Future Trend

As mentioned earlier, purification was simplified by SPE procedure instead of conventional packed column chromatography. This preparation, however, is troublesome and still time-consuming because SPE procedure requires some steps, such as elution by organic solvent from cartridges and concentration not to dry up before instrumental analysis. For the routine screening purpose, a simplified, rapid, cost-effective and accurate process is essential.

MSPD maybe as a simultaneous extraction and cleanup technique. This method is based on dispersion of the sample on adsorbent such as Florisil or C18. Pigments and lipids, which may interfere with the further analytical determination, are retained on the surface of the adsorbent; consequently a further purification is not necessary. MSPD method requires less time and solvent than liquid-liquid or Soxhlet extraction, and is a good alternative to these conventional methods [240].

To reduce solvent consumption and cut down the sample preparation to a minimum, stir-bar sorptive extraction (SBSE) is also useful. In SBSE, an analyte is extracted into organic phase coated on stir bar, based on octanol-water partitioning coefficient. Therefore, optimization for extraction condition (i.e., salt saturation, solvent addition, temperature and pH, etc.) is required for each sample. SBSE is very popular as an extraction procedure for organic micropollutants in environmental water samples [237,240]. However, this technique has hardly been applied to the study of PAHs in food. SBSE may be useful for the analysis of drink.

The on-line LC-GC systems have many advantages of being automated and minimizing sampling losses and contaminations. Moreover, the automated systems are generally important to prevent manual intervention-related errors. The LC-GC systems are not simply a coupling of two well-established techniques [196]. Some optimizations of condition, adaptation and underlying new principles are still required. Although LC-GC systems are a little complicated and not so robust, these on-line systems seem to be ideal for routine analysis [194-197,210].

Nowadays, sample throughput is another important aspect when choosing an analytical method in routine analytical applications. For this purpose, the so-called fast GC is promising method. Recently, interest for very fast separations using GC has increased significantly. Fast GC is designed to minimize analysis time without influencing chromatographic resolution. For example, analysis of EPA 16 PAHs can be carried out in 3min in fast GC. This is a 10-fold improvement in analysis time as compared to the U.S. EPA procedure for PAHs.

This is owing to the many improvements in technology, such as high-speed injection systems, low-pressure (LP) outlet conditions (LP-GC), rapid oven heating/cooling, reduction of column length, diameter and stationary phase thickness (narrow-bore capillaries), fast detection system and improvement of software. Among them, the narrow-bore column, and LP-GC and resistive heating have been the main approaches for faster food analysis. Several

Time (seconds)

Figure 5 PAH analysis in boiled tea using miniaturized LLE. The trace shows the reconstructed ion chromatogram using the quantification masses of PAHs. Peak assignment: 1, methyl salicate; 2, dihydroactinidiolide; 3, anthracene; 4, caffeine; 5, hexanoic acid; 6, fluoranthene; 7, phytol; 8, pyrene; 9, benz[a]anthracene; 10, chrysene; 11, benzo[b]fluoranthene; 12, benzo[k]fluoranthene; 13, benzo[a]pyrene; 14, indeno[1,2,3-cd]pyrene; 15, dibenz[ah]anthracene and 16, benzo-[ghi]perylene. Reprinted from Ref. [151] with permission of Wiley.

Time (seconds)

Figure 5 PAH analysis in boiled tea using miniaturized LLE. The trace shows the reconstructed ion chromatogram using the quantification masses of PAHs. Peak assignment: 1, methyl salicate; 2, dihydroactinidiolide; 3, anthracene; 4, caffeine; 5, hexanoic acid; 6, fluoranthene; 7, phytol; 8, pyrene; 9, benz[a]anthracene; 10, chrysene; 11, benzo[b]fluoranthene; 12, benzo[k]fluoranthene; 13, benzo[a]pyrene; 14, indeno[1,2,3-cd]pyrene; 15, dibenz[ah]anthracene and 16, benzo-[ghi]perylene. Reprinted from Ref. [151] with permission of Wiley.

reviews have been reported describing the concepts and the application of fast GC [237,238,241].

The main limitation of fast GC is the speed of detector response. Fast GC is, therefore, limited mainly to GC-FID, GC-ECD (ECD, electron capture detection) and GC-TOF-MS [169].

The combination of high sensitivity of TOF-MS and narrow peaks of fast GC enables analyte detection at the trace level [191]. Moreover, GC-TOF-MS is successfully used for the fast (3-5 min) analysis of organophosphorus pesticides, triazine herbicides and PAHs in several types of samples [177]. In the case of boiled tea, 11 PAHs from among EPA 16 PAHs were detected at a level of less than 10 mg/L in just over 300 s (Figure 5). GC-TOF-MS may create new possibilities in the field of PAHs analysis in food.

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