Short-term constancy

We differentiate between long-term and short-term constancy... 

Short-term constancy is a way to describe the flow consistencey during peak elution. It is determined using the variation coefficient of the peak area of 6 injections of a component. 

Again long-term constancy does not automatically mean good short-term constancy. See the results of two experiments in Fig. 11-1 Fig. 11-la shows both good long time and short time constancy. Fig. 11 -1 b shows a measurement with good longterm but poor short-term constancy. 

If you prefer to evaluate your data using peak area, a measurement of short-term constancy of the pump is more important than checking the accuracy of the flow rate. 

If short-term constancy not guaranteed, a data evaluation using peak height should be preferred over peak area. 

Figure 11-lb. Pump with good long-term but poor short-term constancy (look at the two V values). 

The main features and operating parameters of pumps have been described elsewhere . They are mainly the maximal pressure available, the constancy of flow-rate in the long term or the flow drift, the short-term pressure fluctuations that might interfere with the detector base signal and result in noise, the minimal and maximal flow-rates available, the convenience of operation, the price and the chemical inertness of the parts that come into contact with the solvents. 

Figure 11-la. Pump with good short-term and long-term constancy V is in both cases excellent. 

Deming also identified 5 deadly sins. These are lack of constancy, short-term profits, performance appraisals, job-hopping and use of visible figures alone. Deming has proposed to use a cycle that he named the Shewhart cycle. It is also called PDCA (plan, do, check and act) cycle. Some of his famous quotations are as follows ... 

Emphasis on short-term profits short-term thinking (just the opposite of constancy of purpose to stay in business), fed by fear of unfriendly takeover, and by pushes from bankers and owners for dividends... 

The small magnitude and short duration of the compositional variation of the stream in flood stage and the constancy of base flow composition suggest that the water-silicate reactions are rapid. The rapidity with which water equilibrates with the fresh and weathered bedrock was tested in the laboratory (term project of Thomas Dunne and Terrance Smith). Two columns of soil were collected from the side slopes of the watershed. Plexiglass tubes 6 inches inside diameter by 3% feet long were forced into the soil, then dug up. 

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