Page:NIOSH Manual of Analytical Methods - Chapter I.pdf/1

 I. PORTABLE GAS CHROMATOGRAPHY

by Judd C. Posner, Ph.D., NIOSH/DPSE

Contents:

Page 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 2. Principles of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 a. Injection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 b. Separation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 c. Detectors (FID, PID, ECD, TCD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 d. Limitations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3. Sampling Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 a. Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 b. Type of Sample. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 c. Column Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 4. Data Acquisition and Treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 a. Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 b. Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 c. Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 d. Indications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 5. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

1. INTRODUCTION

The term "portable gas chromatograph (GC)" as used here refers to any gas chromatograph not requiring external electrical connections. The portable GC may range in size and portability from a self-contained unit the size of a small suitcase easily carried by one person to a much larger unit requiring auxiliary gas supply and requiring more than one person to transport.

2. PRINCIPLES OF OPERATION

A portable GC consists of, at a minimum, an injection system, a separator (column), and a detector.

a. Injection

There are two basic injection systems: (1) gas-tight syringe through a septum [1] and (2) flushing and filling a sampling loop [2]. The loop is usually filled by means of an on-board pump. Injection is usually accomplished by means of a valve system, either manual or automatic.

The loop system is inherently more accurate, but the volume injected is fixed. However, sample loops are available in a range of volumes. The gas-tight syringe is not as accurate, but injection volumes between 10 L and 1 mL may be selected as appropriate for concentrations encountered in the field (the lower the concentration, the larger the injection volume). Both injection systems may require purging to reduce memory effects.

b. Separation

The sample is carried through the column by a carrier gas. Many systems have refillable gas 1/15/98