TO-15 + PAMS + TO-11A = China’s HJ759 + PAMS + HJ683 part 2: Deans switching and TO-15/PAMS

In a previous blog (TO-15 + PAMS + TO-11A = China’s HJ759 + PAMS + HJ683) Jason Herrington mentioned a dual column MS/FID setup for China’s combined HJ759 + PAMS + HJ683 method. While this could be done with a simple Y splitter (such as https://www.restek.com/catalog/view/1983), a more elegant solution is to use a microfluidic switch, or Deans switch, to send some compounds to the secondary column and FID while maintaining the bulk of the analysis on the MS.

So how does it work? The Deans switch is composed of a pressure control module (PCM), a solenoid valve, and a 3 port switching plate. The primary column is connected to the switching plate with a short transfer line to the primary detector (MS), and a second column to the secondary detector (FID). The solenoid valve directs auxiliary carrier gas flow to the plate, with one of the outlet ports at higher pressure than the other, as shown in Fig. 1 below. The larger arrow on the MS output end of the Deans switch shows the higher pressure that directs the flow to the FID when the switch is on, and vice versa. A smaller pressure is applied to the other side to ensure that the flow from column 1 doesn’t backflow to the PCM.

Fig. 1 – Deans switch operation, with the flow from column 1 shown in red.

 

This has several advantages over simply splitting the flow. Since the entire sample isn’t passing through the secondary column it can be chosen without concern over it being robust enough to handle everything in the sample. No worries about trying to elute less volatile compounds off your thick film or plot columns. Also, by not splitting the sample sensitivity is maintained without having to decrease split ratios or increase injection volumes. It is important to note though that the Deans switch does increase carrier gas flow on the restrictor and column 2 due to the extra flow from the switching plate, so your MS may see a slight decrease in sensitivity. The extra flow is either 50% or at least 1mL/min more than column 1, so if your primary column flow is 2mL/min your final flow to the MS will be 3mL/min, so keep in mind the pumping efficiency of your MS.

What does it look like in the end? With no cryogenic cooling we have complete analysis of 112 VOCs in 35 minutes. The Deans switch sends the C2 and C3 hydrocarbons at the beginning of the run to the secondary column and FID for better separation and detection, then switches the rest of the run to the MS.

 

Fig.2 – FID chromatogram of C2 and C3 hydrocarbons at ~1ng on column.

Fig. 3 – MS chromatogram of PAMS compounds at ~1ng on column.

Fig. 4 –MS chromatogram of PAMS + HJ759 compounds at ~1ng on column.

Peaks TO-15 PAMS TR (min) Peaks TO-15 PAMS TR (min)
1 Ethane X 7.677 59 Carbon tetrachloride X 20.927
2 Ethylene X 8.68 60 3-Methylhexane X 21.011
3 Propane X 10.363 61 Benzene X X 21.401
4 Propylene X X 15.583 62 1,2-Dichloroethane X 21.513
5 Acetylene X 17.863 63 Isooctane X X 21.638
6 Dichlorodifluoromethane X 6.567 64 Heptane X X 22.01
7 1,2-Dichlorotetrafluoroethane X 7.148 65 1,4-Difluorobenzene X X 22.312
8 Isobutane X 7.204 66 Trichloroethylene X 22.841
9 Chloromethane X 7.348 67 Methylcyclohexane X 23.348
10 trans-2-Butene X 7.761 68 1,2-Dichloropropane X 23.399
11 n-Butane X X 7.859 69 Methyl methacrylate X 23.422
12 Vinyl chloride X 7.868 70 1,4-Dioxane X 23.506
13 1,3-Butadiene X 8.045 71 Bromodichloromethane X 23.915
14 cis-2-butene X 8.193 72 2,3,4-Trimethylpentane X 24.128
15 1-Butene X 8.621 73 2-Methylheptane X 24.472
16 Bromomethane X 9.322 74 3-Methylheptane X 24.751
17 Chloroethane X 9.796 75 cis-1,3-Dichloropropene X 24.755
18 Isopentane X 10.163 76 4-Methyl-2-2pentanone (MIBK) X 24.988
19 Vinyl bromide X 10.586 77 Toluene X X 25.415
20 Trichlorofluoromethane X 10.888 78 n-Octane X 25.555
21 1-Pentene X 11.013 79 trans-1,3-Dichloropropene X 25.801
22 n-Pentane X X 11.269 80 1,1,2-Trichloroethane X 26.186
23 Ethanol X 11.617 81 Tetrachloroethene X 26.381
24 trans-2-Pentene X 11.831 82 2-Hexanone (MBK) X 26.502
25 Isoprene X 12.24 83 Dibromochloromethane X 26.893
26 cis-2-Pentene X 12.296 84 1,2-Dibromoethane X 27.125
27 Acrolein X 12.63 85 Chlorobenzene-d5 X X 27.84
28 1,1-Dichloroethene X 13.025 86 Chlorobenzene X 27.891
29 1,1,2-Trichlorotrifluoroethane X 13.113 87 Ethylbenzene X X 27.994
30 Acetone X 13.192 88 n-Nonane X X 28.11
31 2,2-Dimethylbutane X 13.215 89 m- & p-Xylene X X 28.179
32 Isopropyl alcohol X 13.796 90 o-Xylene X X 28.769
33 Carbon disulfide X 13.875 91 Styrene X X 28.793
34 Allyl chloride X 14.53 92 Bromoform X 29.127
35 2,3-Dimethylbutane X 15.046 93 Cumene X X 29.285
36 Methylene chloride X 15.06 94 4-Bromofluorobenzene X X 29.573
37 2-Methylpentane X 15.176 95 1,1,2,2-Tetrachloroethane X 29.712
38 Cyclopentane X 15.292 96 n-Propyl benzene X X 29.87
39 Tertiary butanol X 15.469 97 1,2,3-Trimethylbenzene X 29.963
40 Methyl tert-butyl ether (MTBE) X 16.068 98 n-Decane X 30.01
41 trans-1,2-Dichloroethene X 16.096 99 p-Ethyltoluene X X 30.024
42 3-Methylpentane X 16.133 100 2-Chlorotoluene X 30.052
43 1-Hexene X 16.783 101 1,3,5-Trimethylbenzene X X 30.084
44 Hexane X X 17.071 102 m-Ethyltoluene X 30.377
45 1,1-Dichloroethane X 17.587 103 1,2,4-Trimethylbenzene X X 30.609
46 Vinyl acetate X 17.587 104 1,3-Dichlorobenzene X 31.06
47 2,4-Dimethylpentane X 18.711 105 o-Ethyltoluene X 31.171
48 Methylcyclopentane X 18.958 106 1,4-Dichlorobenzene X 31.185
49 2-Butanone (MEK) X 19.194 107 Benzyl chloride X 31.311
50 cis-1,2-Dichloroethene X 19.246 108 m-Diethylbenzene X 31.352
51 Ethyl acetate X 19.297 109 p-Diethylbenzene X 31.483
52 Bromochloromethane X X 19.873 110 n-Undecane, X 31.524
53 Tetrahydrofuran X 19.896 111 1,2-Dichlorobenzene X 31.673
54 Chloroform X 20.128 112 n-Dodecane X 32.853
55 1,1,1-Trichloroethane X 20.551 113 1,2,4-Trichlorobenzene X 33.745
56 2-methylhexane X 20.57 114 Hexachlorobutadiene X 33.866
57 Cyclohexane X X 20.723 115 Naphthalene X 34.172
58 2,3-Dimethylpentane X 20.797

 

 

That covers the PAMS and HJ759 methods, but what about HJ683? Don’t worry, there’s more to come on this application soon.

Leave a Reply


Restek Domestic Customer Service

Subject

Message

Your Full Name

Your Email

Company Name

Address

Spam Block (Please leave this blank)

all fields required

Thank you

Your message has been sent. We will be in touch shortly.

Message not sent

Sorry, your message could not be sent at this time. Please try again later, or contact Restek or your local Restek representative via phone.

www.restek.com/Contact-Us