Analytical Instruments: Spectrophotometers & Chromatography
This sub-cluster covers instruments used for chemical and biological analysis rather than sample preparation: spectrophotometers (measuring light absorbance to quantify concentration, a workhorse instrument across biology and chemistry) and the consumables that support HPLC (high-performance liquid chromatography) work, particularly HPLC vials and crimp vials, where seal integrity and chemical compatibility directly affect data quality. Pages here are selection- and specification-focused, aimed at researchers choosing instruments and consumables for a specific analytical method.
Guides
Internal Standards in Quantitative Mass Spectrometry
Selection criteria for stable isotope-labeled vs structural analogue internal standards in LC-MS/MS quantitation, where in the extraction workflow to add them, and how to diagnose an internal standard that is itself suppressed by matrix effects.
ICP-MS Polyatomic Interference Correction: Collision Cell, Reaction Cell, Math Correction, or Resolution
How to identify a polyatomic interference in ICP-MS and choose between collision cell, reaction cell, mathematical correction, and mass resolution — with where each approach fails.
Annexin V/PI Apoptosis Assay by Flow Cytometry: Controls, Timing, and Setup
How to set up an Annexin V/PI apoptosis panel on a flow cytometer: the calcium-dependent binding mechanism, the buffer error that silently produces false negatives, the controls that separate real apoptosis from handling damage, and the timing window that determines whether cells read as early apoptotic or secondary necrotic.
Lipidomics by Mass Spectrometry: Extraction Method Selection and Acquisition Setup
How to choose a lipid extraction chemistry (Folch, Bligh-Dyer, MTBE), set up shotgun or LC-MS acquisition, and report identifications at the LIPID MAPS annotation-confidence level your MS/MS evidence actually supports.
HPLC Gradient Elution: Designing and Transferring Gradients
How to design an HPLC gradient from a scouting run, scale it correctly when the column or flow rate changes, and why a properly scaled gradient can still shift on a new instrument because of dwell volume.
Photobleaching and Phototoxicity in Live-Cell Imaging: Reducing Photodamage Without Losing Data
How to reduce photobleaching and phototoxicity in live-cell fluorescence imaging by deliberately trading illumination intensity, exposure time, imaging interval and detector sensitivity, plus instrument and reagent choices that shift the trade-off itself.
Optical Microscopy Resolution: The Diffraction Limit and What Costs You Detail
What actually sets and costs you resolution in optical microscopy: the diffraction limit (Abbe/Rayleigh), numerical aperture, wavelength, Nyquist sampling, and refractive-index mismatch.
LC-MS Method Development: Mobile Phase, Source, and MRM Setup
The four LC-method-development constraints MS adds that UV detection does not: volatile-buffer-only mobile phases, flow-rate/source compatibility, diverting the salt front away from the source, and building peak widths that fit an MRM cycle-time budget.
Amino Acid Analysis by HPLC: Derivatization and Method Choice
How to choose between OPA, AQC and ninhydrin for amino acid HPLC derivatization — detection limits, proline coverage, derivative stability — and which residues acid hydrolysis destroys before derivatization even starts.
Selecting and Validating qPCR Reference Genes: geNorm, NormFinder and the Stability Test
A step-by-step workflow for selecting and validating qPCR reference genes: building a candidate panel, running geNorm’s pairwise-variation and minimum-gene test, NormFinder’s model-based variance approach, and calculating the geometric-mean normalization factor MIQE expects you to justify.
Ghost Peaks in HPLC: Sources and Elimination
Ghost peaks in HPLC come from four distinct causes, each with a different fix. This guide separates injector carryover, mobile-phase contamination, late-eluter breakthrough, and gradient-artefact ghosts using two diagnostic runs: a blank injection and a blank gradient.
Analyzing qPCR Data: The Delta-Delta Ct Method, Step by Step
Worked delta-delta Ct arithmetic for qPCR data, the efficiency-corrected Pfaffl variant, and how to tell when the 2^-ΔΔCt shortcut stops being valid.
Metabolomics Mass Spectrometry: Platform Choice and QC Sample Design
A decision guide to metabolomics mass spectrometry: targeted vs untargeted acquisition, LC-MS vs GC-MS platform choice by metabolite class, and the pooled-QC injection design and RSD-based filtering that make batch correction possible.
Multicolor Flow Cytometry: Daily Instrument Setup and QC Beads
Daily QC-bead standardization vs periodic calibration, how to set PMT voltages per detector for a multicolor panel without clipping or losing dim positives, and the record-keeping that makes multi-day experiments comparable.
Western Blot Densitometry in ImageJ: A Defensible Quantification Procedure
A darker band is not the same claim as a band that measured darker. How to verify the linear range with a dilution series, subtract background consistently with the rolling-ball algorithm, measure in ImageJ, and report the procedure so it survives review.
LAL Endotoxin Testing: Gel-Clot, Turbidimetric or Chromogenic, and Calculating MVD
How to choose gel-clot, turbidimetric or chromogenic LAL endotoxin testing, run inhibition/enhancement (PPC) validation, and calculate Maximum Valid Dilution with a worked example.
FMO Controls in Flow Cytometry: When and How to Use Them
When a fluorescence-minus-one (FMO) control is required versus an isotype or unstained control, how to build and read one correctly, and why FMOs matter most on densely multiplexed, spreading-dominated panels.
HPLC Method Development: A Stepwise Workflow
An ordered HPLC method development workflow: a column/pH/organic-modifier screening grid, a disciplined gradient-to-isocratic decision, and robustness testing built in before formal ICH Q2(R2) validation.
Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS): Workflow and QC
A practical HDX-MS guide: the five-stage workflow, why back-exchange is the central QC problem and how it is measured and controlled, standard quench/digestion conditions, and the replicate-and-statistics standard (minimum triplicate, a data-derived global threshold plus a peptide-level t-test) the field uses to call an uptake difference real rather than noise.
Calculating HPLC Column Volume and Void Volume
The worked arithmetic for HPLC column volume, void volume, dwell volume and equilibration volume, plus the step-gradient procedure for measuring dwell volume on your own instrument.
Triple Quadrupole LC-MS/MS: Configuration and Quantitation Setup
How to configure a triple quadrupole (QqQ) instrument for LC-MS/MS quantitation: source and interface parameters, MRM dwell/cycle time budgeting, scheduled MRM, and the ICH M10 calibration and accuracy targets a validated method has to hit.
MIQE Guidelines: The qPCR Reporting Checklist
MIQE 2.0 (2025) turned into a section-by-section reporting worksheet, mapped to the specific gaps — missing efficiency data, unvalidated reference genes, conflated replicates — that actually trigger reviewer pushback on qPCR methods sections.
NIST Mass Spectral Library Search: Match Factor, Reverse Match and the Retention-Index Cross-Check
How to interpret match factor, reverse match factor and probability in NIST mass spectral library search, why a high-scoring hit can still be the wrong compound for isomers and homologous series, and the retention-index cross-check that catches it.
Four-Parameter Logistic (4PL) ELISA Standard Curve Fitting
A practical walkthrough of fitting a four-parameter logistic ELISA standard curve: choosing a weighting scheme from the residual pattern, validating the fit with back-calculated accuracy against nominal concentrations, and the evidence-based criteria for dropping a top or bottom anchor standard.
Fluorescence Polarization (FP) Assays: Tracer Design, Kd Targeting, and Interference Controls
A practical guide to the three decisions that determine whether a fluorescence polarization assay works: tracer size relative to target, target concentration relative to Kd, and the interference controls needed before trusting a hit.
Cell Sorting by Flow Cytometry: Nozzle, Sheath Pressure, Sort Mode, Purity and Post-Sort Viability
How nozzle diameter and sheath pressure are chosen from cell size, why sort mode is a droplet-conflict rule rather than a quality dial, what purity mode actually costs in recovery, and how to verify purity, viability and containment after the sort.
Building and Validating a qPCR Standard Curve
A practical walkthrough of building a qPCR standard curve: dilution series design, the slope-to-efficiency formula, R² and efficiency acceptance criteria, dynamic range vs. LOD/LOQ, diagnosing a non-linear top point, and a cause-ranked fix list for efficiency outside 90-110% (inhibitors, primer design, dilution error, pipetting).
Supercritical Fluid Chromatography (SFC) vs HPLC: When SFC Wins
A practical case-by-case comparison of supercritical fluid chromatography (SFC) and HPLC: where SFC genuinely wins (chiral resolution, prep-scale solvent economics, normal-phase-like selectivity), where HPLC remains the right default, and the back-pressure-regulator and detector constraints that decide which one to buy or run.
HILIC Chromatography: When to Use It and How to Develop a Method
When HILIC beats reversed phase for polar analytes, how to pick a stationary phase, and the equilibration, sample-diluent and buffer/organic-ratio traps that derail HILIC method development.
Protein Identification by Mass Spectrometry: Workflow and Database Search
How bottom-up mass spectrometry identifies proteins, and the database-search parameter choices — enzyme specificity, missed cleavages, fixed/variable modifications, mass tolerance, and target-decoy FDR — that determine whether a given identification is statistically defensible.
Fluorescence Quenching and Photobleaching: Causes and Controls
Static quenching, dynamic (collisional) quenching, inner-filter artefacts and photobleaching all present as falling fluorescence signal but need different fixes. This guide gives the Stern-Volmer test that separates static from dynamic quenching, the inner-filter absorbance correction, and the standard photobleaching controls.
Chiral Chromatography: Column Selection and a Screening Strategy That Knows When to Stop
A practical screening strategy for chiral HPLC method development: which stationary-phase family to try first, which mobile-phase mode to pair it with, and the resolution and robustness criteria that tell you when to stop screening and lock a method.
RNA Integrity Number (RIN): How It Is Computed and How to Read a Trace
What the RIN algorithm actually computes (nine electropherogram regions and a neural network trained on 1,208 samples, not the 28S:18S ratio it replaced), what value each downstream application needs and why that depends on target length, how to read a degraded or atypical trace, and the sample types – prokaryotic, insect, enriched, FFPE – where the number does not apply. Includes how RIN, RINe, RQN and DV200 differ, and what MIQE requires you to report.
qPCR Melt Curve Analysis: Reading Peaks, Primer Dimers and the Confirmatory Check
A diagnostic reading of the qPCR dissociation curve: which peak shapes mean primer dimer, which mean non-specific amplicon, why there is no universal “correct” Tm, why one sharp peak is not proof of specificity, and which confirmatory check — gel or sequencing — settles each case. Includes what MIQE 2.0 expects you to report.
High-Resolution Mass Spectrometry: How Much Resolving Power and Mass Accuracy You Actually Need
Resolving power and mass accuracy specified by job rather than by datasheet: the resolving power needed to separate named isobaric pairs, how many candidate molecular formulas survive at 1, 3, 5 and 10 ppm, the EU 2021/808 thresholds, and where HRMS beats a triple quadrupole and where it does not.
Spinning-Disk vs Point-Scanning Confocal: Choosing by Speed, Photodamage and Optical Sectioning
A selection procedure for spinning-disk versus point-scanning confocal microscopy, built on the three constraints that actually decide it: frame rate, cumulative light dose, and the pinhole-crosstalk limit that rules spinning disk out for thick specimens.
Mass Spectrometry Proteomics: Choosing DDA or DIA, Sample Prep, and Run QC
A decision guide to bottom-up mass spectrometry proteomics: choosing between DDA and DIA acquisition, the digestion, cleanup and fractionation choices that actually set depth, the quantitation strategy trade-offs (TMT vs label-free), and the QC metrics and HUPO-PSI standards that determine whether a run and its data are usable.
Köhler Illumination: A Step-by-Step Alignment Procedure With a Visual Check at Every Step
A bench procedure for setting up Köhler illumination on an upright or inverted transmitted-light microscope. Eight steps, each with the visual check that confirms it worked and the failure signature that tells you which earlier step was wrong.
ATR-FTIR vs Transmission FTIR: Penetration Depth, Crystal Choice, and Spectral Distortion
A sampling-mode selection guide for mid-IR: the penetration-depth equation with its variables and assumptions, crystal choice by sample chemistry, and the intensity, band-shift and dispersion distortions that make an ATR spectrum fail against a transmission library.
Mycoplasma Testing Methods Compared: PCR, Culture, Indicator Cell Culture and Luminescence
A method-selection guide to mycoplasma detection: direct culture, indicator cell culture with DNA staining, NAT/PCR and enzymatic luminescence compared on sensitivity, turnaround, cost and compendial standing under USP and the revised Ph. Eur. 2.6.7 – plus a decision rule for treating versus discarding a positive cell line.
Electrospray Ionization: Source Parameters and How to Tune Them
A source-parameter tuning procedure for electrospray ionization: what each of the six ESI controls physically does, how Waters, Agilent, SCIEX, Thermo and Shimadzu name and unit them differently, and which parameter to change for each observed signal symptom.
Multiple Reaction Monitoring: Building and Optimizing MRM Transitions
A working guide to MRM method development on a triple quadrupole: choosing precursors and product ions, optimising collision energy, and budgeting dwell and cycle time as concurrent transitions grow.
HPLC Column Selection: Stationary Phases & Selectivity
How to choose an HPLC or UHPLC column: what C18, C8, Phenyl-Hexyl, Cyano, PFP and HILIC phases actually retain, how carbon load, silica purity and endcapping change peak shape, and how Tanaka parameters let you compare columns across vendors.
HPLC Vials and Septa Selection: Compatibility Guide
How autosampler vials and septa affect quantitative results: glass type and surface deactivation, crimp versus screw versus snap closures, PTFE and silicone septa compatibility, and how to trace ghost peaks and needle coring back to the wrong consumable.
