Cool on-column injection

More specific methods involve chromatographic separation of the retinoids and carotenoids followed by an appropriate detection method. This subject has been reviewed (57). Typically, hplc techniques are used and are coupled with detection by uv. For the retinoids, fluorescent detection is possible and picogram quantities of retinol in plasma have been measured (58—62). These techniques are particularly powerful for the separation of isomers. Owing to the thermal lability of these compounds, gc methods have also been used but to a lesser extent. Recently, the utiUty of cool-on-column injection methods for these materials has been demonstrated (63). 

Cool on-column injection is used for trace analysis. Ah. of the sample is introduced without vaporization by inserting the needle of the syringe at a place where the column has been previously stripped of hquid phase. The injection temperature must be at or below the boiling point of the solvent carrying the sample. Injection must be rapid and no more than a very few, usuahy no more than two, microliters may be injected. Cool on-column injection is the most accurate and reproducible injection technique for capihary chromatography, but it is the most difficult to automate. 

David et al. [184] have shown that cool on-column injection and the use of deactivated thermally stable columns in CGC-FID and CGC-F1D-MS for quantitative determination of additives (antistatics, antifogging agents, UV and light stabilisers, antioxidants, etc.) in mixtures prevents thermal degradation of high-MW compounds. Perkins et al. [101] have reported development of an analysis method for 100 ppm polymer additives in a 500 p,L SEC fraction in DCM by means of at-column GC (total elution time 27 min repeatability 3-7 %). Requirements for the method were (i) on-line (ii) use of whole fraction (LVI) and (iii) determination of high-MW compounds (1200 Da) at low concentrations. Difficult matrix introduction (DMI) and selective extraction can be used for GC analysis of silicone oil contamination in paints and other complex analytical problems. 

Applications On a comparative basis, HTGC is a relatively new tool and extremely valuable for the analyses of extracted polymer additives, as shown by industrial problem solving. For satisfactory analysis of in-polymer additives by HTGC two specific conditions are to be met. The instrument should be equipped with a cool on-column injection port to better preserve some of the additives and/or their by-products that may be thermally labile. The instrument must also have electronic pressure control so that some of the very high-boiling components, such as Irganox 1010, are... 

Gas chromatograph systems are composed of an inlet, carrier gas, a column within an oven, and a detector (O Figure 1-1). The inlet should assure that a representative sample reproducibly, and frequently automatically, reaches the column. This chapter will cover injection techniques appropriate for capillary columns. These include direct, split/splitless, programmed temperature vaporization, and cool on-column injection (Dybowski and Kaiser, 2002). 

The most reproducible, but most difficult injection technique to automate is cool on-column injection. The sample is injected directly onto a section of column that has been stripped of the stationary phase using a small-bore needle (Dybowski and Kaiser, 2002). 

Conversion and selectivities were determined by GC analysis (cool on-column injection, HP-1 column). Products were identified by GC-MS and NMR spectroscopy. The initial rate (r ) is defined as the epoxide formation in the first 20 min. Hydroperoxide conversion was determined by iodometric titration. Selectivities are calculated as follows ... 

The reactor and separate vaporizers for benzene and nitric acid were placed in a fluidized sand bath at a constant temperature of 443 K. Nitrogen (10 ml/min) was used as the carrier gas. The reactor effluent was recovered in acetone kept at 278 K and periodically analyzed over a time interval of 1 hr. The first sample was taken after a lining out period of 1 hr. The runs were interrupted after about 20 hours on stream. HNO3 was analyzed by acldimetric titration, whereas benzene and the products of nitration were analyzed by off line gas chromatography (cool on column injection), using o-nitrotoluene added to the collected probes as the Internal standard. 

The requirement for volatility often precluded the use of GC for analysis of thermally labile samples. Injection of the sample directly into the column using cool-on-column injection (COC) with volatilisation occurring on the column has meant such samples can be readily analysed [73a,b]. 

Figure 6. Fast separation of palm oil Column 5 m CxO.25 mm i.d, 0.1 pm d methylsilicone temperature 290-350°C at 30°C/min cool on-column injection carrier gas hydrogen at 15 psi ( 5 1 bar) FlDPeaks 32 -36 diglycerides, 46-56 triglycerides...

Column 10 m LxO.53 mm /.column injection carrier gas hydrogen 4 mL/min FID-Peaks (1) acetic acid, (2) propionic acid, (3) isobutyric acid. (4) butyric acid. (5) isovaleric acid, (6) valeric acid. (7) iso-caproic acid. (8)caproic acid. (9)heplanoic acid. (lO)ocia-noic acid. (11) nonanoic acid. (12)decanoic acid... 

Figure 31. Illustrulion of the application of cool on-column injection to the analysis of thermolabile compounds Column 12.5 m LxO.25 mm i.il. 0,25 pm <4CPSi temperature 60- I90 C at 17 °C/min. to 220 C at 6°C/min and to 235"C at 1.5 C/min cool on-column injection carrier gas hydrogen FIDPeaks (I) rmn.v-acitrctin methyl c.stcr, (21 c/.s-acitretin methyl ester. (.3) n ,s-acitretin propyl ester...

On-column Injection. Refers to the method wherein the syringe needle is inserted directly into the column and the sample is deposited within the colunm walls rather than a flash evaporator. On-column injection differs from direct injection in that the sample is usually introduced directly onto the column without passing through a heated zone. The column temperature is usually reduced, although not as low as with splitless injections ( cool on-column injections). 

With the addition of a retention gap and a timed vapor exit valve between the retention gap and the analytical column, cool on-column injection may be used... 

Sample Introduction System—Any system capable of introducing a representative sample onto the front portion of a WCOT column may be employed. Cool on-column injection is preferred, however other injection techniques can be used provided the system meets the speciflcation for linearity of response in 9.6. For cool on-column injection, syringes with 0.15 to 0.25 mm outside diameter needles have been used successfully for columns 0.25 mm inside diameter or larger and standard 0.47 mm outside diameter syringe needles have been used for columns 0.53 mm inside diameter or greater. 

Following the same procedure as for the blank run (see 11.2), inject O.S to 1.0 pL of the wax sample solution from 11.1 into the cool on-column injection port. Immediately start the temperature program, the recorder, and the integrator, and store the acquired detector signal. 

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