ADV06-15_1-412

Figure 1

USP467 solvents by headspace analysis/GC on an

Rtx®-G43 colu mn .

A) Static headspace (loop) technique

RetentionTime (min.)

l. dichloromethane

2. chloroform

3. benzene

4. trichloroethylene

5. 1,4-dioxane

5.n O

9.285

1Ll73

14.647

17.436

Sample Concentration

~g/ml)

12.0

l.2

0.04

l. 6

7.6

of the vial, to sweep the analytes onto an activated

trap. The trap , with the concentrated analytes, was

dry purged to remove the water vapor, then was

heated without flow to desorb the analytes. After

the analytes were desorb ed, the trap was back

flushed to direct the concentrated analytes onto

the analytical column. Between analyses, the trap

was baked at high tempe rature to remove all

residue compounds.

When we compared the results of the system suit

ability analyses for the two headspace techniques,

we determined that, based on area responses, the

dynamic headspace meth od greatly enhanced sen

sitivity for the target Ov ls: area counts were, on

average, 22 times larger than for the static head

space method (Table

1).

We also noted that the

Rtx®-G43capillary column provided excellent res

olution among analytes, with very little drift in

retentio n time or resolution (Table 2).

As with purge and trap systems, or other dynamic

sampling systems, certain system control s must be

taken into account when using a dynamic head

space technique. Factors to consider include

sweeping and desorbing times and flows, adsor bent materials used to trap the analytes, and water

management. In this specific appl ication , we

observed that either prolonged samp le heat ing at

80°C or extended vial sweep times increased the

water content in the sample headspace, ultimately

resulting in poor peak shape for l,4-dioxane and ,

if excessive, extinguishing the FID. 1,4-Dioxane

has a notoriously poor partitioning efficiency and

proved to be the limiting factor when setting sys

tem operating conditions. For samp les heated at

80-85°C in a water matrix, a sweep time of 5 min

utes or less enhanced sensitivity for all compounds

while assurin g proper water man agement.

From this work, we conclude that coupling a

dyn amic headspace sampling technique with

analysis on an Rtx®-G43 column greatly increases

sensitivity for residual solvents, and makes stable

retentio n possible. These enhancem ents can lead

to more achievable system suitability criteria and

lower detection limits, or to effective results with

smaller samples.

Rtx®-G43 Column

(fused silicawith 5-meter

lnteqra-Guard'")

(Crossbond" 6%cyanopropylphenyl/94% dimethyl polysiloxane)

~m)

temp. limits

length cat

0.53mm 3.00

-20 to 240°C

30-Meter 16085-126

GCPH00810

Instrument:

Sample Equilibr,Time:

Mixing:

Mixer StabilizeTime:

Valve OvenTemp.:

Transfer LineTemp.:

StandbyFlow Rate:

1'0

Time (min.)

TeledyneTekmar HT3

15.00min.

levelS, 2.00min.

0.50 min.

150°C

10mL/min.

Platen/SampleTemp.:

80°C

PlatenTemp.Equilibr;Time: 2.00 min.

Pressurize:

15psi, 2.00min.

Pressurize

Equifthr.

Time: 0.50min.

Loop Fill Pressure:

5 psi

LoopFillTime:

2.00min.

Loop FillEQuilibr.Time:

0.50 min.

InjectTime:

1.00 min.

B) Dynamic headspace (trap) technique

RetentionTime(min.)

l. dichloromethane

5.137

2. chloroform

9.260

3. benzene

1Ll45

4. trichloroethylene

14.601

5. 1A·dioxane

17.349

SampleConcentration

~g/ml)

12.0

l. 2

0.04

l.6

7.6

Time(min.)

Instrument:

TeledyneTekmar HT3

TrapStandbyTemp.:

40°C

Sample Equilibr,Time:

15.00 min.

Platen/ SampleTemp.:

80°C

Mixing:

level S, 2.00 min.

Sweep Flow:

75mL/ min., 3.00 min.

Mixer StabilizeTime:

0.50 min.

Dry Purge:

50mL/ min.,

ValveOvenTemp.:

150°C

5.00 min., 25°C

Transfer LineTemp.:

150°C

Desorb Preheat:

245°C

StandbyFlow Rate:

10mL/min.

Desorb:

l.00 min., 250°C

Trap 8ake:

450mL/min.,

6.00 min., 300°C

Chromatography Conditions

Column:

Rtx*-G4330m, 0.53mm!D,

3.0f.lm

(cal.# 16085-126)

Sample:

100f.lLUSP467CalibrationMixture #5 (cal.# 36007) in dimethylsulfoxide, 5mL

water, -

l.Og

sodium sulfatein 22mLheadspacevial. Concentrationslistedon

figure.

Ini.:

staticheadspaee or dynamic headspace

Inj. temp.:

180°C

Carrier gas:

helium, split 2:1

Linear velocity:

5mL/min., constant flow

Oven temp.:

40°C(20min.), to 240°C@ 25°C/ min. (hold 10min.)

Del.:

F!D @ 250°C

hydrogen flow: 40mL/min.; air flow: 450mL/min.;make-up flow: 45mL/ min.

2006 vol. 1

• 15 •

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