HPLC/MS methods

In recent years, much effort has been devoted to developing HPLC-MS methods for natural compounds. The main difficulty lies in the different operating conditions of HPLC and MS. While HPLC operates using high flow rates, high pressures, and liquid phases near room temperature, MS uses low flow rates, high vacuum, and a gas phase ion analyzer. Various interfaces allow for online coupling of these two... 

Full acceptance of HPLC/MS methods by the US EPA OPP as enforcement methods occurred between 1998 and 2001. For example, in 1998, the EPA OPP accepted HPLC/MS (without MS/MS) methods as primary enforcement methods, and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) only was suitable for confirmatory methods. However, in 2001, HPLC/MS/MS methods also became acceptable for primary enforcement. Table 4 summarizes the types of methods that were validated by the EPA OPP method validation program, for both food tolerance enforcement methods and environmental chemistry methods. 

Jacobsen et al. described an HPLC/MS method for the determination and/ or identification of iodixanol and its metabolites in biological samples from animals [108]. 

In particular, the priority pollutant phenols (PPP), identified by EPA since the 1970s are widespread water pollutants that must receive the greatest attention due to their recognized toxicity. For the separation of eleven PPP, an ion-interaction reagent (HR) RP HPLC/UV method has been developed that allows limits of detection lower than 30 J,g in river waters, after LLE in dichlo-romethane and a 500-fold pre-concentration [82]. Through on-line SPE followed by both UV and electrochemical detection [83], 16 priority phenols have been determined in water samples with the LOD value for chlorophenols lower than 1 ng L [84]. LODs at ng L levels were obtained for all the PPPs in samples of river water, employing a relatively small volume of sample through an on-line SPE HPLC/MS method with an APCI source. 

The availability of commercial bench-top mass spectrometry detectors for HPLC is facilitating the development of HPLC-MS methods for many analytes. This is more common in pharmaceutical than food applications. As is generally the case, mass spectrometry is first being applied to standard solutions and relatively simple samples before being applied to more complex food matrices. A standard mixture of ten vitamers, AA, DHAA, PN, PL, PM, thiamine, nicotinic acid, nicotinamide, pantothenic acid and biotin, were recently determined by HPLC-particle beam... 

De Francia S et al (2009) New HPLC-MS method for the simultaneous quantification of the antileukemia drugs imatinib, dasatinib, and nilotinib in human plasma. J Chromatogr B Analyt Technol Biomed Life Sci 877 1721-1726... 

Although the HPLC-MS method was demonstrated to be accurate and precise, as well as specific for I in plasma, the method was not amenable to low sample cost or rapidity of processing. For example, approximately two hours were required to process one sample at a cost of 80.00 per sample. These facts prompted a search for a more expedient and less expensive assay method. 

An HPLC-MS method was employed to test 102 foods and found that 43 foods contained PAs (Gu et ah, 2003a Prior and Gu, 2005). A similar study detected proanthocyanidins in 49 food items out of 99 foods of plant origin (Hellstrom et ah, 2009). These foods included fmits, nuts, cereals/beans, beverages, spices, and vegetables (Gu et ah, 2003a). Fruits and tree nuts are the major dietary sources of PAs. The majority of the fruits and tree nuts contained PAs, whereas most of the vegetables and roots lacked them completely (Gu et ah, 2003a Hellstrom et ah, 2009). 

These efforts are centered around the use of techniques including enzymatic hydrolysis [5,6,7], physical or chemical degradation [8,9], and monodisperse aerosol generation interface (particle beam) for HPLC/MS [10,11] to solve specific problems. This paper discusses the implementation of several HPLC/MS methods which offer a combination of sensitivity and specificity for compounds such as peptides, pharmaceuticals, and pesticides in complex matrices. 

The choice of a HPLC/MS analysis method depends greatly on the characteristics of the sample (i.e. proton affinity, polarity, thermal stability and volatility) as well as the structural information and sensitivity required. The use of various techniques including enzymatic hydrolysis and physical-chemical reactions can assist in achieving the analysis goals for certain compounds. Alternatively, the use of complimentary HPLC/MS techniques such as thermospray and particle beam can be useful for the analysis of a variety of compounds, as demonstrated in this paper. Employing less commonly available instrumentation, such as tandem MS, with thermospray or particle beam can prove valuable in determining structure when other methods are unsuccessful. The further development of existing HPLC/MS techniques and the implantation of new HPLC/MS methods will continue to increase the variety of compound classes that can be routinely monitored with adequate sensitivity and specificity. 

Most often a compound with similar structure is selected. The internal standard method has become a very popular technique not only in chromatography, but also in quantitative HPLC-MS methods [47],... 

A number of specific and sensitive HPLC/MS methods have been developed. An immunoassay for Tac... 

Although it may appear that to start all assays from a standard 10 mM DM SO stock solution will simplify the profiling processes, there are a number of issues that should be taken into account. The presence of this organic solvent may mask or modify important physical properties that will need to be factored into the information before it can be used for any real benefit. It is very important to ensure that the compound is stable in the solvent and therefore QC checks should be carried out before the assay screens commence to have a time zero point from which to reference. If this is carried out using an HPLC-MS method, then it will have the added benefit of confirming compound purity and validity at the outset. It should also be considered that it is possible that the compounds are not present as 10 mM DMSO stock solutions [1]. This will need to be known and calibration curves adjusted to ensure that any quantitative calculations are correct. 

Various HPLC-MS methods were examined to establish the optimal ion source and detector operating conditions for the detection or determination of low molecular mass phenols and flavan-3-ols. Atmospheric pressnre electrospray ionization MS (ESI-MS) in... 

The main criterion for the detector is that it gives a response specifically for tin, rather than the compound. This is because of the detection limits required for environmental analysis, which are not attainable with non-specific detectors. The most popular detection methods for organotin analysis are FPD using a tin selective filter, MS, MIP-AES, and ICP-MS. Recently, HPLC-MS methods based on atmospheric ionization including electrospray, ion spray, or chemical ionization have been used to detect the organotin species. These methods have the advantage that molecular information concerning the analyte is available, rather than just atomic information. 

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