linear signal G(y);
• developing a range signal x representing a desired gradient range;
• multiplying said non-linear signal by said range signal to produce a gradient signal A;
• and
• varying the ratio between the two eluents from an initial to a final concentration in response to the instantaneous value of gradient signal A.