A method for automatically checking a calibration of a mass spectrometer including an ion source, a first quadrupole device, Q1,, a fragmentation cell and a mass analyzer during a sequence of mass analyses of a plurality of samples comprising a plurality of analytes that are analyzed, wherein each of said samples is analyzed for at least one of the plurality of analytes, the method comprising: (a) providing at least one known analyte-specific chemical entity in each of the samples; and during the mass analysis of each sample: (b) ionizing each of at least one known chemical entity within said each sample using the ion source so as to generate ions of a respective known precursor ion species from the at least one known chemical entity; (c) transmitting a portion of the precursor ion species through Q1 to the fragmentation cell so as to be fragmented in the fragmentation cell; and (d) detecting product ions of the precursor ion species by a detector of the mass analyzer; the method characterised in that: each analyte-specific chemical entity is one of an analyte or an internal standard that is chemically similar but not identical to an analyte; the method further characterised by: (e) determining, during the analysis of each sample, if a calibration check is due and, if the determination is affirmative with respect to a sample, executing the steps of: (f) reducing an accelerating voltage applied to the fragmentation cell so as to prevent fragmentation of precursor ions within the fragmentation cell; (g) mass scanning, using Q1, across a region of mass-to-charge, m / z, encompassing an anticipated location and width of a known precursor ion species generated from the sample for which the determination (e) is affirmative and transmitting the mass scanned precursor ions of the known precursor ion species generated from said sample to and through the fragmentation cell; (h) detecting the mass scanned precursor ions of the known precursor ion species generated from said sample by a detector of the mass analyzer; and (i) comparing one or more of peak resolution or peak centroid positions or peak widths, as detected in step (h), to respective expected values. (a) providing at least one known analyte-specific chemical entity in each of the samples; and (b) ionizing each of at least one known chemical entity within said each sample using the ion source so as to generate ions of a respective known precursor ion species from the at least one known chemical entity; (c) transmitting a portion of the precursor ion species through Q1 to the fragmentation cell so as to be fragmented in the fragmentation cell; and (d) detecting product ions of the precursor ion species by a detector of the mass analyzer; each analyte-specific chemical entity is one of an analyte or an internal standard that is chemically similar but not identical to an analyte; (e) determining, during the analysis of each sample, if a calibration check is due and, if the determination is affirmative with respect to a sample, executing the steps of: (f) reducing an accelerating voltage applied to the fragmentation cell so as to prevent fragmentation of precursor ions within the fragmentation cell; (g) mass scanning, using Q1, across a region of mass-to-charge, m / z, encompassing an anticipated location and width of a known precursor ion species generated from the sample for which the determination (e) is affirmative and transmitting the mass scanned precursor ions of the known precursor ion species generated from said sample to and through the fragmentation cell; (h) detecting the mass scanned precursor ions of the known precursor ion species generated from said sample by a detector of the mass analyzer; and (i) comparing one or more of peak resolution or peak centroid positions or peak widths, as detected in step (h), to respective expected values.