This is a hyphenated system, its expected that the species detection by the PDA detector should simultaneously be detected by the MS detector, why the difference in the retention times?
The retention times will be different because you are not operating both detectors in parallel by splitting the column effluent on a system where the dead volumes in both streams are matched so that both streams arrive at the detectors simultaneously. Typically the PDA detector is up stream or in series with the mass spectrometer and the analyte will arrive and be detected in the PDA first then travel through some more tubing to the mass spectrometer and be detected afterwards.
The retention times will be different because you are not operating both detectors in parallel by splitting the column effluent on a system where the dead volumes in both streams are matched so that both streams arrive at the detectors simultaneously. Typically the PDA detector is up stream or in series with the mass spectrometer and the analyte will arrive and be detected in the PDA first then travel through some more tubing to the mass spectrometer and be detected afterwards.
The exit of the HPLC passe across the UV next split 1/10 output next the MS,
You can calculate the delay by (dead volume mL) X (flow rate mL/min.) = time or you can conduct a flow injection experiment (remove the column) to observe the delay. Bruce is also correct in that you can split the flow with a T-connector after the column and trim the two pieces of tubing until both detectors are showing the signal at the same time.
On the same question is there an acceptable delay time range between the two signals; on the PDA and MS?
There is no problem with delay. Many software packages can realign the two signals for a good publication overlay by simply inputting the delay in time.
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