AI10382-GC-MS-Food Safety-Analysis - page 210-211

3 2 This technical note describes results obtained from an
endurance mechanical test performed on “Instant Connect”
modules and typical analytical reproducibility and
accuracy provided by the TRACE 1300 Series GC.
Analytical reproducibility was also measured after switching
modules of the same type in the same application, as
might happen when an injector module is replaced with a
new one in a routine laboratory to keep a contaminated
instrument up and running.
Experimental
A TRACE 1310 GC instrument equipped with various
SSL and FID modules was used in all of the experiments,
and all “Instant Connect” modules are identified by specific
serial numbers for easier tracking in the lab. Four different
modules were alternated in these experiments.
The GC was equipped with a Thermo Scientific AS 1310
liquid autosampler. All tests were performed using a
synthetic mix of normal alkanes ranging from C10 to C40
in hexane, at a concentration of approximately 10 ppm
(10 ng/μL) and using helium as carrier gas. A 1 μL aliquot
of sample was injected in splitless mode into a standard
glass-wool packed tapered liner, while the injector
temperature was maintained at 300 °C. Splitless time
was 0.8 minutes. The FID detector temperature was set
to 350 °C.
A Thermo Scientific TraceGOLD™ column TR-5, 15 m x
0.25 mm id x 0.25 μm, was used in all experiments. Oven
temperature was set at 50 °C for 0.5 min and then ramped
up to 340 °C at 20 °C/min, with two minutes of isothermal
time at the final temperature. A Thermo Scientific Dionex™
Chromeleon™ Chromatography Data System was used for
setting all method parameters, data acquisition, and data
processing.
Results and Discussion
System analytical reproducibility and accuracy
The analytical reproducibility was evaluated using two
new “Instant Connect” modules, a SSL injector
(module serial number S/N: 712100036) and a FID
detector (S/N: 712300088), by injecting the synthetic
hydrocarbon mix automatically (ten repetitions). Results in
terms of peak area and retention time repeatability are
summarized in Tables 1 and 2. No discrimination for both
volatile and high boiling compounds was seen. As shown
in Table 1 the recovery, calculated using C20 peak area as
reference, is close to 100% along the full range of
volatility. Absolute peak area relative standard deviation
is far below 1% for all hydrocarbons. All injector and
detector modules incorporate a new generation of
miniaturized gas controls. These integrated electronic
devices ensure precise control of the inlet pressure and the
flow throughout the column, further contributing to the
excellent reproducibility of retention times. As indicated
in Table 2, the standard deviation is below a thousandth of
a minute. This level of reproducibility is a clear indication
of the accurate temperature profile and column flow
maintained during the ramp and the precise thermo-
regulation of the GC oven. Overall results show full
recovery of hydrocarbons and excellent data precision.
Table 1. Instrument configuration SSL S/N 712100036 and FID S/N 712300088. Absolute peak area RSD% far lower than 1%. Recovery,
measured as ratio vs C20 average area, at 100% for the whole range of hydrocarbons
SSL 712100036
/ FID 712300088
nC10 nC12 nC14 nC16 nC18 nC20 nC22 nC24 nC26 nC28 nC30 nC32 nC34 nC36 nC38 nC40
Injection 1 2600304 2647767 2600941 2619188 2552750 2565809 2543886 2535687 2512699 2527008 2602759 2597807 2534441 2564855 2470270 2525384
Injection 2 2610605 2657856 2601653 2623404 2568557 2579380 2565938 2565679 2545232 2560614 2636265 2629734 2557462 2596729 2495209 2563483
Injection 3 2602666 2653832 2599714 2626029 2553641 2577265 2561577 2558672 2542703 2555406 2632496 2630095 2555743 2580475 2480864 2538819
Injection 4 2636572 2683702 2632897 2656448 2593709 2602685 2584957 2575384 2558834 2574920 2649582 2640082 2566623 2593858 2490053 2549873
Injection 5 2623737 2668679 2617130 2639475 2575209 2588255 2568857 2566489 2551218 2570336 2641759 2632243 2559472 2591033 2487269 2545848
Injection 6 2628675 2671731 2625320 2647746 2586155 2602674 2584119 2578956 2563433 2577945 2652932 2644762 2572449 2600568 2495549 2560371
Injection 7 2633245 2675436 2621623 2640507 2579749 2601553 2603546 2589030 2566470 2580193 2651340 2644782 2575086 2615870 2515378 2552861
Injection 8 2622426 2667773 2618401 2631007 2571368 2588047 2571982 2568771 2543992 2565899 2635937 2628421 2556233 2599156 2491820 2552234
Injection 9 2627383 2675413 2624978 2646945 2578061 2590137 2578171 2582555 2553973 2565982 2637795 2636002 2561603 2598494 2504800 2575965
Injection 10 2621650 2664829 2611668 2634863 2576839 2592681 2577082 2571091 2552087 2567396 2634338 2631176 2560023 2590260 2497076 2558360
Average (counts) 2620726 2666702 2615432 2636561 2573604 2588848 2574011 2569231 2549064 2564570 2637520 2631510 2559913 2593130 2492829 2552320
SD 12355 10941 11571 11889 12894 12092 15913 14767 15078 15223 14298 13319 11161 13430 12358 13908
RSD % 0.47% 0.41% 0.44% 0.45% 0.50% 0.47% 0.62% 0.57% 0.59% 0.59% 0.54% 0.51% 0.44% 0.52% 0.50% 0.54%
Recovery % 101% 103% 101% 102% 99% 100% 99% 99% 98% 99% 102% 102% 99% 100% 96% 99%
Figure 1. Module-to-module repeatability. Modules store all
of their calibration information allowing minimum variation if
replaced on a system.
Module-to-module reproducibility
To simulate a situation where a laboratory needs to quickly
replace a module, such as to avoid interrupting instrument
throughput for maintenance, the “Instant Connect” SSL
injector module (S/N: 712100036) was replaced by a new
module (S/N: 712300021). This required cooling and
powering down the instrument, disconnecting the column
from the original SSL injector module, removing the module
and plugging in the new one, connecting the column, and
powering up the TRACE 1310 GC again. Electronic gas
control permits an automated leak check to be performed
to guarantee that no artifacts are introduced by this
manual operation. The reduced thermal mass GC design
allows a quick recovery of injection-ready conditions after
instrument power-up. As a result, the GC was ready to
resume analytical injections again in only nine minutes
after it was originally powered down. A blank GC cycle
was programmed before injecting samples again, which is
good practice to ensure the entire flow path was not
affected by air introduced during module replacement.
An automated sequence of 10 injections was performed
immediately after the module replacement along with
collecting data. The instrument was then stopped again,
and the FID detector module (S/N: 712300088) was
replaced by a new one (S/N: 712300126). After a blank
run, another sequence of 10 injections completed the
experiments. Tables 3 and 4 and Figure 1 summarize the
repeatability results for the three different instrument
configurations. Variations in peak area measured as a
delta of the average counts are in the range of a few
percentages when changing either the injector or the FID
detector. Such a variation, for many applications, is well
below the required limit of a system suitability check,
eliminating the need to recalibrate the GC system as a
whole. The retention time variations are in the range of a
few hundredths of a minute or even less with no impact
on component retention time.