Term
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Definition
| The analytical process in which analytes are seperated from one another on a column, owing to differences in time that they are retained on the column. |
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Term
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Definition
| a liquid or gas that carries analytes through a liquid or solid staitionary phase |
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Term
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Definition
| a solid or an immobilized liquid on which analyte species are partitioned during passage of a mobile phase |
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Term
| Define distribution constant |
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Definition
| the equilibrium constant for the distribution of an analyte in two immisible solvent, which is approx equal to the ratio of the equilibrium molar concentration |
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Term
| What is the eq for the distribution constant? |
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Definition
| Kc= (aA)stationary/(aA)moble |
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Term
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Definition
| the time between sample injection on a chromatographic column and the arrival of an analyte peak at the detector. |
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Term
| Write the equation for retention time |
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Definition
tr= ts+tm
ts=time in stationary phase
tm=time in mobile phase |
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Term
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Definition
| used to compare the migration rates of solutes in columns |
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Term
| Write the eq for retention factor |
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Definition
K=(tr-tm)/tm
tr=retention time
tm=void time |
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Term
| Define selectivity factor |
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Definition
| the ratio of retention factors of two species. |
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Term
| Write the equation for selectivity factor |
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Definition
alpha=Ka/Kb or
alpha= ((trb)-tm)/((tra)-tm) |
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Term
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Definition
| Describes the efficiency of a chromatographic column. Efficiency in terms of variance per unit length |
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Term
| Write the equation for plate height |
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Definition
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Term
| Define longitudinal Diffussion |
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Definition
| a process in which species migrate from a more concentrate part of the medium to a more dilute region. (Common source of band broadening) |
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Term
| Write the equation for longitudinal diffusion. |
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Definition
B= 2γ*Dm
γ= constant that depends on quality of packing
Dm= diffusion coefficient of mobile phase |
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Term
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Definition
| A diffusion of solutes that contributes to chromatographic band broadening, it is the result of differences in pathways of solutes as they transverse a column |
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Term
| Write the equation for eddy currents |
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Definition
A= 2 lambda*dp
lambda=constant that depends on quality of packing
dp=diameter of packing particles |
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Term
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Definition
| Measures the capability of a column to seperate to analyte bands. |
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Term
| Write the equation for column resolution |
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Definition
Rs=(2[(tr)b-(tr)a])/(Wa+Wb)
(tr)a and (tr)b are retention times
Wa and Wb are peak widths |
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Term
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Definition
| A mobile phase in chromatography that is used to carry solutes through a stationary phase |
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Term
| Describe the elution problem |
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Definition
| Problem found when different distribution constants for solutes are separated by chromotography. When conditions are optimized for late eluting peaks then good results are not obtained for early peaks and vice versa. Problem is fixed by using gradient elution in LC and temp programming in GC |
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Term
| List the 7 variables that lead to zone broadening in chromatography |
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Definition
1)High viscosity in LC
2) Slow injection of sample onto packed column
3) Increased diameter of the particles for column packing
4) Dense layers of liquid stationary phase
5) Large diameter of the column
6) High or slow flow rates of mobile phase
7) High temp in GC |
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Term
| Define gas-liquid chromatography |
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Definition
| separation technique which gas is a mobile phase that gets adsorbed over the liquid stationary phase. The equilibrium established is the adsorption of anaylte between liquid stationary phase and gas mobile phase |
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Term
| Define liquid-liquid chromatography |
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Definition
| Separation technique in which liquid is mobile phase that gets adsorbed over the liquid stationary phase. The equilibrium is a partitioned equilibrium between the two phases which are immscible. |
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Term
| What 4 variables are likely to affect the selectivity factor for a pair of analytes? |
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Definition
1) composition of mobile phase
2) Characteristic feature of stationary phase in column
3) Set temp in column chromatography
4) Use of different chemical reagents such as ion pairing, surfactants and complexing agents |
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Term
| Describe how the retention factor for a solute can be manipulated in GC |
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Definition
1) Changing length of column
2) Changing temp of column
3) Changing the nature of the stationary phase |
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Term
| Describe how the retention factor for a solute can be manipulated in LC |
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Definition
1) Change the composition of the mobile phase
2) Change the nature of the stationary phase
3) Change the length of the column
4) Using different chemical reagents, ion pairing, complexing, or surfactants |
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Term
| What are to methods to improve resolution |
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Definition
1) increase column efficiency
2) Change column selectivity |
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Term
| What is gradient elution? |
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Definition
| Gradient elution is the the change in flow rate of mobile phase or change in composition of mobile phase. Mainly used in LC |
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