Buffer depletion

Buffer depletion often results in a change of the migration times. Thus, the stability of the buffer has to be checked and as a consequence the buffer electrolyte vials have to be replaced after a certain number of runs. 

Even if pinched injection was used, baseline drift of repetitive pinched injections was noted. This was attributed to the meniscus surface tension (Laplace pressure) effect, even though other possible effects (evaporation, buffer depletion due to electrolysis, siphoning, Joule-heat-induced viscosity change) are minimized [553]. 

Wallenborg, S.R., Bailey, C.G., Paul, P.H., On-chip separation of explosive compounds — Divided reservoirs to improve reproducibility and minimize buffer depletion. Micro Total Analysis Systems, Proceedings of the 4th iTAS Symposium, Enschede, Netherlands, May 14-18, 2000, 355-358. 

The selection of the background electrolyte (BGE) fill process can affect the separation, depending on the characteristics of the electrolyte. The two-reservoir method uses inlet and outlet vials. The capillary is filled using the inlet vial. Multiple runs from a single set of vials are possible, but sometimes migration time drift is observed due to buffer depletion [7]. This limits the number of runs from a single set of vials. 

It is important to refresh the BGE reservoirs frequently to avoid a process known as buffer depletion... 

Loose electrode connections Plugged capillary Sample matrix effects Safety interlock off Plugged capillary Broken c illary Buffer depletion Empty capillary Short in system (buffer on reservoir cap)... 

Eurachem guide [285], which discusses when, why, and how methods should be validated. However, for the pharmaceutical industry, the main reference source is the ICH Guidelines [286], which provides recommendations on the various characteristics to be tested for the most common types of analytical procedures developed in a pharmaceutical laboratory. The main characteristics of any analytical method to be tested are specificity, linearity, accuracy, precision, solution stability, limits of detection and quantification, and robustness. Specific aspects should be considered for a CE method including method transfer between instrument manufacturers, reagent purity and source, electrolyte stability, capillary treatment and variations in new capillaries, and buffer depletion. Fabre and Altria [284] discuss CE method validation in more detail and include a number of examples of validated CE methods for pharmaceutical analysis. Included in Table 4.3 are a number of validated pharmaceutical assay methods. 

The separation buffer in the column and inletyoutlet vials should also be replaced—ideally after each run—to prevent buffer depletion. Buffer depletion occurs as the cation and anion components of the buffer migrate toward cathode and anode respectively during a run. Over time, the concentration of anions at the cathode and cations at the anode will be reduced. This reduction of ions will also occur within the buffer in the column itself. When this occurs to an extreme, major performance degradation is the result. 

Buffer Systems. Buffer systems should be preferentially volatile and of low concentration. Detergents are particularly detrimental to the ESI process. Volatile buffers should be prepared fresh every day to maintain a stable pH, EOF, and thus stable ion signal. Solvent evaporation, and/or buffer depletion in the reservoirs, will result in a change in pH, EOF, and ESI signal response. Thus, the buffers should be replenished on a regular basis. The EOF must be maintained in the direction of the ESI emitter, especially when nanospray sources are used (i.e., no liquid sheath or liquid junction fluids are delivered to the source). 

Another factor that can result in migration time variation is buffer electrolysis (buffer depletion). Several approaches have been used to reduce buffer depletion, such as the use of high concentration buffers with optimum buffer capacity, replenishment, changing the vials after a certain number of analyses, etc. During method development, buffer depletion should be investigated before the method is submitted to a validation procedure. ... 

It is important to refresh the BGE reservoirs frequently to avoid a process known as buffer depletion. "" Electrolysis at the respective electrodes produces protons and hydroxide ions. This can cause pH changes in the buffer reservoirs. 

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