A system for determining the concentration of an analyte of interest in a biological sample, the system comprising: a solvent assembly comprising a first volume of a first solvent and a second volume of a second solvent, the solvent assembly further comprising a first outlet fluidly connected to the first volume and a second outlet fluidly connected to the second volume; and a disposable cartridge comprising: a solvent inlet configured to introduce at least one of the first arid second solvents from the solvent assembly into the disposable cartridge, wherein the solvent inlet comprises a first solvent introduction port and a second solvent introduction port, the first solvent introduction port configured to accept the first outlet of the solvent assembly and to fluidly connect to the first volume, the second solvent introduction port configured to accept the second outlet of the solvent assembly and to fluidly connect to the second volume, or wherein the solvent inlet comprises a third solvent introduction port configured to fluidly connect to both the first outlet and the second outlet via a joining portion between the first and second outlets; a sample introduction port configured to receive the biological sample, the sample introduction port fluidly connected to the solvent inlet; a chromatography region fluidly connected to the sample introduction port; and an outlet fluidly connected to the chromatography region, characterized in that to provide an indication that the solvent assembly and the disposable cartridge are compatible for performing an assay to determine the concentration of the analyte of interest, at least a portion of the solvent assembly has an asymmetrical shape that fits together in a specific orientation to at least a portion of the solvent inlet having a shape complementary to the asymmetrical shape. a solvent assembly comprising a first volume of a first solvent and a second volume of a second solvent, the solvent assembly further comprising a first outlet fluidly connected to the first volume and a second outlet fluidly connected to the second volume; and a disposable cartridge comprising: a solvent inlet configured to introduce at least one of the first arid second solvents from the solvent assembly into the disposable cartridge, wherein the solvent inlet comprises a first solvent introduction port and a second solvent introduction port, the first solvent introduction port configured to accept the first outlet of the solvent assembly and to fluidly connect to the first volume, the second solvent introduction port configured to accept the second outlet of the solvent assembly and to fluidly connect to the second volume, or wherein the solvent inlet comprises a third solvent introduction port configured to fluidly connect to both the first outlet and the second outlet via a joining portion between the first and second outlets; a sample introduction port configured to receive the biological sample, the sample introduction port fluidly connected to the solvent inlet; a chromatography region fluidly connected to the sample introduction port; and an outlet fluidly connected to the chromatography region, a solvent inlet configured to introduce at least one of the first arid second solvents from the solvent assembly into the disposable cartridge, wherein the solvent inlet comprises a first solvent introduction port and a second solvent introduction port, the first solvent introduction port configured to accept the first outlet of the solvent assembly and to fluidly connect to the first volume, the second solvent introduction port configured to accept the second outlet of the solvent assembly and to fluidly connect to the second volume, or wherein the solvent inlet comprises a third solvent introduction port configured to fluidly connect to both the first outlet and the second outlet via a joining portion between the first and second outlets; wherein the solvent inlet comprises a first solvent introduction port and a second solvent introduction port, the first solvent introduction port configured to accept the first outlet of the solvent assembly and to fluidly connect to the first volume, the second solvent introduction port configured to accept the second outlet of the solvent assembly and to fluidly connect to the second volume, or wherein the solvent inlet comprises a third solvent introduction port configured to fluidly connect to both the first outlet and the second outlet via a joining portion between the first and second outlets; a sample introduction port configured to receive the biological sample, the sample introduction port fluidly connected to the solvent inlet; a chromatography region fluidly connected to the sample introduction port; and an outlet fluidly connected to the chromatography region, characterized in that to provide an indication that the solvent assembly and the disposable cartridge are compatible for performing an assay to determine the concentration of the analyte of interest, at least a portion of the solvent assembly has an asymmetrical shape that fits together in a specific orientation to at least a portion of the solvent inlet having a shape complementary to the asymmetrical shape.