Procedures: The Module
- Page ID
- 65152
- Outline the experiments you must do to determine the retention factor (capacity factor) for 4 NSAIDs. To determine the retention factor (k’) for four NSAIDs, several steps must be followed. First, the free-zone migration times for both the NSAIDs and a neutral marker (neutral, hydrophilic compound such as dimethylformamide) must be determined in triplicate. Next, the MEKC migration times for the NSAIDs, a neutral marker, and a micelle marker (neutral, highly hydrophobic compound such as n-decanophenone) must be determined in triplicate. All migration times should be determined using the same bare-fused silica capillary, and the length to the detection window (Lw), the total length (Lt), and separation voltage (Vsep) must be known. The run buffer should be the same concentration with respect to the buffering species (CAPs) and pH for both the free-zone and MEKC trials. From the free-zone runs, you should be able to determine the free-zone electrophoretic mobility for each NSAID (μeph_NSAID) using the following equation:
μapparent_NSAID (CE) = [Lw x Lt] / (tNSAID(CE) x Vsep)
μeof free zone = [Lw x Lt] / ( teof marker_DMF x Vsep)
μeph_NSAID = μapparent_NSAID(CE) - μeof free zone
From the MEKC runs, the electroosmotic mobility for each trial (μeof_MEKC) is determined using the following equation:
μeof MEKC = [Lw x Lt] / (teof marker(MEKC) x Vsep)
By combining these two terms, along with the migration times of the eof marker (teof (MEKC)), the NSAID (tNSAID (MEKC)), and the micelle marker (tn-dec_ (MEKC)), all of which are obtained from the MEKC trials, the retention factor (k’) is calculated for each NSAID using the equation below.
\[k' = \dfrac{t_{tolmetin\_MEKC}\left(1+\dfrac{\mu_{eph\_tolmetin}}{\mu_{eof\_MEKC}}\right) - t_{eof\_MEKC}}{t_{eof\_MEKC}\left(1 - \dfrac{t_{tolmetin\_MEKC}}{t_{n−dec\_MEKC}}\right)}\] ttolmetin_MEKC = MEKC migration time tolmetin
μeph_tolmetin = calculated CE electrophoretic mobility tolmetin
μeof_MEKC = MEKC electroosmotic mobility (DMF)
teof_MEKC = MEKC migration time DMF
tn-dec_MEKC = MEKC migration time n-decanophenone
The retention factor for each NSAID per trial should be determined in triplicate. The mean value for k’ for each NSAID should be reported. It is important to note that under optimized conditions, all four NSAIDs can be separated during a single MEKC trial, giving individual migration times for each NSAID. However, for the free-zone trials, each NSAID must be analyzed separately because of the similarity in migration times under free-zone conditions.
- Determine the retention factor (capacity factor) for flurbiprofen, naproxen, sulindac, and tolmetin. These values should be reported as mean values determined from triplicate runs (n = 3). For these runs, the background BGE is 25 mM CAPs, 100 mM SDS buffered to pH 10. You must use a ~25 micron inner diameter fused silica capillary ~42 cm in total length, ~32 cm to the window, 20,000 V.
Free Zone Data
Lw = 32.9 cm, Lt = 42.8 cm, Vsep = 20,000 V, pH 10 CAPSMigration Time μ eof (CE) Marker
Trial
1
2
3
Trial
1
2
3
DMF 105.1 104.7 104.7 0.04019 0.04034 0.04034 Migration Time μ app Analyte
Trial
1
2
3
Trial
1
2
3
Tolmetin
147.4 147.0 147.2 0.2867 0.2874 0.2870 Naproxen
152.8 153.1 152.8 0.2765 0.2759 0.2765 Flurbiprofen
152.3 151.8 152.0 0.2773 0.2784 0.2780 Sulindac 141.5 139.5 140.5 0.2986 0.3028 0.3006 μ eph Analyte
Trial
1
2
3
AVE
Tolmetin
-0.01153 -0.01160 -0.01164 -0.01159 Naproxen
-0.01254 -0.01275 -0.01269 -0.01266 Flurbiprofen
-0.01246 -0.01250 -0.01254 -0.01250 Sulindac -0.01033 -0.01006 -0.01028 -0.01022 MEKC DATA
Lw = 32.9 cm, Lt = 42.8 cm, Vsep = 20,000 V, pH 10 CAPS 100 mM SDSMigration Time μ eof (MEKC) Marker
Trial
1
2
3
Trial
1
2
3
DMF
126.0 125.9 126.0 0.03354 0.03356 0.03353 n-dec 353.4 354.8 355.9 Migration Time k' Analyte
Trial
1
2
3
Trial
1
2
3
AVE
Tolmetin
196.9 196.6 197.4 0.0523 0.0511 0.0569 0.0534 Naproxen
207.2 206.8 208.1 0.186 0.182 0.194 0.187 Flurbiprofen
220.2 219.8 221.1 0.382 0.37 7 0.391 0.383 Sulindac 251.0 250.6 252.4 1.05 1.03 1.07 1.05 - Lab Practical
Through a faculty mentor or collaborator, you should arrange to receive an unknown solution containing some combination of flurbiprofen, naproxen, sulindac, and tolmetin diluted in BGE at a concentration above the limit of quantification for your CE system. Once you receive the unknown solution, you are to determine the analyte composition and concentration in the solution. Your final report should include pertinent data and a clear explanation of your results. When you report your final value, be sure to include uncertainty. You should have access to standard solutions as necessary.