Review on “High Performance Liquid Chromatography (HPLC), Method Development, and Validation”

 

 

1. Solvent Reservoir: A glass reservoir holds the materials used in the mobile stage. The dissolvable, or versatile, stage in high-performance liquid chromatography (HPLC) is generally a mixture of polar and nonpolar liquid segments, the specific fixations of which are dependent on the specimen's arrangement.[7]
2. Pump: A pump draws the adaptable stage from the dissolvent reservoir and passes it via the detector and column of the framework. Working weights of up to 42000 kPa (about 6000 psi) can be achieved, depending on a number of factors such as column measurements, the stationary stage's molecule size, the versatile stage's synthesis, and the stream rate. [8]
3. Sample Injector: The injector may be an automated infusion framework or a single infusion. An injector for an HPLC system should provide high weight (up to 4000 psi) and high reproducibility infusion of the liquid specimen within the range of 0.1–100 mL of volume.[9]
4. Columns: Columns are typically between 50 and 300 mm long, with an interior distance across of between 2 and 5 mm. They are typically constructed of cleaned stainless steel. Usually, a stationary stage containing molecules ranging in size from 3 to 10 μm is fed into them. Columns that have inner spacing of less than 2 mm are commonly referred to as microbore HPLC columns. In an ideal scenario, the temperature of the column and the portable stage should remain constant during the examination.[10]
5. Detector: As the analytes elute from the chromatographic column, the HPLC indicator, which is positioned toward the end of the column, separates them. UV spectroscopy, fluorescence, mass spectrometry, and electrochemical indicators are often used finders.[11]
6. Data Collection Devices: Signals from the indicator can be recorded on electronic integrators or outline recorders, which vary in terms of their multifaceted quality and ability to analyse, store, and reprocess chromatographic data. The PC arranges for the identifier's reaction with each component and loads it into a chromatograph that is remarkably easy to see and understand.[12]
7. Degasser: Gases that are invisible to the human eye, including oxygen, may be present in the eluent used for LC analysis. An unstable baseline results from the presence of gas in the eluent, which is recognized as noise. The most widely utilized techniques include heating and stirring, aspirator use, distillation systems, and sparging (bubbling of inert gas). Nevertheless, the procedure is inconvenient, and the gas will gradually dissolve back into the solvent if it is left for an extended amount of time (such as during a lengthy investigation). Special polymer membrane tubing is used by degassers to extract gases. Column Heater: The temperature of the column frequently has a significant impact on the LC separation. Maintaining constant temperature conditions is crucial for producing repeatable results. Additionally, higher temperatures (50 to 80°C) can yield greater resolutions for particular analyses, such as those involving sugar and organic acid. Even when the sample is evaluated at room temperature, maintaining a steady temperature is crucial for reproducible findings. It's possible that slight temperature variations lead to various separation outcomes. As a result, columns are typically stored within column heaters, or column ovens.

APPLICATIONS OF HPLC

• Industrial Applications:[13]

There is a wide variety of applications throughout the process of creating a new drug from drug discovery to the manufacture of formulated products that will be administered to patients. This Process to create a new drug can be divided into 3 main stages:

• Drug discovery
• Drug development
• Drug manufacturing.
• Pharmaceutical Applications:[14]
• Tablet dissolution study of the pharmaceutical dosage form.
• To control drug stability, Shelf-life determination.
• Identification of active ingredients.
• Pharmaceutical quality control.
• Environmental Applications:[15]
• It is used to test drinking water and to observe air quality.
• To identify very small quantities of contaminants such as PCBs in pesticides and waste oil.

• Clinical Applications: [16]

• Catecholamines such as epinephrine and dopamine are highly important for many biological functions. Analysing their precursors and metabolites can provide diagnosis of diseases such as Parkinson’s disease, heart disease, and muscular dystrophy.
• Quantification of ions in human urine analysis of antibiotics in blood plasma.
• Estimation of bilirubin & biliverdin in blood plasma in case of hepatic disorders.
• Detection of endogenous neuropeptides in extracellular fluids of the brain.

• Food And Flavour Analysis: [17]

• Rapid screening and analysis of components in non-alcoholic drinks.
• Measurement of quality of soft drugs and water.
• Sugar analysis in fruit juices.
• Analysis of polycyclic compounds in vegetables.
• preservative analysis.
• Multiresidue analysis of lots of pesticide.

• Environmental Applications:[18]

• Detection of phenol compounds in drinking water.
• Identification of diphenhydramine in sedimented samples.
• Bio-monitoring of pollutant.
• Rapid separation and identification of carbonyl compounds by HPLC.
• LC/MS/MS solution for pharmaceuticals and personal care products in water, sediment, soil and biosolids by HPLC/MS/MS.
• Determination of 3-mercaptopropionic acid by HPLC.

• Forensic Applications:[19]

• Quantification of the drug biological samples.
• Identification of anabolic steroids in serum, urine, sweat & hair.
• Forensic analysis of textile dyes.
• Determination of cocaine and other drugs of abuse in blood, urine, etc.
• Determination of benzodiazepines in oral fluid using LC/MS/MS.

• Recent applications:[20]

• Analytic method development and validation are key elements of any pharmaceutical development program. HPLC analysis method is developed to identify, quantity or purifying compounds of interest. HPLC helps a lot in stability studies of drug formulations. HPLC helps a lot in stability studies of atropine, antibiotics, & biotechnology-based drugs like insulin, streptokinase, etc.
• It is used in inorganic chemistry for separating anions & cations.
• It is used in forensic science for the separation of phenyl alkylamines (morphine and its metabolites) from blood plasma, and for the detection of poisons or intoxicants such as alcohol, carbon monoxide, cholinesterase inhibitors, heavy metals, hypnotics, etc.
• It is used in environmental studies for analysing the pesticide content in drinking water
• It is utilized in food analysis for separating water soluble and fat-soluble vitamins from variety of food products, fortified food and animal feed.
• It is also used for determining antioxidants and preservatives present in the food.
• It is used in the cosmetic industry for the assay and quality control of various cosmetics like lipsticks, creams, ointments, etc.
• It is used for separating various components of plant products with bear structural resemblance Analysis of cinchona, digitalis, ergot extracts and licorice.
• It is used in the agrichemical industry for the separation of herbicides.

HPLC METHOD DEVELOPMENT:

Developing and validating analytical methods is crucial in pharmaceutical research, development, and production. These methods ensure the identification, purity, potency, and effectiveness of pharmaceutical products. Method development involves considering factors like physicochemical characteristics (pKa, log P, solubility) for selecting the appropriate detection mode, especially in UV detection. The validation of an HPLC method for stability indication is a significant aspect of analytical development. It focuses on separating and quantifying the primary active ingredient, reaction impurities, synthetic intermediates, and degradants, ensuring the reliability and accuracy of the analytical process in pharmaceutical quality control.[21]

RECOGNIZING THE PHYSICOCHEMICAL PROPERTIES OF DRUG MOLECULES

When developing an analytical method for a medicinal molecule, understanding its physicochemical characteristics is essential. Initial considerations include the drug molecule's pH, polarity, solubility, and pKa. Polarity, a key physical characteristic, guides the choice of solvent and mobile phase composition. Molecular solubility, linked to polarity, adheres to the principle "like dissolves like." Selection of mobile phase or diluents is influenced by analyte solubility, ensuring compatibility. Analytes must not react with components and be soluble. Parameters like pH and pKa are critical in High-Performance Liquid Chromatography (HPLC) method development, influencing solvent selection and overall method success. pH equals -log10[H3O+] In High-Performance Liquid Chromatography (HPLC), achieving sharp and symmetrical peaks is often a result of optimizing the pH for ionizable analytes. Sharp, symmetrical peaks are crucial for obtaining low detection limits, low relative standard deviations between injections, and repeatable retention durations in quantitative analysis, ensuring the precision and sensitivity required for accurate measurements and reliable results.[22]

•  Choosing Chromatographic Conditions

During the initial development of a method, a set of conditions, including the detector, column, and mobile phase, is chosen to generate the sample's initial "scouting" chromatograms. Commonly, reversed- phase separations using a C18 column with UV detection are employed. At this stage, the decision arises on whether to develop a gradient method or opt for an isocratic approach, each offering distinct advantages depending on the specific separation requirements and characteristics of the analytes in the sample.

• Selection of Column

The column is the cornerstone of a chromatograph, playing a pivotal role in achieving reliable and accurate analyses. A well-chosen column ensures good chromatographic separation, contributing to trustworthy results. Conversely, improper column selection can lead to inadequate and confusing separations, rendering results invalid or challenging to interpret. In High Performance Liquid Chromatography (HPLC) systems, the column is central, and altering it significantly influences analyte resolution during method development. Considerations like particle size, retention capacity, stationary phase chemistry, and column dimensions are crucial for selecting the ideal column tailored to a specific analytical application. In an HPLC column, the three essential components are the hardware, matrix, and stationary phase. Matrices, such as alumina, zirconium, polymers, and most commonly silica, support the stationary phase. Silica matrices are favored for their strength, consistent spherical size, ease of derivatization, and resistance to compression under pressure. When selecting the ideal column, considerations encompass particle size, retention capacity, stationary phase chemistry, and column dimensions. These factors collectively influence the efficiency and effectiveness of the column in achieving accurate and reliable separations for specific analytical applications. In an HPLC column, the key components include hardware, matrix, and stationary phase. Various matrices, including alumina, zirconium, polymers, and most commonly silica, support the stationary phase. Silica matrices, widely used, offer strength, consistent spherical size, ease of derivatization, and resistance to compression under pressure. These characteristics contribute to the efficiency and reliability of HPLC columns in achieving precise separations for analytical applications. Silica is chemically stable in the majority of organic solvents and low pH environments. However, a drawback is that traditional silica-based solid supports disintegrate above pH 7. Recently developed silica- supported columns allow operation at higher pH levels. The composition, shape, and particle size of silica contribute to effective separation, with larger particle sizes increasing the number of theoretical plates. The suitability of the separation selectivity in HPLC can vary between columns from different manufacturers and even within batches from the same manufacturer. Key factors influencing this variability include parameters of the bonded stationary phase, properties of the silica substrate, and column diameters. Silica-based packing is commonly preferred in modern HPLC columns due to its favourable physical features, offering versatility and efficiency in achieving diverse and precise separations for analytical applications.[23]

• Selection of Chromatographic mode

Chromatographic modes are dictated by the analyte's polarity and molecular weight. Reversed- phase chromatography (RPC) takes precedence in case studies, especially for small organic compo ends. RPC is extensively utilized for separating ionizable substances, such as acids and bases, employing ion-pairing reagents or buffered mobile phases to prevent analyte ionization.

Optimization of Mobile phase

• Buffer Selection

Various buffers, including acetate, sodium phosphate, and potassium phosphate, were evaluated based on overall chromatographic performance and system suitability criteria. Through a series of experiments, potassium dihydrogen phosphate emerged as the most suitable buffer for successful separation of all peaks. Test concentrations of 0.02 M, 0.05 M, and 0.1 M were examined. Interestingly, altering the buffer concentration did not significantly impact the elution pattern and resolution, although the 0.05 M concentration enhanced the sensitivity of the technique without substantial changes in the separation characteristics.[24]

• Effect of pH

For ionizable analytes, determining the appropriate mobile-phase pH is crucial, guided by the analyte's pKa. This ensures that the target analyte is either in a neutral or ionized form. The ability to adjust the pH of the mobile phase is a powerful tool in the chromatographer's toolkit. This capability allows simultaneous modifications to retention and selectivity, providing a strategic means to optimize separation conditions, particularly for critical pairs of components in the sample. pH adjustment plays a vital role in tailoring chromatographic conditions to achieve desired separation outcomes.[25]

•  Effect of organic modifier

Selecting the organic modifier for reverse- phase HPLC is typically straightforward, with acetonitrile and methanol being the most popular choices (occasionally THF). Achieving optimal elution for every component in complex multicomponent samples under isocratic conditions, where the solvent strength remains constant, can be challenging. Hence, gradient elution is often employed, allowing for varying solvent compositions between k (retention factor) 1 and 10. This dynamic approach enhances separation efficiency and is particularly useful in handling intricate mixtures in high performance liquid chromatography.[26]

• Selection of detector and wavelength

After chromatographic separation, the target analyte is identified using appropriate detectors. Common detectors in liquid chromatography (LC) include UV, fluorescence, electrochemical, refractive index (RI), and mass spectrometry (MS). The choice of detector is influenced by the nature of the sample and the analytical objectives. For example, in multicomponent analysis, the absorption spectra may shift to longer or shorter wavelengths than those of the parent chemical, influencing the choice of a suitable detector for accurate and selective identification. Detector selection plays a crucial role in achieving the desired sensitivity and specificity in LC analysis. In UV detection, the spectra of the target analyte and contaminants must be acquired at various levels, superimposed, and then normalized. Selecting a wavelength is crucial to ensure a sufficient response for the majority of analytes, allowing for accurate and reliable detection in liquid chromatography. The careful consideration of UV spectra at different levels ensures that the analytical method is sensitive to all relevant components in the sample, contributing to the precision and reliability of the analysis.[27]

•  Creating an analytic approach

The initial stage in developing an analytical method for Reverse Phase High- Performance Liquid Chromatography (RP-HPLC) involves selecting various chromatographic parameters such as the mobile phase, column, mobile phase flow rate, and mobile phase pH. Through trials, each characteristic is optimized and then compared against system suitability parameters. Typical parameters include a retention time of more than five minutes, a theoretical plate count exceeding 2000, a tailing factor less than two, a resolution greater than five, and a percent Relative Standard Deviation (R.S.D.) of the area of analyte peaks in standard chromatograms not exceeding two percent. These parameters ensure the reliability and precision of the RP-HPLC method. In simultaneous estimation of two components, the detection wavelength is typically chosen at an isobestic point. Following this, the linearity of the drug is assessed to determine the concentration range exhibiting a linear pattern. The established approach for simultaneous estimation is further validated by analyzing a laboratory combination. Subsequently, the commercial product is diluted to match the linearity concentration range for analysis. This systematic process ensures the practicality, accuracy, and reliability of the method for simultaneous estimation in liquid chromatography.[28]

• Sample preparation

Sample preparation is a crucial step in High-Performance Liquid Chromatography (HPLC) analysis, ensuring a homogeneous and repeatable solution for injection onto the column. The goal of sample preparation is to create an interference-free aliquot that is column-compatible and compatible with the desired HPLC method. This involves selecting a sample solvent that dissolves in the mobile phase without compromising retention or resolution. The initial steps in sample preparation involve sample collection and injection into the HPLC column, laying the foundation for accurate and reliable chromatographic analysis.

•  Method optimization

Identify the weaknesses in the approach and employ experimental design to enhance it. Assess the impact of the approach on various samples, equipment configurations, andenvironmental factors. This iterative process helps refine the methodology, ensuring robustness, reliability, and applicability across diverse conditions in High-Performance Liquid Chromatography (HPLC) analysis.[29]

•  Validation

Validation is the systematic process of assessing and providing objective evidence that specific requirements for a particular intended use are met. It involves evaluating a method's performance and demonstrating its capability to meet specific criteria. Essentially, validation provides a thorough understanding of what your technique can reliably produce, particularly when dealing with low doses or challenging conditions in analytical methods like High-Performance Liquid Chromatography (HPLC).

METHOD VALIDATION [30]

Validation is the process of laboratory testing to demonstrate that the performance characteristics of an analytical method meet the requirements of the intended analytical application. Whether used by multiple operators with the same equipment in the same or different laboratories, any new or updated method must be validated to ensure it consistently produces repeatable and reliable results. The specific method and its intended uses determine the type of validation program required, ensuring that the analytical process is robust and fit for its purpose in various settings. Method validation results are a crucial aspect of any robust analytical procedure, providing an evaluation of the quality, consistency, and reliability of analytical results. Essential to the validation process is the use of equipment that meets specifications, is correctly calibrated, and is operating and functional. The validation process ensures that analytical methods are thoroughly assessed and either validated for use or invalidated if they do not meet the required criteria. This ensures the accuracy and dependability of analytical results in various applications.

The following are typical parameters recommended by the FDA, USP, and ICH.

1. Specificity

2. Linearity & Range

3. Precision

I. Method precision (Repeatability)

II. Intermediate precision (Reproducibility)

4. Accuracy (Recovery)

5. Solution stability

6. Limit of Detection (LOD)

7. Limit of Quantification (LOQ)

8. Robustness

9. Range

10. System suitability

1. Specificity

Selectivity and specificity are often used interchangeably in the context of method validation. Specificity refers to the ability to unequivocally assess the analyte in the presence of other components that may be present. This is the capacity to distinguish the analyte with absolute certainty in the presence of potentially interfering substances. To determine specificity, a comparison is made between test results from an analysis of samples containing contaminants, degradation products, or placebo ingredients and those from an analysis of samples without such elements. This comparison controls and evaluates the method’s ability to selectively identify and quantify the analyte of interest amidst potential interferences, ensuring the reliability and accuracy of the analytical method.

2. Linearity and range

Linearity in an analytical process refers to its ability to produce test results that are directly proportional to the concentration of the analyte in the sample, within a specified range. It is crucial to evaluate this linear relationship across the spectrum of the analytical technique. The suggested approach involves diluting a normal stock solution containing the constituent parts of the medicinal product to directly demonstrate linearity on the drug substance. In establishing linearity, the confidence interval around the slope of the regression line is commonly employed. According to ICH recommendations, a minimum of five concentrations is proposed for establishing linearity. The range of an analytical method is defined as the interval between the higher and lower values that have been demonstrated to be determined with precision, accuracy, and linearity using the method. This comprehensive assessment ensures the reliability and validity of the analytical method over a defined concentration range.[31]

3. Precision

Precision in the context of analytical methods represents the degree of agreement or scattering between a series of measurements made under specific conditions from several samplings of the same homogeneous material. Precision is a critical parameter for assessing the entire analytical process's reproducibility. Precision consists of two components: repeatability and intermediate precision. Repeatability is the variation experienced by a single analyst on a single instrument. It does not distinguish between variance introduced by the sample preparation procedure and that caused by the instrument or system. During validation, numerous replicates of an assay composite sample are analysed using the analytical procedure to determine repeatability, and recovery value is calculated. Intermediate precision refers to the fluctuation that occurs within a laboratory on different days, with different instruments, and involving different analysts. These components of precision assessment ensure a comprehensive understanding of the reliability and reproducibility of the analytical method under varying conditions and across different operators.[32]

4. Accuracy

Accuracy is the extent to which a measured value aligns with the true or accepted value. In practice, accuracy refers to the discrepancy between the true value and the mean value obtained. To calculate accuracy, the method is applied to samples with known analyte concentrations, which are then compared to blank and standard solutions to ensure there is no interference. Accuracy is computed as a percentage of the analyte recovered by the assay based on the test results. It is commonly expressed as the assay-based recovery of known, additional analyte levels, providing a measure of how well the analytical method reflects the true values.[33]

5. Solution stability

During validation, the stability of standards and samples is assessed under various conditions, including normal settings, standard storage conditions, and sometimes within the instrument. This evaluation helps determine whether specific storage conditions, such as refrigeration or protection from light, are necessary to maintain the stability of standards and samples. Understanding the impact of storage conditions is crucial for ensuring the reliability and integrity of analytical results over time, and it informs the appropriate handling and storage practices for the substances involved in the analysis.[34]

6. Limit of Detection (LOD)

The detection limit of a single analytical method is the most basic measure of an analyte in a sample that can be identified but not accurately quantified. This limit represents the lowest concentration at which the presence of the analyte can be reliably detected, providing a fundamental indicator of the method's sensitivity.[35]

7. Limit of Quantification (LOQ)

The quantitation limit of a specific analytical system is the lowest quantity of analyte in a sample that can be precisely and accurately measured quantitatively. This limit serves as a quantitative test parameter for assessing low levels of analytes in test matrices. The quantitation limit is crucial in identifying impurities and/or contaminants in samples and provides a threshold for reliable quantitative measurements in analytical methods.[36]

8. Robustness

The robustness of an analytical procedure isa measure of its reliability under typical conditions and its ability to withstand small but intentional alterations in method parameters. This quality assessment ensures that the analytical method remains dependable and produces consistent results even when subjected to minor variations or deliberate adjustments in its parameters. Robust methods are less sensitive to changes and variations, contributing to the method's reliability in real world analytical applications.[37]

9. Range

The range of an analytical method refers to the interval between the higher and lower values of an analyte that have been demonstrated with sufficient linearity, precision, and accuracy. This range is typically determined based on a linear or nonlinear response curve and is expressed in the same unit as the test findings. Establishing a defined range is essential for accurately assessing and reporting results within the method's validated and reliable concentration limits Range determination.[38]

10. System Suitability

System suitability tests are a standard practice in liquid chromatographic procedures. They serve as a guarantee that the chromatographic system's repeatability, resolution, and detection sensitivity are sufficient for the intended analysis. These tests are based on the concept that the tools, electronics, processes involved in the analysis, and the samples to be examined are all components of a larger system that can be assessed as a whole. Key parameters such as peak resolution, the number of theoretical plates, peak tailing, and capacity are examined during system suitability tests to assess the adequacy and performance of the employed analytical method. This comprehensive evaluation ensures the reliability and fitness of the chromatographic system for accurate and reproducible analyses.[39]

FUTURE PERSPECTIVES

Future advancements in HPLC are expected to focus on miniaturization, automation, and the development of greener chromatographic techniques. The integration of HPLC with hyphenated technologies such as LC-MS/MS, HPLC-NMR, and microfluidic systems will further expand its application in metabolomics, proteomics, and biomarker discovery. The use of eco-friendly solvents, high-speed columns, and artificial intelligence-driven method optimization will address current challenges of cost, time, and environmental impact. Additionally, the growing need for real-time and point-of-care analysis will push HPLC technology toward portable, high-throughput, and user-friendly systems. As pharmaceutical research evolves, HPLC will continue to adapt, offering unparalleled accuracy, sensitivity, and efficiency for future drug discovery and development.

CONCLUSION

High Performance Liquid Chromatography (HPLC) stands as an indispensable analytical tool for the separation, identification, and quantification of pharmaceutical and biological compounds. Its ability to deliver highly precise and reproducible results has made it a gold standard technique in drug development, quality control, and regulatory analysis. Method development strategies focusing on physicochemical properties, mobile phase optimization, and detector selection play a pivotal role in achieving robust and accurate results. Moreover, method validation ensures reliability, compliance, and reproducibility, thereby establishing HPLC as an essential component of pharmaceutical sciences.

ACKNOWLEDGEMENT   

The authors express sincere gratitude to all researchers whose valuable contributions have formed the basis of this review. The support and insights from mentors, colleagues, and institutions involved in facilitating access to relevant resources are also gratefully acknowledged.

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