Running Very Dilute Solutions

A well characterized broad polystyrene standard, Dow 1683, was run on the Alliance system with the dRI detector and THF as the eluent. The concentration was 0.15%, and a 300ul injection was made. The broad standard was injected again, (also 300ul) but this time at a 0.015% concentration (10 times less). You can see the comparisons in the figures below. Note that the signal for the 0.15% concentration is ~15mV. With the baseline noise being 14 uV, we have a S/N of >1000:1. The signal for the 0.015% injection is only 1.5mV, but we still are able to attain a S/N of >100:1, and is easily integrated. The smoothness of flow, along with the integrated degasser, allows us to run very dilute polymer solutions, and still get the S/N needed for reproducible GPC work. This is very important when we need to run very low concentrations of high molecular weight samples. We can now run extremely low concentrations and still get the correct results without sacrifice of S/N.