A method of analysing a sample comprising: (i) surveying a sample in a first mode of operation by directing a spray of charged droplets onto said sample when said spray has a first cross-sectional area or first pixel size at a point of impact with said sample and by scanning said spray of charged droplets across said sample at a first speed so as to produce a survey image of said sample, wherein said charged droplets comprise a first solvent or solvent composition; (ii) determining one or more regions of interest in said sample based on analysis of said survey image; and (iii) analysing said one or more regions of interest in a second different mode of operation by directing a spray of charged droplets onto said sample when said spray has a second different cross-sectional area or second different pixel size at a point of impact with said sample and by scanning said spray of charged droplets across said one or more regions of interest at a second different speed, wherein said charged droplets comprise a second different solvent or solvent composition; wherein directing said spray of charged droplets onto said sample comprises ionising said sample using Desorption Electrospray lonisation ("DESI"); wherein the second cross-sectional area or second pixel size is smaller than the first cross-sectional area or first pixel size; wherein the first speed is greater than the second speed; wherein the first solvent or solvent composition is selected to provide acceptable signal levels from a range of compound classes that may be present in the sample; and wherein the second solvent or solvent composition is selected to provide enhanced signal levels from compound classes of interest that are determined to be present in the sample based on data obtained from the first mode of operation. (i) surveying a sample in a first mode of operation by directing a spray of charged droplets onto said sample when said spray has a first cross-sectional area or first pixel size at a point of impact with said sample and by scanning said spray of charged droplets across said sample at a first speed so as to produce a survey image of said sample, wherein said charged droplets comprise a first solvent or solvent composition; (ii) determining one or more regions of interest in said sample based on analysis of said survey image; and (iii) analysing said one or more regions of interest in a second different mode of operation by directing a spray of charged droplets onto said sample when said spray has a second different cross-sectional area or second different pixel size at a point of impact with said sample and by scanning said spray of charged droplets across said one or more regions of interest at a second different speed, wherein said charged droplets comprise a second different solvent or solvent composition; wherein directing said spray of charged droplets onto said sample comprises ionising said sample using Desorption Electrospray lonisation ("DESI"); wherein the second cross-sectional area or second pixel size is smaller than the first cross-sectional area or first pixel size; wherein the first speed is greater than the second speed; wherein the first solvent or solvent composition is selected to provide acceptable signal levels from a range of compound classes that may be present in the sample; and wherein the second solvent or solvent composition is selected to provide enhanced signal levels from compound classes of interest that are determined to be present in the sample based on data obtained from the first mode of operation.