Pumps flow pulsation

Reducing the non-shot Category III noise sources of the fixed wavelength detector will require attention to Improved thermomechan-Ical detector design to reduce noise due to thermal variations Imposed on the mobile phase/flow cell and on the sample and reference photodiodes, and continued reduction In HPLC reciprocating pump flow pulsations. 

In order to evaluate pump flow rate reproducibility and pulsation, one method is commonly used to assess gradient formation capability. A certain amount of an analyte with adequate molar absorptivity at the wavelength employed for detection is introduced into one of the mobile phases employed to create the gradient. In the case described, 5% acetone was introduced into the mobile phase, distributed to the system by pump B. No UV-absorbing analyte was introduced into mobile phase A. The fractional flow rate of pump B relative to the total flow rate of the system (mandated by the sum of the flow rates of pumps A and B) was increased in individual steps to account for 0, 3,6,12.5,25, 50, and 100% fractional rates. The total flow for the system was maintained at 300 /jL/ min (for 24 columns), resulting in a per column flow rate of 12.5 /iL/min/column. 

Manufacturers publish their product s performance characteristics as specifications, which are often used by the customer for comparison during the selection process. Table 1 shows the specifications of an Agilent 1100 Series Quaternary Pump, which is quite representative of other high-end analytical pumps. Note pulsation is particularly detrimental to the performance of flow-sensitive detectors (e.g., mass spectrometer, refractive index detector). Differences in dwell volumes and composition accuracy between HPLC systems might cause problems during method transfers. 

Pump Flow Accuracy and Pressure Pulsation Tests 7... 

Figure 10. Feedback flow control system for high-speed pump with pulsating flow...

This analysis is performed using a Dionex Model 12 ion chromatograph with 200pL sample loop, an eluent flow rate of 2.3ml min 1 (30% of full capacity) and a sample pump flow rate of 3.8ml min 1 (50% of full capacity). Pulse damper is installed just before the injection valve to reduce flow pulsation. A Dionex amperometric detector... 

FIGURE I Expanded-bed affinity chromatography (EBAC) setup Tl and T2, tanks for homogenate, washing, elution, and reequilibration buffers P, peristaltic pump C, expanded-bed column W, wastes collector E, eluent collector VI, V2, V3, and V4, three-way valves V5, four-way valve K, knitted silicone tubing used to reduce flow pulsation. 

Figure 1 shows a triplex plunger pump and its flow pulsation at a volumetric efficiency of 95 %. The volumetric efficiency, representing the ratio of the actual volume flow Q to the theoretical flow (equation (1)), depends essentially on the fluid and working chamber elasticity... 

Flow rate. The flow rate from the pump should be accurate, regardless of the system in which the pump is used. This means that the flow rate actually produced by the pump is the same as that dialled up on the front panel, and that this should not be affected by the rest of the HPLC system (for constant flow pumps, at least). The flow rate should be reproducible and practically free of pulsations. Pulsatile flow can limit the sensitivity of HPLC assays, resulting in a rhythmic variation in the apparent refractive index of the mobile phase flowing through the detector, which ultimately manifests itself in the chromatogram as baseline noise. Various means are employed to attempt to eliminate flow pulsation (see section 5.3). 

The RSD of the peak area is influenced by 1) Injection mode and volume 2) pump flow and pulsation 3) detector noise, drift, and response and 4) samphng rate and integration parameters of the data system. 

Pulsating flows are beneficial with regard to segmented flow analysis, as the bubble additions are synchronised with the flow pulsation. In order to enhance the pulsating nature of the confluent stream of air to be added, some peristaltic pumps (including the widely used Technicon AAII) incorporate a lifting bar to successively pinch the air delivery tubing. 

A steady concentration of the reactant is not observed when the confluent reagent stream is not properly added. Pronounced differences in matrix composition (e.g., colour and suspended matter), flow rates and viscosity of the carrier and confluent streams may result in a pulsed addition of the confluent stream. The effect is random, but if the fluid-propelling device is a peristaltic pump, it is characterised by a typical frequency, dictated by the rotation speed of the peristaltic pump. A pulsating flow is then established, leading to undulations in the recorded peak. The effect is reduced if the involved streams converge with similar mean linear velocities. As the effect is characterised by a constant frequency, the modulated signal (ripple) is easily filtered out. 

Does the pump provides pulsation-free flow to allow the use of an electrochemical detector at 1.2 V ... 

Lobe pump Low pulsations High flow applications... 

More recently, HNP Mikrosysteme GmbH [14] has commercialized a type of rotary pump called micro annular gear pump. This t3q>e of pump is a positive displacement pump with an externally toothed rotor and internally toothed ring, which are assembled with a small eccentricity of their rotation axes with respect to each other. The rotation of the internal rotor forces the fluid pockets which are interlocked between two gears to flow. The pump flow rates vary from product to product, but are in a range of 1 pL/h to 1.2 1/min. Advantages of this product include accurate control of flow rate and minimum pulsation in delivery. 

Valve-Less Rectification Pumps, Fig. 10 The flow pulsation caused by the absence of driving flow during the suction part of the cycle of the basic pump (Fig. 1) may be reduced (cf. Fig. 7) in the multi-phase pumps. While the version in Fig. 8 works with two phases, an even better smoothing is here achieved with three rectifying halfbridges... 

Samples collected should be full shift (at least 7-hour) samples. Sampling should be done using a personal sampling pump with pulsation damper at a flow rate of 2 liters per minute. Samples should be collected on 0.8 micrometer pore size silver membrane filters (37 mm diameter) preceded by Gelman glass fiber type A-E filters encased in three-piece plastic (polystyrene) field monitor cassettes. The cassette face cap should be on and the plug removed. The rotameter should be checked every hour to ensure that proper flow rates are maintained. 

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