Jaap de Zeeuw Restek Middelburg, The Netherlands. Copyrights: Restek Corporation

Transcription

1 Liner Selection in GC Jaap de Zeeuw Restek Middelburg, The Netherlands

2 What is a liner? A liner is an inert glass tube that is positioned inside the injection port of the GC The sample solution is introduced into the liner using a syringe In the liner the sample solution will evaporate and the gas phase will be transferred to the capillary column

3 Many different liners are available, but which one is the best for our application? The challenge is, that once a certain liner design has been tried, the customer will be reluctant to change

4 Cyclosplitter mini-lam Split Liners Open wool Laminar cup Precision

5 Liners for GC Characteristics: Volume [length, ID] Material Design [Cups, Cyclo, Gooseneck.. ] Packing [wool, other] Deactivation

6 Position of column inlet in the injection port liner Ideal position of column in liner Column in de center of liner Minimal 2-3 cm distance between top of needle and column inlet Check manual of GC type Use ferrules that fit the fused silica OD

7 Liners for Split Injection

8 Split injection: Considerations 1-3 ml/min into the column Carrier gas ml/min in the inlet (mostly split vent flow) Split Split Ratio: Column flow rate: 1.2 ml/min Split vent flow rate: 120 ml/min Split ratio = split vent flow rate = 120 = 100 column flow rate 1.2 Split ratio = 1:100 Column flow

9 Split injection Sample evaporation, homogenization and injection takes place in a fraction of second.. Need: FAST injection FAST evaporation FAST mixing FAST transfer

10 Split Liners Designed to help vaporize the sample; Mixing chambers Tortuous flow paths To help evaporation Fused silica deactivated wool Beads CarboFrit packing

11 Split injection FAST evaporation Use a plug of deactivated wool; Increases heat capacity of insert Minimized the temperature drop caused by evaporation Results in highest reproducibility Traps part of the matrix and septa particles Sky Precision Liner

12 Using quartz wool provide < 1% repeatability Sky Precision liner

13 Septa particles stay on top of wool

14 Split Liners Design of Sky Precision liner performed very well Low discrimination and excellent repeatability But it has wool: Active components could show lower responses Important Point! Wool leads to good homogenization of sample for split injection and traps dirt and septa particles. Usable with most injection techniques (hot and cold needle, fast auto sampler..)

15 Wool cannot be used when interaction with components interaction with matrix (water, hydrolization) memory effects ghost peaks Solutions: Use a different insert without glass wool.. Use hot needle injection technique (Thermo, CTC)

16 Hot Needle injection Sample is taken up in syringe and Needle is inserted in injection port; Wait for 2-3 seconds (needle heats up), Inject; Ideal for: Difficult to evaporate samples When sample/components interact with wool and wool cannot be used Even better when solvent flush is used Limitations: Not possible with all injection systems

17 Example: Injecting a difficult sample Glycol aldehyde in mono ethylene Glycol Issues: Highly Polar compounds Difficult to evaporate (high viscosity) Technique: Injection :Split Detection :FID

18 Injection of Glycol aldehyde in MEG Wool filled liner Ref: J.Luong, Dow Chemical Canada

19 Injection of Glycol aldehyde in MEG Need a liner without glasswool Good peak shape Injection :Split Ref: J.Luong, Dow Chemical Canada Detection:FID

20 What about liner diameter? Smaller diameter liners have higher gas velocities Transfer to column is faster, injection band will be narrower Especially important for: Fast eluting components Smaller column diameters

21 Example of injection error on a 10m/0.10mm Poster presentation at conference Gasoline on a 10m x 0.1mm ID column Note: Broad peaks = injection challenge: Split too low; They only use plates while are available..

22 Impact of liner diameter on fast eluting peaks Column : 12m x 0.18mm Rxi-5ms Injection : 0.5 ul; 20 ppm 8270 mix Split : 1:10 Later peaks are OK because of focusing effect of phase Ref: Chris Rattray, Innovations, Restek 4mm Precision liner 2mm Precision liner

23 When choosing smaller diameter liner with splitted injection 4mm Precision liner Best is to start with 4mm ID liners Only consider a smaller ID if the early eluting compounds are to broad or tail.

24 Liners: Split Injection If matrix/sample interacts with wool If matrix/sample has no interaction with wool Cyclo liner Precision + hot needle injection

25 What s wrong with these liners? To get higher Split flows with Agilent Split injection systems

26 Split Injection: Back Flash Expansion Volume Solvent > Liner Volume poor peak area reproducibility tailing solvent peaks ghost peaks / memory effects

27 Split Injection: Back Flash Expansion Volume Solvent > Liner Volume poor peak area reproducibility tailing solvent peaks ghost peaks / memory effects

28 Back flash Liner Volumes Theoretical* Effective 1.0mm ID = 59 µl 2.0mm ID = 236 µl 3.0mm ID = 530 µl 4.0mm ID = 942 µl 30 µl 118 µl 265 µl 471 µl * Liner volume actually available for vaporization with carrier gas present is < ½ theoretical! From Grob, Split and Splitless Injection, 3 rd ed.

29 Maximum injected amounts Table 1 Maximum Injection Volume Solvent Expansion factor Maximum Injection Volume 50% liner volume [μl] 250 ºC, 73 kpa 1 mm liner 2mm liner 4mm liner Isooctane Toluene Methanol Water

30 Liners for Splitless Injection

31 Splitless Injection Injection of 1-3 μl of sample with the Split-vent CLOSED Need to re-focus sample components on the column Use low column (oven) temperature to condense the solvent: usually 20 ºC UNDER the Boiling Point of the solvent used.. After 98% of the sample solvent has been transported to the column, the Splitvent is OPENED and the oven temperature program is started..

32 Solvent peak shape in splitless injection The Solvent peak in correct splitless injection will always look like the trunk of a tree.. If the solvent peak is tailing, the splitless conditions are not correct

33 Splitless Liners Splitless liners must be able to hold the sample in the liner between 0.5 and 2.0 minutes. The volume must be as large as possible as we like to inject larger volumes: use 4-5 mm ID liners; A large surface area for sample evaporation is not needed for splitless injections.

34 General purpose liner for splitless injection Sky - Single taper (goose neck) with wool on the bottom Works for all solvents/matrices Also allows large volume splitless injection Wool will retain salts, matrix and septum particles

35 Packing materials Packing materials: dirty samples Wool: promote sample vaporization; Trap nonvolatile residue If compounds are sensitive a problem may be observed..

36 Impact of Glass wool on Carbamates under same splitless injection conditions aminocarb carbaryl Decomposition due to presence of Glass wool bendiocarb dioxacarb dimethoate Without glass wool With Glass wool Use of glass wool in the injection system must be prevented.. Ref. J. of HRC. Vol 13, nov.1990, p.759

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38 For some applications wool in splitless liners can be a problem Injection time is relative long and temperatures are high Components are exposed at high temperature in presence of matrix Result: Reactivity & decomposition: Lower response for sensitive components Need to use splitles liners without Wool

39 Liners for SplitLess Injection Single taper with wool at bottom Single Taper at bottom For all samples that do not interact with Quartz wool For all samples that show interaction with Quartz wool

40 For the best results: Consider Double Taper Will also reduce potential losses and interactions at top of the liner.. Is more expensive..

41 Liner replacement Liners will contaminate / activate when used Septum After 28 injections Matrix (acidity, non-volatile compounds, particles, chemicals) Carrier gas, leaks, air injection

42 Impact of liner (replacement) on pesticide response 4mm Sky with wool, single taper

43 Impact of a dirty liner

44 Liners for Direct Injection

45 Uniliner for Direct Injection A Uniliner is designed with a press tight fit connection at the bottom No contact with metal inlet parts at the base of the splitless injection port. seal

46 Direct injection Direct injection Is used if we have to measure < 10 ppm impurities and: We cannot use Splitless Injection Because of the Sample matrix: polarity, boiling point We cannot use Splitted injection Need to measure LOW levels

47 Direct injection: principle Sample is EVAPORATED in a HOT injection port.. The column is kept at a temperature where NO CONDENSATION can occur.. NOTE Everything we inject is transferred into the column Need a good seal between column and liner (uniliner)

48 Needs for a good Direct injection Inject smallest possible amount Inject FAST Use 0.53mm or 0.32mm columns Use oven temperature > bp of main solvent/matrix

49 When use Direct injection? Low level (<10 ppm) measurement of (volatile) compounds in higher boiling matrices: Traces in water, toluene, glycol or any other high boiling material When we have discrimination using split and splitless injection, and we cannot use on-column..

50 Liners for PTV Injection

51 PTV injection (Gerstel, Gl Sciences, MMI) Principle: Injection of sample into the cold liner of the PTV; Vent off the solvent Concentrate the components on an adsorbent Program the PTV to evaporate, (Injection) Separate components in the capillary column

52 PTV liners are often open liners; They have a smaller diameter (2mm) 2mm Dimple liner for Agilent MMI 2mm single baffle for Agilent Cis4/PTV 2.4mm AC TPI liner 1.8mm Shimadzu PTV 2.0mm Thermo PTV

53 Sometimes PTV liners aree filled with a material to trap the components.. Wool Deactivated Silica Carbofrit filled

54 Liners for Headspace / SPME

55 Liners for Headspace (and SPME) The sample is already a gas, so no wool is required to help evaporation In headspace, most components are volatile and elute fast, increasing risk of injection errors Need fast injection and low split ratio s to see trace levels open liner with small inner diameter of mm is preferred

56 Unique Restek solution for petrochemical applications for Sulfur compounds Use of Siltek or Sulf-Inert deactivated liners

57 Siltek / Sulf-Inert deactivated liners If high inertness for Sulfurs is required

58 Normal liner Reactive sulfur compounds disappear Hydrogen Sulfide COS methylmercaptan Sulfurs elute with high response

59 Some applications require frequent liner change Improve liner life time: Inject LESS (if possible) 59

60 Increase life time Only if concentrations allow this

61 Some applications require frequent liner change Improve liner life time: Inject LESS (if possible) More or different sample prep Lower liner temperature 61

62 Liner contamination by Septum particles Liner is hot Degradation siloxanes products are formed Liner has more retention broadening injection bands

63 Impact of Needle on Septum scoring BTO-septa Center guide minimal scoring.. Ideal with tapered or side-hole needles Limitations: At higher pressures it can leak Gets sticky in some inlets

64 Merlin micro seal.. With the Merlin seal no issues with metal or septum particles.. Usable up to 400ºC Long life time Needs a thoroughly aligned auto sampler and Tapered Needles Available for most GC brands

65 Merlin seal: Need to use the correct needles!! Agilent auto sampler 20167, 10µL, ASN, 23s, Agilent, each, Hamilton syringe 20168, 5µL, ASN, 23s, Agilent, each, Hamilton syringe 24785, 10µL, F, 23, Cone, each, SGE syringe 24781, 5µL, F, 23, Cone, each, SGE syringe CTC auto sampler 22757, 10µL, 23s, AS, each, Hamilton syringe 24921, 10µL, F, 23, Cone, each, SGE syringe for 24923, 5µL, F, 23, Cone, each, SGE syringe for CTC

66 Liner handling tool.. The Claw Takes hot vials and liners No contamination No more burned fingers Arnold S. in Running Man..

67 Latest Developments..

68 New injection port liner: Sky liner Inert by a new deactivation In- situ deactivated quartz wool Blue color All popular dimensions : higher recoveries : very clean, low background and inert : easy to pick : for any brand of GC No mistake on installation: The R of Restek, is always the oven -side

69 (Re)activity of liner surface p.p -DDT Endrin/DDT response are direct indicators for completeness of deactivation reaction endrin Up to 4 times less (re)activity

70 Inertness: response factor for 2,4-dinitrophenol Highly polar analytes transfer well from Sky surface

71 Summary Choose a liner for the type of injection you will be performing and the type of compounds that are in the sample. Review all the variables, results are more accurate and downtime is decreased.