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

In a previous blog 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, 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.