Chromatography

UHPLC Phases

Raptor - RESTEK

Raptor maximum pressure: 1,034 bar (1.8 μm), 600 bar (2.7 μm); 400 bar (5 μm). For maximum lifetime recommended maximum pressure for 1.8 µm particles is 830 bar.

PINNACLE DB - RESTEK

Troubleshooting

Many GC and LC problems can be avoided with routine preventive maintenance. If you are seeking the cause of the chromatography problem, go step by step. Never make more changes in your instrument at the same time, otherwise you will never find, what caused the problem.

Select your category of chromatography to read more about the troubleshooting:

GC troubleshooting

LC troubleshooting

dSPE (QuEChERS)

Resprep™ QuEChERS Products

QuEChERS Tubes For Extraction and Clean-Up of Pesticide Residues From Food Products

• Fast, simple sample extraction and cleanup using dSPE.
• Fourfold increases in sample throughput.
• Fourfold decreases in material cost.
• Convenient, ready to use centrifuge tubes with ultra pure, preweighed adsorbent mixes.

Quick, Easy, Cheap, Effective, Rugged, and Safe, the QuEChERS ("catchers") method is based on work done and published by the US Department of Agriculture Eastern Regional Research Center in Wyndmoor, PA.⁽¹⁾ Researchers there were looking for a simple, effective, and inexpensive way to extract and clean pesticide residues from the many varied sample matrices with which they routinely worked. They had been using the Modified Luke Extraction Method, which is highly effective and rugged, but is both labor and glassware intensive, leading to a relatively high cost per sample. Solid phase extraction also had been effective, but the complex matrices the investigators were dealing with required multiple individual cartridges and packings to remove the many classes of interferences, adding costs and complexity to the process. A new method would have to remove sugars, lipids, organic acids, sterols, proteins, pigments and excess water, any of which often are present, but still be easy to use and inexpensive.

The researchers developed a simple two-step procedure. First, the homogenized samples are extracted and partitioned, using an organic solvent and salt solution. Then, the supernatant is further extracted and cleaned, using a dispersive SPE technique. Multiple adsorbents are placed in a centrifuge tube, along with the 1mL of organic solvent and the extracted residues partitioned from step 1. The contents are thoroughly mixed, then centrifuged, producing a clean extract ready for a variety of GC or HPLC analytical techniques.⁽²⁾ Validation and proficiency data for the QuEChERS method are available for a wide variety of pesticides in several common food matrices at www.quechers.com.

Using the dispersive SPE approach, the quantity and type of adsorbents, as well as the pH and polarity of the solvent, can be easily adjusted for differing matrix interferences and "difficult" analytes. Results from this approach have been verified and modified at several USDA and Food and Drug Administration labs, and the method now is widely accepted for many types of pesticide residue samples.

Restek products make this approach even simpler. The centrifuge tube format, available in 2mL and 15mL sizes, contains magnesium sulfate (to partition water from organic solvent) and PSA* adsorbent (to remove sugars and fatty acids), with or without graphitized carbon (to remove pigments and sterols) or C18 packing (to remove nonpolar interferences). Custom products are available by quote request. If you are frustrated by the time and cost involved with your current approach to pesticide sample cleanup, we suggest you try this simple and economical new method.

We have products compliant with AOAC, Multi-miniresidue and Draft European methods.

Inforamtion about products is available here.

References:

1. Anastassiades, M., S.J. Lehotay, D. Stajnbaher, F.J. Schenck, Fast and Easy Multiresidue Method Employing Acetonitrile Extraction/Partitioning and "Dispersive Solid-Phase Extraction" for the Determination of Pesticide Residues in Produce, J AOAC International, 2003, vol 86 no 22, pp 412-431.
2. Schenck, F.J., SPE Cleanup and the Analysis of PPB Levels of Pesticides in Fruits and Vegetables. Florida Pesticide Residue Workshop, 2002

MEPS Phases

SGE

*C8+SCX BINS are labelled as M1.

The BINs can be used up to 40 - 100 extractions. General preparation time is 1 - 2 minutes.

Stationary phases

Chromatography, either GC, HPLC, SPE, FLASH or preparative, uses many types of stationary phases. Here you wil find detailed information about stationary phases.

Stationary phases for analytical separation

• Core-shell technology
• GC
• HPLC
• UHPLC

Stationary phases for sample preparation

• SPE
• dSPE (QuEChERS)
• IAC (Immunoaffinity Columns)
• MEPS (Micro Extraction by Packed Sorbent)
• FLASH
• BULK (media for preparative 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