Pressure problems

Soiled mobile phase (and, as a consequence, also soiled frits, capillaries, valve and/or column)  

Replace the frit. If black particles are visible on the frit (rather common) it is necessary to replace the high-pressure seal and perhaps also the piston. In addition, check if the seal is resistant to the solvent in use. (However, today s seal materials should be resistant to all common solvents, including water.) 

Replace the capillaries or install them in reverse direction. Caution do not overtighten the fittings of peek capillaries. 

Wrong fitting (or only wrong ferrule) installed  

Practical High-Performance Liquid Chromatography, Fifth edition Veronika R. Meyer 

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The fix for the erratic reflux drum pressure problem was to provide for separate pressure control of the fractionator column and the reflux drum. A new pressure control valve was installed upstream of the condenser and the old condenser outlet control valve was removed. A hot gas bypass, designed for 20% vapor flow, was installed around the pressure control valve and condenser. A control valve was installed in the hot gas bypass line. The column pressure was then maintained by throttling the new control valve upstream of the condenser. The reflux drum pressure w as controlled by the hot gas bypass control valve and the psv saver working in split range. The new system is shown in the figure below. 

High or low fuel gas pressure ean have a dramatic effect on the operation of a firetube heater. Burners are typically rated as heat output at a specified fuel pressure. A significantly lower pressure means inadequate heat release. Significantly higher pressure causes overfiring and over heating. The most common causes of a fuel gas pressure problem are the failure of a pressure regulator or an unacceptably low supply pressure. 

It was shown that the effect of the particle size is not significant in HOPC (1). The experiments were conduced using silica gels of the same pore size but with a different average particle size between 15 and 100 /urn. A kinetic effect— enrichment of the mobile phase with high MW components is better at short times before equilibrium is reached—was cited as a possible reason for almost equal quality of separation by large particles. The back-pressure problem was not serious in that range of the particle size. 

No loss-of-circulation problem No formation damage Very high penetration rate Low bit costs Low water requirement No mud requirement No ability to counter subsurface pore pressure problems Little ability to carry formation water from hole Hole erosion problems are possible if formations are soft Possible drill string erosion problems Downhole fires are possible if hydrocarbons are encountered (gas only) Specialized equipment necessary... 

Improved penetration rates (relative to mud drilling) Ability to counter high subsurface pore pressure problems ... 

The Ballestra Neutrex SV system (Fig. 10) has been developed to obtain, in a single process step, products with high AM at high purity. Neither solvents nor hydrotropes (sometime used to overcome viscosity and consequent high-pressure problems in the loop) are required to operate with these highly viscous products. 

For true wall-jet behaviour rja should be >4. This means that the jet diameter should be decreased when the electrode diameter is decreased, which can cause pressure problems. 

The use of in-line filters between injectors and colunm can prevent the accumulation of particulate material on the inlet frit of an analytical column, and can avoid back-pressure problems. A second, and often overlooked, site for filter installation is between the column and the detector. Cartridge-type filtration-units that contain readily changed, 0.2-/i,m filters are commercially available, and they contribute insignificantly to peak broadening. These filters are essential for the prevention of clogged detectors when laboratory-packed columns are used. 

The Sulfide Ores (e.g., sulfides of iron, nickel, zinc, copper, lead, cobalt, cadmium, mercury, silver).— These must be studied both in their dry melts (to obtain their fundamental characteristics) and in relation to water solutions under atmospheric pressure (problems of oxidation and... 

All test solutions, except otherwise mentioned, were degassed by hree freeze-pump-thaw cycles with a vacuum line operated under 10 torr pressure. Problems of background fluorescence originating from sulfonates themselves could be adequately minimized by proper choice of probe/sulfonate ratios. The excitation wavelength was set at 340 nm. Emission spectra were obtained in constant energy mode. The spectral resolution was 3 nm. 

Pressure Problems Many of the older and some of the new smaller mass spectrometers have relatively low pumping capacity. Often there is no differential pumping to minimize the source load on the analyzer chamber. Extra pumps have been successfully added to spectrometers but this requires a major alteration to the spectrometer manifold. 

Do not switch from organic solvents to buffer solution or vice versa. Always do an intermediate wash with water. Buffer precipitation is a major cause of system pressure problems. You may be able to go from less than 25% buffer to organic and get away with it, but you are forming a very bad habit and that will get you into trouble later on. I usually keep a bottle of my mobile phase minus buffer on the shelf for column washout at the end of the day. This also can be used for buffer washout, but a water bridge is still the best. 

Be sure not to jump from buffer to pure organic or from organic to buffer. This can lead to buffer precipitation, plugging, and pressure problems. Always use a wash out, intermediate solvent or wash out with water. Allow six column volumes for reequilibration true equilibration takes as much as 24 hours, but this six-volume equilibration is reproducible and sufficient. 

The first step is to locate the point of the pressure increase. Since most problems are column problems, we can simplify our task by eating the elephant one bite at a time. Remove the column from the system and turn on the pump. If the pressure problem goes away, it was in the column. If not, it s in the system leading up to the column. I ll deal here only with the column pressure problems, the system problems will be dealt with in Chapter 10 on troubleshooting. 

As we said in the column section, the first step is to remove the column and see if the problem goes away. Pressure problems can be determined by looking at the pump pressure. Other problems can be diagnosed from the detector s digital display and the recorder baseline. Of course, with the column gone, there is no path to the detector. Here is where the column blank shows... 

In the first edition of this book, I forecast that the ultimate HPLC column would be a wall-bonded capillary column that would avoid the voiding and back-pressure problems seen with packed columns. A new type of column, the monolith silica column, recently emerging from research laboratories very closely fits this description. A monolith column has a honeycomb foam of silica, which is bonded with an organic separating phase, completely filling the inside of the column. 

Shortly after the valve to the sump was opened and the valve to the hopper was closed, the No. 4 reactor began experiencing erratic pressure problems. The system pressure troubles continued for about 15 minutes. As the supervisor and operator were troubleshooting the problem the relief valve on the reactor heat transfer chest opened with a loud report, signaling real troubles. The two employees started to head out of the unit. About 20 seconds later a large section of a 9 ft. (2.7 m) in diameter expansion joint burst. The initial explosion and the resulting thrust shifted the massive reactor. 

You might have noticed that torr and mm Hg have the same value. On the AP test, units of pressure are usually expressed as atm in the ideal gas problems (R uses atm as the pressure unit) and mm Hg in partial pressure problems. 

Finally, there is one more aspect of partial pressures that must be included. Most of the partial pressure problems that appear on the AP test involve gases that have been collected over a liquid. (In other words, they have been collected by displacement of the liquid, usually water.) The significance of this is that in the container, along with the collected gas, is vapor from the liquid, so the pressure in the collection vessel is the sum of the pressure of the gas and the vapor. Since we know that the total pressure in the container is equal to the sums of... 

This problem is fairly representative of the partial pressure problems on the multiple-choice portion of the test. On the free response, the questions are more complex. 

The correct answer is (D). This is a partial pressure problem. To solve it, you need to use two equations (both from Chapter 8) ... 

Again, there s no doubt in the scientific and medical communities that potassium is one answer to the blood pressure problems in Western countries around the world. 

Happily, today physicians around the world recognize the potential benefits of alcohol consumption, even for people with blood pressure problems. Moderate drinking may actually be good for them. The watchword, of course, is moderation, as it should be for everyone. 

This study confirmed the findings of another project, the Atherosclerosis Risk in Communities Study, which found that retinal blood vessel narrowing predicted hypertension within three years. Doctors point out that by knowing the risk of future blood pressure problems, one can immediately take lifestyle modification steps to avoid them. 

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