Modern Sample Preparation Techniques: A Brief Introduction

Due to fast growth in microprocessors, analytical instrumentations in spectroscopy, chromatography, microscopy, sensors and microdevices have been subjected to significant developments. Despite these advances, a sample preparation step is indispensable before instrumental analysis. Main reasons are low sensitivity of the instruments, matrix interferences and incompatibility of the sample with the analytical device. Most of the time spent and most of the errors occurring during a chemical analysis is on sample preparation step. As a result, any improvements in this essential process will have a significant effect on shortening the analysis time and its precision and accuracy and lowering the cost. This introductory chapter intends to draw the readers’ attention to the importance of sample preparation, the procedures of sampling and the source of errors that occur in the course of sampling. The chapter then continues with a heading on sample preparation techniques, including exhaustive and non-exhaustive methods of extraction. Microwave, sonication and membrane-based extraction techniques are more emphasized as exhaustive methods and under a new title, miniaturized methods are discussed. Automation, on-line compatibility and simplification is an important aspect of any sample preparation and extraction which is discussed at the end of this chapter.

Aerosol Analysis Using Handheld Raman Spectrometer: On-site Quantification of Trace Crystalline Silica in Workplace Atmospheres

A method for aerosol chemical analysis using handheld Raman spectrometer has been developed and its application to measurement of crystalline silica concentration in workplace atmosphere is described. The approach involves collecting aerosol as a spot sample using a wearable optical aerosol monitor, followed by direct-on-filter quantitative analysis of the spot sample for crystalline silica using handheld Raman spectrometer. The filter cassette of a commercially available optical aerosol monitor (designed to collect aerosol for post-shift analysis) was modified to collect 1.5-mm-diameter spot sample, which provided adequate detection limits for short-term measurements over a few tens of minutes or hours. The method was calibrated using aerosolized α-quartz standard reference material in the laboratory. Two Raman spectrometers were evaluated, one a handheld unit (weighing less than 410 g) and the other a larger probe-based field-portable unit (weighing about 5 kg). The lowest limit of quantification for α-quartz of 16.6 μg m−3 was obtained using the handheld Raman unit at a sample collection time of 1 h at 0.4 l min−1. Short-term measurement capability and sensitivity of the Raman method were demonstrated using a transient simulated workplace aerosol. Workplace air and personal breathing zone concentrations of crystalline silica of workers at a hydraulic fracturing worksite were measured using the Raman method. The measurements showed good agreement with the co-located samples analyzed using the standard X-ray powder diffraction (XRD) method, agreeing within 0.15–23.2% of each other. This magnitude of difference was comparable to the inter- and intra-laboratory analytical precision of established XRD and infrared methods. The pilot study shows that for silica-containing materials studied in this work it is possible to obtain quantitative measurements with good analytical figures of merit using handheld or portable Raman spectrometers. Further studies will be needed to assess matrix interferences and measurement uncertainty for several other types of particle matrices to assess the broader applicability of the method.

Determination of Cyanide in Blood for Forensic Toxicology Purposes—A Novel Nci Gc-Ms/Ms Technique

One of the recently evolving methods for cyanide determination in body fluids is GC-MS, following extractive alkylation with pentafluorobenzyl bromide or pentafluorobenzyl p-toluenesulfonate. The aim of this study was to improve previous GC methods by utilizing a triple quadrupole mass spectrometer, which could enhance selectivity and sensitivity allowing for the reliable confirmation of cyanide exposure in toxicological studies. Another purpose of this study was to facilitate a case investigation including a determination of cyanide in blood and to use the obtained data to confirm the ingestion of a substance, found together with a human corpse at the forensic scene. The blood samples were prepared following extractive alkylation with a phase transfer catalyst tetrabutylammonium sulfate and the PFB-Br derivatization agent. Optimal parameters for detection, including ionization type and multiple reaction monitoring (MRM) transitions had been investigated and then selected. The validation parameters for the above method were as follows—linear regression R2 = 0.9997 in the range of 0.1 µg/mL to 10 µg/mL; LOD = 24 ng/mL; LOQ = 80 ng/mL and an average recovery of extraction of 98%. Our study demonstrates the first attempt of cyanide determination in blood with gas chromatography-tandem mass spectrometry. The established method could be applied in forensic studies due to MS/MS confirmation of organic cyanide derivative and low matrix interferences owning to utilizing negative chemical ionization.

The Pitfalls of Using Research Grade Immunoassays for Thyroid Health Measurements

Introduction: Immunoassay technology is subject to matrix interferences that can produce inaccurate results and incorrect conclusions when using samples not previously validated. While many commercially available research grade (RG) immunoassay kits are available, caution should be applied when using RG kits for thyroid health assessments, particularly on samples from pregnant individuals whose blood chemistry is unique to non-pregnant individuals. Question: Do RG immunoassay kits reliably provide precise and accurate measurements of thyroid health biomarkers in serum Standard Reference Materials (SRMs) from pregnant and non-pregnant donors? Methods: T4, T3, rT3, Tg and TSH measurements were conducted on SRMs 971, Hormones in Frozen Human Serum, and SRM 1949, Frozen Prenatal Serum, using RG immunoassay kits. When available, performance was assessed against validated FDA approved immunoassays or mass spectrometric (MS) methods. Results: RG kits were variable, inaccurate, or imprecise for four of the six biomarkers assessed. RG kit total thyroid hormone measurements overall performed comparably to MS methods, except rT3 measurements, which were twofold greater than mass spectrometric measurements (971M RG mean = 0.51 ng/mL, MS mean = 0.20 ng/mL, p < 0.0001; 971F RG = 0.48 ng/mL, MS = 0.18 ng/mL, p < 0.0001) and had CVs over 30 %. RG kit Tg measurements varied sometimes by as much as tenfold (971M means of 6.50 ng/mL up to 63.3 ng/mL, p < 0.0001; 971F means of 0.350 ng/mL up to 14.5 mg/mL, p < 0.0001). TSH values differed by RG kit manufacturer (971M means of 1.27 µIU/mL up to 1.82 µIU/mL, p < 0.0001; 971F means of 1.36 µIU/mL up to 2.27 µIU/mL, p < 0.0001) and by dilution scheme using the same manufacturer with one case indicating a diagnosis of hypothyroid versus normal TSH levels (1949 non-pregnant undiluted mean = 2325 pg/mL, half dilution mean = 1631 pg/mL, p < 0.0001). Conclusions: RG immunoassays are often used for research projects because they do not require expensive equipment and are simple to conducted. However, we demonstrate here that not all kits are accurate for all patient samples. By utilizing a matrix matched SRM with well-defined quantities of thyroid health biomarkers, one can assess method accuracy, making measurements from different methods comparable. Thereby, data can be harmonized to contribute reliable data on thyroid biomarkers to advance the field of thyroid health.

Selective Solid-Phase Extraction Using Molecularly Imprinted Polymers for the Analysis of Target Pesticides in Cannabis Bud

ABSTRACT A molecularly imprinted solid-phase extraction (MISPE) procedure was developed for the GC-MS analysis of four high priority pesticides (atrazine, terbuthylazine, acetochlor and alachlor) in a cannabis bud sample matrix. The study demonstrated that the synthesised polymer had a high affinity and good selectivity for either chloroacetamide or triazine classes of pesticide used as a template molecule during the molecularly imprinted polymerisation reaction. The MISPE procedure was optimised in terms of loading, washing and elution fractions utilising a range of aqueous methanol solutions for optimal recovery and minimal matrix interferences. The optimal wash fraction was 20% (v/v) methanol in an aqueous solution, whilst 70% (v/v) was used for the elution fraction. The selectivity, accuracy and recovery of the MISPEs were verified using a synthesised non-imprinted polymer and a commercial C18 cartridge as reference sorbents in comparative experiments. Approximately 3 g of the cannabis bud sample was spiked at a 0.05 mg/kg maximum residue limit (MRL) concentration. The recovery of the four selected pesticides extracted from the spiked samples ranged between 76.4-85.0% when utilising the optimised MISPE methods, compared to 91.6-96.9% for the C18 SPE. However, the use of the MISPE resulted in enhanced selectivity, as evidenced by GC-MS analysis, due to the extraction of less matrix interferences. Therefore, it can be concluded that the MISPE is a viable pre-treatment method for selective pesticide analysis in cannabis flowers using GC-MS when selectivity is valued for the extraction of target pesticides from a complex sample matrix. Keywords: molecularly imprinted polymer; solid-phase extraction; Cannabis; pesticides; atrazine; terbuthylazine; acetochlor; alachlor

Presence of anthraquinone in coffee and tea samples. An improved methodology based on mass spectrometry and a pilot monitoring programme

The developed method prevents the occurrence of matrix interferences in the analysis of anthraquinone in coffee and tea.

Differences in the Phenolic Profile by UPLC Coupled to High Resolution Mass Spectrometry and Antioxidant Capacity of Two Diospyros kaki Varieties

Background: phenolic compounds are bioactive chemical species derived from fruits and vegetables, with a plethora of healthy properties. In recent years, there has been a growing interest in persimmon (Diospyros kaki L.f.) due to the presence of many different classes of phenolic compounds. However, the analysis of individual phenolic compounds is difficult due to matrix interferences. Methods: the aim of this research was the evaluation of individual phenolic compounds and antioxidant capacity of the pulp of two varieties of persimmon (Rojo Brillante and Triumph) by an improved extraction procedure together with a UPLC-Q-TOF-MS platform. Results: the phenolic compounds composition of persimmon was characterized by the presence of hydroxybenzoic and hydroxycinnamic acids, hydroxybenzaldehydes, dihydrochalcones, tyrosols, flavanols, flavanones, and flavonols. A total of 31 compounds were identified and 17 compounds were quantified. Gallic acid was the predominant phenolic compounds found in the Rojo Brillante variety (0.953 mg/100 g) whereas the concentration of p-hydroxybenzoic acid was higher in the Triumph option (0.119 mg/100 g). Conclusions: the results showed that the Rojo Brillante variety had higher quantities of phenolic compounds than the Triumph example. These data could be used as reference in future phenolic compound databases when individual health effects of phenolic compounds become available.

Development and Validation of a Method for the Detection and Quantification of Antidepressants and Antipsychotics in Bone Samples by GC–MS

Bone marrow is the tissue contained inside the bones and can be considered one of the potential alternative tissues in forensic toxicology. This matrix could be particularly useful in those cases where the routine sample is not available due to an advanced state of decomposition or skeletonization of the corpse. The aim of this study was to develop, validate and apply an analytical method of extraction and analysis of different antidepressants and antipsychotics, commonly used in therapy, from spiked pig ribs. Pig ribs, each of 5 g and 5 cm long, were spiked at 3 concentration levels (100, 200 and 500 ng/g). For each concentration, 10 pig ribs were prepared. The method involves the leaching by ethanol at different pHs of nine drugs from the inside of ribs, in particular from the bone marrow, without the fragmentation of bone tissue. Following a liquid–liquid purification and extraction, analysis was performed by gas chromatography coupled with mass spectrometry in selected ion monitoring mode. For method validation was assessed linearity, sensitivity, precision and accuracy, matrix interferences and, finally, carryover. Analytical method performance was acceptable respect to acceptance criteria for validation. No matrix interferences were detected; for this reason, it is possible to affirm that this method has a good selectivity. Moreover, the method was not affected by carryover. Considering that the study conducted on pig ribs has given encouraging results, it can be assumed that this method can be used in forensic toxicological protocols (human autopsy cases) as alternative to classic procedures.