Oil in water - comparative results for Shimadzu fast GC determination
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Oil in water - comparative results for Shimadzu fast GC determination
Keyword: Oils
Fast analysis and high sample throughput without loss of resolution is made possible with short, narrow-bore columns with a maximum internal diameter of just 0.1mm. Optimum linear carrier gas velocities (the minimum value in the van Deemter plot) increase with decreasing column diameter. High column head pressures are therefore required when carrying out fast GC using narrow-bore columns.The Shimadzu GC-17AV3 gas chromatograph features Advanced Flow Control(AFC) for electronic setting of chromatographic parameters, such as split ratio and linear carrier gas velocity, and there is an optional high-pressure Automatic Flow Controller - AFC - (AFC-17H) for setting column head pressures of up to 970kPa and gas flows up to 1,200ml/min. This ensures adequate pressure ranges to maintain the high linear gas velocities needed for fast GC.
A sufficiently high injection velocity is another requirement of fast GC, and one which Shimadzu has answered with its AOC-20i autosampler. The AOC-20i allows high velocities for needle insertion and sample delivery, both of which can be selected independently. The flexible needle guide ensures that the injection needle remains unbent.
The determination of oil in water is a routine task in many water analysis laboratories.The existing DIN 38409 H 18 method is intended for extraction using Freon 113 with subsequent IR/FTIR detection. A new chromatographic method - H 53- is now being submitted as a standard method which, in contrast to H 18, is not applicable to volatile hydrocarbons. Upon acceptance, it is intended that this method will be adopted as ISO 9377-4.
The method requires the use of a non-discriminating injector, such as the Shimadzu OCI-17, which features two injection modes - temperature programmed split/splitless injection (PTV), and on-column injection (OCI). The Shimadzu GC-17AAF/OCI GC chromatograph can be equipped with these injection systems as standard.
Fast GC also demands more of the data system, which must accurately track the fast signal changes with a sufficient sampling rate. Shimadzu CLASS-VP software,in combination with the GC-17AV3, will accurately detect peak widths down to 0.4sec, within a user-friendly data environment.
Shimadzu recently conducted tests to compare analytical results from a standard and narrow-bore column, using the GC-17AAF with AFC-17H, AOC20i/s autosampler and OCI-17 injector operated in PTV mode.
A standard diesel sample was extracted from an aqueous matrix and analysed using a 25m,0.25mm ID column, with a pressure programme between 87kPa and 113kPa to compensate for the decrease in linear carrier gas velocity with increasing oven temperature. An identical sample was then analysed using a narrow-bore column and pressure programming between 638 and 965 kPa.
A comparison of chromatograms from both methods shows a comparable peak resolution with a vastly reduced analysis time for the narrow-bore method (3.4 minutes compared to 10.7 minutes using the standard method - further information available on request).
The conclusion is that fast GC using a narrow-bore column yields reliable and consistent results for analysis of diesel in water, with much improved speed -an answer to the throughput needs of most laboratories - without any sacrifice in the quality of results.
For more information, contact: Ross Heaven, Strong Words, 32 Cranstoun Street, Northampton NNI 3BH, UK. Tel/Fax: +44 (0)1604 250221; e-mail: MAILTO:rossheayen@aol.com or Stephanie Parish,Shimadzu Europa (UK Branch), Mill Court, Featherstone Road, Wolverton Mill South, Milton Keynes MK12 5RE, UK. Tel: +44 (0)1908 552200; Fax: +44 (0)1908 552211. E-mail: Sales@Shimadzu.co.uk
