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Optimize your methods quickly with the LC Calculator app
By John Henderson
Agilent Applications Chemist
Asking “what if?” has always been a great way to increase speed and improve productivity. Now Agilent’s new LC Calculator makes it easy to explore all the possibilities when you’re developing methods. It includes hundreds of Agilent column configurations and other method parameters to help you quickly determine both flow rate and back pressure under a wide variety of conditions and column dimensions. This mobile app works with the iPhone™ and iPod touch® and allows you to set up “what if” scenarios with a tap of your finger.
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Figure 1. Existing method of active ingredients in Sunscreen. (Enlarge image.)
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Figure 3. Sunscreen ingredients on a ZORBAX Eclipse Plus C18 2.1 x 50 mm. (Enlarge image.)
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Figure 4. Sunscreen ingredients on a ZORBAX Eclipse Plus C18 RRHD 2.1 x 50 mm at 1.0 mL/min. on the 1290 Infinity LC. (Enlarge image.)
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Figure 5. Sunscreen ingredients on a Poroshell 120 SB-C18 3.0 x 50 mm at 1.5 mL/min. (Enlarge image.)
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Sunscreen method sheds light on the advantages of the LC calculator
To demonstrate how quickly the LC Calculator creates helpful scenarios, imagine you need to optimize an old method for separating active ingredients in sunscreen lotion with a run time of 25 minutes. Is it possible to reduce the analysis time to under two minutes on your 1200 Series system (pressure limit 600 bar)? (See Figure 1.)
Choosing a shorter column length and smaller particle size generally decreases analysis time. However, the large number of column configurations can make finding the best column choice overwhelming. So we’ll shorten the process by running scenarios with the LC Calculator.
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Figure 2. Calculator Screen showing 608 bar with sunscreen parameters.
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Our first scenario uses a ZORBAX Eclipse Plus C18 Rapid Resolution HT (RRHT) 2.1 x 100 mm, 1.8 µm (P/N 959764-902) which is as efficient as 4.6 x 250 mm, 5 µm columns. However, when the sunscreen method parameters and 2.1 x 100 mm, 1.8 µm column configuration were input, the column pressure calculated to be 608 bar (Figure 2). This exceeds the LC system’s 600 bar pressure limit – thus, not the best column choice. Actual system pressure includes both column pressure plus instrument pressure, and would be even higher, as the LC Calculator calculates only column pressure.
Next, a 2.1 x 50 mm ZORBAX RRHT column was entered into the calculator. The LC Calculator quickly tells us that the 50 mm column generates half the pressure of the 100 mm column – well within the 600-bar limit of the instrument. Figure 3 shows the 50 mm column reducing analysis time by 19 minutes and mobile phase consumption by 94%. This is a dramatic improvement, but still over the two-minute goal. What other possibilities are there for reducing the analysis time even more?
The LC calculator lets you increase pressure incrementally by moving the flow rate bar to approximate a maximum of 550 to 600 bar. Doubling the flow rate from 300 bar to 600 bar cuts retention time in half, but won’t work with a 600 bar system. However, upgrading to a higher pressure system like the Agilent 1290 Infinity LC System, which has a 1200 bar pressure limit and 5 mL/min. maximum flow rate would solve this problem.
Figure 4 shows the sunscreen analysis on a 2.1 x 50 mm ZORBAX RRHD column on the 1290 Infinity LC at a flow rate of 1.0 mL/min., reducing analysis time to about two minutes. The LC Calculator indicates that these method conditions produce a column pressure of 760 bar. Actual system pressure is still within limits at 805 bar.
If a high pressure system is not available, you could use a shorter 30 mm column, although some resolution would be lost. Or consider an Agilent Poroshell 120 column containing 2.7 µm particles comprised of a 1.7 µm solid core and a 0.5 µm porous shell. It provides efficiencies nearly equal to 1.8 µm totally porous particles, yet produces approximately half the backpressure. Entering a 3.0 x 50 mm Poroshell 120 column into the LC Calculator returns a significantly lower pressure.* The flow rate slider lets us see that we can double the flow rate for an under two-minute analysis.
Figure 5 shows the final method using the Poroshell 120 column, which reduces analysis time by 94%, solvent consumption by 95%, and increases sensitivity by a factor of ten!
Save time and increase productivity with the tap of a finger
If you are exploring ways to increase speed and improve productivity, try the LC Calculator. This new free app makes working through scenarios easy and quick. It’s designed to be compatible with the original iPhone, iPhone 3G, and iPod touch, so you can carry it with you anywhere. Find out how to use this new mobile app to improve your chemical applications. Then download it from App StoreSM for free, and watch productivity soar.
* Porosity value varies from column to column. For LC calculator calculations, the Agilent Poroshell 120 columns porosity value was 0.38, for all other columns used it was the default 0.40.
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