Environmental analysis, reproducibility

The application of HPLC in routine environments, like pharmaceutical, food, or environmental analysis and particularly quality assurance, makes not only great demands on the robnstness of HPLC hardware, comprising pumps, column thermostats, and detection units, bnt in addition to the column reproducibility. Column reproducibility can be investigated at different levels of complexity Run-to-run reproducibility compares consecutive chromatographic runs, whereas long-term stability describes the column variance over several hundreds of injections. Column-to-column (batch-to-batch) reproducibility finally explores the match of independently fabricated chromatographic columns. Column characteristics that are routinely consulted for the determination of the robustness are retention, selectivity, column efficiency, and peak symmetry. 

Figure 7.2 The basic Soxhlet extraction system. From Dean, J. R., Extraction Methods for Environmental Analysis, Copyright 1998. John Wiley Sons Limited. Reproduced with permission.

The significant development of chromatography in quantitative analysis is essentially due to its reliability and its use in standardized analyses. Trace and ultratrace analyses by chromatography are used, particularly the EPA methods for environmental analysis, although their costs are rather high. This type of analysis relies mainly on reproducibility of the separation and on the linear relationship between the injected mass of a compound onto the column and the area of the corresponding peak on the resultant chromatogram. This is an excellent comparative method used in many protocols, which, allied with software used for data treatment allow automation of all the calculations associated with these analyses. 

Reproducibility of measurement - the best results for laser mass spectrometry, reported in literature, point standard deviations better than 8%. In respect to environmental analysis, the decisive factor is the homogeneity of the sample and the quality of the reference material. 

The first of the separation techniques to be used in process measurement was gas chromatography (GC) in 1954. The GC has always been a robust instrument and this aided its transfer to the process environment. The differences between laboratory GC and process GC instruments are important. With process GC, the sample is transferred directly from the process stream to the instrument. Instead of an inlet septum, process GC has a valve, which is critical for repetitively and reproducibly transferring a precise volume of sample into the volatiliser and thence into the carrier gas. This valve is also used to intermittently introduce a reference sample for calibration purposes. Instead of one column and a temperature ramp, the set up involves many columns under isothermal conditions. The more usual column types are open tubular, as these are efficient and analysis is more rapid than with packed columns. A pre-column is often used to trap unwanted contaminants, e.g. water, and it is backflushed while the rest of the sample is sent on to the analysis column. The universal detector - thermal conductivity detector (TCD)-is most often used in process GC but also popular are the FID, PID, ECD, FPD and of course MS. Process GC is used extensively in the petroleum industry, in environmental analysis of air and water samples" and in the chemical industry with the incorporation of sample extraction or preparation on-line. It is also applied for on-line monitoring of volatile products during fermentation processes" ... 

As many sample solutions, particularly samples from environmental analysis, may contain unknown complexing agents it is probably a good idea to add a chosen strong complexing agent to ensure a known reproducible state of complexation. 

Stage that requires high efficiency as well as speed, due to the complexity of the sample matrix, and hence it is particularly challenging to achieve the goals. Therefore, the development of a rapid, sensitive, and reproducible method has been required for separation and determination of capsaicinoid compounds. The addition of ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) method fulfilled these aforementioned demands and showed some complementary advantages to the conventional HPLC-MS, u-HPLC methods in terms of shorter analysis times, low sample volume, and much improved sensitivity [71]. Therefore, nowadays this UPLC-MS technique is routinely performed in pharmaceutical industries and related contract research institutes, laboratories concerned with biochemistry, biotechnology, environmental analysis, natural product research, and several other research fields. The UPLC-MS method has successfully been applied for the determination of n-DHC, C, DHC, h-C, and h-DHC present in the varieties of hot peppers [71]. 

Quantitative analysis. should deliver reproducible and reliable information about the composition of the sample investigated. Since end of the 1980s, quantitative analysis has become extremely important for product quality control (e.g., food industry, pharmaceutical industry) and environmental analysis. It is of great economic importance, and an erroneous quantitative analysis can result in fatal consequences. Therefore, this chapter introduces different quantification methods for HPLC and describes some often-occurring sources of error. 

The application of FIA and biosensors in environmental analysis is attractive because enzyme biosensors operate on the principle of inhibition. The process is economical because only small quantities of substrate are required and because the incubation, reaction and reactivation times can be controlled. The process can therefore yield high reproducibility. This method has been used to measure insecticide levels in sea water [269], Finally, FIA is particularly suitable for the construction of automated systems. 

Table 5.16 LC-MS-MS signal responses" obtained from wheat forage matrix samples using various mobile-phase additives (injection volumes of 50 p,l). From Choi, B. K., Hercules, D. M. and Gusev, A. I., LC-MS/MS signal suppression effects in the analysis of pesticides in complex environmental matrices , Fresenius J. Anal. Chem., 369, 370-377, Table 2, 2001. Springer-Verlag GmbH Co. KG. Reproduced with permission...

One of the known disadvantages of the use of GC is the need for previous derivatization of some of the most polar pesticides before analysis can be carried out [40]. These derivatization steps might produce low-efficiency results in complex wastewater matrices, which make the analysis rather difficult and cumbersome. However, the reproducibility in retention times when using GC techniques is so precise, that specific identifications of pesticides can be made even in complex environmental samples. 

The ability to provide accurate and reliable data is central to the role of analytical chemists, not only in areas like the development and manufacture of drugs, food control or drinking water analysis, but also in the field of environmental chemistry, where there is an increasing need for certified laboratories (ISO 9000 standards). The quality of analytical data is a key factor in successfully identifying and monitoring contamination of environmental compartments. In this context, a large collection of methods applied to the routine analysis of prime environmental pollutants has been developed and validated, and adapted in nationally or internationally harmonised protocols (DIN, EPA). Information on method performance generally provides data on specificity, accuracy, precision (repeatability and reproducibility), limit of detection, sensitivity, applicability and practicability, as appropriate. 

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