A Study on the Determination of Azithromycin by High-Performance Liquid Chromatography

Objective: To analyze the effect of high-performance liquid chromatography (HPLC) for the determination of azithromycin and to provide references for related research work. Methods: The mobile phase was ammonium dihydrogen phosphate at 0.067 mol/L (mixed with triethylamine; pH value was adjusted to 6.5). The chromatographic column was Kromasil C18 (250 mm × 4.6 mm; 5.0 ?m) and the relative standard deviation (RSD) of the drug content level was 1.25%. The injection volume was set to 20 ?L, the detection wavelength was set to 210 nm, the external standard method was used to complete the quantitative work, and the theoretical plate number should be more than 1000 according to the drug peak calculation. The effect of HPLC on the determination of azithromycin was analyzed. Results: The concentration of azithromycin was 1.40-3.40 mg/mL, and the linear relationship was good. RSD of the drug content level was 1.25%. The representative test product had strong stability within 8.0 hours and the method had good repeatability. According to the recovery experiment method, the recovery rates of three standard samples from low to high were 99.87%, 100.15%, and 100.62%. The average recovery rate was 100.21%. RSD value was 0.39%. It means that the recovery rate of HPLC is good. Conclusion: In the determination of azithromycin, the use of HPLC to complete the work was of high sensitivity, simple, and fast. The method had good repeatability in the determination of drug components which is worthy of further promotion.

Characterization of linearly coupled capillaries with various inner diameters in the context of capillary electrophoresis

As a result of continuous instrumental progress, capillary electrophoresis has become an established separation technique. However, the choice of the suitable capillary inner diameter is sometimes difficult due to different instrumental requirements concerning injection, separation, or detection. To overcome this problem, we assembled two capillaries with different inner diameters, meaning that the inner diameter of the capillary at the injection side was different from that at the detection side. Since this was a rather uncommon approach, we focused on the associated effects in this proof-of-concept study. For the experiments, a non-aqueous model system was used, consisting of an acetonitrile-based background electrolyte and the two ferrocene derivates, ferrocenemethanol and decamethylferrocene. Using capillary flow injection analysis hyphenated to capacitively coupled contactless conductivity detection, it could be shown that fragmented capillaries of the same inner diameter had slightly lower volume flow rates than non-fragmented capillaries. With non-aqueous capillary electrophoresis hyphenated to UV detection, it was found that the coupling of capillaries with different inner diameter had a much stronger effect on the capillary electrophoresis flow than combinations with the same inner diameter. Additionally, if the inner diameter of the second capillary was larger than the inner diameter of the first capillary, a higher theoretical plate number and an increased sensitivity were found. Furthermore, it was found that there was no significant peak tailing introduced by the coupling. Graphic abstract

Retention behavior of selected alkaloids in Reversed Phase micellar chromatographic systems

In this work, the effects of sodium dodecyl sulfate (SDS) concentrations on retention, separation selectivity, peak shapes and systems efficiency were investigated. Herein, the retention data for 11 alkaloids were determined on an RP18 silica column with mobile phases containing methanol as organic modifier, with acetate buffer at pH 3.5, and, subsequently, with the addition of sodium dodecyl sulfate (SDS). The results of this study indicate that the retention of alkaloids decreases with the increase of SDS concentration in the mobile phase. The increase of SDS concentration, however, leads to the significantly improvement of peak symmetry and the increase of theoretical plate number in all cases. The best system efficiency for most of the investigated alkaloids was obtained in a mobile phase containing 0.1 M SDS, while most symmetrical peaks were obtained through the addition of 0.3 M of SDS to the mobile phase.

Studies on Citronellal Extract Column Reflux Ratio and Theoretical Plate Number Design

In this paper, the batch rectification operation is adopted to keep distillate constituting constant high vacuum, in the operation process, the operation of variable reflux ratio is carries out. Through studying the relational system of reflux ratio, column top product composition, rectification time and theoretical plate number, when the concentration of citronellal extract column product is 99%, the appropriate reflux ratio is 0.8-15, and the graphic method is used to design13 pieces of theoretical plate number of citronellal extract column, providing powerful data support for the process design of citronellal extract column.

Action of Flow Rate of Mobile Phase in Chromatography

Chromatography has found an increasingly wide utilization in scientific and technological fields, even in some cases, has become indispensable methods for analysis and separation. Compared with its application, some common queries in chromatography still lack for good theoretical explanations, for instance, the action of flow rate of mobile phase on symmetry of peak. As is familiar to people, an increase in flow rate of mobile phase always causes theoretical plate number to decrease under normal conditions. At the same time, maybe the symmetry of chromatographic peak obviously increases, on the contrary. This result is self-contradictory. Why does the theoretical plate number not increase under the condition? Utilizing our prior paper on five plate numbers in chromatography, this paper points out why theoretical plate number decreases with an increase in symmetry of peak when flow rate of mobile phase increases. Based upon gas-solid chromatography results, the relation between flow rate of mobile phase and frequency of partition of solute, and the relation between flow rate and plate number are deduced. From the angle of theoretical model, this paper discusses the relation between solute partition in static mobile phase such as partition between two phases in plate theory and solute partition in flowing mobile phase such as Martin-Synge partition in slip mechanism, and their characteristics.

Study on the Accurate Determination of Polycyclic Aromatic Hydrocarbons in Coal Tar Utilization

The determination of polycyclic aromatic hydrocarbons (PAHs) in coal tar was systematically studied by the high performance liquid chromatography (HPLC), in which involved separation, qualitative and quantitative determination of PAHs. The series of key techniques and experiences were summarized. To ensure finely separation of PAHs PAH, using C18 bonding silica gel column, mobile phase of methanol-water, and theoretical plate number of column more than 5600 were needed. For quantitative determination, the external standard (E-X) quantitative method and external standard - response factor (E-F) quantitative method were recommended. For accurately quantitative determine PAHs, the key technologies were recommended including choice of the optimum solvent of samples preparation and optimum concentration and using ultrasonic treatment, etc. In addition, some determination typical coal tars were also given and recommended. .

The Impact of Reflux Ratio on Rectification Column Theoretical Plate Number

In this paper, the computer-aided calculation is introduced to study the influences of the reflux ratio on the theoretical plate number of rectification column. It is found that the number of theoretical plates of rectification column is increasing as the decreasing of the reflux ratio, which is mainly caused by the increasing of the plate number in rectifying section. On the other hand, it is found that when reflux ratio is reduced in small interval, the theoretical plate number is increased in a zigzag shape. This interesting phenomenon is analyzed in depth and a reasonable explanation is given.

New Progress of Plate Model of Chromatogram: Five Distinct Plate Numbers

The five plate numbers were peak plate number (q’), slip-mechanism plate number (q), theoretical plate number (n0), real plate number (n) and plate-model plate number (q0). Slip mechanism was introduced into plate model and then a new equation of elution curve was deduced. The relational expression of five plate numbers was deduced through the new equation. Peak plate number and slip-mechanism plate number were new plate numbers derived from slip mechanism, and the physical pictures of them was discussed. Peak plate number would be regarded as an asymmetry index of peak, as column plate number is regarded as an efficiency index of column.