HPLC

According to "Column Watch" Editor Ron Majors, Type C silica is a term introduced by Dr. Joseph Pesek of San Jose State University (California).

John Dolan considers some techniques to improve detection limits, no matter what the application is.

HPLC is among the most dynamic markets in the laboratory analytical and life science instrument industry. The market can be segmented into six different categories, which include conventional HPLC, capillary/nano LC, fast LC, preparative HPLC, amino acid analyzers, and gel permeation chromatography systems. Conventional HPLC systems, which account for the majority of the market, are standard HPLC instruments with typical flow rates between 1–10 mL/min. However, other HPLC systems designed for specific applications and that remedy some of the shortcomings of conventional LC systems, are becoming more significant in the market.

Excess variability is not acceptable in a pharmaceutical method.

This article gives an overview of the performance of a previously developed system for the ranking of C18 reversed-phase columns applied to different pharmaceutical analyses. The separation of eight different drug substances from their respective impurities was studied. The chromatographic procedure for acetylsalicylic acid, clindamycin hydrochloride, buflomedil hydrochloride, chloramphenicol sodium succinate, phenoxymethylpenicillin and nimesulide was performed according to the corresponding European Pharmacopoeia monograph. The separations of dihydrostreptomycin sulphate and vancomycin were performed according to literature. It was found that that the column ranking system is a helpful tool in the selection of suitable columns in these analyses.

In any field there are often "misconceptions" or "myths" that are perpetuated and passed on to the next generation. These myths are often driven by a lack of understanding by practitioners of the real issues. In this instalment of "Column Watch", the 10 most popular myths around high performance liquid chromatography (HPLC) column technology will be demystified by discussing the issues at hand. Among some of the popular myths that will be dispelled are that "All C18 (L1) columns are the same", "You can't reverse an HPLC column", "High temperature always leads to better separations" and "The higher the carbon load the better the reversed-phase column".

This month's instalment of "LC Troubleshooting" presents two examples of sample degradation inside the liquid chromatography (LC) column. Depending upon the type of samples you analyse, sample degradation might or might not be a problem that you encounter regularly. However, most of us run a sufficiently wide variety of sample types over our careers that we will probably run into some samples that do not behave as expected.

Chromatographers worldwide suffer from the same problems.

The authors describe a study that was conducted to evaluate the correlation between the slope of the response line and the response factor of an ELSD that are ordinarily regarded as independent numerical coefficients.

Sometimes it is easy to ignore the fittings and tubing that are used to connect various parts of the liquid chromatography (LC) system. After all, it's the pump, injector, column and detector that do all the work - right? Well, yes and no. It is possible to compromise an otherwise excellent separation by the improper use of fittings, but with reasonable care, you should not have problems with most applications. This month's instalment of "LC Troubleshooting" takes a look at the important components that are used to connect various parts of the LC system and how to use them wisely.

What do you do when the sample changes inside the column?

Measurement of chiral purity is a necessary means of quality control for drug substances that exhibit chiral centers. This article describes a simple and practical approach to setting up system suitability and validation for chiral purity assays.

In any field there are often "misconceptions" or "myths" that are perpetuated and passed on to the next generation.

Software traditionally used to control and process data in analytical instruments is now being expanded to include functions such as automated system monitoring with maintenance feedback alerts and interactive diagnostic routines that enable users to quickly track and resolve the source of many system problems. As a back up to these functions, a second layer of expert support is being made available by some instrument vendors to address more complex servicing issues. For larger or more elaborate instrument installations, monitoring and diagnostic software functions can be integrated with remote servicing expertise in a networked configuration to provide continuous proactive instrument maintenance. The benefits of these innovations include lower and more predictable operating costs, reduced system downtime, and more efficient utilization of the instrument user's time.

Dissolution testing is a mandatory test for the physical evaluation of solid dosage forms such as capsules, tablets, ointments, and creams. The most basic form of testing measures the rate of dissolution or solubility of a drug tablet. Dissolution testing also can be used in ADME and bioavailability studies, release rates of a drug substance under different conditions, as well as provide information as to the efficacy of in-vivo performance.

This month's "LC Troubleshooting" takes a look at the important components that are used to connect various parts of the LC system and how to use them wisely.

Because each sample is unique, you will need to check for carryover under the conditions of each method.

John Dolan addresses two column-related problems reported by readers - the first deals with a column that takes several injections to "settle down" for each batch of samples while the second problem relates to short column life due to early fouling of the column.

The gradient linearity and step tests are two of the most useful performance tests that can be made for a liquid chromatography (LC) system. These check the linearity of gradient generation and the accuracy of mobile phase proportioning. These tests, and examples of problems detected as a result of these tests, have been the subject of at least seven "LC Troubleshooting" columns over the last 18 years.1–7 We strongly recommend that every LC system undergo these tests at least on an annual basis, and preferably semiannually. When a new and different example of a problem detected by these tests is discovered, it is hard to bypass the opportunity to share it with our readers. So this month, you get yet another example of how an LC system can fail.

If cyclohexane is mixed with even low amounts of other solvents, the melting pressure increases remarkably.