AL
inputs determined the split factor, compensa- tion flow rate and dilution flow rate. From the stock solutions, manual dilutions were also performed at the same dilution ratios in order to compare the results obtained by automatic dilution.
The MS was operated in negative ion polarity mode, with scanning rate of 1 spectrum/sec and mass range of 100–500 m/z. Nitrogen with a flow rate of 10 L/min was used as the drying gas. Source temperature was at 350 °C and nebulizer pressure was 40 psig. The following voltages were applied: capillary 3500 V, frag- mentor 175 V and skimmer 65 V.
System settings A mixture of ACN/H2
O (40/60%) was used as
the carrier solvent stream to the MS. Methanol was used as diluent by the dilution pump and compensation pump. Other settings were flow rate ratio of the educt pumps 1:1, total reac- tion volume 12.18 mL, carrier solvent flow rate 0.6 mL/min, sampling time 0.2 sec, sampling interval 18 sec and sampling repetition 7. Each dilution was repeated at least twice.
Results and discussion
Dilution results with stock solution 2 (182 mg/L OS + 91 mg/L 4-MOS in MeOH) are shown in Figure 3 and in Table 1 for OS (similar behavior was observed for 4-MOS; thus only the results of OS are presented). In every dilution ratio, the average peak area of each reaction stage (3, 6 and 12 min) was calculated. The average peak area of all peaks for every dilution ratio and standard deviation was also determined. These results show a logical increase of the sampling peak areas (from 549,566 to 5,993,738 for OS and 356,885 to 4,196,049 for 4-MOS)
as the dilution ratio decreases (from 1:500 to 1:50). They are also equivalent to the manually diluted solutions of similar ratios. Manual dilu- tion is not affected by the microreactor flow rate variation in the testing range because the sampling loop is only 5 μL (see Table 1). Due to the (possibly) different settings of the dilution module (for split factor, compensation flow rate and dilution flow rate) and microreactor flow rates for each reaction stage, the standard deviations measured with automatic dilution (4.3–14.4% for OS) are normally higher and more wide-ranging than those with manual dilution (7.5–10.7%). Further comparison of the signal intensity between different dilution ratios (1:50, 1:100, 1:300) with a dilution ratio of 1:500 yielded values in two rows—expected quotient and actual quotient. It is expected that the signal intensity of dilution ratio 1:50 would be 10 times that with a dilution ratio of 1:500. The actual quotient (5,993,738/549,566) was 10.91, which is acceptable. Other logical quo- tients were obtained, i.e., expected quotient: 5 – actual quotient: 5.77 (3,168,592/549,566) with dilution ratio 1:100 and with dilution ratio 1:300—expected quotient: 1.67 – actual quo- tient: 1.93 (1,062,333/549,566).
Figure 4 shows the results of automatic dilu- tion with the same dilution ratios but different concentrations of stock solution (solutions 1, 2 and 3). Only the signal of octanoic acid is plotted. As can be seen, for every concentration of the stock solution, the signal intensity of the diluted solution increases as the dilution ratio decreases from 1:500 to 1:50. In addition, for each of the same dilution ratios, the peak areas of stock solution with higher concentration are higher. This results in a much steeper slope of the green curve (from stock solution 3), red
The Mini-Beadbeater-24
disrupts microorganisms and tissue preparations with better than 95 percent effi ciency. Nucleic acids and proteins are isolated with the highest possible yields. Cells are disrupted quickly and safely in the sealed 2 ml
microvials containing small beads. No cleaning between samples is required. The apparatus has a small footprint and is essentially maintenance free.
• Uses proven, more effi cient near horizontal vial shaking motion.
• 24 – 2.0ml microvials capacity with removable vial-holding cassette.
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• Digital 5 minute timer with auto reset.
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Figure 3 – Automatic and manual dilution with ratios of 1:500, 1:300, 1:100 and 1:50 of OS in MeOH. AMERICAN LABORATORY 39 JANUARY/FEBRUARY 2017
www.biospec.com
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