Sample preparation time

Instrument type Specificity/sensitivity Sample preparation time Data quality Cost effectiveness... 

Table 2.2 shows a comparison of various extraction methods for solid samples [17]. It appears that one can take anywhere from 0.1 to 24h for the extraction process. Microwave-assisted sample preparation requires minimal time however, if cost is a consideration, Soxhlet extraction is least costly but requires the longest sample preparation time. 

Section II covers the latest trends in reducing sample preparation time, including direct sample infusion/injection and on-line solid phase extraction (SPE). In Section III, we focus on newer trends in stationary phases and how these phases hope to offer different selectivities compared to current CIS-based phases. Section IV briefly provides a few observations on how new detectors are increasing the versatility of HPLC. Finally, in Section V we examine monolithic columns, small particles packed in short columns, high-temperature LC, ultra high-pressure LC, and parallel injection techniques. 

The effect of subtle particle changes as a function of temperature, sample preparation, time, solvent, and other changes can be measured using DLS. Such changes can then be related to performance variations eventually interrelating structure, shape, and biological or physical property. 

Although not a real sample preparation procedure, direct injection of the sample into the LC can save hours of sample-preparation time. Packing materials for this technique have been available in many versions for nearly a decade, but the technique is still relatively unknown to many analysts, even those involved in food analysis. 

For GLC and HPLC analysis, the extraction of total lipids from food requires overnight separation of the organic layer. If the sample volume is small, however, centrifugation of the extract may shorten the sample preparation time. Cholesterol derivatization requires <2 hr depending on the number of samples. The peak of TMS ether and cholesterol benzoate derivatives will be eluted within 10 min after the injection of the sample. 

The Alternate Protocol has a longer sample preparation time (15 to 20 min) and a considerably longer analysis time of 75 min between injections. 

Here, one needs to consider the logistics i.e., sample loading, sample preparation time (some samples may require complicated treatment like preenrichment steps for Salmonella detection), assay procedures i.e., time consuming protocols entailing numerous pipetting and washing steps could be automated to free up personnel time. Other considerations include assay design for multiple assay to be performed at the same time. 

Direct analysis of the enantiomers in biological fluids is very important because it reduces both analysis time and sample preparation time. Indeed, when there is risk of the quick racemization of the enantiomer, direct analysis is essential. It has been observed that CD-based CSPs employ mobile phases that are generally compatible with biological samples, hence can be used for the direct analysis of the enantiomers in biological fluids [67,80]. Stalcup et al. [58] employed coupled column chromatography to isolate scopolamine from a plant extract and found that the extent of racemization depends on the isolation... 

LC-MS/MS techniques moved the bottleneck for analyzing NCEs from sample analysis to sample preparation. Several methodologies have been developed to reduce sample preparation time. Online extraction methods are becoming more popular and have many advantages over offline techniques. For example, online sample preparation is easier to automate and minimizes recovery issues. 

Online coupling of supercritical fluid extraction and high-performance liquid chromatography considerably decreases sample preparation time and analysis time [175]. Dunkers [128] showed that by using dilute dichloromethane as a static modifier, 20-30 minute supercritical fluid extractions gave results comparable to those obtained by conventional four-hour sampling methods in soil extractions. 

Hydride generation inductively coupled plasma atomic emission spectrometry has been used to determine arsenic in soils. This technique was found to greatly reduce sample preparation time [38]. 

SPME is a fast, universal, sensitive, solventless, and economical method of preparing samples for GC or HPLC analysis, enabling detection limits at a level of 5-50 ppt for volatile, semivolatile, and nonvolatile compounds to be achieved. The approximate sample preparation time is usually 2-15 min.49-50... 

Reducing labor and energy demands, for example, reducing sample preparation time when direct chromatographic analysis is not possible... 

Yandenburg et al. [92] compared extraction of additive Irganox 1010 from freeze-ground polypropylene polymer by pressurized fluid extraction (PFE) and MAE with reflux, ultrasonic, shake-flask, and Soxhlet extraction. PFE and MAE were faster than any conventional method with comparable extraction efficiency. The times to reach 90% recovery by PFE using propan-2-ol at 150°C and acetone at 140°C were 5 and 6 minutes, respectively. Reflux with chloroform was found to be the fastest method performed under atmospheric pressure with 90% recovery in 24 minutes. Reflux with cyclohexane propan-2-ol (1 1) required 38 minutes. Ultrasonic, shake-flask, and Soxhlet extraction required about 80 minutes (90%) extraction). The total sample preparation time for PFE was 15 minutes, MAE 28 minutes, and reflux with chloroform was 45 minutes. 

Additional advantages are realized with headspace sampling. Sample preparation time is minimized because the sample in many cases is simply placed in a vial which is then sealed and capped. The compound(s) of interest may be released from the matrix by heat or chemical reaction, and aliquots of the headspace gas are collected for assay. Columns last longer because a gaseous sample is much cleaner than a liquid sample. The solvent peak is much smaller for a vapor sample than for a solution sample. 

Greater efficiency (sample preparation time, run set-up time, instrument time). 

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