In this three-part series blog post on trace elemental analysis, I will discuss key focus areas for a laboratory intent on maximizing its productivity and improving its profitability. In this first post, I will discuss the use of a switching valve to conduct elemental analysis and describe the use of a segmented stream during sample analysis and highlight its advantages over those when a continuous flow stream is employed.
There are a number of factors that affect the costs associated with trace elemental analysis:
Lengthy and/or complicated sample preparation and dilution procedures increase the risk for contamination or error, and reduce the number of samples that can be prepared in a day.
Preparation of multiple calibration standards can be costly and time-consuming, particularly if the elements are relatively unstable in solution and must be prepared fresh on a regular basis.
Inefficient software can lengthen data collection procedures and complicate sample reporting.
Instruments with complex setup procedures increase the startup time required before each day’s analysis and may require sophisticated training to use.
Instruments with frequent QC failures consume extra time, argon and sample solution, and generate extra waste, all of which reduces the productivity of your laboratory.
A key advantage offered by one of our ICP-OES systems (Thermo Scientific iCAP 7600 ICP-OES) is a switching valve to maximize sample throughput, reduce carryover and memory effects and minimize rinse requirements in between samples. As the valve is fully controlled through the ICP-OES software (Qtegra Intelligent Scientific Data Solution Software), its function can be built into the instrument method for easy setup and seamless operation. When you compare this with a standard sample introduction setup (i.e. no switching valve present), it is clear the benefits of this setup. In a standard sample introduction setup, the solution must be pumped from the autosampler probe, through the connective tubing to the peristaltic pump tubing, and to the nebulizer. Given the typical distance between an ICP-OES and its autosampler, each sample solution may be traveling through over two feet of tubing before it reaches the instrument’s nebulizer. Given the average peristaltic pump speed used during analysis, the time required for solution to travel this distance is typically 30-45 seconds. When solution travels that distance, it undergoes dispersion into the rinse solution inside the tubing. Therefore, a mixture of rinse and sample solution is initially delivered to the nebulizer and produces a gradual increase in emission, similar to that illustrated in the image below.
An additional 5-10 sec delay is required before the nebulizer receives a consistent flow of just sample solution. Once data acquisition is complete, the autosampler probe moves to the rinse station and pumps solution through the tubing that connects the autosampler probe to the nebulizer. This setup slowly rinses the sample introduction components and produces a gradual decrease in emission until the original baseline value is reached. Typical washout times are between 30 and 45 seconds; however, significantly more time may be required if samples contain high levels of dissolved solids or contain elements that produce memory effects such as B or Hg.
Now let’s contrast this setup to one in which a switching valve is being used. A switching valve is based on the principles of flow injection (link to the Wikipedia page). Using this analysis approach, a relatively small, fixed volume of solution is injected into a moving carrier stream solution. The switching valve consists of a 6-port valve and has 2 operating positions: the load position and the inject position. In the load position, a carrier solution is continuously pumped to the instrument nebulizer while sample from an autosampler vial is loaded into a sample loop. Since the valve resides a few inches from the nebulizer, sample solution travels from the sample loop to the nebulizer in a matter of a few seconds. Since the solution travels such a short distance before reaching the nebulizer, the solution has undergone almost no dispersion and produces a steady state emission signal relatively quickly.
Once data acquisition is complete, the switching valve switches back to the load position and the carrier solution immediately starts rinsing the sample introduction components. Emission rapidly decreases back down to the baseline, as illustrated in the emission profile below.
The presence of a switching valve offers several benefits. As described above, the valve nearly eliminates uptake and rinse routines during sample analysis which will double or triple your sample throughput. Each sample solution resides solely in the sample loop and only remains there for the time required for the instrument to complete its analytical measurement. The sample never comes into physical contact with the peristaltic pump tubing which is one of the main contributors to memory effects. So even in the presence of samples known to produce carryover issues, washout is incredibly rapid with a switching valve and emission signals come back down to their original baseline levels without extra rinsing steps.
Benefits of this switching system include the following:
Every minute saved in analysis time translates to a reduction in operating costs in your laboratory.
Your instrument will consume less argon and electricity, it will produce less hazardous waste, and it will consume a smaller volume of each sample during analysis.
You will spend less money on second source QC standards, as well as high purity stock standards and acids.
Most importantly, your laboratory personnel will spend less time performing routine tasks, such as preparing calibration standards, samples and rinse solutions.
On-demand webinar, titled, Speed and Cost of Ownership (link to on-demand webinar page where you will need to fill out a short registration form before watching the webinar)
Our recently launched Expect More Productivity webpage, a portal for featuring many useful resources to help you maximize the productivity in your laboratory. The site is updated on a regular basis so check back regularly for the latest helpful tips and tricks.
Stay tuned for my next post which will focus on in-line, intelligent auto-dilution for internal standard addition, standard preparation, over-range sample dilution and check standard preparation.
If you have questions or concerns about maximizing the efficiency and productivity in your laboratory, let us know in the comments box below. We’re here to help.
Maura Rury is a former applications chemist and product manager with deep experiences working with atomic absorption and inductively coupled plasma-based instruments for a wide range of applications. She currently provides marketing for trace elemental analysis in the Chromatography and Mass Spectrometry Division at Thermo Fisher Scientific, Inc. Via her integrated marketing initiatives, she supports the development of food and beverage, pharma/biopharma, environmental and industrial vertical markets in North America and Canada. Maura received her ACS Certified B.Sc. in Chemistry from Union College and her Ph.D. in Analytical Chemistry from the University of Massachusetts, Amherst.