Essential List of Chromatography Supplies
Chromatography is a separation technique that allows scientists to analyze complex mixtures and is often used in research and clinical labs. A few of the common techniques include gas chromatography (GC) and high-performance liquid chromatography (HPLC).
Many consumables are required for chromatography testing and can be acquired through chromatography consumables suppliers, such as Chrom Tech. Here is an essential list of chromatography supplies.
Vials and Closures
Chromatography vials and closures are commonly used in gas and liquid chromatography for sample analysis, collection, and storage. Vials are most often made of glass but can be plastic as well. Vial dimensions and physical specifications are crucial to trouble-free operation with autosamplers and other instrumentation. For example, crimp closures are used for more volatile samples, whereas amber glass or black plastic is used for light-sensitive samples.
Closures are the combination of a cap and septa that protect the compound mixtures within the vials. Like vials, closures must be inert and uncontaminated as to not alter the results. Different applications require specific closure types, such as push-on caps and screw caps for convenience when you are not concerned with evaporation and crimp caps for volatile samples and chain-of-custody requirements.
Sample Preparation Consumables
Sample preparation is an important step in the analytical process, as it removes interferences before the sample is analyzed to prolong the system’s life.
Syringe filters are used to remove particulates from a liquid sample before analysis and are commonly used for HPLC or ion chromatography.
To select the proper syringe membrane filter, the size must be based on the volume of the sample being filtered. Further, the porosity is based on the size of the potential particles in the sample, and the membrane type depends on the solvent and analytes you need to filter.
The main selection criteria for syringe filters are solvent compatibility and porosity. The Chemical Resistance Table lists the most popular solvents in chromatography along with the compatible membrane types.
Solid Phase Extraction
The purpose of solid-phase extraction (SPE) is to clean the sample before injection. In SPE, you load the sample onto the cartridge (selecting media that retains the analytes of interest) and wash off the impurities. Then, elute analytes of interest for downstream analysis.
Agilent Bond Elut C18 is the most hydrophobic, bonded silica sorbent available. C18 is the most popular SPE sorbent due to its extreme retention of nonpolar compounds. Bond Elut C18 retains most organic analytes from aqueous matrices. When analyzing small to intermediate molecules, Bond Elut C18 can be used for desalting aqueous matrices before ion exchange, as salts pass through the sorbent unretained.
Tubing and Fittings
To use an HPLC system, plumbing your system with the appropriate tubing and fittings is important, as it impacts your instrument’s up-time. A fitting refers to a system comprised of a nut and ferrule. Determining what fitting system to use depends on the threads of the receiving port, the geometry of the receiving port, size and type of tube used, material of the port, and the amount of pressure expected.
The tubing used in your system can also have a dramatic impact on the quality of your system connections, and the tubing material can also impact your system’s performance. For example, FEP and PFA materials offer optimal chemical resistance but have poor pressure resistance—this type of tubing is typically used from the solvent inlet reservoir to the pump (at atmospheric pressure). Whereas PEEK and stainless steel tubing have excellent pressure resistance but are not as chemically inert—this type of tubing is typically found after the pump (where pressure is typically high). Pre-cut stainless steel tubing is electrolytically cut, providing a flat-burr-free end with a clean finish. This is recommended over cutting tubing in the lab.
Columns are the heart of the chromatography system and are also where the separation occurs. Different compounds pass through the column at different rates due to their polarity, molecule size, and its interaction with the stationary phase, allowing for the sample to be analyzed.
Columns for liquid chromatography are typically made from cylinders of stainless steel or PEEK, containing bonded silica or polymer particles. Columns are available in various dimensions to meet the needs of different applications. Column dimensions affect sensitivity and efficiency and determine the amount of analyte that can be loaded onto the column. For example, small id columns improve sensitivity compared to larger id columns, but with reduced loading capacity.
Column selection criteria can be straightforward, such as column phase for application and sizes for system pressure limits. In many cases, a specific phase or column dimension may be specified for a pre-defined method, so your selection will mostly have to do with meeting these specifications and ensuring a reliable, high-quality column provider.
Instrument Specification Replacement Parts
To maximize uptime, it is important to have commonly serviced replacement parts available in the lab. Chrom Tech offers Agilent parts for Agilent HPLCs, GCs, and Mass Spectrometers. We also offer OEM equivalent parts for commonly replaced items in your HPLC and GC, featuring parts for Agilent, Shimadzu, Thermo, and Waters.
LC Instrumentation Replacement Parts
For LC systems, Chrom Tech offers replacement parts such as pump pistons, seals, and detector lamps for Agilent, Waters, Thermo, and Shimadzu systems.
GC Instrumentation Replacement Parts
For GC systems, Chrom Tech offers Inlet liners, seals, septa, detector FID jets, and mass spec electron multipliers for Agilent, Shimadzu, and Thermo instruments.
Gas chromatography and liquid chromatography rely on syringes to transfer a sample from a vial into the inlet. Syringes are used for manual injection or autosamplers and come in various sizes, needle gauges, point styles, and terminations.
A syringe must have a tight and secure fit in the injection port to withstand repeated injection cycles without bending or breaking. Syringes must also be able to withstand chemical forces within a defined range, must be inert, should not introduce interfering compounds to a sample, and should deliver accurate volumes with no dead volume or carryover between injections.
Solvent and Reagents
Solvents are liquids used to extract and or dissolve substances and are the mobile phase in liquid chromatography. For the selection of mobile phase solvents in reverse phase chromatography, HPLC grade or better solvents are always recommended. Whereas LC/MS grade solvents or better are always recommended for UHPLC and mass spectrometry.
Selectivity differences and sample retention vary between mobile phases. Sample solubility is also likely to differ and dictate the use of a specific solvent or solvents.
With ionic compounds, retention shows significant changes with pH, meaning it is important to control pH to stabilize retention and selectivity. A pH between two and four is recommended for method development with most samples, including basic compounds and typical weak acids.
For reproducibility, the pH used should be ± 1 pH unit above or below the pKa of the solutes being separated. You may not know the pKas of your analytes, so testing more than one mobile phase pH may provide the best results. Most reversed-phase columns can be used between pH 2 through 8 or more for a wide range to find the optimum mobile phase pH for your separation. When you are determining the mobile phase pH, measure and adjust it on the aqueous component before mixing with organic modifiers for the most accurate and reproducible results.
Reagents are used to improve the selectivity and specificity of compounds. Derivatization is performed in GC to modify an analyte’s functional groups to enable separation, detection, or both. The benefits of derivatization include increased sample volatility, improved selectivity and chromatographic efficiency, and enhanced detectability.