Wasson-ECE Instrumentation - Vietnam

30/03/2015

Gas filter proper installation
Source: Agilent Technologies

Installation of Gas Clean Carrier Gas Kit for 7890 GC (Part No. CP17988) For more information see http://www.agilent.com/chem/gasclean

26/03/2015

Wow what a milestone !!! So excited that the previous post has reached 651 people. Thank you so much for your interest.

Now it's a great pleasure to share the bonus tip below on how to insert a column to the common inlets and detectors (Source: Agilent Technologies).

25/03/2015

Good morning. How are you doing ? It's been a while since the last post. So let's configure a Dean's switch to "heart-cut" the components which are not fully resolved (picture 1) today.

Assume that we have a sample containing 4 components A, B, C and D. The column chosen can separate A and D pretty well. B and C, however, are merged to each other (picture 2).

Here a heart-cutting technique is used to send the non-resolved pattern (B+C) to another appropriate column for separation. Let's take a look at picture 3 for how to make connections to a Dean's switch. Pay special attention to the solenoid valve V1 at the bottom left corner.

V1 is first at the "NC" position, A is diverted through the restrictor to FID 1 (picture 3). Prior to the elution of B+C, V1 is switch to the "NO" position (picture 4). This allows B+C to travel to column 2 for separation and elute to FID 2. Once B+C have eluted to column 2, V1 is returned back to the "NC" position in order for D to elute to the restrictor and FID 1. Eventually two chromatograms are recorded: FID 1 for A and D, FID 2 for B and C.

As seen above it requires an additional detector for the unresolved peaks' quantification. There is another way which eliminates the extra detector for cost saving, however, it's a bit more time consuming. This will be introduced in the near future.

Meanwhile please do not hesitate to clear your doubts if any.

11/03/2015

SIMDIS Seminar

10/03/2015

Let's make a splitter with back-flush capability using a Dean's switch today. Please refer to the pictures below for connections. Once the last component of interest has eluted to the restrictors, the heavier ones are back-flushed to the inlet split vent by increasing the supply flow from the PCM (or Aux EPC) and reversing the flow through column 1.

06/03/2015

This post is going to share another application of a Dean's switch as a splitter. Sometimes we like to analyze samples by two detectors simultaneously, FID and ECD for instance. Doing so helps customer gain information for many different types of components associated with their concentrations.
The picture below shows how to make connections to the Dean's switch. Choosing different dimensions of the two restrictors, we can decide how much of a sample is split to FID and ECD.

04/03/2015

Let's enjoy the video below with the basic concepts of capillary column back-flushing.
Source: Agilent Technologies.

02/03/2015

Besides back-flushing, fore-flushing is also another helpful technique which may reduce cycle time, avoid column overloading as well as detector saturation. This can be done with a Dean's switch and an external solenoid valve.

Let's consider an example of analysing propane and propadiene in propylene matrix (picture 1). To avoid the analytical column from retaining the bulk propylene and its saturated peak at the FID, one wishes to vent it out of the system. With the solenoid valve (V1) in the "NO" position, the flow is diverted upwards to column 2 for normal analysis (picture 2). Once it's switched to "NC" position, components from column 1 is fore-flushed through the restrictor and gotten vented eventually (picture 3). To do so three timed events are added as shown in picture 4 with V1 "NO" and V1 "NC". The chromatogram will end up with a non-bulk proplyene peak as in picture 5.

In fact column 1 usually doesn't have enough separation power to create a clear gap between the bulk matrix peak and its adjacent peaks. Thus the cut often includes a small amount of the matrix. It won't however saturate the detector.

Some cases the matrix peak is eluting as the last one in mixture, C1-C5 impurities in hexane for instance, this technique would reduce significantly total run time since the bulk matrix (hexane) is eluting via the restrictor (no stationary phase) which has no or very weak affinity to hexane.

Hope you enjoy this share. Please feel free to speak out your thought.

27/02/2015

Typically back-flushing can be done by mean of a rotary valve or a Dean's switch. This post is to share the idea of deploying a Dean's switch to back-flush heavy components.

A Dean's switch is the best choice when the highest application temperature is greater than 320oC. This is because most of the rotor material in rotary valves can't handle that high temperature.

Basically a Dean's switch is comprised of two plates. The upper one has 5 connections on it while the lower is produced with a thin tunnel which links the 5 connections together. In order to back-flush heavy components, the 5 connections are connected and operated like a "Tee" in which two holes are plugged and the other three are connected to a column, a detector and a pressure supplying device such as PCM or Aux-EPC (attached picture). At first both PCM and the inlet provide positive flows. Once the last component of interest has eluted out of the column, the inlet pressure is set to low whereas the PCM pressure is increased. This maintains a positive flow to the detector and reverses the flow through the column. Thus the heavy components remained in the column are back-flushed to the inlet split vent.The picture below shows this technique reduces the total run time by 26 minutes.

26/02/2015

Good morning, this post is to share how to determine the back-flush time of an application. Let's recall the example of injecting a mixture of C1-C9 in the previous post. Assume that now we change the configuration to back-flush C6-C9 group to a detector, i.e. FID for instance. Before we start, one has to make sure column 1 must have enough theoretical disks to separate C1-C5 and C6-C9 groups. This is to ensure there is a clear gap between the groups in order to back-flush properly. Please w**d through the two pictures below to determine your own back-flush time.

The next post will be how to build this back-flush capability for your own GC. We are happy to hear back from you of anything in doubt.

25/02/2015

This post is to share with you the idea of "back-flush" technique and how you would benefit from applying it.

Back-flush is an technique to reverse an effluent on its flow path. The advantages of back-flush are to complete the analysis in a shorter time and protect the analytical columns from strong affinity of heavy components.

Considering a simple system with two columns in series and injecting a mixture of C1-C9 onto column 1. Let's assume the goal is to separate individual components from C1-C5 and vent out C6-C9. Once C1-C5 is eluting to column 2, the flow to column 1 is reversed while maintaining the same flow direction to column 2. Doing so allows C1-C5 to elute normally to the detector and "back-flush" C6-C9 group to a vent.

So instead of wasting time for all C1-C9 eluted, now the analysis time is shortened to C1-C5 only. This also helps protecting column 2 from contamination/carry-over due to C6-C9 being back-flushed.

The next post will share with you how technically a back-flush time can be determined.

Meanwhile, please do not hesitate to comment if you have any questions.

24/02/2015

Collection of Wasson-ECE Analytical Challenges