calibration curve comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
Practical HPLC testing depends on careful sample preparation and instrument maintenance. Samples may require filtration, dilution, pH adjustment, or extraction to avoid column damage and matrix interference. Mobile phases are degassed and filtered, and columns are equilibrated before injection. Common problems include peak tailing, baseline drift, ghost peaks, carryover, and co-elution of analytes. Documentation of instrument logs, calibration records, and electronic audit trails supports data integrity and traceability. Ongoing training and routine maintenance help reduce variability between analysts and laboratories.
Quality control laboratories use HPLC to check identity, purity, concentration, and stability of raw materials and finished products. A validated method specifies the column, mobile phase, flow rate, detection wavelength, injection volume, and run time. Samples are prepared and compared against reference standards of known concentration. The resulting chromatogram provides quantitative data, such as assay values and impurity levels. This approach is common in pharmaceutical, food, environmental, and industrial testing where consistent measurements are required.
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
| Parameter | Typical acceptance criterion | Notes |
|---|---|---|
| Resolution | ≥ 1.5 | Baseline separation of adjacent peaks |
| Tailing factor | ≤ 2.0 | Peak symmetry measure |
| Theoretical plates | > 2000 | Column efficiency indicator |
| Injection repeatability | ≤ 2% RSD | Relative standard deviation for replicate injections |
| Linearity | r² ≥ 0.995 | Calibration curve over the working range |
Routine quality control includes blanks, duplicates, spiked samples, and certified reference materials. Calibration curves are prepared with standards at several concentrations, and the detector response is checked for linearity. Carryover, column aging, mobile phase evaporation, and temperature drift can shift retention times or peak areas. Maintenance such as replacing seals, filters, and columns helps prevent failures. Records of injections, integration, and deviations support traceability. Audits may request raw data and instrument logs for each batch.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
Routine quality control monitors retention time shifts, baseline noise, system pressure, and peak shape. Trends can reveal column aging, mobile phase preparation errors, detector drift, or sample degradation. Corrective actions may include replacing the column, preparing fresh mobile phase, or recalibrating the detector. Stability testing often uses HPLC to measure parent compound loss and degradation product formation. Open questions remain about how accelerated stability results extrapolate to long-term storage under varied conditions.
Quality control for HPLC testing combines scheduled checks, documented procedures, and review of results. Before sample analysis, system suitability testing confirms that the instrument, column, and method meet predefined criteria. Common criteria include resolution between critical peaks, retention time precision, peak tailing, and theoretical plate count. Failure triggers investigation before results are reported. Records link raw data, calculations, instrument logs, and analyst identity to each batch, supporting audits and repeat analysis.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it through a packed column under pressure. A pump delivers a mobile phase at a controlled flow rate, and an injector introduces the sample into the stream. Differences in interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
Outbreaks of disease Food-born illness Bioterrorism Natural disasters APHL plays a critical role in crisis response to these public health emergencies through the Laboratory Response Network (LRN). The LRN was formed in 1999 in a cooperative effort between APHL, the CDC and FBI to rapidly detect, and respond to public health emergencies. The Department of Defense has joined in the effort to support biological response activities. In addition to their leadership during times of crisis, APHL has a strong focus on preparing public health laboratories on how to respond to emergencies when they happen through training and capacity-building, as well as creating model frameworks that labs around the country can use in order to have procedures in place to handle a crisis when it happens.
In the presence of air and various cofactors and enzymes, fatty acids are converted to acetyl-CoA. The pathway is called beta-oxidation. Each cycle of beta-oxidation shortens the fatty acid chain by two carbon atoms and produces one equivalent each of acetyl-CoA, NADH, and FADH2. The acetyl-CoA is metabolized by the citric acid cycle to generate ATP, while the NADH and FADH2 are used by oxidative phosphorylation to generate ATP. Dozens of ATP equivalents are generated by the beta-oxidation of a single long acyl chain. In oxidative phosphorylation, the key control point is the reaction catalyzed by cytochrome c oxidase, which is regulated by the availability of its substrate – the reduced form of cytochrome c. The amount of reduced cytochrome c available is directly related to the amounts of other substrates: 1 2 NADH + cyt c ox + ADP + P i ⇌ 1 2 NAD + + cyt c red + ATP {\displaystyle {\frac {1}{2}}{\ce {NADH}}+{\ce {cyt}}\ {\ce {c_{ox}}}+{\ce {ADP}}+{\ce {P_{i}}}\rightleftharpoons {\frac {1}{2}}{\ce {NAD^+}}+{\ce {cyt}}\ {\ce {c_{red}}}+{\ce {ATP}}}
Following TNF-R1 and Fas activation in mammalian cells a balance between proapoptotic (BAX, BID, BAK, or BAD) and anti-apoptotic (Bcl-Xl and Bcl-2) members of the Bcl-2 family are established. This balance is the proportion of proapoptotic homodimers that form in the outer-membrane of the mitochondrion. The proapoptotic homodimers are required to make the mitochondrial membrane permeable for the release of caspase activators such as cytochrome c and SMAC. Control of proapoptotic proteins under normal cell conditions of nonapoptotic cells is incompletely understood, but in general, Bax or Bak are activated by the activation of BH3-only proteins, part of the Bcl-2 family.
Work-related roadway crashes are the leading cause of death from traumatic injuries in the U.S. workplace. They accounted for nearly 12,000 deaths between 1992 and 2000. Deaths and injuries from these roadway crashes result in increased costs to employers and lost productivity in addition to their toll in human suffering. Truck drivers tend to endure higher fatality rates than workers in other occupations, but concerns about motor vehicle safety in the workplace are not limited to those surrounding the operation of large trucks. Workers outside the motor carrier industry routinely operate company-owned vehicles for deliveries, sales and repair calls, client visits, etc. In these instances, the employer providing the vehicle generally plays a major role in setting safety, maintenance, and training policy. As in non-occupational driving, young drivers are especially at risk. In the workplace, 45% of all fatal injuries to workers under age 18 between 1992 and 2000 in the United States resulted from transportation incidents.
Sources: en.wikipedia.org
The α2 receptor couples to the Gi/o protein. It is a presynaptic receptor, causing negative feedback on, for example, norepinephrine (NE). When NE is released into the synapse, it feeds back on the α2 receptor, causing less NE release from the presynaptic neuron. This decreases the effect of NE. There are also α2 receptors on the nerve terminal membrane of the post-synaptic adrenergic neuron. Actions of the α2 receptor include: decreased insulin release from the pancreas increased glucagon release from the pancreas contraction of sphincters of the GI-tract negative feedback in the neuronal synapses - presynaptic inhibition of norepinephrine release in CNS increased platelet aggregation decreases peripheral vascular resistance α2 agonists (see actions above) can be used to treat: hypertension – decrease blood pressure-raising actions of the sympathetic nervous system α2 antagonists can be used to treat: impotence – relax penile smooth muscles and ease blood flow depression – enhance mood by increasing norepinephrine secretion Subtype unspecific β agonists can be used to treat:
Cells require a full and functional cellular machinery to live. When they belong to complex multicellular organisms, they need to communicate among themselves and work for symbiosis in order to give life to the organism. These communications between cells triggers intracellular signaling cascades, termed signal transduction pathways, that regulate specific cellular functions. Each signal transduction occurs with a primary extracellular messenger that binds to a transmembrane or nuclear receptor, initiating intracellular signals. The complex formed produces or releases second messengers that integrate and adapt the signal, amplifying it, by activating molecular targets, which in turn trigger effectors that will lead to the desired cellular response.
The reaction happens with two metal cofactors (Mg or Mn) coordinated to the two aspartate residues on C1. They perform a nucleophilic attack of the 3'-OH group of the ribose on the α-phosphoryl group of ATP. The two lysine and aspartate residues on C2 selects ATP over GTP for the substrate, so that the enzyme is not a guanylyl cyclase. A pair of arginine and asparagine residues on C2 stabilizes the transition state. In many proteins, these residues are nevertheless mutated while retaining the adenylyl cyclase activity. There are ten known isoforms of adenylyl cyclases in mammals: These are also sometimes called simply AC1, AC2, etc., and, somewhat confusingly, sometimes Roman numerals are used for these isoforms that all belong to the overall AC class III. They differ mainly in how they are regulated, and are differentially expressed in various tissues throughout mammalian development.
Peptides are very useful as therapeutic and diagnostic substances. Their use is getting more popular, and display systems offer a useful way to engineer peptides and optimise their binding capabilities. Cells express surface proteins which can be involved in a whole host of responses including recognition of other cells, interaction with other cells, and cell signalling. Many types of bacteria have cell surface proteins such as the enteropathogenic E. coli intimin protein which is involved in binding to host cells, or the OmpA protein of E. coli cells which is important in keeping the structure of the outer membrane. Many surface proteins are involved in bacterial cell attachment and invasion of the host cell. By using bacterial display, target proteins on the host cell can be identified. These surface proteins need to first be translocated across the bacterial cell membranes from the cytoplasm to the cell surface. Gram-negative bacteria have an additional periplasmic space, which Gram-positive bacteria lack, so they have a harder task of translocating proteins. The display of heterologous proteins on the bacterial cell surface normally requires the fusion of the protein with a surface protein, called a scaffold.
Bactericidal permeability-increasing protein (BPI) is a 456-residue (~50kDa) protein that is part of the innate immune system, coded for in the human by the BPI gene. It belongs to the family of lipid-binding serum glycoproteins. BPI was initially identified in neutrophils, but is found in other tissues including the epithelial lining of mucous membranes. It is an endogenous antibiotic protein with potent killing activity against Gram-negative bacteria. It binds to compounds called lipopolysaccharides produced by Gram-negative bacteria. Lipolysaccharides are potent activators of the immune system; however, BPI at certain concentrations can prevent this activation. BPI was discovered by Jerrold Weiss and Peter Elsbach at New York University Medical School.
Sources: en.wikipedia.org
The Department was founded in 1934 in Kazan Teachers’ Institute to educate future teachers of chemistry. In November, 2011 the Department of Chemical Education became a structural unit of A. M. Butlerov Institute of Chemistry of Kazan (Volga Region) Federal University. Educational research was combined with fundamental and applied research in chemistry. International, All-Russian and regional research-to-practice conferences on chemical education organized by the Department are of the utmost interest. The Department has received letters of gratitude from school principals for instructing students in research and methodology in their preparation for teaching practice. Today 3 Doctors of Science and 5 Doctors of Philosophy are involved in the educational and bringing-up process at the Department. Since 2010 teachers have been retrained in the field of “Teacher of Chemistry”.The head of the Department is Suria I. Gilmanshina, Doctor of Philosophy in Chemistry, Doctor of Science in Education. The Department conducts research in the following fields:
Acetyl phosphate (AcP), a precursor to ATP, can readily be synthesized at modest yields from thioacetate in pH 7 and 20 °C and pH 8 and 50 °C, although acetyl phosphate is less stable in warmer temperatures and alkaline conditions than in cooler and acidic to neutral conditions. It is unable to promote polymerization of ribonucleotides and amino acids and was only capable of phosphorylation of organic compounds. It was shown that it can promote aggregation and stabilization of AMP in the presence of Na+, aggregation of nucleotides could promote polymerization above 75 °C in the absence of Na+. It is possible that polymerization promoted by AcP could occur at mineral surfaces. It was shown that ADP can only be phosphorylated to ATP by AcP and other nucleoside triphosphates were not phosphorylated by AcP. This might explain why all lifeforms use ATP to drive biochemical reactions.
Tight junctions are very important in embryo development. In the blastula, these cadherin mediated cell interactions are essential to development of epithelium which are most important to paracellular transport, maintenance of cell polarity and the creation of a permeability seal to regulate blastocoel formation. These tight junctions arise after the polarity of epithelial cells is established which sets the foundation for further development and specification. Within the blastula, inner blastomeres are generally non-polar while epithelial cells demonstrate polarity. Mammalian embryos undergo compaction around the 8-cell stage where E-cadherins as well as alpha and beta catenins are expressed. This process makes a ball of embryonic cells which are capable of interacting, rather than a group of diffuse and undifferentiated cells. E-cadherin adhesion defines the apico-basal axis in the developing embryo and turns the embryo from an indistinct ball of cells to a more polarized phenotype which sets the stage for further development into a fully formed blastocyst. Xenopus membrane polarity is established with the first cell cleavage. Amphibian EP-cadherin and XB/U cadherin perform a similar role as E-cadherin in mammals establishing blastomere polarity and solidifying cell-cell interactions which are crucial for further development.
For each diprotic acid titration curve, from left to right, there are two midpoints, two equivalence points, and two buffer regions. Due to the successive dissociation processes, there are two equivalence points in the titration curve of a diprotic acid. The first equivalence point occurs when all first protons from the first ionization are titrated. In other words, the amount of OH− added equals the original amount of H2A at the first equivalence point. The second equivalence point occurs when all protons are titrated. Therefore, the amount of OH− added equals twice the amount of H2A at this time. For a weak diprotic acid titrated by a strong base, the second equivalence point must occur at pH above 7 due to the hydrolysis of the resulted salts in the solution. At either equivalence point, adding a drop of base will cause the steepest rise of the pH value in the system.
Tight junctions are very important in embryo development. In the blastula, these cadherin mediated cell interactions are essential to development of epithelium which are most important to paracellular transport, maintenance of cell polarity and the creation of a permeability seal to regulate blastocoel formation. These tight junctions arise after the polarity of epithelial cells is established which sets the foundation for further development and specification. Within the blastula, inner blastomeres are generally non-polar while epithelial cells demonstrate polarity. Mammalian embryos undergo compaction around the 8-cell stage where E-cadherins as well as alpha and beta catenins are expressed. This process makes a ball of embryonic cells which are capable of interacting, rather than a group of diffuse and undifferentiated cells. E-cadherin adhesion defines the apico-basal axis in the developing embryo and turns the embryo from an indistinct ball of cells to a more polarized phenotype which sets the stage for further development into a fully formed blastocyst. Xenopus membrane polarity is established with the first cell cleavage. Amphibian EP-cadherin and XB/U cadherin perform a similar role as E-cadherin in mammals establishing blastomere polarity and solidifying cell-cell interactions which are crucial for further development.
Sources: en.wikipedia.org
Method validation is the documented process of confirming that an HPLC procedure is suitable for its intended use. It evaluates accuracy, precision, specificity, linearity, range, detection limits, and robustness. Validation criteria depend on the regulatory context and the sample type.
System suitability tests are short checks performed before or during an HPLC run to verify instrument and method performance. They often include resolution, tailing factor, theoretical plates, and injection precision. Results must meet predefined limits for sample data to be accepted.
HPLC retention time alone cannot definitively identify an unknown substance. A match with a reference standard under identical conditions provides supporting evidence. Confirmation typically requires mass spectrometry, nuclear magnetic resonance, or another orthogonal technique.
System suitability is a set of checks performed before and during an HPLC run to confirm that the instrument and method are working as expected. It may include retention time repeatability, resolution between peaks, peak symmetry, and signal intensity. Failing suitability criteria usually invalidates the run.