Porous Graphitic Carbon (PGC) Chromatography Columns: Creating New Selectivity for Challenging Separations through Molecular Shape and the π-Electron Cloud on the Graphitic Surface

1. What challenging separations is porous graphitic carbon (Porous Graphitic Carbon, PGC) intended to address?

In high-performance liquid chromatography (High Performance Liquid Chromatography, HPLC), octadecylsilane-bonded stationary phase (Octadecylsilane, C18) is the most commonly used reversed-phase stationary phase. The main separation basis of C18 is hydrophobic partitioning: the more hydrophobic a molecule is, the more easily it is usually retained. This rule applies to many moderately polar and nonpolar small molecules, but it often becomes insufficient for the following types of samples.

1) Insufficient retention of polar small molecules

Amino acids, organic acids, nucleotide-related molecules, sugar phosphates, and some polar metabolites often show insufficient retention on C18. Their elution times may be close to those of unretained components, resulting in low peak capacity and a narrow separation window. A 2024 polar metabolomics study pointed out that conventional reversed-phase liquid chromatography provides limited retention for metabolites with an octanol–water partition coefficient, logP, below zero, and that polar metabolites usually require hydrophilic interaction chromatography (Hydrophilic Interaction Chromatography, HILIC) or derivatization-based gas chromatography methods.

2) Difficulty distinguishing structurally similar compounds

Positional isomers, epimers, configurational isomers, drug degradation products, and glycan isomers may have the same molecular weight, similar polarity, and similar hydrophobicity. When C18 relies mainly on hydrophobicity differences, co-elution can easily occur.

3) Liquid chromatography–mass spectrometry (Liquid Chromatography-Mass Spectrometry, LC-MS) methods are not suitable for strong ion-pairing conditions

Ion-pairing reagents can improve reversed-phase retention of charged or highly polar compounds. However, these reagents may adsorb onto liquid chromatographic components, chromatographic columns, and the mass spectrometer ion source, causing signal suppression in subsequent analyses, loss of column efficiency, or system carryover.

The value of porous graphitic carbon (Porous Graphitic Carbon, PGC) is not simply to enhance retention, but to provide a separation logic different from that of C18. It can use the π-electron cloud on the graphitic surface, molecular shape, the position of polar groups, and the effective surface contact area to generate new retention and selectivity for certain compounds that are difficult to handle with C18 or HILIC.

2. Why PGC is not a “more hydrophobic C18”

The main body of the PGC stationary phase is porous graphitic carbon. Graphite is composed of stacked planar layers formed by six-membered carbon rings, and a single plane can be regarded as a graphene layer. Each carbon atom bonds with three neighboring carbon atoms within the plane, while the remaining electrons participate in the formation of a delocalized π-electron cloud. PGC is formed by high-temperature treatment of an amorphous carbon template, producing interwoven graphitized ribbon-like structures. Its surface contains relatively flat graphitic planes as well as edge regions between graphitic ribbons.

A C18 stationary phase can be understood as a layer of hydrophobic alkyl chains. After analytes enter this hydrophobic environment, separation occurs mainly according to differences in hydrophobicity. PGC, by contrast, is more like a rigid graphitic surface with a π-electron cloud. Whether an analyte is retained depends not only on hydrophobicity, but also on whether it can approach the graphitic surface, whether it contains polarizable groups, and whether it can form a sufficiently large surface contact area.

Comparison item	C18 stationary phase	PGC stationary phase
Nature of the stationary phase	Hydrophobic alkyl chains bonded to a silica surface	Porous graphitic carbon surface
Main separation basis	Mainly hydrophobic partitioning	Adsorption, dispersion interactions, electronic interactions, shape selectivity
Behavior toward polar compounds	Increased polarity usually leads to reduced retention	Some polar molecules can show enhanced retention through the polar retention effect on graphite
Sensitivity to molecular shape	Relatively weak	Strong, especially affected by planarity and effective contact area
Typical uses	General reversed-phase separations	Challenging separations of polar small molecules, isomers, glycans, and structurally similar compounds

3. What interactions contribute to PGC retention?

PGC retention is affected simultaneously by dispersion interactions, the polar retention effect on graphite, and effective surface contact area.

3.1 Dispersion interactions: PGC has some reversed-phase characteristics

The PGC surface is composed of carbon atoms and can generate dispersion interactions with hydrophobic molecules. For some homologous series such as alkylbenzenes and nitroalkanes, the retention trends on PGC show a certain correlation with those on C18.

This indicates that PGC is not completely detached from reversed-phase behavior. An increase in hydrophobic surface area may still enhance retention. However, dispersion interactions can only explain the aspect in which PGC resembles C18. They cannot explain the special selectivity of PGC toward polar cyclic molecules, conjugated molecules, and isomers.

3.2 Polar retention effect on graphite: polar groups may participate in electronic interactions

The polar retention effect on graphite (Polar Retention Effect on Graphite, PREG) is a key concept that distinguishes PGC from C18. It refers to possible electronic interactions between polar or polarizable groups in the analyte and the π-electron cloud on the graphitic surface.

The exact mechanism of this effect has not been fully clarified. It may be related to charge induction, lone-pair electron donor–acceptor interactions, π–π overlap, and the position of the analyte’s polar groups relative to the graphitic plane.

Polar compounds that are weakly retained on C18 are not necessarily weakly retained on PGC. When a molecule can approach the graphitic surface, has sufficient contact area, and is under suitable mobile-phase conditions, molecules containing heterocycles, carbonyl groups, hydroxyl groups, carboxyl groups, amino groups, phosphate groups, aromatic rings, or conjugated structures may form additional interactions through their polar groups and the graphitic π-electron cloud.

3.3 Effective surface contact area: planar fitting ability affects retention strength

PGC is highly sensitive to molecular shape. The larger the area over which an analyte can approach the graphitic surface, the more likely it is to be strongly retained. Molecules with good planarity, high rigidity, aromaticity, or a high degree of conjugation are usually more likely to form effective contact with the graphitic surface.

For example, uracil has a more planar structure and can form a larger contact area with the graphitic plane. Dihydrouracil, because its ring becomes more nonplanar after saturation, has a reduced contact area and therefore shows markedly weaker retention.

From the perspective of method development, PGC retention strength can be understood qualitatively as:

PGC retention strength ≈ dispersion interactions + polar retention effect on graphite + effective contact area between the molecule and the graphitic surface

4. Which samples are worth trying on PGC first?

PGC is suitable for problems involving insufficient retention or insufficient selectivity on conventional stationary phases. Whether PGC is worth trying should first be judged by the structure of the analyte, rather than by polarity alone.

Analyte feature	Whether PGC should be tried first	Rationale
Planar aromatic molecules, heterocyclic molecules, conjugated molecules	Suitable	They can easily form a relatively large contact area with the graphitic surface and may also undergo π-related interactions
Nucleobases, nucleosides, and some polar drug scaffolds	Suitable	They contain polar groups, cyclic structures, and a certain degree of planarity
Organic acids, amino acids, sugar phosphates, and other polar metabolites	Worth trying	C18 often provides insufficient retention, and PGC may offer alternative selectivity
Sugars, oligosaccharides, and glycan isomers	Suitable	PGC is sensitive to differences in linkage type, configuration, and local spatial structure
Positional isomers, epimers, and configurational isomers	Suitable	The shape selectivity of PGC may amplify structural differences
Very small, highly polar molecules lacking planar structure	Use with caution	They may be strongly solvated by the mobile phase and have insufficient contact area with the graphitic surface
Highly flexible molecules with many conformations	Use with caution	Effective surface contact may be unstable, making retention difficult to predict
Complex matrices containing strongly adsorbing impurities	Worth trying, but requires focused validation	Matrix components may alter the PGC surface state, leading to retention drift or carryover

Note: PGC is primarily suitable for “polar compounds with structural features,” not for all polar compounds.

Even if small polar analytes contain carbonyl groups, planar structures, or uneven charge distributions, they may still show weak retention because they are too small or have insufficient contact area with the graphitic surface. In contrast, polar cyclic compounds such as uracil and cytosine can be retained on PGC.

5. Three valuable application scenarios for PGC

5.1 Polar metabolite analysis

Polar metabolites are involved in energy metabolism, amino acid metabolism, nucleotide metabolism, sugar metabolism, and phosphorylated intermediates. They are often insufficiently retained on C18. When HILIC is used, the method may also be limited by high-organic initial conditions and sample solvent compatibility.

PGC can serve as a complementary route beyond C18 and HILIC. A 2024 polar metabolomics study showed that a PGC-LC-MS method could reliably retain polar metabolites with logP as low as approximately -9.1, covering a metabolite range of approximately -9.1 to 5.6 in logP, and evaluated repeatability, recovery, and quantitative performance through a quality-control system.

In polar metabolite analysis, PGC is mainly used to address the following method development needs:

1. The target analytes are insufficiently retained on C18, with elution times close to those of unretained components;

2. HILIC places high demands on sample solvent, initial mobile phase, or column equilibration conditions;

3. Ion-pairing reagents are not suitable for shared LC-MS systems;

4. There is a need to reduce derivatization steps and directly analyze water-soluble metabolites;

5. The method needs to cover polar to moderately polar metabolites within the same run.

5.2 Analysis of sugars, oligosaccharides, and glycan isomers

The difficulty of glycan analysis lies not only in their high polarity, but also in the large number of isomers. Glycans with the same composition may differ in linkage position, branching pattern, configuration, or sialic acid linkage, and these differences may have distinct biological significance.

PGC is commonly used in glycomics for the separation of glycan isomers. A 2021 study on N-glycans pointed out that PGC chromatography is suitable for N-glycan separation because of its high resolving ability, but robust and reproducible implementation is not always easy. In that study, in-house packed PGC columns were used to detect multiple structural and compositional isomers in ovarian cancer tissue samples.

In sugar and glycan analysis, PGC is mainly used to amplify the following structural differences:

1. Whether glycans with the same composition contain multiple structural isomers;

2. Whether the glycosidic linkage positions differ;

3. Whether the branching structures differ;

4. Whether the sialic acid linkage types differ;

5. Whether specific isomer ratios change among different sample groups.

5.3 Analysis of drug impurities, degradation products, and structurally similar compounds

In drug development and quality control, challenging separations often arise from highly similar impurities, degradation products, positional isomers, and epimers. These compounds may have very similar retention on C18.

PGC can serve as an orthogonal-selectivity stationary phase. It considers not only hydrophobicity differences, but also molecular planarity, the spatial orientation of substituents, the position of polar groups, and the way the molecule contacts the graphitic surface. A 2024 review on PGC also listed isomer separation as one of the important application directions of PGC stationary phases.

In the analysis of drug impurities and structurally similar compounds, PGC is mainly used to supplement reversed-phase chromatographic selectivity:

1. The main component and polar impurities are insufficiently separated on C18;

2. Degradation products co-elute with the main peak or known impurities;

3. Positional isomers, epimers, or configurational isomers are difficult to distinguish;

4. Ion-pairing methods are not suitable for LC-MS detection;

5. Selectivity remains insufficient after switching among different C18, phenyl, or polar-embedded reversed-phase columns.

6. Common problems and troubleshooting in PGC methods

The special selectivity of PGC also brings challenges in method development. Common problems include retention drift, carryover, strong adsorption, insufficient column equilibration, and matrix effects.

Observation	Possible cause	Troubleshooting approach
Retention time changes from injection to injection	The column surface state has not stabilized; re-equilibration after the gradient is insufficient	Extend equilibration time under the initial mobile-phase conditions; inject standards repeatedly to observe stability
Severe peak tailing	The analyte interacts too strongly with the graphitic surface	Increase elution strength; adjust pH, buffer salts, or organic solvent type
Carryover peaks appear in blank injections	Strongly adsorbed components are not fully eluted	Add a stronger wash step; check carryover from the injection needle, tubing, and post-column system
Standard retention changes after matrix samples	Matrix contamination or strongly adsorbing matrix components alter the column surface	Strengthen sample pretreatment; use a guard column; include matrix blanks and washing procedures
Polar molecules are still not retained on PGC	The molecule is too small, strongly solvated, in an unfavorable charge state, or has insufficient effective contact area	Switch to HILIC, ion-exchange, or derivatization strategies; do not judge only by polarity
Poor batch-to-batch method reproducibility	Column equilibration, cleaning, and initial state control are insufficient	Fix the column maintenance procedure; record column age, injection amount, and cleaning history

Bapiro and co-workers proposed that retention loss and variability in PGC methods may be related to the inability to maintain a consistent PGC surface state before and after the gradient. By regulating the preparation, elution, and maintenance stages in the mobile-phase program, retention loss and variability can be reduced.

Three points deserve special attention in PGC method development.

① Do not optimize only the elution gradient. Column equilibration, strong washing, re-equilibration, and cleaning procedures are equally important.

② Do not evaluate only standard solutions. Complex matrices may alter the PGC surface state. Matrix blanks, matrix-spiked samples, and repeated-injection experiments are needed.

③ Do not directly apply all C18 experience rules. Small molecules such as uracil, which are often used on C18 to estimate dead time, may be retained on PGC and therefore cannot be used directly as dead-time markers.

7. What PGC contributes to scientific research and experimental design

PGC is not only a backup chromatographic column for solving insufficient retention. It can also serve as a tool for studying molecular structural differences. It converts differences in molecular planarity, electron distribution, polar-group position, and spatial configuration into differences in chromatographic retention.

7.1 Using multiple stationary phases to compare and infer separation mechanisms

The same group of compounds can be tested on C18, HILIC, and PGC. Differences in retention across the three stationary phases can help determine:

1. Whether the separation is mainly controlled by hydrophobicity, or by polarity and shape;

2. Whether the differences among isomers arise from spatial configuration;

3. Whether polar groups may participate in the polar retention effect on graphite;

4. Whether the molecule has a planar contact region suitable for PGC separation.

This comparison is not simply “trying different columns.” Instead, it uses retention behavior on different stationary phases to infer molecular interaction characteristics.

7.2 Building PGC method-development hypotheses from structural features

PGC method development can start by forming hypotheses based on the following structural features:

1. Planarity;

2. Number of aromatic rings;

3. Degree of conjugation;

4. Number of rotatable bonds;

5. Polar surface area;

6. Dipole distribution;

7. Polarizability;

8. Molecular projected area;

9. Number of hydrogen-bond donors and acceptors;

10. Charge state.

These parameters cannot determine retention on their own, but they can help experimentalists judge which compounds are worth screening first on PGC.

7.3 Using PGC to reveal isomers hidden by conventional methods

In complex samples, a single peak does not necessarily represent a single structure. For glycans, natural products, metabolites, and drug impurities, PGC may split a single peak observed on C18 into multiple isomeric peaks.

Research questions suitable for investigation include:

1. Whether a single peak on C18 is separated into multiple peaks on PGC;

2. Whether the separated peaks have the same accurate mass;

3. Whether tandem mass spectrometry fragments suggest differences in linkage mode or configuration;

4. Whether isomer ratios change under different biological states;

5. Whether chromatographic separation differences can explain differences in function, activity, or metabolic pathway.

The scientific value of PGC lies in the fact that it not only helps researchers “see peaks,” but may also help them “see structural differences.”

8. Product Selection Navigation for Porous Graphitic Carbon Chromatography Columns: From Method Conditions and Retention Mechanisms to Sugar and Polar Small-Molecule Analysis

Research or experimental goal	Recommended table to consult first	Why consult this table first	Recommended linked tables	Navigation guidance
Establish basic method conditions for porous graphitic carbon chromatography columns	Table 1. Basic materials for method development, mobile phases, and volatile additives	Table 1 lists commonly used method-development reagents such as acetonitrile, methanol, formic acid, ammonium formate, ammonium acetate, ammonium bicarbonate, and trichloroacetic acid. It can be used first to determine the organic phase, acidic additive, buffer salt, and sample pretreatment conditions.	Tables 2 and 4	First determine the detection mode, ionization state of the target analytes, and sample matrix, then select the mobile-phase system and buffer salt conditions.
Compare the effects of different mobile-phase conditions on retention, peak shape, and elution strength	Table 1	Porous graphitic carbon stationary phases are sensitive to organic solvent type, acidity, buffer salts, and column equilibration conditions. The reagents in Table 1 can be used to build method-screening combinations.	Tables 2, 3, and 4	Nucleobases or nucleosides in Table 2, sugars in Table 3, and organic acids in Table 4 can be used as representative analytes to observe changes in retention time, peak shape, and carryover.
Verify the effects of molecular planarity, polar groups, and effective surface contact area on retention	Table 2. Retention mechanism evaluation compounds, nucleobases, nucleosides, and nucleotides	Table 2 includes uracil, dihydrouracil, cytosine, adenine, and multiple nucleosides, which can be used to compare the effects of planar heterocycles, nonplanar structures, and polar groups on retention by porous graphitic carbon.	Table 1	First use structurally well-defined standards to establish retention patterns, then adjust the mobile phase and buffer salt conditions. Avoid judging the mechanism directly from complex samples.
Analyze polar small molecules related to nucleobases, nucleosides, and nucleotides	Table 2	Table 2 covers representative nucleobases, nucleosides, and phosphorylated nucleotides, and can be used to establish a retention-screening system for polar heterocycles and phosphorylated molecules.	Tables 1 and 4	Nucleosides can be used to evaluate the effects of planar heterocycles and hydroxyl-containing structures; adenylic acid can be used to examine elution and peak shape for highly polar, charged molecules.
Compare the effects of monosaccharide configurational differences and disaccharide linkage differences on separation	Table 3. Sugars, disaccharide isomers, and glycan-related units	Table 3 includes glucose, fructose, galactose, mannose, lactose, maltose, and cellobiose, and is suitable for evaluating separation based on sugar configuration, isomeric relationships, and glycosidic linkage differences.	Table 1	Sugar retention is strongly affected by mobile phase, buffer salts, and column equilibration. It is recommended to screen mobile-phase conditions in parallel with Table 1.
Design analyses related to glycans, acidic sugars, and sialylated structures	Table 3	N-Acetylneuraminic acid in Table 3 can serve as a representative structure for acidic sugars and sialylated glycans, and is suitable for introducing analysis of glycan terminal structures and local acidic groups.	Tables 1 and 2	Monosaccharides and disaccharides can first be used to establish a retention basis, followed by introduction of acidic sugar representatives to observe the influence of acidic groups on retention and peak shape.
Establish methods for polar metabolite analysis	Table 4. Polar metabolites, highly polar ionic analytes, and pesticide-residue representatives	Table 4 lists representative compounds such as lactic acid, pyruvic acid, citric acid, succinic acid, fumaric acid, malic acid, α-ketoglutaric acid, and amino acids, which can be used for polar metabolite method screening.	Table 1	First use organic acids and amino acid representatives to judge retention, peak shape, and compatibility with aqueous samples, then adjust volatile buffer salts and acidity conditions.
Analyze tricarboxylic acid cycle-related organic acids and polycarboxylic acid metabolites	Table 4	Table 4 includes various dicarboxylic acids, hydroxy dicarboxylic acids, and polycarboxylic acid representatives, and is suitable for evaluating retention and elution of compounds with multiple ionizable sites on porous graphitic carbon columns.	Table 1	Focus on acidity, buffer salt concentration, peak tailing, and retention reproducibility. Avoid judging method feasibility based only on a single retention time.
Screen highly polar zwitterionic compounds such as amino acids	Table 4	Table 4 includes glycine, serine, and glutamic acid, which can be used to observe retention differences among small amino acids, hydroxy amino acids, and acidic amino acids.	Tables 1 and 2	Amino acids are often insufficiently retained in reversed-phase systems. Porous graphitic carbon columns can be used to evaluate whether dependence on derivatization or ion-pairing conditions can be reduced.
Conduct method screening for highly polar pesticide residues or ionic analytes	Table 4	Table 4 includes glyphosate, aminomethylphosphonic acid, glufosinate-ammonium, methyl viologen, and diquat dibromide, and is suitable for method evaluation of highly polar phosphonic acid compounds and cationic analytes.	Table 1	Pay close attention to buffer salt conditions, carryover, cleaning procedures, and matrix effects. Avoid strongly adsorbing components altering retention in subsequent injections.
Compare the selectivity differences between porous graphitic carbon columns and conventional reversed-phase columns	Tables 2, 3, and 4	Table 2 can represent planar polar heterocycles, Table 3 can represent sugar isomers, and Table 4 can represent polar metabolites and ionic analytes. These three groups of standards cover different separation challenges.	Table 1	It is recommended to use the same set of standards on different stationary phases to compare retention, peak shape, and resolution, and to determine whether porous graphitic carbon columns provide new selectivity.

Table 1 | Basic Materials for PGC Method Development, Mobile Phases, and Volatile Additives

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Basic material for graphitized carbon	7782-42-5	G103922	Graphite	≥99.95% metals basis, D50＜600 nm	A material reference for understanding graphitized carbon surfaces, π-electron clouds, and adsorption features of carbon materials; it is not equivalent to commercial PGC chromatography column packing and cannot directly replace a PGC stationary phase.
Organic mobile phase	75-05-8	A433531	Acetonitrile (ACN)	Mass spectrometry grade (MS), UltraPureChrom™, UHPLC grade	A commonly used organic phase in PGC liquid chromatography and LC-MS, useful for adjusting elution strength, peak shape, and mass spectrometric response.
Organic mobile phase	67-56-1	M116126	Methanol	HPLC Plus grade, ≥99.9%	Can be compared with acetonitrile to evaluate differences in mobile-phase selectivity, and used to investigate retention changes of polar molecules, sugars, or aromatic heterocycles on PGC.
Acidic mobile-phase additive	64-18-6	F433212	Formic acid (FA)	Pharmaceutical grade, PharmPure™, ≥98%	Commonly used under acidic LC-MS conditions; can improve the peak shape of some polar compounds and regulate ionization state.
Acidic mobile-phase additive	76-05-1	T103293	Trifluoroacetic acid	For protein sequencing, ≥99%	Can be used to compare peak shape and retention changes under strongly acidic conditions; when used in LC-MS, ionization suppression and system carryover should be considered, and it is generally not used as a first-choice additive.
Volatile buffer salt	540-69-2	A432863	Ammonium formate	Anhydrous grade, reagent grade, ≥97%	Suitable for LC-MS-compatible buffer systems, and used to regulate retention and peak shape of charged polar compounds on PGC.
Volatile buffer salt	631-61-8	A112057	Ammonium acetate	HPLC grade, ≥99%	Can be used under weakly acidic to near-neutral mobile-phase conditions, and is suitable for method development involving nucleosides, sugars, organic acids, and polar metabolites.
Volatile buffer salt	1066-33-7	A110536	Ammonium bicarbonate	Reagent grade	Can be used in weakly alkaline or near-neutral volatile buffer systems, and is suitable for examining retention changes of charged polar analytes on PGC.
Sample pretreatment reagent	76-03-9	T433650	Trichloroacetic acid (TCA)	For electrophoresis, ≥99%, suitable for fixing solution (for IEF and PAGE gels)	Can be used for protein precipitation and aqueous metabolite extraction, and is suitable for designing sample pretreatment methods for PGC polar metabolomics; before LC-MS analysis, residual acidity and matrix effects need to be controlled, and it is not used as a routine mobile-phase additive.

Table 2 | PGC Retention Mechanism Evaluation Compounds, Nucleobases, Nucleosides, and Nucleotides

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Mechanism evaluation compound for planarity	66-22-8	U102087	Uracil	Moligand™, ≥99%	A representative planar polar heterocycle, useful for illustrating the response of PGC to molecular planarity, polar groups, and effective surface contact area.
Nonplanarity control evaluation compound	504-07-4	D113497	Dihydrouracil	≥97%	Can be compared with uracil to investigate how decreased planarity after ring saturation affects PGC retention.
Nucleobase / polar heterocycle	71-30-7	C104336	Cytosine	Moligand™, ≥98%	A representative nitrogen-containing polar heterocycle, useful for evaluating PGC retention and selectivity for nucleobase-type molecules.
Nucleobase / polar heterocycle	73-24-5	A108805	Adenine	≥99.5% (HPLC)	A purine-type planar heterocycle, useful for examining PGC retention of nitrogen-containing aromatic heterocycles and electronic interactions.
Nucleoside standard	58-96-8	U755611	Uridine	UltraBio™, ≥99%	A representative polar nucleoside molecule, suitable for comparing retention differences between PGC and hydrophilic interaction chromatography.
Nucleoside standard	58-61-7	A108807	Adenosine	Moligand™, analytical standard	Contains both a purine ring and ribose hydroxyl groups, and can be used for PGC nucleoside method screening and comparison of retention patterns.
Nucleoside standard	65-46-3	C100358	Cytidine	Moligand™, ≥99%	Can serve as a representative pyrimidine nucleoside for evaluating retention and peak shape of polar nucleoside compounds on PGC.
Nucleoside standard	118-00-3	G103965	Guanosine	Moligand™, ≥98%	A representative purine nucleoside, suitable for use together with adenosine, cytidine, and uridine to establish a PGC screening mixture for nucleosides.
Nucleotide / phosphorylated metabolite	61-19-8	A136967	5'-Adenylic Acid (5'-AMP)	Moligand™, ≥98% (HPLC)	A representative phosphorylated nucleotide, useful for examining PGC retention of highly polar, charged metabolites and LC-MS-compatible conditions.

Table 3 | Sugars, Disaccharide Isomers, and Glycan-Related Units

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Monosaccharide representative	50-99-7	D432810	D-(+)-Glucose	Anhydrous grade, PharmPure™, USP, BP, European Pharmacopoeia (Ph. Eur.), ACS	A representative monosaccharide, useful for basic evaluation of retention, peak shape, and polarity response in PGC sugar separations.
Monosaccharide isomer	57-48-7	F108332	D-Fructose	Analytical standard, ≥99.5%	A monosaccharide isomer of glucose, useful for examining the ability of PGC to separate structural differences among sugars.
Monosaccharide epimer	59-23-4	D274314	D-(+)-Galactose	High purity, ≥99%	A representative glucose epimer, useful for evaluating the response of PGC to differences in the spatial orientation of hydroxyl groups.
Monosaccharide epimer	3458-28-4	M103970	D-(+)-Mannose	Moligand™, analytical standard	Can be used together with glucose and galactose to examine PGC selectivity toward monosaccharide configurational differences and local polarity distribution.
Disaccharide representative	63-42-3	L103493	Lactosum, anhydrous	PharmPure™, USP, JP, European Pharmacopoeia (Ph. Eur.), NF	A representative disaccharide, useful for evaluating retention strength, peak shape, and glycosidic linkage differences in PGC sugar methods.
Disaccharide representative	69-79-4	M120965	Maltose solution	BioReagent, molecular biology grade, ~20% in H₂O	Can be used to compare the effect of glycosidic linkage mode on PGC retention in disaccharide systems.
Disaccharide isomer	528-50-7	C111867	D-(+)-Cellobiose	Analytical standard	Like maltose, it is composed of glucose units but differs in glycosidic linkage configuration, making it suitable for evaluating PGC separation of disaccharide isomers.
Glycan-related unit	131-48-6	A100555	N-Acetylneuraminic acid	≥98%	A sialylated glycan-related unit, useful for developing PGC methods for glycan, acidic sugar, and terminal glycosyl structure analysis.

Table 4 | Polar Metabolites, Highly Polar Ionic Analytes, and Pesticide-Residue Representatives

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Organic acid metabolite	50-21-5	L108839	DL-Lactic acid	AR, 85–90%	A representative small hydroxy acid, useful for evaluating PGC retention of polar organic acids and compatibility with aqueous samples.
Organic acid metabolite	127-17-3	P104138	Pyruvic acid	≥98% (T)	A representative α-keto acid, suitable for evaluating peak shape, stability, and retention in PGC polar metabolite methods.
Tricarboxylic acid cycle metabolite	77-92-9	C434175	Citric acid	Anhydrous grade, PharmPure™, USP, JP, BP, European Pharmacopoeia (Ph. Eur.), powder	A representative polycarboxylic acid metabolite, useful for evaluating the retention ability of PGC toward highly polar organic acids and molecules with multiple ionizable sites.
Tricarboxylic acid cycle metabolite	110-15-6	S431422	Succinic acid	PharmPure™, ChP, JP, ACS, NF, crystalline	A representative dicarboxylic acid, useful for PGC method screening of tricarboxylic acid cycle-related polar metabolites.
Tricarboxylic acid cycle metabolite	110-17-8	GMP1491392	Fumaric acid	PharmPure™, JPE, NF	A representative unsaturated dicarboxylic acid, useful for comparing the effect of a double-bond structure on PGC retention of organic acids.
Tricarboxylic acid cycle metabolite	97-67-6	M105696	L-(-)-Malic acid	Chemically pure (CP)	A representative hydroxy dicarboxylic acid, useful for evaluating retention and separation of related polar organic acids on PGC.
Tricarboxylic acid cycle metabolite	328-50-7	K105571	α-Ketoglutaric acid	Moligand™, ≥98%	A multifunctional dicarboxylic acid metabolite, useful for developing PGC-LC-MS methods for polar metabolites.
Amino acid metabolite	56-40-6	G432934	Glycine	UltraBio™, molecular biology grade, ultrapure grade, ≥99% (NT)	A representative small amino acid, useful for evaluating the retention behavior of highly polar zwitterionic compounds on PGC.
Amino acid metabolite	56-45-1	S137887	L-Serine	Animal-origin-free, USP, Moligand™, European Pharmacopoeia (Ph. Eur.), ≥98.5%	A representative hydroxy amino acid, suitable for PGC analysis of polar amino acids and peak shape evaluation.
Amino acid metabolite	56-86-0	G103979	L(+)-Glutamic acid	Ultrapure grade, ≥99.5% (NT)	A representative acidic amino acid, useful for examining PGC retention and elution conditions for metabolites with multiple polar groups.
Highly polar phosphonic acid analyte	1071-83-6	P109921	N-(Phosphonomethyl)glycine solution	Analytical standard, 10 μg/mL in water	A representative highly polar phosphonic acid compound, useful for evaluating retention, sensitivity, and LC-MS compatibility in PGC methods for highly polar pesticide residues.
Highly polar phosphonic acid analyte	1066-51-9	A151006	(Aminomethyl)phosphonic Acid	≥97% (T)	A representative glyphosate-related metabolite, useful for developing separation and quantitative methods for highly polar phosphonic acid compounds on PGC.
Highly polar pesticide standard	77182-82-2	G114499	Glufosinate-ammonium	Analytical standard	A representative highly polar herbicide, suitable for screening and method validation of PGC analysis for ionic pesticide residues.
Highly polar cationic analyte	1910-42-5	M106760	Methyl viologen dichloride	Analytical standard, ≥99%	A representative highly polar quaternary ammonium salt, useful for evaluating PGC retention, carryover, and cleaning conditions for cationic analytes.
Highly polar cationic analyte	85-00-7	D350633	Diquat Dibromide	Moligand™, ≥98%	A representative cationic herbicide, useful for evaluating retention, peak shape, and matrix effects in PGC methods for ionic pesticide residues.

Note: The products listed above are representative Aladdin products. More product specifications can be searched on the Aladdin website by “product name / CAS / catalog number.”

References

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[2] Russo M., Testa Camillo M. R., La Tella R., Rigano F., Donato P., Mondello L., Dugo P. Principles and applications of porous graphitic carbon stationary phase in liquid chromatography: An update. Journal of Chromatography A, 2024, 1719, 464728. DOI: 10.1016/j.chroma.2024.464728.

[3] Pereira L. Porous Graphitic Carbon as a Stationary Phase in HPLC: Theory and Applications. Journal of Liquid Chromatography & Related Technologies, 2008, 31(11–12), 1687–1731. DOI: 10.1080/10826070802126429.

[4] Knox J. H., Kaur B., Millward G. R. Structure and performance of porous graphitic carbon in liquid chromatography. Journal of Chromatography, 1986, 352, 3–25. DOI: 10.1016/S0021-9673(01)83368-9.

[5] Hanai T. Separation of polar compounds using carbon columns. Journal of Chromatography A, 2003, 989(2), 183–196. DOI: 10.1016/S0021-9673(02)02017-4.

[6] Bapiro T. E., Richards F. M., Jodrell D. I. Understanding the complexity of porous graphitic carbon chromatography: Modulation of mobile-stationary phase interactions overcomes loss of retention and reduces variability. Analytical Chemistry, 2016, 88(12), 6190–6194. DOI: 10.1021/acs.analchem.6b01167.

[7] Day F., O’Sullivan J., Ramzan F., Pook C. Polar metabolomics using trichloroacetic acid extraction and porous graphitic carbon stationary phase. Metabolomics, 2024, 20, 77. DOI: 10.1007/s11306-024-02146-7.

[8] Young C. Y. C., Condina M. R., Briggs M. T., Moh E. S. X., Kaur G., Oehler M. K., Hoffmann P. In-House Packed Porous Graphitic Carbon Columns for Liquid Chromatography-Mass Spectrometry Analysis of N-Glycans. Frontiers in Chemistry, 2021, 9, 653959. DOI: 10.3389/fchem.2021.653959.

[9] Stavenhagen K., Kolarich D., Wuhrer M. Clinical Glycomics Employing Graphitized Carbon Liquid Chromatography-Mass Spectrometry. Chromatographia, 2015, 78(5–6), 307–320. DOI: 10.1007/s10337-014-2813-7.

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