Sample introduction system
A sample introduction system includes at least two, and preferably three, syringe pumps. The flow rates of two of the syringe pumps are varied, while keeping the overall flow rate constant. The sample introduction system is preferably utilised in an analytical instrument, such as to determine the concentration of an analyte in a sample.
1. A sample introduction system for an analytical instrument comprising:
a first fluid dispensing device for dispensing a first fluid comprising a sample with an unknown concentration C s of an analyte of interest at a sample flow rate V s ;
a second fluid dispensing device for dispensing a second fluid comprising a calibration solution with a known concentration C c of said analyte of interest at a calibration solution flow rate V c ; and
control means for automatically varying said sample and calibration solution flow rates whilst maintaining the sum of said sample flow rate and said calibration solution flow rate at a substantially constant value V wherein the control means determines the unknown concentration C s of the analyte of interest.
2. A sample introduction system as claimed in claim 1 , wherein said control means decreases said sample flow rate and increases said calibration solution flow rate.
3. A sample introduction system as claimed in claim 2 , wherein said control means decreases said sample flow rate and increases said calibration solution flow rate in steps.
4. A sample introduction system as claimed in claim 2 , wherein said control means continuously decreases said sample flow rate whilst simultaneously continuously increasing said calibration solution flow rate.
5. A sample introduction system as claimed in claim 1 , wherein said control means increases said sample flow rate and decreases said calibration solution flow rate.
6. A sample introduction system as claimed in claim 5 , wherein said control means increases said sample flow rate and decreases said calibration solution flow rate in steps.
7. A sample introduction system as claimed in claim 5 , wherein said control means continuously increases said sample flow rate whilst simultaneously continuously decreasing said calibration solution flow rate.
8. A sample introduction system as claimed in claim 1 , further comprising a mixing device for mixing first fluid dispensed from said first dispensing device with second fluid dispensed from said second dispensing device.
9. A sample introduction system as claimed in claim 1 , wherein said first and second dispensing devices comprise syringe pumps.
10. A sample introduction system as claimed in claim 1 , wherein said sample introduction system is arranged to introduce a sample to an ion source of a mass spectrometer.
11. An analytical instrument comprising: a sample introduction system including:
a first fluid dispensing device for dispensing a first fluid comprising a sample with an unknown concentration C c of an analyte of interest at a sample flow rate V s ;
a second fluid dispensing device for dispensing a second fluid comprising a calibration solution with a known concentration C c of said analyte of interest at a calibration solution flow rate V c ; and
control means for automatically varying said sample and calibration solution flow rates whilst maintaining the sum of said sample flow rate and said calibration solution flow rate at a substantially constant value V wherein the control means determines the unknown concentration C s of the analyte of interest.
12. An analytical instrument as claimed in claim 11 , wherein said analytical instrument is selected from the group consisting of: (i) an Inductively Coupled Plasma (“ICP”) mass spectrometer; (ii) an Inductively Coupled Plasma optical analyser; (iii) a flame spectrophotometer; (iv) an Atmospheric Pressure Chemical Ionisation (“APCI”) mass spectrometer; and (v) an Electrospray Ionisation (“ESI”) mass spectrometer.