INSTRUMENTATION AND CHARACTERIZATION OF A WATER STATIONARY PHASE IN cGAS CHROMATOGRAPHY

PRESENTED BYP.ANURADHA614275804016Shri Vishnu College of Pharmacy(M.PHARMACY)Pharmaceutical Analysis&Quality Assurance

INTRODUCTION

Gas chromatography (GC) is a widely used separation technique in analytical chemistry. The purpose of GC is the separation of different chemical species in a sample based on their interaction with a stationary phase fabricated from a non-volatile liquid or solid. The sample is transported over the stationary phase by an inert carrier gas. The weakly interactive compounds will move over the stationary phase quicker than the strongly interactive compounds.

GAS CHROMATOGRAPHY OVERVIEW

Carrier Gas

Flow Control Injector

Column

Oven

Detector

Analyte peaksRecorder

THE MODERN GC INSTRUMENT

GC COLUMNS

• In the early years of GC, the majority of work was performed on columns that were a few meters long, had a diameter of a few millimeters, and were packed with particles with a non-volatile liquid coating . This mode of separation was termed packed GC (pGC) due to the column containing a packed stationary phase.

• In 1957, Martin suggested using an open tubular design for a GC column in which a stationary phase could be coated on the inside walls of the column .

• This concept was also independently realized by Golay in 1958. Their combined efforts began the field of what is now known as capillary gas chromatography (cGC).

• The columns used in cGC can typically separate closely eluting compounds from a sample more clearly than columns used in pGC and can allow for a lower amount of analyte to be detected in a sample.

• This is mainly due to lower flow rates in cGC resulting in lower detector noise and better signal to noise ratios.

• Some of these differences include the fact that cGC columns are typically much longer (15 - 100 m) than pGC (1 - 5 m),cGC columns also possess a smaller I.D. (typically 240 - 530 µm) than pGC columns (3 - 6 mm) .

• The stationary phase is the primary component in GC that causes analytes to separate. • A variety of stationary phases have been applied to a fused silica capillary

substrate in cGC, including methyl polysiloxanes, phenyl polysiloxanes, cyano-propyl polysiloxanes and polyethylene glycol (PEG).

One compound that may provide a highly polar stationary phase with interesting selectivity is water. Water is a very polar compound which has several advantages in a laboratory setting such as low economic cost,low ernvironmental impact and the ease andf safety of use.

DIFFERENT STATIONARY PHASES IN MODERN cGC

CURRENT cGC STATIONARY PHASE RESEARCH

PROPERTIES OF WATER AS A STATIONARY PHASE

• A water stationary phase can offer a very high polarity stationary phase at little cost

to create and use. This also does not involve any harmful chemicals. • Here we are disscussing on the formation, maintenance, characterization and

utilization of a water stationary phase in cGC.

The first part of the study will investigate the formation and maintenance of a water phase in cGC.

The second part of this study will focus on the characterization of this stationary phase in cGC.

STATEMENT OF PURPOSE

General Instrumentation

He

Tank Transfer Line

Humidifier

Pre-Heating Coi

Inj.

SS Column

Restrictor

FID

ZDV

Union

Schematic diagram of the water stationary phase instrument.

Humidifier and Pre-Heating Coil

• To properly humidify the carrier gas , a custom humidifer was developed for this novel stationary phase and its schematic is represented by

He Flow Inlet

Swagelok Cross Union

Pre-Heating Coil

Humidified HeFlow Outlet

Humidified HeWater in the SS tubing

Injector

SS Column

SS Tee union

Sample injection needle

Septum

SS Pre-heating coil

Carrier gas flow

SS Tee union modified injector.

Post –Column Restrictor

• Once the analytes eluted from the column, they entered the restrictor.

• Several advantages in the system such as: further determent of the depletion of the water stationary phase on the column, increased oven temperatures that could be used with the water stationary phase and direct column effluent deposition at the base of the FID flame.

• The dimensions of the fused silica capillary tubing for this restrictor was optimized at 350 µm O.D. × 50 µm I.D. × 11 cm length and this fused silica was replaced every 5-6 trials. The end of the restrictor was placed at the base of the flame in the FID to guide the effluent into the FID flame directly.

Flow pathway

SS column

SS Zero Dead Volume union

PEEK Tubing Sleeve

Fused Silica Capillary Restrictor

Diagram of the column and restrictor connection.

Water stationary phase deposition

• To deposit this water stationary phase on the SS column, a unique method and apparatus was employed

• This method and apparatus is similar to the standard dynamic coating of a stationary phase.

N2

N2 Transfer line

ReservoirSS Column

ZDV union

Water

CHARACTERIZATION OF THE WATER STATIONARY PHASE

THE CARRIER GAS HUMIDIFER

• Taking this into account, the carrier gas was humidified and its effect on the stability of the cGC water stationary phase was studied by comparing the loss in the retention time of a consecutive series of acetone injections.

• This was done with identical stationary phase formation and operating conditions, except for the presence or the absence of the humidifier.

As is shown, the % loss with the humidifier is significantly lower than without thehumidifier. Therefore, the humidifier significantly stabilized the stationary phase at a large range of temperature.

Figure:Retention time of acetone over time showing the increase in stationary phase stability provided by the humidifier. The oven was set to 70 şC.

POST COLUMN RESTRICTION

• Even with the increased stability which was provided by the water humidifier, at temperatures at or above 100 C, the water stationary phase experienced rapid depletion.

• To aid in its stability at these higher oven temperatures, a post-column restrictor was employed that introduced backpressure on the column and the stationary phase.

This figure demonstrates that the restrictor does improve the stability of the stationary phase even at low oven temperatures

Figure:Retention time of acetone over time showing the effect of the post-column restrictor on water stationary phase stability. The oven was kept at 70 şC and the restrictor dimensions were 323 µm O.D. × 50 µm I.D. × 11 cm length, requiring 90 psi of column head pressure.

Optimizing of Post Column Restrictor

Peak shapes for acetone injections showing the optimization of the post-column restrictor. The column head pressures and dimensions used were A) 90 psi with 50 µm I.D. × 11 cm length, B) 50 psi with 100 µm I.D. × 1 m length and C) 30 psi with 250 µm I.D. x 14 cm length. The carrier gas linear velocity was 26 cm/s for all profiles. The temperatures indicated are the oven temperature for the elution below them.

CUSTOM INJECTOR

Chromatogram demonstrating the peak shape provided by the modified injector. The conditions for this injection were as follows: 5 µg of acetone in CS2, 220 şC injector, 60 şC oven and a carrier gas linear velocity of 26 cm/s.

MAXIMUM OVEN TEMPERATURE

As seen, properly shaped peaks were obtained up to a maximum operating temperature of 140 şC. However, higher temperatures began to onset peak asymmetry and complete disruption of the separation system. Going forward then, 140 şC was determined to be the maximum that could be used for this current water stationary phase setup.

APPLICATIONS

1. For determination of straight chain alkanes

The chromatogram for a series of straight chain alkane (C6-C20) injections on the water stationary phase at 140 şC.

2. For BTEX analysis which are collectively knowm as benzene,toulene,ethyl benzene,m-xylene,o-xylene which are significally in air pollution and soil contanimation investigation.

3.For determination of oxygenates,sulfur compounds in gasoline matrix

4.For investigation of 3 different aqueous products tequila,vanilla,window cleaner examined for alcohol content.

REFERENCES

• Gallant, Jonathan A., and Kevin B. Thurbide. "Properties of water as a novel stationary phase in capillary gas chromatography." Journal of Chromatography A 1359 (2014): 247-254.

• Murakami, Jillian N., and Kevin B. Thurbide. "Coating properties of a novel water stationary phase in capillary supercritical fluid chromatography." Journal of separation science 38.9 (2015): 1618-1624.

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