after adding an internal standard, after being diluted with another solution or after having being mixed with reagents e.g. A sample may be used directly as obtained from the source in some cases or following a pretreatment and/or sample preparation workflow to modify the character of the sample, e.g. The sample can be pretreated prior to use, such as preparing plasma from blood, diluting viscous fluids, lysis or the like methods of treatment can involve filtration, centrifugation, distillation, concentration, inactivation of interfering components, and the addition of reagents. The sample can be derived from any biological source, such as a physiological fluid, including, blood, saliva, ocular lens fluid, cerebral spinal fluid, sweat, urine, milk, ascites fluid, mucous, synovial fluid, peritoneal fluid, amniotic fluid, tissue, cells or the like. For instance, a user might schedule or trigger the automated steps of the techniques of the present disclosure. The automated steps can be part of a method including also steps requiring user interaction. The terms "automated" or "automatically" according to the present disclosure refers to operations carried out by a machine without user interaction. The term "time series" is used in the present disclosure as referring both to "raw data" (e.g., as retrieved from a current sensor) as well as processed raw data (e.g., by using signal processing techniques) as long as the processing step still reflects the time-dependence of the monitored parameter (e.g., an ionization current of the ESI source). A time series can include values at equidistant points in time or at non-equidistant points in time. For instance, an averaged measurement value obtained by averaging over multiple measurements of a parameter can also be included in the time series according to the present disclosure. The term "point in time" shall not limit a measurement window for obtaining a measurement value included in the time series to a particular accuracy. A time series can include (much) more than two values at respective points in time in some examples. A "time series" according to the present disclosure refers to at least two of a particular parameter values (e.g., of the ionization current of the ESI source) at two different points in time (e.g., at least one earlier point in time and at least one later point in time). Therefore, the technique of the present disclosure taking into account an electrospray ionization current of the ESI source (also referred to as ESI current in the present disclosure) allows for a more precise identification of a condition of the analyzer. For instance, column aging can cause changes in the chromatographic features as shown in FIG. However, similar changes in the chromatographic features can also be caused by different other conditions than the presence of a post-column dead volume. 3a, chromatographic features (e.g., a retention time, a peak width or a peak height) change due to post-column dead volume. 3b, monitoring a pressure of the LC stream might not be helpful as post-column dead volumes might have little or no effect on the pressure curve. Post-column dead volumes are errors which can be difficult to detect when considering other parameters of the LC stream. Firstly, the monitoring technique of the first general aspect of the present disclosure can allow identifying dead volumes downstream of an LC column of the LC stream (also referred to as "post-column dead volume" in the present disclosure).
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