Chromatography

Glossary

• BEH = Bridged ethyl hybrid (HPLC particle)
• DAC = dynamic axial compression
• DAD = diod array detector
• ECD = electron capture detector
• EI = electron ionization
• ELSD = evaporative light scattering detector
• FIA = flow injection analysis
• FID = flame ionization detector
• FPD = flame photometric detector
• FPP = fully porous particles
• GC = gas chromatography
• GCTQ = gas chromatographs with Triple Stage Quadrupole
• GCxGC = multidimensional gas chromatography
• GPC = gel permeation chromatography
• HETP = height equivalent of theoretical plate
• HID = helium ionization detector
• HILIC = hydrophobic interaction liquid chromatography
• HPLC = high performance liquid chromatography
• HPTLC = high performance thin layer chromatography
• IC = ion chromatography
• IHPLC = intermediate high performance liquid chromatography
• LVI = large volume injection
• MCSGP = Multicolumn countercurrent solvent gradient purification
• MEPS = Micro Extraction by Packed Sorbent
• MLC = micellar liquid chromatography
• MS = mass spectrometry
• MSPE = Micro SPE
• NP = normal phase
• NQAD = Nano Quantity Analyte Detector
• ODS = octa decyl silicagel
• PDD = pulsed discharged detector
• PFPD = pulsed flame photometric detector
• PID = photo ionization detector
• PTV = programmable temperature vapourizer
• RI = refractive index
• RP = reversed phase
• RRLC = rapid resolution liquid chromatography
• SBSE = Stirring Bar Sorbent Extraction
• SEC = size exclusion chromatography
• SFC = supercritical fluid chromatography
• SIM = single ion monitoring
• SMB = simulated moving bed
• SPE = solid phase extraction
• SPP = superficially porous particles (core-shell)
• SPME = solid phase micro extraction
• TCD = thermal conductivity detector
• TIC = total ion current
• TLC = thin layer chromatography
• TOF = MS analyzer "Time of Flight"
• UFLC = ultra fast liquid chromatography
• UPLC = ultra performance liquid chromatography
• UHPLC = ultra high pressure liquid chromatography, ultra high performance liquid chromatography

Signal to noise ration improvment in GC

Today's laboratory needs are:

• Lower detection and quantitation limits (LOD, LQD)
• Stability improvment in GC and GC/MS systems
• More inert and stable GC parts (columns, septa, vials, liners, ...)

Lower detection and quantitation limits can be achieved by:

• Reducing the Noise
• Increasing the signal

Leak Free SilTite metal ferrules for GC & GC/MS

SilTite ferrules are a unique metal ferrule specifically designed for connecting fused silica GC columns and tubing to mass spectrometer interfaces and injectors. Once fitted, SilTite ferrules provide a continuous leak free connection without the need to re-tighten the nut after a few temperature cycles. SilTite ferrules make Graphite/Vespel® ferrules obsolete for use in GC-MS connections. Their performance and cost effectiveness also makes them ideal for connecting GC columns to injectors and atmospheric detectors.

Why choose SilTite ferrules?

• Eliminates leaks (See figures below)
• Never needs re-tightening, even after temperature cycling
• Ferrule remains permanently fixed to the column but does not adhere to the SilTite nut
• No contamination from Vespel or graphite materials - 100% metal
• Ideal for high pressure applications
• Also available for injector interfaces
• >500°C maximum temperature

Figure 1. MS trace using a graphite Vespel ferrule after 5 temperature cycles.

Figure 2. MS trace using a SilTite ferrule after 5 temperature cycles. (Using an MS, no leaks can be detected, even after 400 temperature cycles between 70ºC and 400ºC).

Agilent S/SL inlet seal improvment

Washerless, Leak-Tight Seal for Agilent GCs ensures better tightness and easier handling than original part.

• Prevents oxygen from permeating the carrier gas, increasing column lifetime.
• Vespel^® ring in top surface reduces operator variability by requiring minimal torque to seal.
• Vespel^® ring in bottom surface simplifies installation—eliminates the washer.

In Agilent split/splitless injection ports, it can be difficult to make and maintain a good seal with a conventional metal inlet disk. The metal-to-metal seal dictates that you apply considerable torque to the reducing nut, and, based on our testing, this does not ensure a leak-tight seal. Over the course of oven temperature cycling, metal seals are prone to leaks, which ultimately can degrade the capillary column and cause other analytical difficulties.

Agilent and Restek seal tightness comparison

Patented Dual Vespel^® Ring Inlet Seal (Restek) greatly improves injection port performance—it stays sealed, even after repeated temperature cycles, without retightening the reducing nut| This seal features two soft Vespel® rings, one embedded in its top surface and the other embedded in its bottom surface. These rings eliminate the need for a washer, and ensure very little torque is needed to make a leak-tight seal. The rings will not harm the critical seal in the injector body, or any other surface, and are outside the sample flow path. Tests using a high sensitivity helium leak detector show Dual Vespel^® Ring Inlet Seals will seal equally effectively at torques from 5 in. lb. to 60 in. lb.

Why trust a metal-to-metal seal when you can make leak-tight seals quickly and easily—and more reliably—without a washer, with a Restek Dual Vespel^® Ring Inlet Seal. Use a stainless steel seal for analyses of unreactive compounds. To reduce breakdown and adsorption of active compounds, use a gold-plated or Siltek^®-treated seal. The gold surface offers better inertness than untreated stainless steel. Siltek^® treatment provides inertness similar to that of a fused silica capillary column.

Seal options

• Stainless Steel
• Gold plated
• Siltek deactivated

GC septa selection

Agilent GCs

DANI GCs

Perkin-Elmer GCs

Shimadzu GCs

Varian GCs

Thermo Scientific GCs

Syringes

Syringe Cleaning and Maintenance

Chromatography syringes are the finest quality precision fluid measuring devices available. With proper care and handling, syringes will provide unsurpassed performance in precision fluid measuring year after year. The life of your syringe is directly related to its cleanliness!

Some solvents, such as halogenated hydrocarbons, may attack and deteriorate the highly resistive adhesives (cements) used to affix needles and other terminations to Hamilton syringes, which may result in frozen plungers and plugged needles.

Cleaning Syringe Barrels

To clean Hamilton syringes, it is best to use solvents known to be effective in solvating the sample and preferably are non-alkaline, non-phosphate and non-detergent based. A biodegradable, non-phosphate, organic Cleaning Concentrate is available from Hamilton (ordering number 18311).

Rinse the syringe thoroughly after use with deionized water, acetone, or another solvent compatible with the sample. Allow the syringe to air dry. Avoid prolonged immersion of the syringe while cleaning.

MICROLITER™ Syringes (Series 600, 700, 800 and 900)

• Rinse the syringe thoroughly with a solvent known to be effective in solvating the sample. Residual dissolved solids may result in frozen plungers and plugged needles.
• To clean the plunger, remove it from the syringe barrel and gently wipe with a lint-free tissue. Reinsert the plunger into the barrel and pump deionized water, acetone or another solvent compatible with the sample through the needle and syringe. Allow syringe to air dry. When working with dissolved solids, storing the plunger outside of the syringe will reduce the possibility of frozen plunger.

GASTIGHT® Syringes (Series 1000, 1700 and 1800)

• Rinse the syringe thoroughly with a solvent known to be effective in solvating the sample. Residual dissolve d solids may result in frozen plungers and plugged needles.
• To clean the plunger, remove it from the syringe barrel and gently wipe with a lint-free tissue. Insert the plunger into the barrel and pump deionized water, acetone or another solvent compatible with the sample through the needle and syringe. Allow syringe to air dry. When working with dissolved solids, storing the plunger outside of the syringe will reduce the possibility of frozen plunger.

Syringe Storage

We recommend to store syringes in the original packaging. This with help to protect the syringe, and allows for easy identification. Remove product description label from the end of the box, and placing it to the outside packaging. This will make re-ordering the same syringe quick and easy.

Thermal desorption

In this section you will finde informations important in the area of thermal desorption. It is quite difficult analytical technique and these informations can help you with your work with it. If you do not find required information, do not hesitate to contact our specialists.

Sorbent parameters

Material emission monitoring

Storage and transportation of sorbent tubes

ChromShell columns and solvents

There are several critical characteristics that must be taken into consideration when selecting the appropriate organic solvent to use in the mobile phase with ChromShell^® columns. Viscosity is one of the most important as high viscosity solvents may produce backpressures that are too high for the HPLC system used. Other important solvent characteristics include UV cutoff, cost and polarity index; where a solvent with a high UV cutoff will result in poor sensitivity with UV/Vis detection and use of high cost solvents will result in a poor laboratory that can't afford to buy new columns. Solvents with low polarity indices generally result in faster elution of organic compounds and are commonly used for column cleaning.

Acetonitrile

is arguably the best organic solvent as it results in the lowest system backpressure in water mixtures and also has a very low UV cutoff for better UV/Vis detection sensitivity. Although acetonitrile production is starting to increase with the turnaround of the economy, thus dropping cost, this still remains a major drawback of acetonitrile usage.

Methanol

is another popular organic solvent as it is comparable in elution strength to acetonitrile, has a relatively low UV absorbance, and is significantly less expensive than acetonitrile. The major drawback of methanol, especially when used with small particle size HPLC columns, is that its use can result in backpressures that exceed many HPLC system limits.

Acetone

is less commonly used as it has high UV absorbance, but can be used successfully if analytes absorb at higher UV wavelengths or if other detector types such as MS are used as it has similar elution properties to acetonitrile but is significantly less expensive.

Ethanol

is generally not recommended as it results in very high backpressures in water mixtures.

Iso-, n-propanol

have relatively strong elution strength and are most commonly used in column cleaning at low flow rates as they also results in high backpressures.

Tetrahydrofuran

has similar elution strength to n-propanol but is less commonly used as it is much more expensive.

Glassware deactivation

Glassware deactivation with DMDCS

Dimethyldichlorsilane (DMDCS) reacts with active hydroxyl groups present on glass surface producing a deactivated layer. This ensures inert glassware used for sensitive compounds.

Procedure

During the deactivation process, the reaction releases hydrogen chloride (HCl). So we strongly recommend to do this procedure in a fume hood.

• Use 5% DMDCS solution in toluene. You can prepare this solution by diluting 20 ml of DMDCS with 400 ml toluene. Store the solution in an amber glass at room temperature.
• Soak glassware in 5% DMDCS solution for 15 to 30 minutes.
• Rinse glassware twice with toluene.
• Soak glassware in methanol for 15 minutes.
• Rinse glassware with methanol.
• Dry glassware with high purity nitrogen (moisture and hydrocarbon free).

Setting linear velocity

The linear velocity is an important parameter in chromatography. It has an influence on chromatography resolution and therefore setting the dead volume is basic part of method development.

Linear velocity measurement in GC

To set a dead time, inject 2 µl of a non-retained gaseous substance, which is compatible with the detector. Take a gas-tight syringe and draw the headspace over neat compound. Accurately mark the injection starting time and peak elution time.

Note: Some compounds may be slightly retained on thick-film phase, however, they will be reproducible for similar column types.