Determination Of Relative Response Factors Research Articles

Correction Factors in Formulas for Calculating Impurity Contents: Essence and Determination Methods and Their Limitations

Formulas for calculating relative response factors (RRFs) and correction factors (Fs) of impurities and those necessary for understanding the essence of RRFs and Fs are presented. The main methods for determining Fs and their limitations (conditions necessary for correct determination of RRFs and Fs) are considered. These limitations do not appear in the European and US pharmacopoeias although they must be considered to determine the correct Fs. Examples and recommendations are given for reliable determination and correct use of the Fs.

Determination of Relative Response Factors of Cefazolin Impurities by Quantitative NMR.

The relative response factors (RRFs) of ten cefazolin impurities were determined by quantitative nuclear magnetic resonance (qNMR) and high-performance liquid chromatography (HPLC) equipped with an ultraviolet (UV) detector. The purities of these ten cefazolin impurities were successfully measured by qNMR for the purpose of RRFs determination by HPLC. The RRF values and their uncertainties determined by the two approaches are comparable. While the qNMR approach is effective and makes it easier to determine the RRFs for impurities, it also has the advantage of allowing the universal detection of protons without the limitations of common mass detectors. The use of qNMR provides a reliable and universal method for the RRF determination of impurities.

Identification of impurities in artemisinin, their behavior in high performance liquid chromatography and implications for the quality of derived anti-malarial drugs

Previous work [1] on the HPLC analysis of artemisinin tentatively identified the two impurities present above trace levels. This identification was based on LC–MS results and NMR of impurities isolated from artemisinin. In this work the impurities have been synthesized allowing verification of their identity by LC–MS. It is found that the previously suggested elution order is incorrect. A determination of relative response factors strongly impacts suggested limits on impurity levels and explains the erroneous peak assignment. The fates of the identified impurities are explored in the transformation of artemisinin to its derivative active pharmaceutical ingredients. A survey of a wide variety of artemisinin samples isolated from different geographical regions, different growing seasons, different plant backgrounds and using different extraction and purification approaches showed that artemisinin has sufficient purity for its intended use as a raw material for anti-malarial drug products.

Determination of relative response factors of the opium alkaloids with HPLC-DAD

In this work, a convenient method for determination of relative UV response factors (RRFs) of morphine, codeine, thebaine, oripavine, noscapine and papaverine by high performance liquid chromatography (HPLC) equipped with a diode array detector (DAD) was presented. Pholcodine was selected as the reference compound for calculating the relative response factors of the alkaloids. The separation of all seven compounds was obtained with optimized gradient elution with high pH value of the mobile phase on a reversed phase column with bidentate C18-C18 bonding technology. The RRFs of the alkaloids were determinate by three different approaches: ‘regression analysis/mass concentration’, ‘regression analysis/molar concentration’and ‘detector sensitivity’ approaches. The ‘regression analysis/molar concentration’ approach gave the accurate approximation of the exact amount of the substance that enters in the detector and the statistically relevant calculation includes several points of different concentrations (at least five), which makes this approach most advantageous one. This method is suitable for quality assessment of the standardised opium dry extract, raw opium and standardised opium tincture by quantitative analysis of not only morphine and codeine as indicated in the respective European Pharmacopoeia monographs, but as well as the major impurities that originate from opium poppy Papaver somniferum L. (Papaveraceae).

Practical Approach for the Determination of Response Factors of Impurities in Drugs by HPLC

For the determination of accurate quantity of impurities in the samples authentic impurity standards or response factors at a given wavelength must be known. In the presented work a convenient method for determination of relative response factors of impurities has been described without using an authentic impurities standard. An approach for the determination of response factors of the impurities where impurity standard is physically not available was developed and verified using different approaches. One such method was developed and verified by RP-HPLC using Cosmosil C18 MS-II column at UV 238 nm. Two different approaches were employed and the verification of correctness of approach was done using a known related substance of known response factor.

Determination of relative response factors for chromatographic investigations using NMR spectrometry

In the absence of suitable reference materials for impurity quantitation, laboratories have developed techniques using mass detectors such as the chemical luminescence detector (CLND) and the charged aerosol detector (CAD) to normalize the UV response of each impurity of interest by their molar ratios and thus generate relative response factors without requiring isolated and purified compound-specific standards. While effective, these detectors are limited in response and are effective only with specific mobile phase requirements. Nuclear magnetic resonance (NMR) spectrometry has the advantage of allowing the universal detection of protons while not suffering from the limitations observed for CLND, CAD, and other common detectors. The determination of relative response factors using NMR has been successfully applied to several LC methods. An overview of this technique and representative results are presented.

Determination of relative response factors of impurities in paclitaxel with high performance liquid chromatography equipped with ultraviolet and charged aerosol detectors

A case study was conducted to determine the relative response factors (RRFs) of paclitaxel-related impurities by high performance liquid chromatography (HPLC) equipped with an ultraviolet (UV) detector and charged aerosol detector (CAD) in tandem. The peak response using CAD was independent of analyte structure in an isocratic analysis for this application. After a sample containing known and unknown impurities was analyzed with HPLC–UV–CAD, an empirical approach was developed to calculate the RRFs for all impurities. The RRFs of known impurities were also determined by linear calibration curves. For known impurities, the RRFs values determined with two approaches are comparable. The new approach is effective yet simpler to determine the RRFs for unknown impurities or degradation products since the need for obtaining authentic pure materials was eliminated.

Influence of relative response factor in the determination of organic microcontaminants with isotopically labeled standards

The use of isotopically labeled internal standards in the analysis of organic microcontaminants entails the determination of relative response factors (RRFs) of the unlabeled with respect to the labeled compounds. RRFs were measured daily during 28 replicate polychlorobiphenyl (PCB) analyses on two different sets of samples. Daily RRFs allowed more precise results to be attained than those provided by mean RRFs, the latter being the mean of all the daily RRFs obtained during the same series of analyses. Analytical applications to food matrices are presented, including the PCB contamination profile of an olive oil and that found in a matrix of Italian national mean diet. Based on the latter sample, also the polycyclic aromatic hydrocarbon (PAH) daily intake of Italians is assessed. Seven PAHs are determined.

“Direct” (on-column) sampling into glass capillary columns : Comparative investigations on split, splitless and on-column sampling

On-column (direct) sampling is superior to other techniques of sampling into capillary columns, especially for analyses with quantitative objectives, for example the precise and accurate determination of relative response factors. Discrimination by volatility of sample constituents is minimal and only slightly dependent on solvent volatility and column inlet temperature, but is independent of the type of carrier gas. Prior heating of the sample for vaporization before entering the column is avoided and decomposition of labile sample components is reduced to a minimum. The performances of two different on-column sampling techniques for quantitative analysis were compared. A new construction of an on-column sampling device for very low sample volumes (columns loads) is described, which allows for the introduction of volumes as low as a few nanolitres of samples into capillary columns.

Quantitative gas chromatography

This experiment consists of the determination of relative response factors for a multicomponent mixture and the use of these factors in determining the percent composition by weight of an unknown mixture.